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Question: Jupiter and Saturn at 200x?

  1. Aug 30, 2004 #1
    How would Saturn and Jupiter look in a telescope of 6 or 8 inch aperture at about 200 to 250 power? I've read some extremely varying answers to this on the internet, so I was hoping someone with firsthand observational experience could help me out here. For example, what size would they appear in comparison to the naked eye moon? I'm asking because I'm looking into buying a telescope of such aperture, and would like to keep my expectations realistic.
    Thanks
     
  2. jcsd
  3. Aug 30, 2004 #2

    chroot

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    At its closest, Jupiter is 4.2 AU away from Earth. It's 142,984 km gives it an angular diameter of about 47 arcseconds in our sky:

    http://www.google.com/search?num=30...)+/+(4.203+AU))+*+2+in+arcseconds&btnG=Search

    Magnified 200 times, it would have an angular size of about 2.6 degres, a little over 5 times the angular size of the Moon (0.5 degrees) viewed with the naked eye.

    Saturn would be a little over a degree in angular size at the same magnification.

    You should be able to see at least four of Jupiter's moons, along with several differently-colored cloud bands. The great red spot should be very obvious. On a good night, you should be able to see considerable detail in the regions where the cloud bands mix.

    Saturn will appear five times smaller in the same eyepiece, but will easily show its rings. On a good night, the Cassini gap, the division between the inner and outer rings, should be quite easy to see. Several moons would be visible if you know where to look for them on the night in question. The planet may show some color gradations on the disc, but it is generally featureless.

    Before buying a telescope, I strongly urge you to find a public star party in your area. Attend it and try out various kinds of telescopes. Ask the owners as many questions as you can. Choosing a telescope involves a lot more criteria than just the kind of detail it'll show on a planet!

    - Warren
     
  4. Aug 30, 2004 #3

    Chronos

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    At 200x Jupiter will appear to be about the size of a half-dollar held at arms length. Saturn will be about a third that size. Neither image will be very clear except on nights of exceptional seeing. Cold, still nights give the best views. See link for some views I consider very representative of what you could expect to see through an 8" telescope under decent seeing conditions.
    http://www.siowl.com/index.html?realview.html
     
  5. Aug 30, 2004 #4
    Thanks chroot and Chronos, that's all I needed. Don't worry Warren, planet views are by far not my only criteria. I've been using a variety of telescopes (mostly borrowed from friends) for several years, and am considering the 6 or 8 inch dob largely because it's capabilities seem to be the best value for my budget- I'm only a high school student so I don't have a lot of cash to throw around. As this telescope comes after many years of astronomy with my eyes and with binoculars, I'm very excited!
     
  6. Aug 30, 2004 #5

    chroot

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    LastOneStanding,

    Outstanding! You can't really go wrong with a nice dob. As others have mentioned, Orion makes an excellent instrument at an excellent price. Pair it up with some good eyepieces and a Telrad or Rigel QuickPoint finder, and you won't be disappointed!

    - Warren
     
  7. Aug 30, 2004 #6

    turbo

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    That's a pretty good site, Chronos - at least for the extended objects. You are right about the cold still nights. If those nights are good for visual observing, they are great for astrophotography. Here in Maine cold still nights usually result in temperature of 10-20 degrees below zero or colder, and those are the nights that are the very best for astrophotography. Now imagine holding absolutely still for 20-40 minutes or more and staring into the ocular of your guidescope, keeping the guide star centered. Can you imagine being happy and comfortable while doing so? I can. I have cloth Air Force arctic type flight-line boots in size 13 with two sets of nesting felt liners (my feet are size 8), and I have many layers of fleece, goose down, etc, with windproof nylon at the perimeters. I weigh only about 150 lb, but when I suit up and put on my big Russian Army rabbit-fur hat with ear-flaps, I am way less attractive than the Michelin man, but similar in proportions. I can stay out all night in those conditions with no problems.

    For astrophotography in nothern climates, dress like are going ice-fishing all day, then put on twice as much down and fleece as you think you might need, and quadruple the protection for your feet. You'll be fine. When your feet are aching, and you're shaking all over, you cannot guide a decent astrophoto.

