Happy New Year! Again!

By Phil Plait | January 1, 2011 12:02 am

I don’t usually repost blog entries, because it’s lazy. But it’s 2.5 hours before New Years as I sit here, and you know what? Tonight I’m lazy (though not so lazy to make a few edits to bring the post up to date). Plus, this post was last seen three years ago, on December 31, 2007, and I have a lot of new readers since then so it’s new to them. Also? This post is one my favorites I’ve ever written. So enjoy it, but fair warning: if you’re hungover I can almost guarantee this’ll make it worse.


Yay! It’s a new year!

But what does that mean, exactly?

The year, of course, is the time it takes for the Earth to orbit the Sun, right? Well, not exactly. It depends on what you mean by "year", and how you measure it. This takes a wee bit of explaining, so while the antacid is dissolving in your stomach to remedy last night’s excesses, sit back and let me tell you the tale of the year.

First, I will ignore a few things. For example, time zones. These were invented by a sadistic watchmaker, who only wanted to keep people in thrall of his devious plans. So for now, let’s just ignore them, and assume that for these purposes you spend a whole year (whatever length of time that turns out to be) planted in one spot.

However, I will not ignore the rotation of the Earth. That turns (haha) out to be important.

Let’s take a look at the Earth from a distance. From our imaginary point in space, we look down and see the Earth and the Sun. The Earth is moving, orbiting the Sun. Of course it is, you think to yourself. But how do you measure that? For something to be moving, it has to be moving relative to something else. What can we use as a yardstick against which to measure the Earth’s motion?

Well, we might notice as we float in space that we are surrounded by zillions of pretty stars. We can use them! So we mark the position of the Earth and Sun using the stars as benchmarks, and then watch and wait. Some time later, the Earth has moved in a big circle and is back to where it started in reference to those stars. That’s called a "sidereal year" (sidus is the Latin word for star). How long did that take?

Let’s say we used a stopwatch to measure the elapsed time. We’ll see that it took the Earth 31,558,149 seconds (some people like to approximate that as pi x 10 million (31,415,926) seconds, which is an easy way to be pretty close). But how many days is that?

Well, that’s a second complication. A "day" is how long it takes the Earth to rotate once, but we’re back to that measurement problem again. But hey, we used the stars once, let’s do it again! You stand on the Earth, and define a day as the time it takes for a star to go from directly overhead to directly overhead again: a sidereal day. That takes 23 hours 56 minutes 4 seconds = 86,164 seconds. But wait a second (a sidereal second?) — why isn’t that exactly equal to 24 hours?

I was afraid you’d ask that — but this turns out to be important.

It’s because the 24 hour day is based on the motion of the Sun in the sky, and not the stars. During the course of that almost-but-not-quite 24 hours, the Earth was busily orbiting the Sun, so it moved a little bit of the way around its orbit (about a degree). If you measure the time it takes the Sun to go around the sky once — a solar day — that takes 24 hours, or 86,400 seconds. It’s longer than a sidereal day because the Earth has moved a bit around the Sun during that day, and it takes a few extra minutes for the Earth to spin a little bit more to "catch up" to the Sun’s position in the sky.

Here is a diagram from Nick Strobel’s fine site Astronomy Notes that will help explain this:

See how the Earth has to spin a little bit longer to get the Sun in the same part of the sky? That extra 4 minutes (really 3 m 56 s) is the difference between a solar and sidereal day.

OK, so we have a year of 31,558,149 seconds. If we divide that by 86,164 seconds/day we get 366.256 days per year.

Wait, that doesn’t sound right. You’ve always read it’s 365.25 days per year, right? But that first number, 366.256, is a year in sidereal days. In solar days, you divide the seconds in a year by 86,400 to get 365.256 days.

Phew! That number sounds right. But really, both numbers are right. It just depends on what unit you use. It’s like saying something is 1 inch long, and it’s also 2.54 centimeters long. Both are correct.

Having said all that, I have to admit that the 365.25 number this is not really correct. It’s a cheat. That’s really using a mean or average solar day. The Sun is not a point source, it’s a disk, so you have to measure a solar day using the center of the Sun, correcting for the differences in Earth’s motion as it orbits the Sun (because it’s not really a circle, it’s an ellipse) and and and. In the end, the solar day is really just an average version of the day, because the actual length of the day changes every, um, day.

Confused yet? Yeah, me too. It’s hard to keep all this straight. But back to the year: that year we measured was a sidereal year. It turns out that’s not the only way to measure a year.

