Tag: Jupiter

Jupiter gets rocked by an impact again

By Phil Plait | September 17, 2012 10:00 am

By now you’ve probably heard that on September 10, Jupiter got whacked by an asteroid or comet again. It was seen directly by amateur astronomer Dan Peterson, and video was taken by George Hall, who kindly posted a fairly awesome a four-second clip on Flickr:

[You may need to refresh this page to see it.]

You can read more about it at Scientific American.

I tweeted about this shortly after it happened (I was returning from the UK and didn’t have time to write about it here), and got a lot of people wondering how big the flash was. On the video it looks like it’s thousands of kilometers across! But that’s not real; the size you see is due mostly to the optics of the telescope and video camera Hall used (plus other factors like atmospheric blurring). Given the brightness I guessed the object was a kilometer or so across, but I heard a radio interview the other day (I missed the guest’s name; sorry) where an astronomer said it may have been only 10 meters across – the size of a large truck.

I was surprised at first when he said that, but then realized something critical: Jupiter is a lot bigger than Earth.

The energy released by an asteroid upon impact depends primarily on two things: how big it is and how fast it’s moving. For a given asteroid, that means it’ll explode with far more energy if it hits Jupiter, because Jupiter’s gravity is much stronger than Earth’s, and pulls the rock in faster. Simply because of this, impacts on Jupiter can be greater than 20 times more energetic than on Earth. There are other factors (like orbital speeds, what direction the asteroid was moving, and so on), but in general and pound for pound Jupiter impacts are bigger than on Earth.

A 10-meter rock hitting the Earth will release roughly as much energy as a 0.1 megaton bomb, whereas on Jupiter that same rock will release about 2 megatons. A rock twice that size will have 8 times the mass (volume increases with the cube of the radius) so even if it were 20 meters across, the explosion could’ve been in the 15 – 20 megaton range, which is starting to get to the size of the largest nuclear weapons ever detonated on Earth.

So yeah, that’s a lot of power. It doesn’t take a big rock to make a bright flash when you’ve got Jupiter pulling the strings.

And the big planet gets hit a lot. The last one seen was on August 20, 2010, and it got whacked in June 2010 as well as in July 2009 (not to mention the ferocious series of impacts in 1994 from comet Shoemaker-Levy 9). That’s pretty close to one biggish impact seen per year, and remember we only see half of Jupiter at a time, and it’s not observed constantly! So the real rate is probably far higher.

I also got a lot of people asking why we call it an impact when Jupiter has no solid surface. That’s because the rock will still explode as it rams through Jupiter’s dense atmosphere; I wrote an explanation of this for an earlier impact. The 1908 Tunguska event here on Earth was an air blast, as well.

It’s amazing we can see these planetary at all, but that’s due to the digital revolution: amateur astronomers take video of Jupiter and other objects to maximize the number of frames they get, which they then can combine into amazing images. A nice side-effect from this is the collection of rapidly-taken data providing long coverage of the planets, which means significantly increasing the odds of seeing something like this. That is precisely why we’re seeing more impacts now than ever before. They’ve always been happening, we’re just a whole lot better at seeing them.

Which is a sobering thought. The Universe is worth investigating, if only for our own self-interest.


Related Posts:

ANOTHER Jupiter impact?
FOLLOWUP: Jupiter impact video and a color picture
Jupiter: bringing the hammer down
Hubble pix at Jupiter’s scar

BAFact Math: Jupiter is big enough to swallow all the rest of the planets whole

By Phil Plait | August 22, 2012 9:46 am

[BAFacts are short, tweetable astronomy/space facts that I post every day. On some occasions, they wind up needing a bit of a mathematical explanation. The math is pretty easy, and it adds a lot of coolness, which I’m passing on to you! You’re welcome.]


Today’s BAFact: Jupiter is so big you could fit every other planet in the solar system inside it with room to spare.

Volume is a tricky thing. Our brains are pretty good at judging relative linear sizes of things: this thing is twice as long as that thing, for example. But volume increases far more rapidly than linear size. Take a cube where each side is one centimeter. It has a volume of one cubic centimeter (cc). Now double the length of each side to 2 cm. It looks twice as big, but its volume goes up to 8 cc! The volume of a cube is a the length x width x height, so there you go.

Spheres are the same way: the volume increases with the cube of the radius. Specifically, volume = 4/3 x π x (radius)3. So one sphere might look slightly larger than another, but in fact have a lot more volume.

