# How far away is the Moon?

By Phil Plait | February 24, 2011 7:00 am

I’m sometimes asked what’s the one thing I wish people would understand better about the Universe. My answer is always the same: scale. We humans have a miserable sense of just how big space is, and I’ve spent a lot of time over the years working out ways to express it better.

Most people don’t really grasp just how far away the Moon is, and it’s the closest astronomical object in the sky! So I’m glad this video came out, and is actually getting spread around the web a bit:

When I see something like this, my first reaction is: I’d better check that math. So, first question: is the basketball/tennis ball size ratio the same as for the Earth/Moon? IN other words, if the Earth is a basketball, does a tennis ball get the size of the Moon right?

The Earth is 12,740 km (7900 miles) across, and the Moon 3474 km (2150 miles) in diameter, for a ratio of 3.7.

A standard NBA basketball is 24 cm (9.4 inches) in diameter, and a tennis ball 6.7 cm (2.6 inches), for a ratio of 3.6. Pretty good! I’ll have to remember that; it’s pretty useful.

So how far away would a tennis ball Moon have to be from the basketball Earth to be to scale? On average the moon is 380,000 km (235,000 miles) from the Earth, a distance of about 110 times its own diameter. A tennis ball would then have to be 110 x 6.7 cm = 7.37 meters (about 24 feet) from the basketball. That’s a lot farther than most people would think!

So let’s ramp that up a bit. On this same scale, how far away do you think the Sun is? Don’t cheat! The answer is below the fold.

The average distance to the Sun from the Earth is about 150 million km, or 11,750 times the Earth’s diameter. Since our basketball is 24 cm across the Sun would be a staggering 2.8 km (1.75 miles) away! To scale the Sun would be 26 meters across, the size of a house. A big one.

And the nearest star? It would be — to scale, mind you — 800,000 km (480,000 miles) away: twice as far as the real Moon is from the real Earth!

Space is big. Very, very big.

Tip o’ the scale bar to reddit.

CATEGORIZED UNDER: Astronomy, Cool stuff
MORE ABOUT: Earth, Moon, scale, Sun

### Comments (144)

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1. Stoy

“Space, it says, is big. Really big. You just won’t believe how vastly, hugely, mindbogglingly big it is. I mean, you may think it’s a long way down the road to the chemist’s, but that’s just peanuts to space…”

-The Hitchhiker’s Guide to the Galaxy

2. Nihilismus

Over the years, I’ve done a few of these calculations for friends wrt the Sun-Alpha Centauri distance.

If the Sun were the size of a dime, Alpha Centauri would be about 320 miles away. Earth would be a speck about 6 feet, 4 inches distant.

If the Sun were the size of the period at the end of this sentence, Alpha Centauri would be about 5 1/2 miles away. The Earth would be an invisible speck 1 1/4 inches away.

Or, make the Earth the size of a period. The Sun would be a ball about 2 1/8 inches across sitting at a distance of 19 feet, 3 inches. This scale is especially useful because it makes Alpha Centauri almost an even 1000 miles away.

3. Ohio Mike

Would that nearest star be our sun or Alpha Centauri?

4. Messier Tidy Upper

@ ^ Ohio Mike : Our Sun – & well spotted! 8)

Actually Alpha Centauri is 4.32 light years distant which is a bit more than just 4 years light travel time away.

Proxima Centauri (or Aloha Centauri C) at 4.2 light years distant :

http://en.wikipedia.org/wiki/Proxima_Centauri

might perhaps be the closest single star if it does NOT orbit the Alpha Centauri binary.

Otherwise, as Heinlein pointed out in his Friday novel :

http://en.wikipedia.org/wiki/Friday_(novel)

it will still be at the same average distance as the other two stars of Rigel Kentauros as Alpha Centauri is also known.

Good clip and intersting scale demonstration though.

****

“To get a sense of the scale of the Jovian system, consider that if the Earth was placed at the centre of Jupiter, our Moon would lie inside the orbit of [Jupiter’s nearest large moon] Io, while distant [outer moon] Sinope would be a third of way to Mars.
- P. 186, Ferris, ‘Seeing in the Dark’, Simon & Schuster, 2002.

5. lamanga2004

Nice vid. PS recently subscribed to your blog via RSS and it rocks.

6. Murff

@ Ohio MIke

I think Proxima Centauri is the nearest actual star to the Sun, it is a companion to Alpha Centauri.

Edit: Found this snippet: “The nearest stellar neighbors to the Sun are three stars that make up a multiple system. To the naked eye the system appears as a single bright star, Alpha Centauri. Alpha Centauri is a double star — two stars revolving about each other that are too close to be seen as seperate by the naked eye. Near them is the third member of the system, a faint star known as Proxima Centauri. Discovered in 1915, it is smaller than Alpha and Beta. Proxima (meaning nearest) it is slightly nearer to the Sun than the other stars in this triple star system.”

7. Tom K

For a long time I’ve had an inflatible globe of the Earth at my desk, and it’s about a foot in diameter. I cut out a circle of paper to represent the Moon at the same scale and from time to time would ask people how far away it should be to represent the Earth-Moon distance. Not many people put it 30 feet away, which is where it should be at this scale.

I then ask them where the space shuttle would be when it’s in orbit. Nobody puts it about a third of an inch off the surface of the Earth globe. This illustrates what an amazing undertaking the Apollo missions were, and how by comparison the shuttle just barely gets off the ground. Man, those Apollo guys actually went somewhere.

It also shows how utterly isolated the Apollo astronauts were. And when Mike Collins was in the Command Module on the far side of the moon, while Buzz and Neil were on the surface on the other side? He was the most alonest person, evar. 2000 miles from the nearest human beings, with no hope of contact if anything went wrong. No desert island was ever so isolated.

8. Nihilismus

Ohio Mike: The Sun is the nearest star to the Earth. The trinary system Alpha Centauri is the next closest after that.

9. Timmy

I can’t wait for the day my son has to make a diorama of the solar system for school. I actually have been hoping for this since before I had kids. Yes, I am a geek. Why do you ask?

10. Phil;
Reminds me of when I discuss sizes of subatomic particles relative to the size of atoms. People have a hard time grasping nothingness.

One Hydrogen atom is around 500,000 femtometers across, while one Proton is around 1-2 femtometers across. Between them is nothing but unicorns. Also, electrons are green.

11. Nihilismus

Well, yes, technically Proxima Centauri is closer than the two main components of Alpha Centauri by 1/8 of a light-year, but I simply used the rounded 4.3 light-year figure for the whole system (if it is a truly associated trinary, but that’s another discussion).

12. IVAN3MAN_AT_LARGE

Two Californian blondes were chatting with each other during a moonlit evening when one of them looked up at the Moon and asked: “Which do you think is more farther away — the Moon or Australia?”

“Hello!”, replied the other blonde, “Can you see Australia?!”

13. Joshua Green

Technically, the Sun is the nearest star. (I remember catching the same mistake on an exam in graduate school.)

14. Nihilismus

And if the Sun were the size of a basketball, Proxima Centauri would be a ping-pong ball 4,360 miles away.

15. Tage

Some astronomers in Sweden decided to tackle the scale problem in an easy to grasp way and created the Sweden Solar System (http://en.wikipedia.org/wiki/Sweden_Solar_System) – a model using the Stockholm Globen arena as the sun and a number of planetary installations on the correct distances away from the huge, spherical arena complex.