You could, for example, measure it from the exact moment of the vernal equinox in one year to the next. That’s called a tropical year. But why the heck would you want to use that? Ah, because of an interesting problem! Here’s a hint:

The Earth precesses! That means as it spins, it wobbles very slightly, like a top does as it slows down. The Earth’s wobble means the direction the Earth’s axis points in the sky changes over time. It makes a big circle, taking over 20,000 years to complete one wobble. Right now, the Earth’s axis points pretty close to the star Polaris, but in a few hundred years it’ll be noticeably off from Polaris.

Remember too, that our seasons depend on the Earth’s tilt. Because of this slow wobble, the tropical year (from season to season) does not precisely match the sidereal year (using stars). The tropical year is a wee bit shorter, 21 minutes or so. If we don’t account for this, then every year the seasons come 21 minutes earlier. Eventually we’ll have winter in August, and summer in December! That’s fine if you’re in Australia, but in the northern hemisphere this would cause, panic, rioting, bloggers blaming each other, etc.

So how do you account for it? Easy: you adopt the tropical year as your standard year. Done! You have to pick some way to measure a year, so why not the one that keeps the seasons more or less where they are now? This means that the apparent times of the rising and setting of stars changes over time, but really, astronomers are the only ones who care about that, and they’re a smart bunch. They know how to compensate.

Okay, so where were we? Oh yeah– our standard year (also called a Gregorian year) is the tropical year, and it’s made up of 365.24 mean solar days, each of which is 86,400 seconds long, pretty much just as you’ve always been taught. And this way, the vernal equinox always happens on or around March 21 every year.

But there are other "years", too. The Earth orbits the Sun in an ellipse, remember. When it’s closest to the Sun we call that perihelion. If you measure the year from perihelion to perihelion (an anomalistic year) you get yet a different number! That’s because the orientation of the Earth’s orbital ellipse changes due to the tugs of gravity from the other planets. It takes about 100,000 years for the ellipse to rotate once relative to the stars! Also, it’s not a smooth effect, since the positions of the planets change, sometimes tugging on us harder, sometimes not as hard. The average length of the anomalistic year is 365.26 days, or 31,558,432 seconds. What is that in sidereal days, you may ask? The answer is: I don’t really care. Do the math yourself.

Let’s see, what else? Well, there’s a pile of years based on the Moon, too, and the Sun’s position relative to it. There are ideal years, using pure math with simplified inputs (like a massless planet with no other planets in the solar system prodding it). There’s also the Julian year, which is a defined year of 365.25 days (those would be the 86,400 seconds-long solar days). Astronomers actually use this because it makes it easier to calculate the times between two events separated by many years. I used them in my PhD research because I was watching an object fade away over several years, and it made life a lot easier.

So there you go. As usual, astronomers have taken a simple concept like "years" and turned it into a horrifying nightmare of nerdy details. But really, it’s not like we made all this stuff up. The fault literally lies in the stars, and not ourselves.

Now if you’re still curious about all this even after reading my lengthy oratory, and you want to know more about some of these less well-known years, then check out Wikipedia. They have lots of info, but curiously I found it rather incomplete. I may submit something to them as an update (like how many seconds are in each kind of year; they only list how many days, which is useful but could be better).

I have to add one more bit of geekiness. While researching this entry, I learned a new word! It’s nychthemeron, which is the complete cycle of day and night. You and I, in general, would call this a "day". Personally, if someone dropped that word into casual conversation, I’d beat them with my orrery and astrolabe.

Incidentally, after all this talk of durations and lengths, you might be curious to know just when the Earth reaches perihelion, or when the exact moment of the vernal equinox occurs. If you do, check out the U.S. Naval Observatory website. They have tons of gory details about this stuff.

Hmmmm, anything else? (counting on fingers) Years, days, seconds, yeah, got those. Nychthemeron, yeah, Gregorian, tropical, anomalistic… oh wait! I know something I forgot to say!

Happy New Year.

CATEGORIZED UNDER: Astronomy, Cool stuff, Geekery, Humor

Comments (60)

  1. Messier Tidy Upper

    HAPPY NEW YEAR Y’ALL! :-)

    Thanks Bad Astronomer for a superluminous blog which I’ve loved reading and participating on for many years now & hope to keep doing so for many more. :-)

    BTW. Don’t worry about the odd re-post, its not all that lazy in my view & some things bear repeating. ;-)

    Plus – aha! Have I scored the first BA blog comment of 2011? :

    http://blogs.discovermagazine.com/badastronomy/2010/12/27/another-exoplanet-joins-the-hr-8799-family/#comment-349772

    Hmm .. I think I might’ve. Yay! :-)