Such is the way of Jupiter. I see pictures of it compared to the other planets, and honestly Saturn looks only slightly smaller – Saturn’s radius is about 60,000 km compared to Jupiter’s 71,000. But that turns out to make a huge difference in volume!

Here’s a table I created to compare the planets. The first number column is the planet’s equatorial radius in kilometers (the biggest planets aren’t perfect spheres, but as you’ll see this doesn’t matter). The second number column is the volume in cubic km based on that radius. The third is the volume of the planet divided by the volume of Jupiter (so that ratio = 1 for Jupiter itself). The last column is the same, but rounded to two decimal places to make it easier to read.

The big conclusion here is pretty obvious when you look at that last column. Even though Saturn is only a little smaller than Jupiter, it only has 60% of the big guy’s volume! Uranus and Neptune together are only another 9%. If you combine all the planets in our solar system, they add up to only about 70% of Jupiter’s volume. That leaves a lot of room left over for all the moons and asteroids in the solar system, too!

So Jupiter really is a monster. There’s a half-joke astronomers say: The solar system consists of the Sun, Jupiter, and assorted rubble. As you can see, that’s really not that far off from the truth!

Image credit: NASA


Related Posts:

BAFact math: Give him an inch and he’ll take a light year
BAFact math: how big does the Sun look from Pluto?
BAFact math: How bright is the Sun from Pluto?
Announcing BAFacts: a daily dose of sciencey fun

MORE ABOUT: BAFacts, Jupiter, math, Saturn, volume

Planetary alignment pyramid scheme

By Phil Plait | August 20, 2012 12:46 pm

What the heck is in the air this past week? First we see a simulated image of the sky from Mars go massively viral because people thought it actually showed Earth in the Martian sky, then a clearly Photoshopped pic of two "Suns" setting on Mars gets passed around.

And now a new slice of oddness enters the field: a picture of a planetary alignment over the Giza Pyramids, saying this only happens once every 2737 years. Because planetary alignments and the pyramids play such a large role in New Age/astrological beliefs, there is clearly some sort of spiritual message implied here.

Well, I hate to be a thricely-bursting-bubble person, but here we go again, again. Let me be clear: while there will be an event more-or-less like this in December, and it should be pretty and quite cool to see, the claims being made are somewhat exaggerated. The picture itself isn’t real, and the planets won’t really look like that from Giza. Also, alignments like this happen fairly often, though to be fair getting them spaced out to fit over the pyramids in this way probably is relatively rare.


Busting your Cheops

Here’s the picture making the rounds:

It clearly shows the three pyramids in Giza, Egypt, with three planets above them. There are various versions of this picture I’ve seen; most are like this with almost no explanation. Some say the planets are Mercury, Venus, and Saturn, and some mention this is what it will look like on December 3rd, 2012, just before sunrise.

First, this obviously cannot be an actual photo if the event hasn’t happened yet! This must be a Photoshop job. That’s fine if it’s only to show what things are supposed to look like, and no one is claiming this is an actual photo.

However, it hardly matters. There are lots of other problems with this planetary alignment claim.


What’s your angle?

The first thing I did when I saw this was ask: is there really going to be a close conjunction of three planets on December 3rd?

The answer is yes! Mercury, Venus, and Saturn will all be within a relatively small distance of each other in the sky on that date. This isn’t a particularly tight configuration like Venus and Jupiter were earlier this year – in this case, they’ll be 14 degrees apart, nearly 30 times the width of the full Moon on the sky – but it’s still pretty nifty.

The second thing I did, though, was ask myself: will they really look like that in the sky as seen from Giza?

The answer this time is no. I used the software planetarium program SkySafari to show what the three planets would look like in the sky before sunrise on December 3rd as seen from the location of the pyramids, and got this:

In this picture, the yellow line is the ecliptic, the path of the Sun in the sky through the year. The green horizontal line is the horizon, and the three planets are labeled.

Note the angle of the planets: in the picture going viral, the planets are much closer to horizontal, but in reality the line connecting the planets is at a much steeper angle. It’s nearly vertical, in fact. This may not seem like a big deal, but having the planets closer to horizontal like in the viral picture is more spectacular than what will really happen, exaggerating the claim.

Not only that, but in the pyramid picture the planets are almost exactly on a line, like beads on a string. But as you can see in the picture above, they’re not nearly that colinear. Again it’s looking like the pyramid picture is exaggerating the situation.


