On January 21, 2012, the Cassini spacecraft was about 2.5 million km (1.6 million miles) from Saturn when it took this shot of the planet’s clouds:
That long, distorted black smudge is actually the shadow of Mimas, one of Saturn’s moons! Mimas was way off to the side when this picture was taken, so the shadow it cast was stretched out due to the curvature of the planet itself. Think of it this way: if Mimas had been directly between Saturn and the Sun, the shadow would be a nice circle right in the middle of the planet’s face. But because it was off to the side, the shadow happened to fall where the planet was curving away, so it got elongated.
In the image I noticed a faint, circular feature above and to the right of the shadow that looked like either a storm or perhaps a camera defect — sometimes dust in the camera makes circular donut shapes in the pictures, which have to be corrected. So I went to the Cassini raw image database and found the shot — it’s real! It’s a storm of some sort, and it just didn’t show up well in the first picture (note I had to rotate the image to match the one that was released of Mimas’s shadow). What’s funny is, you can see one of those small donuts in the picture, off to the left!
Pretty cool. And I love that the raw images are so accessible, so if someone has a question like that, in many cases the answer is just a few clicks away.
Images credit: NASA/JPL-Caltech/Space Science Institute
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
Here in Boulder we get magnificent sunsets, especially in the summer when the clouds interplay with the mountains to the west. But I have never seen anything like this: the shadow of Washington state’s Mt. Rainier cast along the clouds at sunrise:
Holy (yes, in this case appropriately) Haleakala! [Click to cascadenate.]
That’s amazing. Mt. Rainier is a volcano, climbing to a height of over 14,000 feet (4300 meters). There are no other mountains anywhere near that height nearby, so it’s really prominent in the landscape (by comparison, there are several fourteeners, as they’re called, in the Rockies, so they don’t stick out as much though they’re still breathtaking). The rising Sun catches the peak, and the shadow is cast on the underside of the cloud layer. The dramatic sunrise colors really make this an incredibly beautiful shot.
The KOMO news site has lots more pictures of this, too. Go take a look!
And remember, when you’re outside, it always pays to look around you for a moment. You never know what incredible vista nature may have in store for you.
Tip o’ the snow cap (har har) to John Baxter.