    Also happy 210th anniversary to the wonderful little world of Ceres, the smallest dwarf planet (unless you count Vesta or another asteroidal one) and largest asteroid making up 1/3rd the whole mass of the asteroid belt and possibly holding more water than fresh water on Earth* which was discovered on 1 January 1801 by Giuseppe Piazzi :

    http://en.wikipedia.org/wiki/Ceres_(dwarf_planet)

    Interesting, I think, to note that Isaac Asimov once noted hopefully that :

    “I consider it quite conceivable that the day may come when Ceres will be the astronomical centre of the solar system.”
    – Page 66, chapter 5 “The World Ceres” in ‘The Tragedy of the Moon’ by Isaac Asimov, Mercury Press, 1973.

    Based, if I recall right, on its solar system vantage point and atmosphere-less skies. I think I read somewhere (there?) that from the Cerean surface you can see the large Jovian moons with unaided eyes but I could be wrong.

    Anyhow, once again, Happy New Year everyone. :-)

    _______________________________________

    *

    “Once thought to be rocky, we now believe Ceres may contain 200 million cubic kilometres of water in its mantle. This is more than the amount of fresh water on the Earth.”
    – Page 10, “Ceres may be a failed miniplanet” by Jeff Foust in Astronomy Now magazine, November, 2005.

    Yes, going a little off-topic I know, sorry, I hope that’s alright.

  2. Brian

    Happy new year, whichever one you prefer.

  3. Messier Tidy Upper

    @ ^ Brian : You mean the Western, Jewish or the Chinese New Year there? ;-)

    Or can we just pick any year as our own? (I’ll have 2061 when Halley’s comet returns again & when the third Space Odyssey novel is set I think – thanks!) ;-)

    NB. I love the palindromic nature of the date today 1 / 1 / ’11. 8)

    PS. Very minor point & I’m sure there’s an explanation but :

    ..sidus is the Latin word for star.

    Not stella(r)?

  4. Orlando

    Great post! And Happy New Year (any of them) from Spain!

    +1 Nychthemeron (I admit I’ve practised its spelling several times). Now, it’s time to find how it is said in my mother language.

  5. Jim

    And a happy New Year to you too! I love the nerdy details!

  6. psuedonymous

    “That’s fine if you’re in Australia, but in the northern hemisphere this would cause, panic, rioting, bloggers blaming each other, etc.”
    Cats and dogs! Living together! Mass hysteria!

  7. Let’s just use stardates and be done with it all!

  8. MadScientist

    @Messier#2: There are various names used through the ages, including ‘astrum’. I wonder if it’s a bit like the numerous words for snow: whitesnow, yellowsnow …

  9. bloggers blaming each other

    I blame people who comment on blogs. They’re the worst sort.

    Happy New Year.

  10. DrFlimmer

    With this bit of nerdy geekieness the year 2011 (based on whatever unit system) started quite well! :)

    So, happy new year to all of you and your beloved! :)

    May the force be with you! :-D

  11. Messier Tidy Upper

    It’s nychthemeron, which is the complete cycle of day and night. You and I, in general, would call this a “day”. Personally, if someone dropped that word into casual conversation, I’d beat them with my orrery and astrolabe.

    Isn’t that a bit rough …

    … on your orrey &/or astrolabe? ;-)

    Also, BA, *which* word would you beat them for saying – nychthemeron or day? ;-)

    @7. MadScientist : Could well be. Sidus, stella, astra / astrum, .. do those all mean ‘star’ in Latin? Hmm. Is there a slight difference in meaning, anyone know?

  12. Kevin

    My head hurts now!

  13. Fizzics Teacher

    Wow, Latin lessons, a new Greek word, math, and astronomy on the 1st day of 2011 (Common Era). I’m glad BA did not go into the various ways we have of numbering/naming the years.That would be too much nerdiness for the 1st day.

  14. Pete Jackson

    An easy way to remember the length of a year? Try the lyrics of the song “Seasons of Love” (written by Jonathan D. Larson) in the musical Rent:

    Five hundred twenty-five thousand six hundred minutes
    Five hundred twenty-five thousand moments so dear
    Five hundred twenty-five thousand six hundred minutes
    How do you measure, measure a year?

    Of course, that is just for an ordinary, non-leap year. Leap years have five hundred twenty-seven thousand and forty minutes. If we consider only every fourth year as a leap year (Julian calendar), then that averages to five hundred twenty-five thousand nine hundred and sixty minutes.