Mirror, mirror

I noticed something else funny as well.

Here’s a satellite view of the three pyramids, courtesy Google maps:

Read More

An unreal Mars skyline

By Phil Plait | August 10, 2012 9:59 am

Well folks, it’s been a while, so it’s time for a good ol’ fashioned BA debunking.

This morning I got an email from BABloggee Joshua Frost as well as a note on Twitter from scifi author Diane Duane telling me about a picture making the rounds on teh interwebz, purporting to be taken from Mars. It shows the Martian landscape at twilight, and claims that the three lights in the sky are Earth, Venus, and Jupiter:

Pretty, isn’t it? You can find endless copies of it online; just search on the term "mars skyline". It’s been picked up on tons of Tumblrs and other social media.

But yeah, there’s just one problem: it’s not real.

I knew right away it wasn’t legit, but it’s hard to say exactly how. I’ve run into this problem before; I have a lot of experience looking at space images, and you just get a sense of what’s real and what isn’t. This one screams fake. The landscape color is a bit too saturated for Mars*. The sky’s the wrong color. The clouds are too numerous, the wrong color as well, and they have that "rendered by software" look to them.

But that’s not proof, of course. Gut sense may not be a bad place to start, but it makes for lousy evidence. The thing is, there is solid evidence the picture isn’t real! Look to the lower left corner of the image; see the letters there? Here’s a zoom:

See? The arrow points to the letters, and I zoomed in and enhanced the brightness and contrast a bit. The letters are "NE". As in, "northeast".

This is exactly what you see when you use planetarium software on a computer to display the sky. Programs like Starry Night, SkySafari, and so on will put the cardinal directions (north, south, and so on) along the horizon to indicate what direction you’re looking. And many of them will display the appearance of the sky from other planets. It’s clear that’s what we have here: a rendered view from Mars using planetarium software. I’m not sure which one (there are quite a few packages available) but I bet someone out there in BAland would recognize it. Any takers?

Interestingly, fiddling with some of software I have that displays solar system planetary positions, I found that a couple of years ago (mid-2010) the view from Mars right after sunset would show Venus, Earth, and Jupiter lined up something like that. Had you been on Mars looking west you would’ve seen something very much like the vista in the picture. Thing is, had one of the rovers taken this picture, it would’ve been all over the web at the time… including here on Bad Astronomy. I wouldn’t have passed up the chance to post a picture that cool. [Note: there is a real picture of the Earth seen by a Mars rover: from Spirit, in 2004, inset above.]

Mind you, the picture itself isn’t a hoax! It’s just a computer generated image probably meant to represent a real scene. But it got spread around the net, and before you know it people think it’s real.

I’ll note that I love that people think images like this are so beautiful and interesting that they pass them around and get a sense of wonder from them. But it bugs me that it’s possible that an unreal picture gets treated as real. In this case there’s no harm done, but it’s not hard to imagine a case where a forged image showing something damaging to someone’s reputation gets treated as real and spreads like wildfire. It’s happened before, many times.

The problem here is that people pass it from one place to another without attribution, without a link to the original source (usually it’s linked to the place they got it from, one link down the line in a very long chain). In this case, I searched for a while and still have no idea where the original for this came from. It got picked up wholesale from blog to blog and Tumblr to Tumblr so rapidly that the pedigree of it got lost. Maybe someone more patient than me can find the source.

I’ve been fooled on Twitter by fake posts before, too. Everyone has at some point. I’m just glad to be able to interject a little dose of reality in this case.

And remember: we have actual, real, amazing, breath-taking images coming from Mars right now. And the fact that they are real, and mean we have a presence on another world, is far more moving and stirring than any fake could ever be.


* I’ll note that the color of the landscape in the picture does look similar to that from the old Viking images of Mars from the 1970s. The color of those images was probably too saturated when displayed, in my opinion; getting the color right in those old shots was actually fairly tough.


Related Posts:

An unreal picture of sunset at the north pole
A fake and a real view of the solar eclipse… FROM SPACE!
NASA FAKED A SHUTTLE IMAGE!!!!! (a joke post I put up that some folks took seriously; see the followup post for more silliness)
Holy UFO hoax!
Latvian meteorite impact: fake

CATEGORIZED UNDER: Debunking, Pretty pictures, Skepticism

Venus orbital plane

By Phil Plait | June 10, 2012 7:03 am

Local (to me) photographer Patrick Cullis was filming the Venus Transit last week from Colorado, and got a surprise:

Pretty cool. That’s part of a longer video he made of the transit that’s nice, too.