It’s a great way to explain size and you do realize a few things. The solar system is huge! And the typical image of the solar system with planets spread out about evenly spaced away from the sun is totally wrong. Mercury, Venus, Earth and Mars are all located in Stockholm and the outer planets are spread out in the northern part of the country.

I heard a lecture by one of the astronomers behind it and he said one of the most startling revelations when building the model was when he was traveling north by train for the opening ceremony for the Pluto and he realized that the train was actually moving very near light speed, on scale.

/Tage

16. Katie S.

@ Larian LeQuella

There’s a wonderful “to scale” model in Boston, with the Sun in the Science Museum and the planets located in various points throughout the city (there’s something in South Station, I think it’s one of the outer planets but don’t hold me to it).

17. Peter B

Timmy @ #9 said: “I can’t wait for the day my son has to make a diorama of the solar system for school. I actually have been hoping for this since before I had kids. Yes, I am a geek. Why do you ask?”

Heh, beat you. My oldest (3 year old) son already has the Solar System hanging from the ceiling of his bedroom.

Okay, it’s not to scale, and the colours of Jupiter and Saturn are off. But he likes batting them before going to bed, and lifting him up that high is good exercise for the tummy.

For those interested, it’s a kit of polystyrene balls of varying sizes, with a rather thick ring to represent Saturn’s rings, ready for the buyer to paint. The kit also contained a number of metal rods to stick into the balls so they could form a single sculpture, but that didn’t seem like a good idea with small kids. So after painting them I hung them from the ceiling with sticky tape and loops of cotton. And one of the smallest balls was intended to be Pluto, but I made the executive decision to exclude it and instead use that ball as the Moon.

My only concern is what to do for our latest family member – a second Solar System seems a bit over the top…

BTW, I picked the kit up from Lincraft. No idea if they still have them in stock.

18. Brian

Google Latitude dashboard has a a neat feature that tells you how far you’ve traveled and then how much further you have until you get to the moon.

After a year of history and a couple cross country trips, i’m approximately…. 10% of the way there!

19. dan

I remember an old Dr Who episode where the Doctor explained why the inside is bigger than the outside. He said that the inside was further way in space than the outside. Therefore the inside was scaled down and is able to fit inside the little blue box.

20. Nigel Depledge

Tom K (7) said:

It also shows how utterly isolated the Apollo astronauts were. And when Mike Collins was in the Command Module on the far side of the moon, while Buzz and Neil were on the surface on the other side? He was the most alonest person, evar. 2000 miles from the nearest human beings, with no hope of contact if anything went wrong. No desert island was ever so isolated.

Well, Mike Collins and the CM Pilots from Apollos 12, 14, 15, 16 and 17.

These six men shared one thing that was quite profound. They had to contemplate the possibility of coming home alone if anything went wrong with the LM while it was on the surface of the moon or in transit between the CSM and the moon’s surface.

21. Jimmy

Here is a link to the Sweden Solar system, a huge model of our system and in scale. http://en.wikipedia.org/wiki/Sweden_Solar_System

22. critter42

Monty Python’s Galaxy song really sums it up:

So remember, when you’re feeling very small and insecure,
How amazingly unlikely is your birth,
And pray that there’s intelligent life somewhere up in space,
‘Cause there’s bugger all down here on Earth.

23. I had attempted something very similar :
http://filya.wordpress.com/2009/04/25/how-big-is-our-solar-system/

I would love to have your view on this Phil!

24. I agree with you that people (especially science fiction writers) don’t think about this enough. At the speed of light it would take over four years to reach the nearest star! Even at ten times the speed of light that’s still months.

25. Kristin C.

Oh, dagnabbit, Phil, I was about to blog about the same thing (right down to the calculations), and now everybody’s going to think I copied you and everything. *sulks*

26. Lara

This is exactly how I start my high school astronomy class each year. The students always say that the sense of scale is one of the most memorable things they get out of the course.

27. Gus Snarp

Every possible demonstration of the scale of the universe is important. The more ways it can be shown dramatically, like this video, the better. You’ve got to see it a lot of ways and keep being reminded of it because the brain just can’t hold it. I wouldn’t have put the tennis ball far enough away, and I was thinking along these lines: 24,000 miles around the equator (roughly), 250,000 miles to the moon (roughly), so unwind the basketball, multiply by ten…..but then, you can’t gauge the circumference that well when looking at a ball, so I’d have come up short.

I’ve been thinking of doing something similar at a local park with a large exercise ball as the sun, a ball a little smaller than a tennis ball for Jupiter, and a ball bearing for the earth. I’ve mapped out the relative distance in the park, which has a nice long field of grass that’s just about right. But I think that only gets the distance from Sun to Earth, not Jupiter, but I think I can drive up onto a nearby hill from where I can see the park for Jupiter.

28. Gus Snarp

@Tom K – I’ve been reading books and watching documentaries about Apollo a lot lately, I had the same though, Michael Collins, farther by far from any other human being in the Universe. What a lonely spot. And as mission control mentioned to him, the only one not watching Neil Armstrong walk on the moon. Those guys all had a special kind of courage, and what a dedication to the mission it takes to be the guy who says, I’ll take almost all the same risks, then sit alone and isolated while they make history and only be remembered by the more space obsessed geeks, because somebody has to do it to make this happen.

29. rob

if the sun was a sphere with radius of about 695,500 km, and the earth was a sphere with radius of 6,378 km, then the sun would be about 149 million kilometers away! amazing!

i love this site.

30. You had a thread that had some thing to do with scale last week. At that time I commented that I thought it would be cool if someone manufactured a moon globe 3.25 inches in diameter. That would be in the right scale for a 12 inch moon globe. Every classroom in the world has a 12 inch earth globe, and 30 feet is a common size for a classroom. I have a PDF on my web site with a print at the right size.
http://idea.uwosh.edu/nick/moon-earth_scale.pdf (TomK: I also have a correctly sized picture of the moon on a wall 30 feet out from the globe in my office. Everybody is surprised how far away it is,.

31. Rich

It’s much easier to remember if you think of the Moon as ~30 Earth diameters away. In this example, the tennis ball Moon is 30 basketball diameters away from the basketball Earth. Earth-Moon distance / Earth diameter = (235,000 miles / 7,900 miles) = 29.75.

32. Pete Jackson

Another mind-bending property of the scale setup (basketball and tennis ball) that Phil has put here is that if you fill the basketball with iron until it is as dense as the Earth (making it like a real heavy bowling ball), and there were just this dense basketball and tennis ball in empty space, then the tennis ball would take the same amount of time, 27 days, to orbit the dense basketball under its gravitational pull as the Moon takes to orbit the Earth!

It gives a intuitive feeling for how weak gravity really is.

33. Sam H

@ Tom #7

Indeed the isolation faced by the CSM pilots was the greatest any human had ever faced. But Mike Collins has stated he enjoyed that feeling of solitude (which only came when he was on the far side, out of Houston’s and Eagle’s line-of-sight), and he felt that he was close to “God-only-knows-what” when he was all that was between the moon and the black infinity.

Anyway, I am looking at giving a presentation on space for a grade 1 class at my school for a volunteer opportunity (but also because I sincerely want to do this). Coming up with exacts to go over is still an issue, but I want to keep a focus on the scale of space – basically, I want to completely WOW them, and give them a feeling of childhood wonder that can stay with them for the rest of their lives and possibly lead to careers in science. What I know I must include is the Pale Blue Dot and VY Canis Majoris, as well as the moon scale experiment. I’ll be giving a gradual progression from the solar system to interstellar space (while wearing a Trek science officer uniform). Any suggestions on further points to include, or any tips? Fortunately, they can understand the concept of orbit, but explaining the basics of radiation and the spectrum would really help as well…

34. I have to admit I never really thought about how far away the moon actually is. I’ve always been aware of the distance we are relative to things like the sun and other stars and galaxies, but never the moon. I think that’s why that image of the earth and moon from MESSENGER was so fascinating to me.

