Shadows are created when a source of light is blocked. Obvious, right? Also obvious is the brighter the source, the easier it is to see the shadow cast. So you might wonder, how faint an object can you use as a light source and still be able to detect a shadow?

We know the Sun and Moon cast shadows, and Venus is well-known for this as well. The entire sky is bright enough, even at night, to throw shadows under the right conditions. But what about the next brightest light source in the night sky: Jupiter? There have been claims for decades (I found one from 1905!) but I’ve never seen any proof.

Canadian "amateur" astronomer Laurent V. Joli-Coeur wondered about this as well. So he set about dreaming up a way to do it: build a rig that would allow him to set up a "Jupiterdial" — like a sundial, with a gnomon (a post) that would cast a shadow, but which he could aim at Jupiter — and take a time exposure on his camera.

So with some help, he built it… and it worked! Here’s the result:

The hammer-shaped shadow is from his gnomon, and the light source is from Jupiter. To make sure, he rotated the rig a bit, and the shadow moved as well, indicating it was from a point source. Also, he pointed his rig well away from Jupiter and got no shadow when he took a third picture, showing it wasn’t from the glow of the night sky, either.

All in all, a very well-done, proper scientific inquiry.

Oh — did I mention that Laurent was 14 years old when he started this project?

Amazing. When I was 14 I was deeply into astronomy and had my own ‘scope, but I was nowhere near this sort of thing. Sure, tech is a lot better now and all that, but clearly Laurent is very clever, and has a bright (haha) future ahead of him. He’s taken some very nice pictures, too, including one of the crescent Moon I like quite a bit.

If you watch the news it’s pretty easy to despair for our future. But it’s really important to remember that there are smart kids out there who will grow up into smart adults. The future is in their hands, too. A kid today such as Laurent who shows such curiosity and the desire to explore boundaries will make a fine inhabitant of that future.

Tip o’ the dew shield to Russel Bateman on Twitter

The Pic du Midi observatory in France is renowned for its very stable atmospheric conditions, allowing high resolution pictures to be taken. Our air commonly blurs out finer details of astronomical objects; there are ways to compensate, but it’s nice to not have to worry about it in the first place.

So pictures of the planets taken from the 2800-meter-elevation observatory are surpassingly beautiful. I was searching online for some Jupiter info yesterday, and stumbled on a video of the King of the Planets made using observations from Pic du Midi from October 10 – 15, 2001, and, well, it’s stunning. See for yourself:

WOW. Make sure you set the resolution to 720.

I love how it feels like you’re floating over Jupiter as it spins beneath you! Of course, the Great Red Spot is visible, as well as many other circular and highly-elliptical storms. Jupiter is huge, 140,000 km (86,000 miles) across — 11 times the diameter of the Earth. So even in this high-res video, the smallest features you’re seeing are hundreds of kilometers wide!

Despite its enormous size, Jupiter’s day is only about ten hours long. In this video, the bulk motion you see is the planet rotating on its axis, but it’s essentially impossible to see any movement in the clouds themselves. Incredibly, those storms are swept along for hundreds of thousands of kilometers as the planet spins, but in that short time the structure of the clouds hardly changes at all. It’s a study in contrasting velocity.

Right now, Jupiter rises in the east at sunset, making it available all night for observing. When I was in Texas earlier this week the UTPA astronomy folks had some telescopes set up, and Jupiter was a favorite target. All four Galilean moons were visible, and the planet itself showed beautiful detail. If you get a chance to see it through a telescope over the next couple of months, take it! You won’t regret it.

Credit : S2P/IMCCE/OPM/JL Dauvergne/Elie Rousset/Eric Meza/Philippe Tosi/François Colas/Jean Pajus/Xavi Nogués/Emil Kraaikamp

Last night, my in-laws came over for dinner. As I was helping them take leftovers out to their car around 9:00, I do what I always do when I walk outside at night: I looked up.

And man oh man, am I glad I did. Because this is what I saw:

Wow! [Click to refractenate.]

As soon as I saw this, I ran back inside, grabbed my camera, and took this shot. The bright blob in the middle is the Moon — it was just past half full. The "star" to the left is Jupiter, now shining brightly in the east shortly after sunset (the blue and green patches are reflections of the bright Moon inside the camera). You can also see a couple of stars in the constellation Aries just above Jupiter. But dominating the sky was the bright ring around the Moon, called the 22° halo.

Halos like this are caused by ice crystals suspended in the air. The crystals are hexagonal, and light entering one face of the hexagon gets slightly bent, and then bent again as it comes out. The total angle of bending is (at least) 22°, and this is what forms the ring 22° in radius.

Different colors are bent by different amounts; red is bent slightly less than blue, so the inner edge of the halo is red (look at the picture carefully and you’ll see that’s true). The inside of the halo is slightly darker than the sky around it, because no light is bent less than 22°. Light coming to you from the Moon inside that 22° limit gets bent away from you, so you don’t see it. Light outside that limit gets bent toward you, making the bright ring. The halo is actually pretty broad, but fades rapidly outside 23 or so degrees from the Moon, so it looks like a halo. In reality it’s more like a disk with a hole in it.

I love how Jupiter is sitting just outside the ring; in a couple of days the Moon will swing past the giant planet in our sky, missing it by just about 4° (roughly 8 times the size of the Moon’s disk itself). That’ll be a lovely sight.

The picture above was a ten second exposure at f/2.8 and an ISO of 400. Those are standard settings, so it can be pretty easy to take dramatic pictures of the night sky… when the subject is this beautiful.