While I’m at it, he made a really pretty time lapse of the sky over Boulder, including footage of Venus and Jupiter setting over the Flatiron mountains; it’s well worth a moment of your time to watch. You can see the moons of Jupiter, too!

http://vimeo.com/42052493

The Flatirons are huge slabs of rock hundreds of meters high that used to be seabed, but were pushed nearly vertical when the Rocky Mountains broke through. They make a stunning backdrop to these videos by Patrick, too.

CATEGORIZED UNDER: Astronomy, Cool stuff, Pretty pictures

As promised: Jupiter and moons seen by SOHO

By Phil Plait | May 17, 2012 1:56 pm

A little while back, I wrote about Jupiter appearing in an image from NASA’s SOHO Sun-observing satellite. I promised that it would soon appear in a SOHO camera that had higher magnification, and we’d be able to see its moons.

I am not one to break promises:

Awesome. It helps to set the resolution to 720p to see the moons when they’re pointed out.

And just you wait: in early June, Venus will appear in the LASCO C3 and C2 cameras, on its way for a date transiting the Sun for the last time in over a century. I’ll have more about that event in a few days… I promise!

Tip o’ the occulting bar to SungrazerComets on Twitter.


Related Posts:

Jupiter, acting all superior
Lovejoy lives!
The Sun fries a comet and we got to watch
The Galilean Revolution, 400 years later

CATEGORIZED UNDER: Astronomy, Cool stuff, Pretty pictures
MORE ABOUT: Callisto, Ganymede, Jupiter, SOHO, Sun

Fire, water, and ice

By Phil Plait | May 12, 2012 7:00 am

Because you simply cannot have enough incredibly beautiful photographs of aurorae in your life, here’s one taken near Tromso, Norway, on March 28, 2012 by photographer Helge Mortensen:

[Click to coronalmassejectenate, and you should.]

What a shot! Dead center in the picture is the Pleiades, the small cluster of bright stars. The bright object is the Moon, and to the lower right is Venus. If you look carefully, just above the horizon, lies Jupiter. To see it, start at the Pleiades, let your eyes move down and to the right to Venus, then keep going; Jupiter is in line with the clouds, just at the edge of the aurora itself.

I love how that one long swooshing ribbon of aurora cuts across the whole picture. See how it looks broader to the left, then narrower as you follow it to the right? That’s almost certainly perspective making it looks smaller. It’s probably something like 100 kilometers (60 miles) above the Earth’s surface and follows the Earth’s curve. The far end of it, near the horizon, is much farther away than the part at the upper left.

And despite all the drama occurring in the sky, my eye keeps getting drawn to the water. In this 10 second exposure, the slow movement of the water softens its appearance. Funny, too: I saw a face in the water and chuckled, then noted that Mortensen got a note from a friend who saw the face as well… or maybe a different one. But the one I see is pretty obvious. Do you see it too?

Mortensen has many more beautiful shots of aurorae on his 500px page, so head over there and soak up the glory of the active sky.

Image credit: Helge Mortensen, used by permission.


Related Posts:

The green fire of the aurora, seen from space
January’s aurora from way far north
Faith and begaurora
The rocket, the laser, and the northern lights

Jupiter, acting all superior

By Phil Plait | May 6, 2012 7:00 am

This is a cool picture:

What you’re seeing is from the NASA/ESA satellite Solar and Heliospheric Observatory, or SOHO. It stares at the Sun all the time, monitoring its activity. This image, from May 3, 2012 is from the LASCO C3, one of the cameras on board. It has a little metal paddle (called an occulter) to block the ferocious light of the Sun; that’s the black bar and circle. The white outline is the position of the Sun and its size in the image.

You can see an emerging coronal mass ejection on the left: that’s the bulb-shaped thingy. It’s actually an incredibly violent expulsion of a billion tons of subatomic particles hurled away at high speed due to the explosive discharge of the Sun’s magnetic field… but that’s not why I posted this picture.

You can also see streamers coming from the Sun; those are places where particles flow freely into space from the Sun. Basically, the magnetic field of the Sun trails into space in those locations, allowing the wind to escape. But that’s not why I’m showing you this picture, either.