    The original poster asked for realistic expactations about the appearance of planetary object in high-power views, and I have strayed off the course. I should add that realistic, satisfying views of planetary objects have a heck of a lot more to do with using a VERY accurate telescope - might I suggest an apochromatic refractor or a very well-figured reflector? I have not yet looked through any 10" commercial Newtonian reflector or Schmidt-Cassegrain that can rival the planetary views through my 6" Astro-Physics APO. I am pretty sure that there are some well-figured 10" newtonians or S-Cs that can blow my scope away. I haven't bumped into one yet though.
     
  8. Aug 30, 2004 #7

    chroot

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    turbo-1:

    Right you are, but the cheapest apochromatics around will cost you at least $500-$700, leaving no funds available for a mount, eyepieces, or other accessories. A 8" dob is practically the traditional first telescope for its combination of ease-of-use, simplicity, versatility, light-gathering capability, and price.

    LOS, if you decide to go for an apochromatic, look into the Orion 80ED. It's probably the only apo that comes even close to your price range, unfortunately.

    - Warren
     
  9. Aug 30, 2004 #8

    turbo

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    With that stated budget, look around for 100mm and larger binoculars first. These became quite popular about 15 years ago or so, and there are quite a few of them floating around.

    If I were into visual astronomy (knowing what I know today) would first buy a pair of large-objective binoculars to use every night, then select scope(s) based on their applicability to my interests. Short focal-length scopes can be tougher to color-correct, but pay dividends in usable field of view and compactness.
     
    Last edited: Aug 30, 2004
  10. Aug 30, 2004 #9

    turbo

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    You are "right on the money". In a previous post, I recommended the 8" Orion dobsonian, based on my past experience with those folks. $400 Dob with a couple of eyepieces. They are reliable people, who promote their products, but who do not make wild unsubstantiated claims. That counts as "honest'" in my book (at least in this field). I recommended a Dob as a strarter, but fully expect enthusiastic users to demand "more", which is where the binoculars and APOs come in. It's tough to make a definitive determination at the entry level, because you don't know where an astronomer's interests might take them, and you have no idea how long their interest will last. If you figure that one out, please email me - we will both be rich.
     
  11. Aug 30, 2004 #10
    I've looked into apos, but as chroot said, the starting price is just a little beyond me right now. Since my interest in astronomy isn't specialized to planetary and lunar observing or deep sky viewing, the "little bit of everything" capabilities of the medium aperture reflectors are pretty attractive for the stage I'm at. Maybe this telescope will show me which type of observing I'm more partial to so that I'll know what second scope to buy in the future. Also, I own (or rather my dad owns) a good quality pair of binoculars that I've been using for years. The cost for extra eye pieces and other accesories really is a limiting factor for me. I live in Canada, so think almost double for anything you (turbo-1 and chroot) would have to pay for all those extras...my country's lack of astronomical resources worries me sometimes...
     
  12. Aug 30, 2004 #11

    Chronos

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    Cold weather tricks: 1] hands: ladies silk glove covered by a surgical glove, warm yet dexterous. Add extra outer glove, if needed. 2] feet: two pair of socks with a baggie [or pantyhose for brutal conditions] in between.
     
    Last edited: Aug 31, 2004
  13. Aug 30, 2004 #12
    Now there's something you can't learn from an astronomy book.
     
  14. Sep 1, 2004 #13

    turbo

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    There are lots of things that you can do to make yourself more comfortable when its really cold. To help keep your core temperature up during long cold nights of astrophotography, you can sip hot soups or hot chocolate or hot herbal teas. Avoid alcohol and strongly caffeinated drinks - both will cause problems.

    My experience is that the best solution is to have some warm/hot foods available with some usable carbohydrates (think starchy/sweet rather than fatty) and wash them down with hot teas or soups. You want to keep your blood sugar stable without driving your metabolism highly positive or negative. Your interest level and involvement will supply the stimulation necessary to keep you alert. You may want to drink a short coffee before driving home, but if you try to try to force yourself through a long winter observing session with no food and only a tall thermos of black coffee, you will be short-changing yourself. VOE here, on this one.
     
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