I was going to stop posting pictures of last week’s conjunction of Venus and Jupiter (see Related Posts below for more), but then photographer Brad Goldpaint went and sent me this ridiculously incredible shot:

You absolutely must click to embiggen that; I had to shrink it to fit the blog here. Brad took this just a few days ago at Smith Rock State Park located in Terrebonne, Oregon. It’s actually a mosaic of nine separate photographs, stitched together to show the grand scene. Venus and Jupiter are obvious enough (Venus is the brighter of the two, above Jupiter) but, as usual in Brad’s pictures, the real scene-stealer is the Milky Way. Usually, the Milky Way is a stream across the sky, but in this mosaic appears curved (that happens when you try to map large straight objects that take up a lot of sky into a rectangular picture frame).

You might see some familiar things if you look closely: on the left is Orion, tilted a bit, and all the way to the left is bright Sirius. Just above the planets are the Pleiades, and the head of Taurus to the left of that. Just to the right of the top of the Milky Way is bright yellow Capella, and farther down to the right the W of Cassiopeia.

What else do you see?

Speaking of Mark Ellis, he also sent me this ethereal, unearthly photo he took of the conjunction of Venus and Jupiter as he was on a beach in Maui:

[Click to enappulsenate.]

I love how the clouds are smeared out a bit, but the stars — and planets! — are solid and sharp. Venus and Jupiter are pulling apart now, but it’s still worth taking a look over the next few days. They’re still well over the horizon for most people even when the sky is full-on dark, and Venus is so bright it’s almost unbelievable.

Astrophotographer Guillaume Poulin sent me this wonderful and lovely picture he took of the Venus/Jupiter conjunction on March 11, 2012:

[Click to embiggen.]

I love the colors of the sky in this! I also like the theme of pairs; the planets, the humans, and the barns. This was taken near the Mont-Mégantic Observatory in Canada, right after sunset, so the silhouettes of Guillaume’s girlfriend and her brother are nice and sharp. Simply beautiful.

And if Guillaume’s name is familiar, that’s because he and Rémi Boucher created an amazing time lapse video I featured here not long ago of the eastern US coast as seen by the space station. I sure hope he keeps making such beautiful imagery so I can feature it here.

… and the two planets are still making a spectacle of themselves to the west. Make sure you go look!

If you’ve been outside just after sunset and faced west, you’ve almost certainly seen two bright "stars" glaring back at you. Those aren’t stars: they’re Venus and Jupiter, the 3rd and 4th brightest natural objects in the sky (after the Sun and Moon, of course, and I say "natural" because the space station can in fact look brighter than both). As they circle the Sun, every year or so the orbital geometry of the two (and the Earth) sets things up such that they appear very close together in the sky. This is called a conjunction, and when it involves planets this bright, it’s really something to see!

[Click to enaphroditenate.]

That stunning shot was taken by German astrophotographer Robert Blasius, and it’s part of an incredible set of photos gathered by Astronomers Without Borders.

Getting pictures of the two planets together is not hard; I rested my phone on a chair at a party in the middle of downtown Austin, Texas, and got a decent shot myself, shown here (click to embiggen). If you have a real camera, great pictures are a tripod and a click away.

The two will be close together for the next few days, too, so you have time.

I’ve been getting a lot of email and tweets about the pair, asking me about them. Venus is the brighter of the two planets, which is interesting: it’s far smaller than Jupiter, and reflects less sunlight overall. So why is it so much brighter?

Because it’s closer!

The brightness of a planet in our sky depends on a handful of things: how big it is, how reflective it is (an icy object is brighter than a rocky one), how far from the Sun it is, how far from us it is, and even our viewing angle. These can all be calculated, so what the heck. Let’s do a little math!

Area of my expertise

The total light reflected by a planet depends on the surface area of that planet, which depends on the radius squared (remember your algebra? The area of a circle is π x (radius)²). Jupiter has a radius about 71,500 km, and the radius of Venus is about 6050 km.

Squaring those two and getting the ratio, we get

area of Venus / area of Jupiter = 0.0072

So all things being equal, Venus should only be 0.0072 times as bright as Jupiter, or, flipping it, Jupiter should be about 140 times brighter than Venus! But all things are not equal…

A planet’s day in the Sun

Jupiter is farther from the Sun than Venus, and that means it gets less sunlight than Venus does. The amount of light an objects gets from the Sun depends on its distance from the Sun squared (this is called the inverse square law of light). We can figure that out too! Just divide the distance of Jupiter from the Sun by Venus’s distance from the Sun, and square that:

Jupiter’s current distance from the Sun is about 746 million km, and Venus is about 108 million km. So,

(746 million / 108 million)² = 47.7

So Venus receives about 47.7 times as much sunlight as Jupiter does, and all things being equal should be 47.7 times as bright. But we’re not done…

Long way home

The light from each planet also has to get from there to here, to Earth. Again, that goes as the square of the distance! So we have to account for that. Right now, Jupiter is about 846 million km from Earth, and Venus is about 121 million km distant. Let’s square those and see what happens:

(846 million / 121 million)² = 48.9

Yikes, another factor of almost 50! So again, due to their respective distances from the Earth, Venus should be 48.9 times brighter than Jupiter. But wait! There’s more …

Pause to reflect

Both Venus and Jupiter are highly reflective — both are covered in clouds, though the clouds of Venus are somewhat more reflective than those of Jupiter. Venus has a reflectivity (called its albedo) of about 67%, and Jupiter is about 52%. That’s pretty close. The ratio is

.67 / 0.5 = 1.29

So Venus wins there too.

And still there is one more thing: phase! We see Venus roughly "half full" right now because it’s off to the side of the Sun, while Jupiter is "full". According to the US Naval Observatory, 57.6% of Venus is lit right now from our view. So we have to account for that by throwing a factor of 0.58 on Venus.

And now we’re ready to put them all together!

So let’s figure out how much brighter Venus is than Jupiter by putting these all together. All we have to do is multiply them all, making sure we do it in terms of Venus to be consistent:

Venus brightness / Jupiter brightness = 0.0072 x 47.7 x 48.9 x 1.29 x 0.58 = 12.6

So Venus should be a bit less than 13 times brighter than Jupiter according to my calculations.

Is that right? Looking up the actual numbers on Heavens Above, I get that Venus is actually about 8 times brighter than Jupiter. My number’s off, but not by much. That’s not bad, considering I just threw some numbers together based on straight geometry and did some very rough math.

I love this aspect of astronomy: using nothing more than a few first principles — how light gets dimmer with distance, how objects reflect that light, and how we see them — I was able to predict that Venus should be brighter than Jupiter, and even by how much! The actual amount may be off, but I wasn’t wrong by a factor of ten, say. Just that basic knowledge got me pretty close, and no doubt there are a handful of other factors that, when accounted for, get this much closer if not bang on the right number.

After all, the Universe knows what it’s doing. And science is a great way — the best way — to understand what the Universe is doing. Make a few assumptions, test them out, see how well they fit what’s really going on, and then look more deeply into the problem. I’ll hold off here from going deeper into the numbers above (though I’ll bet I see some folks in the comments diving in), but this is a great example on how science zeroes in on a solution.

And honestly, you don’t have to do all the math to go outside and take a look. Please do! The math isn’t hard, but what’s easier is facing west and looking up. That is the heart of astronomy.

Look up!

Image credit: Robert Blasius/Astronomers Without Borders; me

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?