    Our Gregorian calendar drops the leap year in three out of every four ‘century’ years (like 1900), giving an average length of 365.2425 days or five hundred twenty-five thousand nine-hundred and forty-nine point two minutes. The actual tropical year currently has 365.2422 days or five hundred twenty-five thousand nine-hundred and forty-eight point eight minutes.

    But neither of these can possibly fit into the song. Geekiness spoils romance every time.

    Happy New Year!

  15. Radwaste

    525,600 minutes?
    That’s so useful. Like there being 9192631770 oscillations between the hyperfine ground states of the Cs-133 atom in each second. Treat it like a phone number.

    Or that there are about 41253 square degrees in a sphere. It’s an unassigned Zip code that might be used in Kentucky some day.

  16. magetoo

    but fair warning: if you’re hungover I can almost guarantee this’ll make it worse.

    Good thing I stayed up and kept drinking then.

    nychthemeron

    The lack of a good word for that in English has really been bothering me. I dare say “nychthemeron” doesn’t really look like the ideal solution either. (How about you guys adopt “dygn” for it instead? It’s a heckuva lot less to type. You could even pronounce it “dyne” which sounds all buckminsterfullery and stuff.)

    Happy New Year, everyone.

  17. Hi Phil,

    In how many different directions are we moving, if say as you say, we’re planted (reading science blogs all year, for example). And if it’s not too much trouble, we’d like to have velocities and vectors, including a cool final one.

    So far I have:

    – Rotation around the earth
    – Lunar effects
    – Planetary effects, mainly Jupiter’s (should we ignore the others, for all practical purposes?)
    – Rotation around the Sun
    – Our solar system’s bobbing up and down perpendicular to The Milky Way’s plane (once every 60 million years, I believe)
    – Sol’s rotation around The Milky Way
    – The Milky Way’s mutual attraction to the Andromeda galaxy in our Local Group (should we ignore the LG’s other galaxies, for all practical purposes?)
    – Our Local Group’s attraction to the Virgo Cluster
    – the Virgo Cluster’s attraction to the Virgo Supercluster
    – The Virgo Supercluster’s attraction to The Great Attractor
    – Whatever the heck The Great Attractor is attracted to
    – The expansion of space

    Thanks in advance, and Happy New Year Phil, to you and yours.

  18. Tom K

    Most people just don’t realize that the universe makes a TERRIBLE clock. Nothing is evenly divisible by anything else, and it’s always changing.

  19. John Baxter

    Phil, things could be worse. You could have done your PhD research in Bali, contending with the Balinese calendar systems.
    http://en.wikipedia.org/wiki/Balinese_calendar
    and
    http://www.indo.com/culture/calendar.html

    I went to sleep about 22:00 (local time) on Dec 31, and woke up around 01:00. And said to myself: “So far, this year is going better than last year.”

  20. Gary Ansorge

    16. Tom K

    “Nothing is evenly divisible by anything else, and it’s always changing.”

    Someone once noted, “If the universe was created by chaotic processes, rather than by intelligence, it would look pretty much like this.”

    Happy new year.

    Gary 7

  21. Daniel J. Andrews

    Another year over and what did you get?
    Another year older and closer to death.

    ;)

    with apologies to George Davis.

    Happy New Year.

  22. I decided to look for some science blogs today, and stumbled across this post. Glad I did; not only did I learn something, I LOL’d several times. I salute your teaching style and your sense of humor. Happy New Year.

  23. Love science like this! And Gary, that is so true! Gotta add it to something one of these days.

  24. John Sandlin

    Well, Happy New Year to those celebrating it today.

    Personally, I always celebrate the beginning of a new year on March 24.

    I’m joking, of course.

    jbs

  25. JMW

    Happy New Year, all!

  26. Garry-former astrology believer

    Does the planet Mercury influence our radio waves and cell phone communications?
    The first person I met this year was a master’s student at a New York City university (Columbia) who told me that without Mercury we could not have our cell phone communications.

    He even told me that his Professor thinks astrology is nonsense, but this has not changed the student’s mind.

    Specifically what can anyone tell me about the planet Mercury affecting our cell phone technology?
    Is it a myth spread by astrologers desperate to justify their ancient and unscientific beliefs?

    Needless to say I am completely skeptical about astrology although I used to be interested in it.
    Here are more reasons to be skeptical:
    The distance from Mercury to the Earth varies greatly as both planets orbit the Sun. At its closest approach, Mercury is about 77 million kilometers (48 million miles) from Earth*. At its farthest, about 222 million kilometers (138 million miles).
    Read more: http://wiki.answers.com/Q/How_far_away_is_the_planet_Mercury_from_Earth#ixzz19o01w3cz

  27. kevbo

    Hey! My calendar ended yesterday, and the world didn’t come to an end? What’s with that?

