Jupiter at Opposition

Jun 06 2007 Published by under What's Up?

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Jupiter was at "opposition" yesterday, which means that it's still almost at opposition today. "Opposition" means that it's on exactly the opposite side of the Earth from the Sun. The picture to the right shows diagrammatically the layout of the Solar System when Jupiter is at opposition. This means a few things. First, we're closer to Jupiter than we are at any other time. This means that Jupiter is both brighter and, if you have a telescope, a bit bigger than it usually is. Second, it means that Jupiter is as high in the sky as it will get right at local midnight (which is generally some time close to local 12:00AM).

If Jupiter is opposite the Sun, that means it will be rising in the East right as the Sun is setting in the West. Look for a very bright "star" in the Eastern sky a bit after Sunset. It's not a UFO; it's the planet Jupiter. if you're up at midnight, the very bright "star" that is nearly overhead is Jupiter.

You can see the four Galilean moons of Jupiter with binoculars... if you can hold them still enough! Get a pair of 7x35, 7x50, or 10x50 binoculars, and point them at Jupiter. Try leaning on something, or laying down on the ground, to hold your binoculars still enough. If you can, you will see up to four small specs of light lined up on one or both sides of Jupiter. Sometimes stars will happen to be there, but some of those specs of light are, indeed, the moons of Jupiter. Watch them from one day to the next, and you'll see that they change positions with each other.

11 responses so far

  • bigTom says:

    Those of us here with telescopes are loudly complaining about the king of the planets. The fact that it is opposition near the summer solistice, means that Jupiter is near the southermost point of the ecliptic. So its very low in the sky, even at midnight. The seeing at low elevations is considerably worse than higher up, so we don't get very good views. Since Jupiters orbital period is roughly twelve years this sorry state of affairs isn't going to change soon.

  • Rob Knop says:

    Since Jupiters orbital period is roughly twelve years this sorry state of affairs isn't going to change soon.
    I dunno... six years doesn't sound as long to me as it used to.

  • HP says:

    So, if I were looking at the sun from the neighborhood of Jupiter right about now, what would I see? Would I see the Earth outlined against the solar disk? Would earth even be noticeable against the sun from that distance? (With, say, naked human eyes.)
    Would it be a "transit of Earth" from a Jovian perspective, a Terran eclipse, or something else?

  • Rob Knop says:

    I will have to check this to make sure, but almost certainly something else. The planes of the planets' orbits are not perfectly aligned. If they were, we'd have transits of Venus all the time -- but, in fact, we only get a couple of transits of Venus every hundred years. Similarly, transits of Earth as viewed from Jupiter are rare, and I doubt that right now there's one going on.
    Earth would not really be visible. The lighted side of Earth is pointing away from Jupiter, so it would be dark. From the point of view of Jupiter, Earth is either above or below (i.e. North or South) of the Sun in the sky -- again, I'd have to dig a bit to figure out which. But, being dark, it would be very hard to pick out, even if you were outside an atmosphere and blocked out the glare of the Sun.
    -Rob

  • bigTom says:

    Earth from Jupiter would make a great telescopic object. Diffraction of sunlight by the earth's atmosphere would give the planet a glowing orange ring. If you had real sensitivity, you might also see the lights of the planet's urban areas. Not a bad sight, but you'd probably need pretty high magification, and some sort of sunshade to keep its glare from overwhelming your view.

  • Lab Lemming says:

    Big Tom, you just live in the wrong hemisphere. Down here it is almost directly overhead at midnight, and its way brighter than Canopus or Alpha Cent. But seeing Earth from Jupiter would be even harder than seeing Mercury from Earth- although it wouldn't move as fast. And on that point, it might be worth noting that the relative size of the orbits in Rob's figure puts Jupiter about where Mars is.
    For the true astro-geeks around here, though, I do have a question: If I'm planetwatching on Mars, which is brightest in the sky under optimum viewing conditions: Venus, Earth, or Jupiter?

  • Rob Knop says:

    And on that point, it might be worth noting that the relative size of the orbits in Rob's figure puts Jupiter about where Mars is.
    This is true. And the Sun is too big, and the two planets are way too big. It was just schematic....
    -Rob

  • bigTom says:

    Lab Lemming, you are lucky. The Southern Hemisphere was way more than its share of celestial eye-candy.
    That's an interesting question. Venus recieves about twice as much solar radiation as the earth, and it's albedo is roughly twice as high as well, so it should be four times as bright. I don't think Earths closer distance would be nearly enough to overcome a 4x luminosity advantage. But of course Venus would never get very far from the sun either.

  • David Williamson says:

    It's definitely not in transit. If you use the NASA Solar System Simulator, you can find that Earth is a bit south of the Sun, and is at a phase of 179.3 degrees. Assuming I got this right, here's a highly zoomed image.
    On the other hand, it looks like there will be a transit by the Earth as seen from Jupiter next year, on July 9, 2008 at around 03:30 to 11:20 UTC.

  • David Williamson says:

    The Mars question is a bit harder to sort out without some reasonably sophisticated software. From poking around a bit and doing some math, it looks like Jupiter gets to about -1.8 as seen from Mars, while Earth and Venus both get to about -2.5. Someone else will need to get more exact data fro Venus and Earth to determine which is brighter. I'm also not sure if our Moon is resolvable with the naked eye from Mars, so it's brightness (around +1, more or less) would add to the apparent brightness of Earth, which might be enough to tip the apparent brightness in favor of the blue planet.
    Ugh, that's enough hard math for one night. I made a lot of shortcuts in those numbers, so they shouldn't be seen as accurate to more than about +/- 0.5 magnitudes.

  • Lab Lemming says:

    According to my star program, Jupiter is currently -2.1 from here on Earth. It is certainly way brighter than mag -1.4 Sirius. The difference in Mj between Earth an Mars at opposition with Jupiter should be 0.2 to 0.4 mag (assuming mag is log 2.5). This assumes circular orbits for Earth and Jupiter, taking only Martian eccentricity into account.
    So that rough calculation also puts Jupiter at about -2.5, when Mars is in opposition at apahelion.
    Earth-Moon is resolvable- there is a rover pic that shows that, and Europa, with roughly the same orbital radius, is resolvable at a much greater distance. Assuming the moon has 1/4 earth radius and 1/3 the albedo, it is 50 times dimmer, so only gives 0.02 mag anyway.