Look on the left. See that weird dot with the horizontal line through it? That’s Jupiter! The line is not real; it’s where the camera got overexposed by the planet (digital detectors — like your phone camera — convert photons of light into electrons, and if a source is too bright, the electrons overflow the pixels like water from a bucket. The way the camera works, the electrons flow along the horizontal grid of pixels, creating these lines. This is called "blooming").

Jupiter has been gracing our sky for months, but has been getting further west every night, closing the apparent distance between it and the Sun. It’s on the opposite side of the Sun from us, at a distance of almost 900 million kilometers (550 million miles). When two objects get close in the sky, it’s called a conjunction. When it’s a planet on the far side of the Sun, it’s called superior conjunction. Just so’s you know.

Anyway, I just think this is neat. Jupiter is roughly one-billionth as bright as the Sun, yet there it is in the picture! And even though SOHO is designed to look at the Sun, Jupiter is so bright it’s overexposed. Imagine if the spacecraft moved a bit and the Sun were to peek out from behind the occulter… which can happen. SOHO goes into "safe mode" when that happens, shutting down systems that might get damaged. Every astronomical satellite has contingency plans like that, since it’s hard to send a repair service to most of ‘em. Generally it’s fixable by sending software commands to the spacecraft once the underlying problem has been ascertained.

If you want, SOHO has images online that are updated constantly. Go see what the Sun is doing now! Over the next few days Jupiter will get closer to the Sun, then pass very close to or even behind the disk. LASCO 2, another camera on SOHO that has a smaller field of view but a bit more resolution, should show the moons too when Jupiter moves into its field. I’ll post again when that happens. That’ll be even neater.

Image credit: NASA/ESA/SOHO

CATEGORIZED UNDER: Astronomy, Pretty pictures
MORE ABOUT: CMEs, Jupiter, SOHO

Mesmerizing time lapse of Saturn and Jupiter from spacecraft

By Phil Plait | April 30, 2012 6:29 am

One of the single greatest advantages of the modern age of astronomy, in my opinion, is that digital images from telescopes and spacecraft — and telescopes on spacecraft — have been placed in the hands of everyone. It can take years of training to correctly process and interpret astronomical data, but even without that these images can be put together to make art, scenes of surpassing beauty that professional astronomers might not even think to create.

Dutch video editor Sander van den Berg looked at Cassini and Voyager images, and saw beyond the raw data into the beauty of motion in them. He created a video that is stunning. Stunning. He calls it, simply, "Outer Space".

The events depicted take days, even weeks to play out. Yet somehow, the quick shots and fast cuts — necessary because in many cases there really aren’t very many images to play with — add to the majesty and grandeur of what you see. I suppose that’s no more paradoxical than having canvases far bigger than Earth, yet loaded with detail packed into those vast frameworks.

The Universe is magnificent on every scale, both in space and time. That’s one of the reasons I like working there.


Related Posts:

The stark beauty of Cassini’s Saturn
Video of Cassini’s Hyperion flyby
Cassini takes home video of Saturn’s aurora
Jupiter, the Bringer of Jollity

Celestial PhotoOp: The Moon slides in between Jupiter and Venus

By Phil Plait | March 24, 2012 4:10 pm

Over the next couple of nights, especially Sunday and Monday (March 25 and 26), a very thin crescent Moon will move in between the incredibly bright beacons of Venus and Jupiter in the west right after sunset.

Here’s a map of what it’ll look like on March 25 around 9:00 p.m. local time:

The green line along the bottom is the horizon. Jupiter will be about 15° above the horizon at that time (though the exact orientation will depend on your latitude), and Venus about 10° above it — that’s about the apparent size of your fist held at arm’s length. The Moon’s position will change hour by hour, so where it is depends on when you look! So these three will make an amazing, shifting trio over the course of a couple of days. And all you have to do is face west after sunset and take a look! Here’s more information with details about the triple-conjunction.

This makes for a fantastic photo opportunity, of course. It also presents a great opportunity to see both Venus and Jupiter in broad daylight. Both can be hard to spot on their own, but the crescent Moon is far easier. Be mindful not to look at the Sun! But if you can spot the Moon in the daylit sky Sunday and Monday, you might be able to see the tiny specks of the two planets nearby. You can read about how to do this here.


Related Posts:

See Venus in broad daylight today!
Galactic arch over the conjunction
Paradise above and below
Pic of pairs of planets and people
Juspiter and Venus still blaze in the west

CATEGORIZED UNDER: Astronomy, Cool stuff
MORE ABOUT: Jupiter, Moon, Venus
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