  28. Ed

    Hi Phil – Happy New Year!

    BTW, technically speaking, the average time between any two vernal equinoxes is the Vernal Equinox Year; the Tropical year is the average across all possible days in the calendar.

    I believe these references have some information on this:
    http://adsabs.harvard.edu/abs/1992JBAA..102…40M
    http://www.hermetic.ch/cal_stud/cassidy/err_trop.htm

    I encountered this subtlety while reading Duncan Steel’s book Marking Time:
    http://www.amazon.com/Marking-Time-Invent-Perfect-Calendar/dp/0471298271/ref=sr_1_9?ie=UTF8&qid=1293911938&sr=8-9

    BTW, I wrote a series of articles on TimeZone.com about the units of time in 2001 for the layperson who has some technical interest:
    http://www.timezone.com/library/tmachine/tmachine0004
    http://www.timezone.com/library/tmachine/tmachine0005
    http://www.timezone.com/library/tmachine/tmachine0006

    ed

  29. Bobby Stefanov

    Thank you! I am now a little smarter. And here I was thinking greeting people with “Happy revolution around the Sun” was cool…

    For nychthemeron in Bulgarian we have denonoshtiye (basically “dayonight”) and it’s very common. I always wondered why there wasn’t a word like that in English. Now I see there is, although it looks like “nightmare”.

  30. Mike G

    Around a year ago, one of our instrument scientists circulated an amazing bit of popsci — a 1960s Edmunds Scientific *comic book* on the nature of time. It was sufficiently sophisticated to pass on to our subcontractor building the telescope pointing system. It was clearly aimed at amateurs, but went into sidereal time, the Equation of Time, precession, nutation, refraction, and everything else you might need to blind-point a telescope. It had lots of tables and many clear diagrams, well presented. I was flabbergasted at what they thought was amateur material, and I can’t imagine a modern publication like that.

  31. amphiox

    that without Mercury we could not have our cell phone communications.

    Is your friend actually referring to astrological ideas, or is this statement intended to be a metaphorical one based on a misconception of the history of science?

    ie, the logic could be as follows;

    1. Mercury’s observed orbit deviates from that predicted by Newtonian gravity
    2. Without the observations of these deviations, we would not have had reason to question the validity of Newtonian gravity
    3. Thus General Relativity would either not have been developed, or not accepted as readily
    4. Without General Relativity, GPS and communications satellites would not be possible, or if possible, would not function as well or as precisely as they do
    5. Without these satellites, cell phones would not have been developed.

    Ergo, if Mercury did not exist, human beings would have never invented cell phones.

    Of course all the above except the first are erroneous in one way or another, but it actually has nothing to do with astrology.

  32. Pete Jackson

    @ed No. 29; in tmachine0005:

    “Caesar also changed the length of the days of the months to their modern values”

    Is it just coincidence that the summer quarter: June, July, August when the Earth passes through aphelion is the longest at 92 days whereas the winter quarter: December, January, February when the earth passes through perihelion is the shortest at 90 days? This keeps the equinoxes and solstices all reasonably close to the 21st of March, June, September, and December. I always wondered if the Romans did this concsiously or if it just came out of the wash that way.

    Great articles!

  33. Joseph G

    Thank you, Phil, for an uber-effulgent, super-lambent and hyper-perspicacious year of blogging!
    And happy New Year (adjusted for precession but relying on Gregorian Nychthemeron values) to all! :D

    (yet another reason I love this blog – I relish any fortuitous exigency to accrue a more commodious lexicon!)

  34. Kevin

    It’s come up again that this is the first year of the new decade. I remember the post from last year saying that last January 1st was the beginning of the new decade.

    Heavy sigh.

  35. Tribeca Mike

    Happy New Year, Messr. Plait. Yours is the best damn blog on the intertubes, bar none. Keep up the terrific work!

    And your commenters ain’t bad either.

  36. Messier Tidy Upper

    me @ #1 : Plus – aha! Have I scored the first BA blog comment of 2011?

    D’oh! Wrong link :

    http://blogs.discovermagazine.com/badastronomy/2010/12/27/another-exoplanet-joins-the-hr-8799-family/#comment-349772

    Should be the right one now – comment 27 on that “another exoplanet for HR 8799″ thread. Not sure what happened there, sorry.

  37. pdkl95

    http://www.youtube.com/watch?v=IhqzW97_47w&feature=channel

    an amazing animation of this problem. (also see the “day on earth” video by the same person, for the other half of the problem)

  38. Nigel Depledge

    MTU (3) said:

    PS. Very minor point & I’m sure there’s an explanation but :

    ..sidus is the Latin word for star.