So here’s a fairly valid question(s) – The Earth is 3.7 times the diameter of the moon. The moon is made from the same basic material as the Earth since it was created from it. So why is does the Earth have six times the gravity? Does that mean it’s six times as massive? Why does the mass ratio differ from the diameter ratio? I’m assuming simply the Earth ended up more dense, though being made from the same material I’ m not sure what would cause that…

35. Andrew

I got 2.7 km from the speed of light being about 3×10^8 m/s and the Sun about 8 light minutes away, plus your scale of about 52 million to one.

Proper scale models of the solar system are excellent. I’ll try to remember the basketball (a soccer ball is about the same size) to tennis ball, about 30 Earth diameters away (thanks, Rich).

Powers of ten, all the way up and all the way down.

36. So let’s ramp that up a bit. On this same scale, how far away do you think the Sun is? Don’t cheat!

I did a very rough calculation in my head and guessed about 1.5 miles. Pretty close. (86 million to 1/4 million — 350 to 1. 350 times 24 feet, 8400 feet, a little more than 1-1/2 miles.)

The answer is below the fold.

And how many of your readers have no idea what that means?

Andrew:

Powers of ten, all the way up and all the way down.

I thought it was turtles all the way down?

37. Scale is important working the other way too. In neuroscience we have to have an impression of how large an average neuron is relative to a dendrite relative to the proteins in the dendrite. If you understand that you can see a neuron under light microscopy and that a dendrite is about at the limit for (run of the mill) light microscopy, then you gain an appreciation of just how difficult it is to “see” what happens inside a dendrite or axon terminal during neurotransmitter release.

38. JohnK

The following website has a photoshopped photo of the Earth/Moon system.

http://www.aerospaceweb.org/question/astronomy/q0262.shtml

Phil,

This website has a great description of the tides which I thought you could pass on to Bill O’Reilly

39. wfr

It’s really, really, really far.
http://www.youtube.com/watch?v=dF2HG1PVZok

40. My girlfriend and I were at a museum recently, when she said something about the space shuttle and Mars.

When I realized she wasn’t joking, I told her that the space shuttle doesn’t go to Mars. It doesn’t even go to the moon.

She is still fairly annoyed by this. In her words, “I don’t see why they call it a space shuttle when it doesn’t even go into space!”

When I say that space starts WAY before the moon, she says, “I guess I just thought space was more impressive than that.”

I’ll have to show her this video. :p

41. kevbo

I was on a cycling trip in Holland a couple of years ago, and some local school had set up a demonstration of this on one of the many biking paths between towns over there. They had paper mache models of the planets to scale placed along the path. The starting point was the sun, which wasn’t built to scale, but was supposed to be 4 meters across, which put the inner planets all within a half a km. These planets had to be displayed on big signs so you wouldn’t miss them (each was under a couple of inches across). We kept forgetting about the diorama after that, as Jupiter was a couple km down the road, Saturn another four, etc. Pluto was about 17 km away! (by then it was beer time).

42. Chris

And the people on your basketball Earth would be ~37 nm tall. About 10 turns on a DNA double helix.

43. Donnie B.

“…he was close to “God-only-knows-what” when he was all that was between the moon and the black infinity.”
.
.
.
“I been to the edge. Just looked like… more space.” — Jayne Cobb, “Serenity”

44. Jacob:

When I say that space starts WAY before the moon, she says, “I guess I just thought space was more impressive than that.”

Space is more impressive than that. Just because the Shuttle can only get to the very nearest part of Space doesn’t make Space less impressive.

If she were standing at the edge of the Grand Canyon, and leaned down as far as she could reach, would the fact that you could only reach a few feet down make the Grand Canyon less impressive?

Or, stand by a small stream coming from Lake Itasca, and ask “does this make the Mississippi River less impressive?”

45. Wayne on the Plains

This is wild, I came up with and used THIS EXACT MODEL of a basketball and tennis ball 25 feet away for a Skype interview with third graders from Dublin, Texas last week. I also do a scale Solar System Lab the first week of my Astronomy course, using a globe lamp on campus as the Sun (which I have them calculate the size of using the small-angle formula) and a variety of small balls that I have the students choose from for the planets after they’ve calculated the scale diameters. Unfortunately, we can only place them at their scale distances out to Jupiter, because that’s the size of my campus, but I give them landmarks (ie, the Post Office down the road) for the rest. At this scale, walking speed is a few times the speed of light, and the next closest star would be in Japan (following a great-circle, not direct-line).
I’ve always been fascinated by scale Solar System models, especially since walking from the “Sun” to “Mercury” of the Sweden model mentioned above, and I agree it’s one of the most important things to teach students about the Universe.

46. Gus Snarp

@Endyo – I’m sure others will give you a better, more detailed explanation and that there’s more to it than this, but the short answer is that a diameter ratio is a poor way to demonstrate the size difference between two spheres. It does not translate directly to a volume ratio or a mass ratio.

47. Gus Snarp

@Tage – The Sweden Solar System looks really cool. Sounds like a great vacation I’ll have to take sometime. In summer.

48. Gus Snarp

@Endyo – Also, the Earth’s surface composition is something entirely different from its core, and I would assume that the moon was mostly surface material, therefore considerably less dense than the iron core. But that’s pure supposition on my part, and I could misunderstand that bit entirely.

49. I love this. The sense of scale in space – in the UNIVERSE – is what is just so mind-numbingly hard to comprehend. I assume it is even to astronomers who knock huge numbers around all day long, but especially to the average person who basically just deals with local distances like home-to-work and TV-to-fridge. Anything that helps put these things into perspective is great….thanks Phil for sharing this!!!

50. Phil,

You inspired me to make a custom Google map showing where the planets would be if the Sun was in New York City and Neptune was in LA. The positioning of the planets isn’t exact. (Google Maps wasn’t letting me position the pointers with 0.01 mile accuracy). Still, it is accurate enough that it should show people just how far away the planets are: http://bit.ly/gcfTWD

For the best effect, zoom in on the Earth -> Sun portion and then scroll the map to find Mars, Jupiter, etc. There’s a lot of scrolling to get to the outer planets.

51. Rodrigo Valle

I just did the math on what would scale models look like if I built a solar system model in my city park.
I live in Porto, Portugal, and our city park is 1.4km in length.
If I stretch the scale from the Sun to Pluto, the Sun is ~33cm in diameter, and the Earth is a sphere…. 3mm wide. That’s 3 millimeters…
I don’t think the kids would find it very exciting…

Now, if I do it city wide…. Porto is about 10km across, so then the Sun would be 2.35meters and the Earth 2.1 cm…. Still not very exciting…

Ok, what if I do it between Lisbon and Porto, the 2 main cities, in the Highway?
That’s ~300km, so the Sun would be 70 meters wide (muahahahaha) and the Earth about 65cm.. Barely visible if you’re driving down the Highway, but still cool.

