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Thread: Transits

  1. #1
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    Default Transits

    There have been a couple of posts about the transit of Io recently (see avatar). Are there any others likely to be seen through a telescope, ie Saturn's moons etc, and if so how can i find out when? I have typed this into google and all I get is this astrology nonsense.
    the transit of Venus this year was obviously the creme de la creme but here in the UK it was too cloudy, still there's always next time (lol).

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    Default Re: Transits

    I think i have saw hubble pix of transits or i per fair eclipse's of saturn!any planet that has a moon or moons you will get an eclipse.on jupiter every ten years or so you will get 4 eclipse's at the same time.

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    Default Re: Transits

    It's fairly easy to catch transits of the Galilean moons of Jupiter because the moons are very large. Ganymede is the largest moon in the solar system... bigger than the planets Pluto or Mercury. Jupiter is "about" 5 AUs away from the Sun, so when it's at "opposition" to Earth, it's only about 4 AUs away from Earth. This makes it easy for us to see the moons.

    Saturn is a bit more challenging. It's nearly twice as far from the Sun as compared to Jupiter (about 9.5 AUs but it's probably easier to remember it as being "10" AUs away (even though that's being a bit liberal in the round-off ... the distance of the planets beyond are Earth are 1.5 (Mars), 5 (Jupiter), 10 (Saturn), 20 (Uranus), 30 (Neptune), and 40 (Pluto). The true distances are odd numbers but it's surprising how if you just round to the nearest whole value, these are the numbers you get.

    That means that even when Saturn is at "opposition" to Earth (which will next happen next April 28) it'll still be far enough away that it's moons are mere specs. Saturn "seems" visually larger because it's ring system is so vast and prominent. If you were to remove the rings, your brain wouldn't think of it as appearing to be nearly as large as Jupiter when viewed through the eyepiece. Also, Saturn only has one moon which compares in size to the Galilean moons of Jupiter... Titan. Titan is the 2nd largest moon in the solar system (only Ganymede is larger... and only just barely.) That means you might conceivably be able to see a transit of Titan... but not for a while.

    Saturn's axial tilt is almost 27º (a little more than Earth's axial tilt of about 23.5º). Saturn takes nearly 30 years to orbit the sun once. That means that once every 15 years, the rings of Saturn are "edge on" to Earth and become nearly invisible to us. But what this means to us is that Titan (which orbits slightly inclined relative to Saturns rings) will always pass either above or below relative to our view of Saturn. It'll never transit across the disk in MOST years.

    We don't have this problem as often with Jupiter because Jupiter's axial tilt is only about 3º. We don't always get transits of Jupiter's Galilean moons... but they're considerably more frequent because they tend to be more flatly in line with the plane of the solar system.

    Starting in 2024 however, the rings will appear begin to be nearly "edge" on (not quite) and Titan's orbit relative to our viewpoint here on Earth will finally be close enough that we would be able to see "transits" of Titan across Saturn. You'd need a good scope to see it because everything is roughly twice as far away as compared to Jupiter. These will happen through 2024 and 2025. After that, Titan will pass above Saturn and you wont be able to see transits for roughly another 15 years. Note that you'd need a GOOD telescope to see this because, as I mentioned earlier, it's not that Saturn and Titan are small... but they are about twice as far away as compared to Jupiter.
    Flexie likes this.

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    Default Re: Transits

    Hmm interesting, I'd always wondered if you could see a transit of Titan. I just never considered the axial tilt of Saturn and the rings as hinderences to seeing the moon.
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