Mission Objective: Planet, Moons
Equipment: Naked eye, Binoculars, Telescope
Required Time: 5 minutes
Instructions: Look southeast in the early evening and find the intensely bright star!
The ancients recognized several categories of celestial objects: the Sun and Moon, the fixed stars, transitory and unpredictable phenomena from the commonplace (meteors) to the alarming (comets), and a special category of stars that moved in relation to all the others. The Greeks called this last group the planetes asteres (“wandering stars”) or simply planetoi (“wanderers”), and the term survives little changed to this day.
The ancients could see five wandering stars. Mercury, closest in, swings around the Sun every 87 days, and so was identified with the swift messenger of the gods. Venus, the goddess of love, gave her name to the brightest object in the heavens after the Sun and Moon, the morning and evening star. Blood-red Mars was named, appropriately, for the god of war. Saturn, dimmer than Jupiter and traveling more slowly, was named for the Titan Jupiter displaced, the two-faced god of beginnings and of agriculture.
Was it coincidence that the ancients gave the name of the king of gods to the planet that is, in fact, the largest in the solar system? Possibly not. From Jupiter’s long orbital period they probably deduced that it is very distant from Earth, and yet it is the fourth brightest object in the sky, yielding only to the Sun, the Moon, and Venus. Possibly Jupiter’s stately pace through the heavens was thought more seemly for the king of gods than the frantic Sun-centered scurrying of Mercury and Venus (it would have been obvious, then as now, that the two innermost planets never get very far from the Sun).
If you don’t catch Jupiter in the early evening, don’t fret. It rises near sunset and will be traveling across the southern sky for much of the night. And tonight, Sept. 2, it will be very close to the moon–as it will be again this time next month. (The moon was on the other side of Jupiter last night, but I was too wound up about Mt Wilson to post this then.) That’s an easy twofer whether you’re using binoculars, a small telescope, or the good ole Mark 1 eyeball.
Speaking of binoculars…just for the purposes of this post, I’m going to assume that you’ve either got a scope and know how to use it, or don’t have one and aren’t going to change that by nightfall. We’ll talk about choosing and using telescopes a lot more in the future, but for now I feel that my advice will have maximum impact for people in possession of binoculars. The pool of people who own a pair of binoculars is huge; the fraction of those people who have used them for stargazing is probably tiny. And Jupiter and the moon are the two celestial objects that benefit most from being viewed with binoculars. So here goes.
First off, don’t worry about what kind of binoculars you have. The 10×50 size is most often recommended for stargazing–at 50mm and above, the objective lenses start to really pull in the faint light for chasing star clusters and nebulae. But the Moon and Jupiter are both crazy bright, so light gathering is not the prime consideration. The prime consideration, as always at this blog, is getting out and seeing something you wouldn’t otherwise. (If you don’t have binoculars but want some, consider these).
Second, the view through steady binoculars is a qualitatively different experience than the shaky hand-held view. There are several ways to hold binoculars steady, but the cheapest (i.e., free), fastest, and easiest is just to brace your elbows against something (top of the car works great for me) or to brace the binoculars themselves against something. My first self-conducted astronomical observation, not quite two years ago, was of Jupiter and its moons, using the humble Tasco 7×35 birding binoculars I’d gotten at Wal-Mart back in high school, leaning up against a street lamp to hold the binoculars steady.
What will you see? In even modest binoculars, Jupiter will be a circle, not a point, with between one and four little points of light next to it. The picture above is the simulated binocular view. On one hand, you’re not going to see any detail on the planet. And the four Galilean moons will just be little sparks.
On the other hand–the hand you should be concentrating on–you went to the closet, knocked the dust off whatever binoculars you already had, pointed them at that bright star over there, and now you can see that it is visibly a planet (despite being almost half a billion miles away) and, oh yeah, those little sparks are moons. If you’ve never seen this before with your own eyes, you will have an emotional reaction. Even if you have seen it before, you’ll probably have an emotional reaction. I still do. And usually that reaction is, “Holy BLEEP! That’s BLEEPin’ Jupiter! And its BLEEPin’ moons!” And I want to laugh and cry at the same time, and most of all I want to grab whoever is close and make them look, too. This entire blog is the extension of that feeling.
You want more coolness still? Using only binoculars, you should be able to sketch the positions of the four Galilean moons over several nights (apparently some Italian yahoo dreamt up this diversion like 400 years ago). Drawing in hand, you can open up Stellarium or pick up the current issue of Sky & Telescope or Astronomy and figure out which moon is which. From inside (closest to Jupiter) out, the four biggest moons are Io, Europa, Ganymede, and Callisto. I remember them like this: vowels (I, E) before consonants (G, C), and both sets in reverse alphabetical order.
Alternatively, you can look up the moons’ positions first, quickly commit them to memory (or draw them, or take the magazine or laptop outside with you), and then when you see them in the binoculars you’ll know that that little spark right there is Io, entirely covered in sulphurous volcanoes, or Europa, whose ice-encrusted oceans are the best possibility for finding life elsewhere in the solar system.
As far as I’m concerned, observing Jupiter in binoculars is both a thrill and a blessing. It’s a moving sight, and it can be the basis of a very accessible and very rewarding observing program (like, er, one of these). It only gets better in a telescope. My 90mm Maksutov shows several cloud belts on clear nights, and occasionally the perfectly black, perfectly round pinpoint of a moon shadow transiting the bright face of the planet. My 6-inch reflector shows more bands and more detail, and so on up from there. BUT, as I frequently say, it’s not about the equipment. It’s about the seeing. And Jupiter is one of the best things out there to see.
If you want the fast facts about Jupiter in an attractive, portable, and free format, check out the IYA2009 presentation about Jupiter. It’s part of the upcoming Galilean Nights event on October 22-24, when amateur and professional astronomers all over the world will set up thousands of telescopes to show the general public the wonders of the heavens.
Oh, one more thing: right after sunset, Jupiter is almost directly below Altair. So if you can find Jove, you can find the Summer Triangle, and vice versa. Get after it!