Hey, that’s the exact same scale as the Swedish Solar System !!!
http://en.wikipedia.org/wiki/Sweden_Solar_System

Rodrigo Valle

52. Chris Warren

Also, even though they’re made up of the same stuff in general, the Earth’s molten layers and iron core make it more dense overall than the Moon by about a 5:3 ratio.

The moon’s 27.3% of the size of the earth on one dimension, so by volume, it’s the cube of that, or 2.03% of the Earth’s volume, then multiply by the difference in density, and you’re looking at 1.23% of the mass.

The gravitational pull on an object on the surface (according to my recalled Newtonian basic physics here) should be directly proportional to the mass of the planet and inversely proportional to the square of the radius. So, let’s see. If the Moon has 1.23% of the mass of the Earth and 27.3% of its radius…

G(m)=G(e)*.0123/(.273)^2
G(m)=G(e) * .165

So, yep, one sixth! Science: It works, bitches!

53. réalta fuar

Nice round numbers to remember: moon/earth (diameters) ~ 4,
distance to moon ~ 30 earth diameters,
sun/earth (diameters) ~100, distance to sun from earth ~ 100 solar diameters
jupiter/earth (diameters) ~ 10, which gives us sun/jupiter (diameters) ~ 10
The distance from the sun to Alpha Cen isn’t quite so “round”. If you round Alpha Cen’s parallax up to one arc-second (an error of about 1/3) then its distance is close to 200,000
AU (ok, 206265 for those paying attention). Probably close enough for the type of exercise given above though the error here is much larger than in the other approximations.
For the truly pedantic among us, NBA basketballs are the same size as those used by the rest of the world, except for women’s b-ball in the United States (I’m reasonably sure they’re the only women who use the smaller ball, but I could be wrong about this).

54. toasterhead

20. Nigel Depledge Says:
February 24th, 2011 at 7:54 am
These six men shared one thing that was quite profound. They had to contemplate the possibility of coming home alone if anything went wrong with the LM while it was on the surface of the moon or in transit between the CSM and the moon’s surface.

And Nixon would have delivered this speech. Just reading it gives me the creepies:

Fate has ordained that the men who went to the moon to explore in peace will stay on the moon to rest in peace.

These brave men, Neil Armstrong and Edwin Aldrin, know that there is no hope for their recovery. But they also know that there is hope for mankind in their sacrifice.

These two men are laying down their lives in mankind’s most noble goal: the search for truth and understanding.

They will be mourned by their families and friends; they will be mourned by their nation; they will be mourned by the people of the world; they will be mourned by a Mother Earth that dared send two of her sons into the unknown.

http://watergate.info/nixon/moon-disaster-speech-1969.shtml

55. Jim Ernst

@Endyo –

To get complicated….

The volume of a sphere is found with the following: V = 4/3 pi r^3

As the radius increases, the volume increases as the cube.

The Earth has about 50 times the volume of the Moon. But the Earth is also more dense. It has about 82 times the Mass.

So, you’re 3.7 times as far from the center of mass when you’re on the Earth, which has 82 times the mass.

If you take into account Newton’s gravitational equation: F = G*m1*m2/r^2 you’ll see that the force of gravity on the surface of the Earth is about 6 times the force on the surface of the Moon. (82/(3.7^2) = 5.98

So:

Earth has….
3.7 Moon diameters
50 Moon volumes
82 Moon masses
6 Moon gravities

56. Nadim

I like his other videos as well. This is also good:

http://www.youtube.com/watch?v=u7KpH9_I2Dw

57. Ken

Endyo @34: The Earth has a much larger iron core than the Moon, which increases its average density. That also means our gravity is greater than a simple comparison of radii would suggest. Your post indicates you already know the current theory for the Moon’s formation; see http://en.wikipedia.org/wiki/Giant_impact_hypothesis for some information about the distribution of materials during and after the collision.

58. Alan D

If someone asked me, and my wife was along, I’d ask her for an aspirin. Then, holding the aspirin at arms length, I’d have her walk the tennis ball away until the aspirin just covered it.

Always enjoy doing Guy Ottewell’s 1000 yard model, or “The Earth as a Peppercorn.” It’s a shorter walk now that Pluto got demoted.

Clear skies, Alan

59. hhEb09'1

One thing cool to do with this setup is have participants place their head along side the basketball, and look at the tennis ball. The tennis ball will appear the same size as the moon appears, when you look up at it in the sky. You can stretch out your arms and measure it with your fingers, and compare them.

60. Tom

@4. Messier Tidy Upper

“Proxima Centauri (or Aloha Centauri C)”

I know that was a typo, but it’s a damn good one

61. Dennis

Here’s another people-scale comparison. Sand is defined to be between 0.05mm and 2mm in diameter. If we use the small end of that range and say a person is 2m in height and that a grain of sand represents a person, then the scale diameter of the Earth would be about 318m. That’s about 1044 feet!

Of course sand is more rotund than a person, but 7 billion grains of sand of that size would fit in an extra large flower pot.

The Moon would be almost 87m (285 ft) in diameter and the Earth – Moon distance would be over 9.4km (5.8 miles).

Imagine several grains of sand traveling that far!

62. Tim G

If Alpha Centauri is going to be twice as far as the real moon at that scale more than one scale is needed. The ball in a ball point pen could be useful, being about as small as a sphere can get and still be easily visualized. However, the size of the ball varies. I think some extra-fine pens use 0.5 mm balls, meaning a 25 billion to one scale and putting the sun at 19 feet away and Alpha Centauri at a thousand miles away.

A third scale would take advantage of the fact that the ratio of a light-year to an AU is very close to the ratio of a mile to an inch. So the sun would be an inch away and Alpha Centauri at 4.3 miles.

Perhaps one way to convince people that the tennis ball should be 24 feet away is to get them to hold out a dime (or any small coin) in their outstretched arm and notice how easily the tennis ball can be covered up. They can do the same thing the next time they see the moon.

63. Rob tK

I’ve always liked these types of representations of size. Makes me feel incredibly insignificant!

Here’s my favorite on the relative sizes of planets and stars.

http://www.co-intelligence.org/newsletter/comparisons.html

Rob

64. ThirtyFiveUp

Caltech, is the champion of nerds today!

http://www.pasadenastarnews.com/sports/ci_17468146

65. Michel

Cool fun video´s. I´m going to show them around.

66. DavidR

Unfortunately, the person presenting the video is as wrong as everyone else.

If you take the distance from earth to moon (approx 240,000 mi, round to 250,000 mi) and figure that the circumference of the earth is roughly 25,000 miles, you can see that the distance from earth to moon is roughly 1,000 times the circumference of the earth.

Given that the diameter of the basketball is give as 9.4 inches, 1000 times the circumference (pi*9.4) is 29,530.15 inches, divided by 12 is 2,460.914, or just over half a mile.

Please note that I have used Imperial measurements since most people will have a better visceral feel for them.

67. wfr

Here’s a question for Phil: if we were to scale the Milky Way to the size of the Earth, would we be able to recognize anything at all?

68. DavidR (66): Um, check your math. 250,000 / 25,000 = ???

69. abble

“But don’t let my name fool you. In real life, I’m very big.”

70. J40

AS A STUDENT OF PHYSICS,THIS IS MIND BLOWING TO THINK ABOUT THE CALCULATION FOR THE SO CALLED “MOON TILT” HORSE-COCKY THEORIES GOING ON RIGHT NOW. THE SIZE OF A BODY FOR PLANET X TO ALTER THE MOONS ALMOST PERFECT ORBIT WOULD HAVE TO BE ENORMOUS! AND DEFINITELY VISIBLE .UNLESS THERES A BLACK HOLE CREEPING AROUND BUT WOULDNT THAT EFFECT everything ELSE IN OUR VISIBLE SKY?KEEP CRANKIN THE BRAIN ORGAN PEOPLE.