    Not stella(r)?

    Hmmm, you may have a point. Perhaps the BA refers to different versions of Latin (e.g. ancient versus mediaevel Latin perhaps?). I also understood stella to be the latin for star, as in the mediaevel song Salva Nos, thus:

    Salva nos, stella maris,
    Et regina celorum
    .

    Save us, star of the sea
    And queen of heaven.

  39. Nigel Depledge

    Daniel Sinnott (7) said:

    Let’s just use stardates and be done with it all!

    Heh. Douglas Adams predicted this (sort of) when he named the widely-read newspaper in The Hitchhiker’s Guide to the Galaxy the “Sidereal Daily Mentioner”.
    :-)

  40. Nigel Depledge

    Garry (27) said:

    Does the planet Mercury influence our radio waves and cell phone communications?
    The first person I met this year was a master’s student at a New York City university (Columbia) who told me that without Mercury we could not have our cell phone communications.

    He even told me that his Professor thinks astrology is nonsense, but this has not changed the student’s mind.

    Specifically what can anyone tell me about the planet Mercury affecting our cell phone technology?
    Is it a myth spread by astrologers desperate to justify their ancient and unscientific beliefs?

    This sounds like utter nonsense to me, and fairly easily debunkable nonsense, too.

    First off, if Mercury influenced cellphone communications (or any other form of radio communication), you should be able to use the behaviour of your cellphone to predict the location of Mercury. Challenge this “master’s student” to do this, and see what (s)he says.

    Second, there is pretty much no way that Mercury can electromagnetically influence anything happening here on Earth.

    Let’s look at the numbers. A typical cellphone has a maximum rf (radiofrequency) output power of 5 W. (Normally, your phone will emit less than this to conserve the battery, but if the base-station signal is weak the cellphone increases its output power when trying to connect to it.) Base-stations emit higher power (they have mains electricity), and I don’t know exactly how much they use, but let’s say, for the sake of argument, that it’s 50 W (in reality, I expect it to be less than this because, if this were the case, the base station would become an “alligator” – all mouth and no ears).

    Generally, you need to be within 20 miles of the base station for your phone to be able to connect to it. In reality, you are often much closer than this, even if you have a poor signal, due to local topography, interference from buildings and other nearby dialectric materials and so on. But let’s call it 20 miles for the sake of argument (this is probably the maximum range of a typical phone and base-station combination under ideal conditions).

    Next, I’m going to consider both Mercury and the base station to be point sources, from the point of view of the cellphone, to keep things simple.

    The cellphone has an omni-directional antenna, so emits its power equally in all directions. Since radio waves dissipate according to a 1/r2 law, the distance matters. A lot. I’m not going to get into field-strength calcs here (‘cos I’d have to look it up to make sure I get it right), so we’ll consider the relative distances. Let’s say the cellphone is only just working well enough to make a phone call when it is 20 miles from the base station.

    How far away is Mercury at this point? Well, let’s assume, for the sake of argument, that Mercury and Earth are as close as they get (i.e. are both on the same side of the sun) in their respective orbits (and, again, for the sake of simplicity, I’m going to assume circular orbits).

    Earth’s orbital radius is 149,600,000 km, while Mercury’s is 57,910,000 km (from nineplanets.org). So, the distance between them is 91,690,000 km, or just over 57,300,000 miles.

    Thus, Mercury is 2,865,000 times farther from the base station than is your cellphone. Thus, any rf signal from Mercury arriving at the base station would be 8,208,225,000,000 times weaker than a comparable signal arriving from your phone. Or, to put it the other way around, Mercury would need to emit a signal with an ERP (effective radiated power) of over 41 TeraWatts to have the same signal strength arriving at the base station as the signal from your phone.

    The most powerful radio transmitters I am aware of are only 0.5 MW (the BBC World Service long-wave transmitters), and that’s enough power to give reception around the whole world. And it requires some pretty damn serious amplifiers. I daresay there are systems with higher output powers than this, but probably not by more than an order of magnitude. Of course, antennas can focus the fed power into a narrow beam and increase the ERP in one specific direction. A decent-sized dish antenna can provide a gain of about 50 – 60 dB (5 – 6 orders of magnitude) in ERP over fed power. So an ERP of up to 100 GW is (at least theoretically) feasible with technology that exists.

