What power telescope would a person need to pick up Pluto?


telescope
David C asked:


I have a 12″ Dobsonian telescope with a focal length of 1500mm and an f-stop of 5. And what magnitude is Pluto anyway? No jokes about its being ostricized as a planet please.

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5 Responses to “What power telescope would a person need to pick up Pluto?”

  1. Law Says:
    January 6th, 2010 at 10:05 am

    Pluto’s magnitude varies depending on its position in orbit, but is never brighter than 13.65.
    The dimmest objects visible to the naked eye under perfect conditions are about magnitude 6.5 (the lower the number, the brighter the object). Pluto is about 1000 times dimmer than this.
    The faintest objects visible with the aid of binoculars are about magnitude 9.5. Pluto is still over 50 times dimmer than this.

    So I would go so far as to say no I don’t know that your telescope would cut it or not… light pollution will play a big role in this… Law

  2. Will Says:
    January 9th, 2010 at 12:56 am

    I don’t know the telescope answer, but the mean magnitude is listed as 15.1. Will

  3. Philip J Says:
    January 9th, 2010 at 2:26 pm

    Pluto is presently at magnitude 14, which is about 1600 times dimmer than magnitude 6. To increase the brightness by 1600 x, a person who can see magnitude 6 with the naked eye would need an aperture 40 times wider than his/her dilated pupil.

    I don’t know what size pupil is needed to see magnitude 6. Human pupil sizes vary with age. A young person might have a dilated pupil 8 mm wide. If that is the standard, then that person would need a telescope aperture of 320 mm (12.6″) to see Pluto. An older person, like me, might need a 24″ telescope.

    Of course, time lapse photography is different. You can photograph Pluto with a much small telescope if you have a steady mount, a planetery tracking motor and a CCD camera. Philip J

  4. Nyx Says:
    January 12th, 2010 at 8:16 pm

    With your sized, scope, you should able to see it as a star-like object (given good seeing conditions). What you would need to do to confirm it is to do the old school thing and plot the positions of the star field that you are looking at. Then come back in about 3 - 5 days time and do the same process over again. Pluto doesn’t move that fast, so you can actually take your time.

    Look for any apparent displacement of one “star”. It’s not going to be easy, since Pluto has the Milky Way in its background star field. So careful mapping and note taking will be required.

    To aid you in finding the planet, you need to have a star chart of the region that Pluto is in, with the stars set to the limiting magnitude of you size scope and the field of view for your eyepiece used.
    Example -

    For an eyepiece, I might try for a modest powered lens (around 15mm to 24mm) that has excellent edge to edge sharpness (like a Nagler or Radian) or a good rated planetary eyepiece (check Cloudy Nights website for reviews). Late nights in Spring (after 2am) or Summer when Pluto is at its highest would be your best times to try for an observation.

    Good Luck! Nyx

  5. Geoff G Says:
    January 14th, 2010 at 11:38 pm

    You should be able to see it easily with a 12″. I’ve observed it with 10″ and 11″ Dobs, but that was a few years ago when it was closer to the Sun and brighter. Pluto reaches magnitude 14.0 at opposition on 2010 June 24. Geoff G

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