71. Skrim

Here’s a vid I found really useful for describing the scale of distances:
http://www.youtube.com/watch?v=97Ob0xR0Ut8

Bill Nye, of course. Always effective.

He only goes from the Sun to Pluto though. Using the scale in the video, where 1 AU is shrunk to 100 m, I calculated how far you’d have to bike to reach to reach Alpha Centauri: 27604 km!!! That is, Bill would have had to bike more than half way around the planet to reach a balloon representing Alpha Centauri! Compared to that the 4 km bike to Pluto was peanuts.

And then I calculated how far to the Moon from Earth. 25 cm. Kinda diminishes one of our greatest achievements (Apollo) a bit in the face of the bigger picture.

Then I got intrigued and found out how far you’d have to bike to reach the galactic core: >160,000,000 km. So if you were to take a rocket instead of a bike, you’d have to fly out to a place somewhere in interplanetary space beyond Mars’ orbit in reality to reach a big black sphere representing the resident black hole.

And of course, you’d have to take a spaceship (we’re waaay beyond bikes now) and fly out 16 billion km to the far reaches of the Kuiper Belt in reality to reach a model of the Andromeda Galaxy floating out there.

So yeah… that’s just the nearest other galaxy. But my head asplode too heavily to bother calculating beyond that.

72. mike burkhart

The Moon gets 1 inch farther from the Earth every year.Might not seem like munch but billons of years ago the Moon was only 30000000 miles away and must have been an incredable sight in the sky back then.

73. Ross

“If you take the distance from earth to moon (approx 240,000 mi, round to 250,000 mi) and figure that the circumference of the earth is roughly 25,000 miles, you can see that the distance from earth to moon is roughly 1,000 times the circumference of the earth.”

@DavidR – that my friend is a pretty damn rough estimate :p Out by a few orders of magnitude.

74. mike burkhart

The Moon gets 1 inch farther from the Earth every year.Might not seem like munch but billons of years ago the Moon was only 30000 miles away and must have been an incredable sight in the sky back then.

75. Calli Arcale

DavidR — those numbers are correct for the Earth-Moon distance and Earth circumference, but work out to the Moon’s distance being 10 times the Earth’s circumference, not 1,000 times. The diameter of the Earth is easier to use for this than the circumference, though, and that’s just about 8,000 miles at the equator. 8 x 3 = 24, so 30 Earth diameters is 240,000 miles, which in fact jives with what I’d dimly remembered from my youth and was hoping very much was correct. Yay!

76. Joe

If it wasn’t so empty, they wouldn’t call it “space”.

77. DavidR

DoH! I dropped a decimal point, or several….. Sorry

that’s what I get for trying to do something else at work. I thought that seemed a bit large.

78. dave cortesi

There are at least two websites that are based on “The Earth as a Peppercorn” telling how to build a scale-model solar system. Just put that title into a search engine.

In Eugene, OR, there is a nice solar system scale model with bronze planets on a popular bike path alongside the Willamette river, see: http://www.efn.org/~jack_v/ for pics.

79. Bianca

A friend asked, after reading this article, how close we were to travelling at the speed of light. The answer from Universe Today: the fastest we’ve gone is .000405% the speed of light. That would take us 522 days to reach the sun.

Wow.

80. Keith Bowden

EW! Check this out -

http://www.qrg.northwestern.edu/projects/vss/docs/space-environment/2-how-asteroids-orbit.html

Not only do they seem to show so many asteroids that seem to be hundreds of times the mass of the rest of the solar system, but they have the hysterical line: “Some scientists believe that the asteroid belt was made when a planet that was there exploded or collided with something else and broke up.”

To quote Phil:

Our own asteroid belt is always shown in movies as a flying swarm of zillions of rocks. But the reality is a bit more sparse: Asteroids are really far apart, like millions of miles apart on average. Chances are you could stand on the surface of an asteroid and not even be able to see another one with your naked eye. In fact, if you took all the asteroids in our Main Belt and lumped them together they’d make a single rock about 800 miles across. That’s less than half the size of our moon! Spread that out over a few trillion cubic miles and you get the picture.

http://blastr.com/2011/01/5-biggest-astronomical-mi.php

81. Hi Phil.

I’ve been reading TBA for quite some time but have never commented. I just wanted to drop you a line and let you know that it has appeared on psnt.net‘s list of Top Ten Most Irresistibly Brilliant Blogs:

http://psnt.net/blog/2011/02/6991/

Thanks for doing what you do.

Paul Wallace

82. redbird

This was installed a couple of years ago and it always amazes me when walking down this street.

http://loopplanetwalk.com/map_page.html

83. pk_boomer

Space. It seems to go on and on forever. But then you get to the end and a gorilla starts throwing barrels at you.

84. Randy

The city of Anchorage, Alaska, USA contains the “Anchorage Solar System Walk”, with scale models of the Sun and the planets (including Pluto). On their scale, the Sun is a ball 12 feet (about 3.65 m) across, Earth is down the street (0.4 km away), and Pluto is across the city, about 12.8 km away in Kincaid Park.

85. Gwif

The main dome of the Griffith Observatory in Los Angeles has a diameter of about 26 meters. The Capitol Records building is about 1.75 miles away. Here’s a picture for reference.
http://www.flickr.com/photos/neonspecs/2348606393/
Imagine you’re holding a basketball.

86. Leon

That’s great! I’d love to hear a more extended analogy, where the other planets are done as balls of varying shapes and giving their distance from the Sun–all to the scale of Earth=basketball. And of course, a side note about how big a ball the Sun would be at that scale.

87. Don Gisselbeck

Is it even possible to comprehend a distance further than you can see and reach with your own muscle power in a day? (I’m not even sure bicycling counts.) It seems to me that anything further is only “x” time spent traveling. I would argue that our universe is smaller than that of the ancients. The moon was only a few days away for us, the ancients knew of places years of travel away. “Light year” is an incomprehensible synonym for “very far”. Merely knowing a number does not mean we understand what it means.

88. I love how people always try to get you with the whole “haha, it’s actually the SUN” thing after asking you “what’s the nearest star” and you answer “Alpha (or Proxima) Centauri”. (I recall reading Isaac Asimov mention that he had this experience.)

It’s not really fair, though, since “the nearest star” is an elliptical phrase that does not explicitly state what the star is supposed to be the nearest to. If we assume the phrase to be “the nearest star to the Earth” then the Sun is the correct answer, but I imagine that assuming it to be “the nearest star to the Solar System” is actually more sensible and is how I always thought about the question.

Don’t let them get you on this particular technicality unless “…to the Earth” was made explicit.

89. Senor Molinero

There’s a great scale model of the solar system in New South Wales, Australia.
It’s centred on the dome of the Anglo-Australian telescope near Coonabarabran. The dome represents the sun and the planets are scaled accordingly. The 4 inner planets are along the entry road and the size of various sporting equipment. The outer planets are spread out along the highways for hundreds of kilometres, they really take some finding and sharp eyes. Travelling at the speed limit (110km/h) is the equivalent of 3 times the speed of light and it still takes several hour to reach Uranus. Incredible!!!