    But, hey, don’t you think we might notice a flipping great big dish antenna on Mercury, now that we have high-res photos from a space probe? And, come to think of it, if Mercury is influencing radio communications here on Earth, how the hell are we able to receive signals from the Messenger probe at all?

  41. Pascvaks

    Great piece, helps get the old grey matter churning once more. Rarely visit, can’t recall seeing you address this subject but it may tweek your thoughts some day: “Which Way Is Up?” (It too seems to be debateable;-)

  42. Thunderstar

    Here in Greece the word “nychthemeron” is a very common everyday word.We use it at least 10 times a day.So if you ever visit be gentle with us!!!

  43. Herculoid

    Just to set the record straight…Sir Sanford Fleming was not a “sadistic watchmaker”. He was a Scottish-born Canadian engineer and inventor who proposed worldwide standard time zones, designed Canada’s first postage stamp, engineered most of Canada’s Intercontinental Railway, and founded the Royal Canadian Institute.

  44. QuietDesperation

    The first person I met this year was a master’s student at a New York City university (Columbia) who told me that without Mercury we could not have our cell phone communications.

    o_O

    This sounds like utter nonsense to me, and fairly easily debunkable nonsense, too.

    Agreed, but we need to find out more about what the person meant. Maybe they meant the element mercury as it is used in electronics?

  45. The statement “That’s fine if you’re in Australia, but in the northern hemisphere this would cause, panic, rioting, bloggers blaming each other, etc.” is not entirely correct.
    Republican bloggers would be blaming Obama.

  46. Messier Tidy Upper

    @39. Nigel Depledge Says:

    Perhaps the BA refers to different versions of Latin (e.g. ancient versus mediaevel Latin perhaps?). I also understood stella to be the latin for star, as in the mediaevel song Salva Nos, thus:

    Salva nos, stella maris,
    Et regina celorum.

    Save us, star of the sea
    And queen of heaven.

    Nice reference there – never heard of that one. Thanks. :-)

    I was more thinking of the way ‘stellar’ is used to pertain to stars generally, Stellar nucleosynthesis, stellar associations, stellar performances ( ;-) ), etc ..

    Also from other historical Tycho Brahe’s 1573 book ‘De nova stella’ on the supernova bearing his name (SN 1572) the previous year.

    Source : http://en.wikipedia.org/wiki/Tycho_Brahe#The_1572_supernova

    Or Johannes Hevelius 1662 book Historiola Mirae Stellae naming Omicron Ceti “Mira” (meaning “wonderful” or “astonishing,” in Latin) and suchlike.

    Source : http://en.wikipedia.org/wiki/Mira#Observation_history

    As for ‘astra’ the first example of that that springs to mind is the latin saying quoted by Isaac Asimov :

    Per aspera ad astra – Through difficulties to the stars!

    Source : ‘Trends’ short story in The Early Asimov (one of 3 volumes, pretty sure that was the title – books currently unavailable for citing other details.)

    Oh and in the word Astr(a)-onomy too! ;-)

    I’d love to see the question of the precise meanings & differences between stella, astra & sidus resolved if anyone’s got enough latin knowledge to enlighten us please!

    @#37 : Sorry, still not working. Not sure why but I can’t seem to get that link to go where I want it – afraid you’ll just have to scroll down to comment 27 there. :-(

  47. Happy New Year from Buenos Aires. I just arrived to your blog and I’m in love with it! Beautiful, interesting and a very good sense of humor (somethig that most “serious” people and teachers lack of) I’ll visit you from now on.

  48. JMW

    Happy Asimov’s birthday!

  49. Buzz Parsec

    @#18 Steven Colyer, you left out continental drift ;-)

    For item 2, there are 2 different lunar effects. The Earth and Moon are orbiting their common center of gravity, several thousand miles from the center of the Earth (well inside the mantle.) While the Moon is revolving around the CoG in a big ellipse once a month, the Earth is also revolving in a much smaller ellipse about the same point, but on the opposite side. The 2nd lunar effect is the tides, which I think amount to several inches of twice daily vertical travel even if you are standing on solid rock. (If you’re in a boat on the Bay of Fundy, you would be moving up and down 10 meters or more twice a day.) Also, don’t forget solar tides, which are about half the size of lunar tides!

  50. Dionigi

    @Messier Tidy Upper (47) is it not ‘par ardua’ for difficulties ‘per aspera’ to aspire.
    As in ‘Par ardua ad mona’ through troubles to the Isle of Man the motto of the Isle of Man TT races.

