Saturday, September 29, 2007

Dr Vector discovers the universe

I've mentioned here before Abrell & Thompson's wonderful little book, Moses May Have Been an Apache, a collection of bogus and no-so-bogus "Actual Facts" based on their newspaper cartoon of the same name. One of the entries has a surprisingly evocative doodle of an American Indian GI, and reads, "Charlie Medicine Horn discovered Germany in April, 1945."

Ha ha.

But there's something to that. It does not matter to me that I was not the first to stand in front of the Wall at Dinosaur National Monument, or wander through Beijing's Forbidden City, or hike the beaches on the Isle of Wight. The fact that thousands or millions of people have done those things before did not decrease the thrill of personal discovery for me.

Tonight I found the Galilean moons of Jupiter for the first time by myself. Now, people have been looking at them for 397 years, and our robots have sent back enough data on those worlds to keep a generation of planetary scientists very busy. I had even seen them before with my own eyes, through my astronomy professor's telescope in high school. But tonight was the first time that I found them for myself. And I didn't even need a telescope to see them. Some crappy Tasco 7x35 binoculars that I bought back in high school, steadied against a lamp pole, did the job.

It helps if you know where to look, of course. From our viewpoint Jupiter travels along the same track as the sun and the moon (the ecliptic), and it trails the sun by a couple of hours. Go outside right after sunset and look to the south-southwest, about 25 degrees above the horizon (spread the pinky and thumb of one hand as far as you can at arm's length; that's about 25 degrees). Jupiter will be the first 'star' you see, and it will be a lot brighter than any other stars in that part of the sky once they come out. With the naked eye it looks just like a bright star, but even at 7x magnification you can see a tiny crescent. If your eyes are moderately dark-adapted and you steady the binoculars against something, you will see tiny pinpricks of light near the crescent. Those are the Galilean moons. It may help to focus your vision on some other part of the field of view at first, a technique called averted vision, which helps you detect faint objects.

I had a little help from Stellarium, an open-source planetarium program that you can download for free. You can view the sky from any point on Earth (Wikipedia will give you your latitude and longitude if you don't already know them), and the program is a cinch to navigate. Here's a screenshot from Merced at 7:17 Pacific Time this evening, which I punched up earlier today to figure out where to look. You can turn everything on and off: the grids (alt-az and equatorial), atmosphere, constellation names and lines, and in fact the Earth itself if you want to look straight down and see what folks at the antipodes are seeing. Here I have the alt-az grid and the atmosphere on to show what the sky actually looked like at 7:17 tonight, and where Jupiter was located relative to the cardinal directions and the horizon.

In fact, I did not see all four Galilean moons, just two off the left flank of Jupiter. The chart in this month's Sky & Telescope says those two are Callisto (next to Jupiter) and Io (next one over). Ganymede should be farther off to the left but I didn't see it, and Europa is behind Jupiter tonight. Here's what it looked like through the binoculars:

Now, this is not an awesome spectacle of Nature's grandeur. It's a tiny crescent and two pinpricks almost at the limit of vision. What is awesome is not the size or detail of the view, it's that I got it all, standing under a (blessedly dim and yellow) streetlight with a pair of low-end department store binoculars.

I'll bet most of you have at least some lousy binoculars laying around; many of you probably have a nice pair gathering dust in the closet. Why don't you go outside tomorrow night and discover Jupiter's moons for yourself?

UPDATE: Erp. I couldn't actually have seen a crescent Jupiter. No one has, not with their own eyes. Jupiter is so far out that we are practically right next to the Sun compared to it; therefore we only ever see the lighted face. Anything less can only be seen by space probes. So what did I see? Some kind of aberration that my brain interpreted as a crescent. Three possible causes include lens flare in the binoculars, some other kind of visual aberration in the binos, and astigmatism in my eyes (I wasn't wearing glasses at the time). Percival Lowell ain't got nuthin' on me.

Still, after more than a week of almost nightly binocular viewing, the Gallilean moons are still pretty freakin' sweet.

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Blogger Neil said...

Andromeda should be up this month. It's a favored binocular target for me. Whenever I look at 'M31' I think about how it's been less than a century that we realized the 'white nebulae' were distinct, distant galaxies. crazy.

8:32 AM  
Blogger Dr. Vector said...

Neil, you must be reading my mind. Last night I found Andromeda for the first time. Beautiful! I also discovered that my binoculars were enough to split Albireo and to show just a hint of crescent on Mars.

I have loads more to say about this, but I will save it for a future post.

8:45 AM  

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