90. MattF

I did this with a fourth-grade class studying astronomy, only my Earth was a 12-inch globe and my Moon an origami model to scale. I started with the two of them in contact, telling them that I was going to move them apart slowly and that they should tell me when to stop. Most said something before I had gone a full foot with the Moon; by the time I got to three feet away, all of them were screaming for me to stop. The two of them had to be placed about thirty feet apart — clear across the room from one another. The teacher — my bride-to-be — explained that space is mostly, well, space.

91. Jim Starluck

I got as far as trying to mutiply 480 x 24 ft in my head before I had to bust out a calculator. =P

In the video they said that the Moon is about 1 light-second and the Sun is about 8 light-minutes. Those are *very* rough approximations, but so is “Earth = basketball, Moon = tennis ball”. 8 light-minutes x 60 light-seconds per light-minute = Sun is 480 light-seconds away, so it should be about 480 times farther than the 24 feet you gave for the Moon.

After I resorted to the calculator I got 11,520 feet, or 2.18 miles away. Compared to your 1.75 mi, it wasn’t *too* far off!

92. Dennis

If Earth is a basketball, then Jupiter is a little smaller than a Zorb Globe (human hamster ball).

93. Sawdust Sam

@Don Gisselbeck#76
According to the odometer in my car, I’ve driven it just over half the distance to the moon in about 7 years.
I’m not sure we’re going to make it: things are breaking down and falling off – and the car’s not doing too well, either.

94. Another Josh

Funny, no one to this point has mentioned the Voyage exhibit on the National Mall in Washington, DC. http://www.sites.si.edu/exhibitions/exhibits/voyage/main.htm and http://www.jeffreybennett.com/voyage_scale.html

95. Rich

Here’s another example for time instead of distance:

A meter contains 1000 millimeters;
1 billion (years) = 1000 million (years).

Use a meter stick to represent 1 billion years, then each millimeter is 1 million years.

Put 4 1/2 meter sticks together to represent the age of the Earth (4.5 billion years). The last millimeter represents the last million years – the timeframe of “modern” humans on the planet.

You get the idea.

96. Monkey

@rich (80)

Yeah…its cool to put things in perspectives like that. Another good way is to use the famed toilet-paper roll timeline. The average roll has X squares, each square is X years….I get my students to go to the hall of the school, toss a roll of TP all the way down and then I hand out little pre-made cards that say things like “first eukaryote” “Rocky Mountains forming” “Moon formed” etc for all the major geological and biological events and give them a point in time that it occured (square 4, square 43.5, etc). when all is done, we stand back and look at the real history of EArth. Then I ask them why I didnt hand out any historical or anthropological cards once the whole TP roll is strewn with geo/bio highlights (and a whole lot of gaps, too). They eventually work around to the answer, and I then give out a new set of cards. These are all historical (wars, famines, stock market crash, country formations, invention of the car, etc) and get them to try to put them in the right place. They cant. All the stuff on that scale would have to be crammed into something like the last quarter of the last TP square.

Then I try to get them to imagine their life in perspective to this TP Timescale. where did their graduation fit in? What about today? Etc. Then – boom – we are into evolution and everything is ok…the time issue is solved, the can digest how evolution works.

Perspective, to quote Phil (sort of), is one of the coolest education tools. That is how I start my biology class and I refer to it for the entire year….and the kids get it. The get it!

97. Pretty nice video!

It reminded me about the Solar Pizza idea from NASA’s Earth-Sun-Day project:

http://sunearthday.nasa.gov/2007/materials/solar_pizza.pdf

I have 2 of those posters ready for action in the “Sun Day” activity for AWB’s Global Astronomy Month:

98. Jeffersonian

I wasn’t surprised by the scale until the final metric (star-ball to basketball is > moon to Oyth). Let me peel my scalp off ceiling.

99. Ed. H.

There were a couple of videos posted recently on the Astronomy Picture of the Day (APOD) website dealing with scale and size. The first was posted on 01 Feb and is titled “Powers of 10″; it was made back in the 1960′s. It starts at 1 meter and then zooms out by a factor of 10 every 10 seconds until it gets to something like 10**27 meters, then it returns to the starting point and zooms in by a factor of 10 every 10 seconds until it gets to the atomic (or maybe sub-atomic) scale. (Obviously this latter is just guesswork as this was long befor the invention of the Electon Microscope, the Scanning Tunnelling Microscrope or the Atomic Force Microscope.)

The second was posted on 22 Feb and is titled “Star Size Comparison”; it shows relative sizes from smallest to largest. It actually has Solar System objects in addition to stars. After watching it I now have a better understanding about the current theory of lunar formation.

There is a third video titled “The Known Universe” that was posted on APOD on 20 Jan 2010. As a peice of visual art it is quite nice, but I do not think it is all that good at helping people visualize size and/or scale of the solar system/galaxy/universe.

Here are the links:
Powers of 10: http://apod.nasa.gov/apod/ap110201.html
Star Size Comparizon: http://apod.nasa.gov/apod/ap110222.html
The Known Universe: http://apod.nasa.gov/apod/ap100120.html

100. Jenett

Have you heard of the Community Solar System Project in Peoria, Illinois? I used to live there and it’s pretty darn cool. It really helps people wrap their head around not only how far it is to other objects in our solar system, but also how large they are in comparison to each other. Check it out online at:

http://www.bradley.edu/las/phy/solar_system.html

101. Don Q

After all the movies about the space shuttle going to the Moon, or Mars, or intercepting an asteroid, lots of folks have been given a bad impression about the real scale of shuttle orbits. When I ask for guesses about how high a shuttle orbit is compared to reaching the moon, I hear everything up to “about half way”. I rarely hear any guesses less than about 10%.

The real answer is very close to 1/10th of one percent. (~250/238,000 in miles ~= 0.001)

Another scale example is… if the Earth is the size of an apple, how thick is the atmosphere? Guesses are usually at least some large fraction of an inch. It’s really only about as thick as the skin on the apple. (~20/8000 in miles = .01/4 in inches)

102. SylverHive

Space is big indeed and beautiful, too, those beautiful things are easy to watch but very difficult to touch. It sucks not to be Dr.Manhattan.

103. Joseph G

Whenever I hear “let’s ramp it up,” I immediately think of Adam Savage.
“… so let’s ramp it up and see how much high-explosive it WOULD take to blow the moon up, and get those pieces moving at a velocity sufficient to keep them from re-forming!”

104. Noel Newnam

I have had for many years a piece of software entitled Galaxy Explorer. It allows you to move around the Milky Way, at any speed and in any orientation. You find quickly that if you travel from Earth to another planet–and even more so if to a different star–that you soon become impatient, so you keep speeding up and speeding up. When you get to the speed of light and it STILL takes forever to get anywhere, you start realizing just how big our own galaxy is. The only way to explore more than just our solar system during even a half-hour session is to “cheat” and go to, er–high warp speed, i.e. many, many, many, etc. times the speed of light (you have “spaceship” controls, including a speedometer that allows for almost infinite velocity). And that’s just one galaxy. VERY instructive! (Currently the speed is set at 12 million x c, and I’ve been somewhere out near the Large Magellanic Cloud after 5 minutes) (Oops–at 180 trillion x c, I almost crashed into the LMC; must pay attention to my driving)

105. Charlie in Dayton

Bruce Betts of The Planetary Society has come up with a unique scaling system of The Solar System…

“…if the Sun were the size of a small flake of dandruff on the top of your head, and Pluto were at the soles of your feet, then the distances to the entire inner solar system would be contained within your head. Jupiter would be about where your chin is, Saturn would be about the middle of your chest, and that’s right, Uranus would be exactly where you would expect it to be…”

The full quotation, laughter and all, can be found at http://planetary.org/radio/show/00000431/ — the relevant part of the mp3 starts at about the 23 minute mark.