  51. mike burkhart

    Happy new year!!!!!!! The Earths rotation is slowing down .Millons of years from now the sun will take centurys to cross the sky eventuly it will stop and one side of Earth will face the sun and one side will face away (like the moon one side faces Earth one side faces away) .I see Phil shares my intrest in ancient astronomacal insterments I have a armillery sphere ,witch was used to understand the movements of objects in the sky.All of these instrments were used to chart and mesure positions of objects.The invetion of the Telescope changed Astronomy forever now astronomers could get a close up view of objects.

  52. Foolishly Delicious

    Maybe Mercury refers to the Mercury space missions? I know they made many, many advances in that area of technology during the space race. I certainly hope that is what he is referring to.

  53. Cobb

    The top keeps spinning, so this is all just a dream anyway.

  54. Joseph G

    The bit about “without Mercury we wouldn’t have cell phones” is (I think) a reference to the unexpected rate of the orbital precession of Mercury (which was one of the first directly observable anomalies that showed Newtonian physics to be insufficient). It was first observed way back in the 1850s, and was one of the first concrete observations that supported general relativity.
    Without general relativity, communications satellites would go out of synch and gps would be completely inaccurate, so… eh. It’s a pretty long and tortured road, but I suppose it’s possible that at the very least, general relativity might have gained support more slowly if it weren’t for Mercury. So cell phones might have been delayed a few years.

    By that line of reasoning, though, the moon is much more vital to modern science then Mercury, as Eddington’s measurement of the bending of starlight by the Sun’s gravity during a total eclipse in 1919 was what really put general relativity on solid evidential footing.

  55. mike burkhart

    Intresting note :In the 1800s the devations in Mercurys orbit were thought to be caused by the gravational pull of a planet closer to the sun then Mercury.One Astronomer claimed to have discoverd it and named it Vulcan (no not Mr Spocks homeplanet) other Astronomers could not confrim his discovery and soon the idea of planet Vulcan was abandon .But there are a few who still look for it, the last serious attemp was useing Skylabs telescope with negative results .One Astronomer has sugested there may be an Asteroid belt between Mercury and the Sun but no one has as yet found it.

  56. Messier Tidy Upper

    @51. Dionigi Says:

    @Messier Tidy Upper (47) is it not ‘par ardua’ for difficulties ‘per aspera’ to aspire.
    As in ‘Par ardua ad mona’ through troubles to the Isle of Man the motto of the Isle of Man TT races.

    Could be, I’m just quoting it as I remember seeing it. Which was Isaac Asimov quoting it in one of his short stories written decades ago so, yeah, it may not be exactly right.

    I’d check the book again – fairly sure I got it right from there – but unfortunately all my books are packed into boxes and inaccessible for the next week or so. (Painting & carpeting happening at my house presently.)

  57. Messier Tidy Upper

    @56.mike burkhart :

    Intresting note :In the 1800s the devations in Mercurys orbit were thought to be caused by the gravational pull of a planet closer to the sun then Mercury.One Astronomer claimed to have discoverd it and named it Vulcan (no not Mr Spocks homeplanet) other Astronomers could not confrim his discovery and soon the idea of planet Vulcan was abandon .But there are a few who still look for it, the last serious attemp was useing Skylabs telescope with negative results .One Astronomer has sugested there may be an Asteroid belt between Mercury and the Sun but no one has as yet found it.

    “One astronomer eh?” Another astronomer who is pretty familiar here has also written about this topic too several times incl. quite recently – see :

    http://blogs.discovermagazine.com/badastronomy/2010/12/03/inside-mercurys-orbit/

    for more. ;-)

    Wonder if he could kindly give us a progress update on the Vulcanoid search? Please BA?

  58. This is an awesome post! Thanks for re-posting it – there’s no way I would have seen it otherwise.

    I’ve been learning about this in my astronomy course but didn’t really get it until I read this. Thanks again.

  59. vrk

    Actually, there are two words in Finnish that are translated as “day” in English: päivä and vuorokausi. The former can mean either the daytime day (see below) or the full 24 hour day, and the latter always means the full 24 hour day. So, vuorokausi corresponds to nychthemeron, even if it is always translated (ambiguously) as “day”. Both words are in common use, unlike in English, but probably similar to Greece as commenter #43 pointed out.

    About daytime day… I was about to say päivä is the hours most people are awake, but that discriminates against shift workers. Then I thought about saying it’s the hours during which you have daylight, but that discriminates against North Finland beyond the Arctic Circle, where you have several days or weeks with no sunrise in winter. It’s generally understood as both, even by shiftworkers and the Sami.

    (Yes, my comment is a bit late with respect to the original publishing date. I found this blog entry through a link in 9 Nov, 2011 entry about Carl Sagan’s birthday.)

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