I’ve seen halos many, many times — though this one was really spectacular. Still, the reason I’ve seen so many is quite simple: I look up. Seriously, that’s all it takes. What glories of nature are you missing by not looking around you?

If you go outside shortly after sunset and face east, you’ll see a brilliant white "star" madly shining down on you. That’s no star: it’s Jupiter, king of the planets, the brightest object in the sky right now after the Sun and the Moon. Now is the best time to observe it, since the Earth is placed directly between the giant planet and the Sun, meaning we’re as close to it as we’ll get all year.

"Amateur" astronomer Emil Kraaikamp took advantage of the situation, and, with his friend Rik ter Horst — who crafted his own 40 cm (16") mirror telescope — took this amazing shot of Jupiter:

[Click to enjovianate.]

I found this image on the Astron/Jive image of the day page (you should really subscribe to their RSS feed), and Emil gave me permission to use it here. Isn’t it lovely? The level of detail is quite incredible, about as good as you can possibly get with a 40 cm ‘scope. They used a video camera to capture a lot of frames, and then pick the best ones to add together. Earth’s atmosphere roils and shifts, causing images to blur out, so this technique compensates for that — and Jupiter obliges by being very bright, allowing for lots of short exposures in rapid succession.

The little guy below Jupiter and to the right is the moon Ganymede, which, if Jupiter weren’t there, would be considered a planet in its own right. It’s the biggest moon in the solar system, and actually comfortably larger than Mercury — though also much less massive, because Mercury has lots of iron, while Ganymede is mostly rock and ice. It’s incredible that advances in technology have made it possible to capture such detail on an object 600 million km (360 million miles) away! The image on the right of Ganymede is a NASA map of the moon based on space probe images, showing that those features Emil and Rik captured are real.

Emil tells me it’s been cloudy where he is lately, which is too bad. It’s been touch-and-go here with the weather, but seeing this is making me think of hauling out my own ‘scope and taking a look. I should get on that before the snow starts to fall here in Boulder…

In the meantime, check out the Related posts links below to see more of Emil’s amazing work.

The UK Royal Observatory Greenwich has chosen its annual Best Astrophotographer of the Year. The recipient for 2011 is Damian Peach, for this stunning shot of our solar system’s largest planet:

Wow! [Click to enjoviante.] The detail in the clouds is amazing, and it always shocks me that features on the moons can be seen from here on Earth (that’s Ganymede to the upper right and Io to the lower left).

Now, that’s a beautiful picture, and my congrats to Damian for it. But I have to admit, I’m partial to deep-sky shots, and so I was glad to see Rogelio Bernal Andreo’s incredible "Orion from Head to Toe" make the list as well; after all, I picked it as my Top Astronomy Picture of 2010!

How flippin’ awesome is that? Click it to get a very massively embiggened version, which is well worth your time grabbing. It’s simply amazing. My favorite bit is the (ironically) ghostly-blue Witch Head Nebula at the upper right. Why is it called that? Heh: look at the bigger version to see. You’ll figure it out.

You should look at all the winning entries at the ROG site. And if you think you can do better, then get ready for next year’s contest! And if you happen to be in Greenwich, you should drop by the observatory; they have the winners on display until February 2012.

If you go outside a couple of hours after sunset tonight and look east, you’ll see a very bright "star" in the sky. That’s Jupiter.

If you look at it with a nice telescope equipped with a good camera and filter set, and you have the patience to spend a bit of time afterwards putting the images together into a brief animation, you’ll see this:

Cool, eh? [Make sure you set it to higher resolution to get the full effect.] That was done by Dutch "amateur" astronomer Henk Mannetje Emil Kraaikamp. Jupiter appears to roll across the screen because he aligned all the images on the clouds you can see on the planet; keep your eyes on the Great Red Spot, for example, and you’ll see it doesn’t move inside the frame. So as Jupiter’s rapid rotation (once every ten hours or so) makes it spin visibly even over the time of these observations, which in turn makes it look like it’s rolling.

The dot on the right is the moon Europa, which orbits Jupiter every three and a half days. Its orbital motion relative to Jupiter appears to make it move to the right as Jupiter moves left, and it disappears out of the telescope’s field of view.

My favorite thing is how three dimensional Jupiter looks! The rotation, coupled with how it gets darker near its edge, really gives you the sense that you’re seeing a massive planet spinning. Which, of course, you are.

Jupiter’s moons and even some of its clouds can be seen using binoculars, so if you get a chance, go outside and take a look!

Tip o’ the Equatorial Belt to theritz.

Sometimes, my favorite pictures from space are among the ones that look least interesting… until you understand what you’re seeing.

For example, this doesn’t look like much, does it?

Ah, but that picture shows so, so much. It shows everything!

That’s us. You, me, everyone. That fuzzy blob on the left? That’s Earth. The one on the right: the Moon.

In this one simple picture, you can see everywhere humans have ever been; hundreds of thousands of years spent on Earth, and a few brief days on the Moon. And this picture was taken from much farther than anyone has ever traveled.

This view of our home worlds was seen by Juno, a spacecraft launched on August 5. By August 26th, when it took this snapshot, it was already nearly 10 million kilometers (6 million miles) away. And yet this is merely a baby step compared to its total journey: it will take a long, sweeping path to Jupiter, traveling nearly 3 billion kilometers before arriving at its destination.

Take another look at that picture. See how close together they look? It took humans more than three days to bridge that gulf from one of those clumps of pixels to the other.

Pictures like this are important. They remind us that of where we really are, how much we’ve achieved, how far we have to go. And that our planet really is just a pale blue dot, swimming in a vast, empty black ocean.

Of course, there are better words about this I can muster. Perhaps now would be a good time to refresh yourself about them.