Oh yeah…Neptune would be somewhere around your knees…

106. Eddie Janssen

To understand how big 1 million is, just put 1 million dots in a Word document. Depending on font and fontsize (i used arial 11) you get around 250 pages of dots, dots and more dots. Print it and flip through the pages to get a feeling of the vastness of one million.

107. JRE

Where I live there is a scale model of the solar which is a cycle track

http://www.solar.york.ac.uk/

108. I wanted to visualise the distances to get a grasp on just how big it is, so I created all the planets and the sun in 3D software at their accurate distances. It didn’t take me long to realise what a pointless task it was, as you couldnt see anything after even just a bit of zooming out.

Still, it was interesting to see how big the sun looked from pluto AND also I thought Mercury was much closer to the sun than it is.

109. Nigel Depledge

Endyo (34) (just in case no-one else answered already) said:

So here’s a fairly valid question(s) – The Earth is 3.7 times the diameter of the moon. The moon is made from the same basic material as the Earth since it was created from it. So why is does the Earth have six times the gravity? Does that mean it’s six times as massive? Why does the mass ratio differ from the diameter ratio? I’m assuming simply the Earth ended up more dense, though being made from the same material I’ m not sure what would cause that…

Assuming the same density (IIUC, it’s close enough)…

3.7 times the diameter is about 50 times the volume, so about Earth has about 50 times the mass of the moon.

So, the question should really be : why 6x the gravity and not 50x?

Gravitational field strength depends not only on mass, but also on distance from that mass. To any object outside another, uniformly-spherical object, that sphere may be treated as a point mass for calculating its gravitational influence. Because the Earth is so much larger (and thus its surface is so much farther from its centre of mass), the gravitational field strength at its surface is only 6x that of the moon. If the Earth had the same mass it has now but the same diameter as the moon, it would have 50x the gravitational field strength. Ish.

110. Jon

A bit late, but there’s another solar system model at the Arecibo radio telescope visitor center, in Puerto Rico. The sun is about basketball-size. Each planet (well, the inner ones, anyhow) are placed on the walkway up to the telescope itself, and each is also shown to scale – tiny peas in plastic!

It goes through Saturn (it’s a long walk!) and Uranus is on one of the supporting towers (easily visible with binoculars). They apologize for leaving out Neptune and Pluto, but they’ve good reason to.

J.

111. Gus Snarp

OK, reading about all these scale model solar systems has inspired me. I wonder how hard it would be to get one of my local parks to allow the installation of a scale solar system on one of their trails. Then I just need the money to build some decent planet models and signs and get it installed. Kickstarter might work to raise funds. I think it can be done.

112. Ken (a different Ken)

@33 Sam:

I did an activity recently with my daughter’s Brownie troop.

First, using Google Earth I measured the length of the longest hallway in the school. Then I scaled the Sun-Mars distance to a bit less than that, and figured where the other planets are and how big. I ended up with an 18″ Sun at one end, and a few crumbs of Model Magic for the inner planets. We started at the Sun, and the girls measured the distances (I brought a 100′ tape measure) and placed the planets. They realy enjoyed it, especially seeing the pea-sized Earth with the sun way down the hall (alas, in their excitement Earth got squashed flat, but they got the point anyway ).

After placing Mars I read out to them landmarks where the other planets would go – Jupiter at the traffic light in front of the school, Saturn at the baseball diamond at the adjacent school, Uranus at the local outdoor pool, etc. to Pluto at the Wal-Mart downtown (yes I let Pluto be a planet again for a little while; I didn’t have enough time to explain why it isn’t).

I also did a talk with pictures of galaxies and nebulae, including talk of star birth and death, and answered lots and lots of questions. I’m not an astronomer by any measure; most of what I know came from some guy’s book I read recently (had an orange cover, I forget what it was called.. )

I concluded the session with a bit about Hanny and her Voorwerp, and gave out copies of her graphic novel (kindly autographed by Dr. Gay, which the kids were also very excited to see ["a real astronomer!"]).

All in all, it’s hard to say whether the kids or I enjoyed it more.

113. Brian Regan

The big yellow one is the sun!

114. Steelman

All of these Comments are in 2 Dimensions. What about 3 Dimensions. We think that we are stationery at wherever we are, but think of the complex movement we are making.
We are moving with the earth on its axis, about 1,000 mph at the equator. The earth is moving around the Sun at about 800,000 miles an hour, then the earth is part of the Milky Way which is moving through space and that is mind boggling as to how we are actually moving through space.

115. Steelman

Expanding my previous comment and correcting some numbers, as follows:

Complicated motion !

People take it for granted that when they sit in a chair or lie in bed, that they are stationary.

Individuals do not consider what a complex movement we actually go thru when it feels like we are standing still or driving on the Highway, or Walking.

Consider the following scientific facts. We are on the surface of the Earth, rotating on its axis to give us night and day. The Earth is in an orbit around the Sun, once every 365 ¼ days. The Solar System is moving within the Milky Way Galaxy, and the Galaxy is also moving through Space, as the Universe is Expanding.

The Earth is approximately 8,000 miles in Diameter.
The Moon is approximately 230,000 miles away from Earth.
The Sun is approximately 93,000,000 miles away from Earth.
Our Solar System is just a tiny part of the Milky Way Galaxy.

The complex movements are as follows:

We are on the surface of the Earth, which is rotating about 1,000 miles per hour
The Earth is rotating around the Sun, at about 800,000 miles per hour
Our Solar System is moving within the Galaxy at about 500,000 miles per hour
Our Galaxy is moving through Space at about 900,000 miles per hour

A few other facts are as follows:

The Milky Way Galaxy (containing the Solar System) is about 100,000 light years in diameter.
The thickness of the Galaxy is about 1,000 light years.
Our tiny Galaxy is estimated to contain up to 400 billion stars.

Remember that a light year is the distance light travels in a year at 186,300 miles per second.

Light gets here from the moon in about 1.3 seconds, reflected from the Sun.
Light gets here from the sun in about 8 minutes.

Thought you might like to have this information to make you realize what we are actually doing.

116. CB

From my quick (and maybe incorrect) calculations, if a planet has twice the mass of the earth, you would weigh the same on that planet, if its radius is sqrt(2) times earth’s radius. And at that radius and mass, all other things being equal, the average density would be 1.78 times earth.

117. Don Q

@CB, I think… incorrect.

At twice the mass, and sqrt(2) radius… My math says that since the new volume is proportional to r^3. The new density would be mass/volume = 2/[sqrt(2)^3] = sqrt(2)/2 = .707… With this math, at the same density, bigger planets have higher surface gravity which matches observation.

With CB math, at equal density, the bigger planet would have less surface gravity. For big enough planets, surface gravity would tend toward zero. In that universe, a small enough grain of sand would gravitationally consume all matter that came into contact with it! This does not match observation.

118. Brett

The SETI Podcast, “Are We Alone” just did an episode in which they did this, using a ping pong ball as the size of the sun, and the planets’ distance relative to that.
EDIT
It’s the Feb. 12 episode titled “Outta This World”. Definitely worth checking out!

119. humanzee

@ Monkey (#97)

Just felt a wee bit compelled to express how completely cool & remarkably effective I think your toilet tissue method of conveying a sense of the really, really long-term time scale that the history of planet earth possesses — most especially how, in that full-blown context, the actual written history of everything involving human beings and all things humans have been involved in, barely, just *barely* occupies any space at all — near the very end of the very last square of tissue paper!

I’m pretty, fairly certain that, as a high school student (way back in the day), participating in a truly meaningful learning experience such as this one, I would have been completely astounded — “blown away”, if you will . . . “to infinity & beyond” (courtesy of Buzz LightYear, of course).

Keep up the quality teaching!

120. Grant

Man, it’s almost like the Earth isn’t the center of the universe.

121. Grant

Also, does anyone know why (or know somebody who knows why) Bode’s law works the way it does???

122. Messier Tidy Upper

@ ^ Grant : Afraid, “Bodes law” (actually the Titius-Bode law) does NOT work.

Just heard a good new scale comparison watching the rather good TV documentary series The Universe ( 26th Feb. 2011, “7mate” channel 73 -Milky Way epsiode) from one of the people interviewed or producing that :

“If the solar system was the size of a CD then the Milky Way would be the size of the whole Earth.”

***

Few more possible pertinent quotes here :

“If you put three grains of sand inside a vast cathedral, that cathedral will be more densely packed with grains of sand than stars are found apart in space.”
- Sir James Jeans, British astronomer, quoted on page 28, ‘Skywatching’, David H. Levy, Ken Fin Books, 1995.

“Space isn’t remote at all. Its only an hour away if your car could go straight upwards.”
- Sir Fred Hoyle, P.43, ‘The Wonderful World of Space’, Heather Couper, Octopus Books, 1980.

[But!]

“If it were possible to drive straight from the Earth to Neptune, taking the shortest possible route and keeping up a steady 60 m.p.h., the journey would take nearly 5,200 years.”

– P. 57, ‘The Sky at Night’, Patrick Moore, WW. Norton & Co, 1986.

123. Messier Tidy Upper

See :

http://en.wikipedia.org/wiki/Bode%27s_law

for more on Bode’s law from that usual fount of all knowledge – wikipedia.

124. Ribi

I haven’t read all comments, but wouldn’t it actually be pretty doable to make a video at the scale Phil is describing for Earth, Moon, and Sun? My thought would be to find an old 26-meter radio telescope somewhere, hold up the basketball and tennis ball once in front of it, then keep filming while the team travels 2.8 km from it, and set up the final demonstration at a distance, bringing along a zoom lens to get a slow shot in and back to the telescope’s dish. Super bonus points for getting the rights to film from somewhere on the dish tower or rim and getting either a telescopic shot of the team in place, or a firework/flare shot off from their location, just for another perspective.

125. noen

Knowing trivial facts is no longer important. Anyone with a cell phone (and everyone has them, even farmers in Africa) can find the answer to most trivial facts. What is important is knowing how to reason correctly from known facts. If that is indeed the true legacy of the internet then I count that as a good thing.

126. Mag

Since this article is moon related, I’ll tell a little moon story…

My son (5th grade) came home from school one day last week frustrated with his science “teacher”. His science “teacher” told the class that the moon has no gravity. Her proof? If the moon had gravity it would crash into earth. I was speechless.

127. Grant

Thanks for the link, MTU

@ Mag I know of somebody whose little sister was told by her teacher that the moon only comes up at night, and can’t be seen during the day!

128. Messier Tidy Upper

@128. Grant : No worries.My pleasure.

Incidentally, just saw Brian Cox’s Wonders of the Solar System documentary. Superluminous (beyond merely brilliant or shiny!) show & that noted another great scale point apparently :

If our Earth is 1 cm from our Sun – & Pluto is 50 cm from it – then the edge of the Oort Cloud of Comet’s would be 1/2 a kilometer away!

Paraphrased from memory so hope I’ve got that right but pretty sure I have.

@ Mag I know of somebody whose little sister was told by her teacher that the moon only comes up at night, and can’t be seen during the day!

I “independently discovered” the daytime Moon in high school. I remember looking up seeing this thing in the sky thinking Wait that’s the Moon even though – whoah! It’s up in the day too!* and being pretty buzzed with it.

Then again, when out camping as a kid one night, I saw a very yellow moon set / rise & convinced myself it must have just been hit by a meteor & turned molten (!) so ..

@127. Mag :

My son (5th grade) came home from school one day last week frustrated with his science “teacher”. His science “teacher” told the class that the moon has no gravity. Her proof? If the moon had gravity it would crash into earth. I was speechless.

Wha .. I .. don’t .. just .. what .. the *science* teacher . . said ..what!!!

That is staggering.

Did you take it up with the school’s principal or would’nt that do any good?

129. Nigel Depledge

Steelman (116) said:

The Earth is rotating around the Sun, at about 800,000 miles per hour

Erm … I’m not so sure about this figure (and, BTW, the Earth revolves about the sun and rotates about its own axis).

Assuming a mean Earth-sun distance of 93,000,000 miles, the circumference of Earth’s orbit is about 584,000,000 miles (distance Earth travels around the sun over the course of a year). That’s roughly 1,600,000 miles per day or just under 67,000 miles per hour.

130. Messier Tidy Upper

Just in case someone else is still reading this or will in future :

A scale model : If a galaxy’s central bulge were a hundred miles across, its central supermassive black hole would be roughly the size of a sand grain.

Source : Page 14, “NewsNotes” in ‘Sky &Telscope ‘magazine, April 2011, VP Publishing.

Is another great if rather specific scale comparison that I stumbled on t’other day.

131. Geeky Goblin

Long time blog reader but new teacher-in-training and while doing research for an assignment in science education (on astronomical scale) I remembered this blog post (woot! Extra reference!)

I found a great study into how bad people in general are in estimating distance (Miller & Brewer, [i]Int J of Sci Ed[/i] (2010) 32:1549-60). They used a baseball as the earth and asked undergraduates to estimate the distances to the moon, the sun, the nearest star and nearest galaxy and found that on average the estimates were under by 33%, 64%, 93% and 99% respectively. We are REALLY REALLY bad and wrapping our heads around astronomical distances. Or as the very first person who quoted the great Douglas Adams, Space is big. Really big…

132. Anthony

So wait, the sun is 480 light-seconds away, I read in one of the comments. So this means if something happened to the sun we literally would have no idea about it until 10 minutes after it actually happened?

Does no one else see a scenario in which aliens extinguish the sun then use warp technology to arrive at Earth precisely one minute before the sun goes out forever, thereby increasing the dramatic verve of their arrival and wiping out the entire planet 60 seconds later? HOW CAN I BE THE ONLY ONE THAT SEES THIS TERRIFYING FUTURE?!

There’s only one answer. Develop a system of nuclear powered rocket boosters (a la Isaac Asimov’s “The Gods Themselves”) and push the Earth closer to the sun. Every other program is basically just whistling in the dark.

133. Calin Mauch

I just watched an episode of Terra Nova, in which the moon appeared to be enormous. In the television series they state that the moon moves about .5 centimeters away from the earth each year. The show itself is set 85 million years ago meaning that the moon would have been approximately 697.5 miles closer to the earth. Would that distance truly be perceptible by the human eye?

134. UrConfused

This hurts my head. I love it.

135. Daisy

How many times farther away is the Sun than the Moon?

136. vayenn

Just throw away the tennis ball until it appears the same size as the moon in the sky – there is the disance. The size of the basket ball doesn’t matter.

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