What size of telescope do I need to see the planets as a disc rather than just snother star?

Question

I currently have a 4.5 inch reflector and Mars only appears as a very bright star.

Answer 1

Jupiter and Venus are disks (or crescent in Venus' case) in binoculars. With an 8 inch Newtonian or 8 inch Schmidt Cassegrain, even Jupiter's 4 big moons will begin to show a disk at 250 power.

All the planets respond nicely to four inch and larger telescopes. Larger telescopes have more resolution and will show more moons. Saturn is especially able to show a lot of moons in a 10 inch telescope. Neptune and Uranus are blue and blue-green disks in 8 inch and larger scopes.

Mars is at opposition right now. Morning fog, an ice cap and dark areas ae visible at 100 power of even a small 2.4 inch refractor. That favorable viewing will will last several weeks more until the end of January.

Answer 2

Most of the planets appear as disks in any telescope, even in binoculars. Mars is quite small at this apparition, a maximum of 16 arcseconds, but far larger in diameter than any star. I generally recommend a 4" refractor or a 6" reflector as the minimum to see significant detail on Mars, but I've seen the polar caps and dark markings with a 4.5" Newtonian, though that was four years ago when it was a lot closer and larger.

Is there any chance that you're looking at the star Betelgeuse rather than Mars?

Answer 3

With a 4.5 inch reflector I would be surprised if you cannot see Mars as a disk, albeit a very small one. Jupiter will certainly stand out as a disk as well.
It depends on the overall magnification level amongst other things. My modest telescope is a 2 inch refractor which is roughly equivalent to your 4.5 inch reflector. With a magnification factor of 350x I can see Mars as a disk quite clearly, but it's still very small. To see a disk the same size as some of the pictures published by NASA etc. you'll probably need something in the region of 10-12 inches to get a good-sized disk. Take a look at the Meade website http://www.meade.com/photogallery/lx90_gallery.html to see some examples of what to expect.

Answer 4

4.5 inches is big enough. I have seen Saturn's rings in a 3 inch telescope at only 32 power, but it does look small. A 4.5 inch with high quality optics and a 100 power eyepiece will show an obvious disk, but if the optics are low quality it will just be a blob. 100 power is enough to show details on Jupiter and see the rings of Saturn at a satisfyingly large size. Mars only looks large near opposition (it is near opposition now). Most people can only make out the polar ice cap visually; the rest of the detail is very washed out looking and hard to see without filters or photography. See the source for photos that show the changing size of Mars as if moves in its orbit as well as one photo near the middle of the page that is processed to show it with more realistic colors. All the pictures on that page as at the same magnification; the changing size is due to the changing distance from Earth as Mars moves closer and farther from Earth in its own orbit around the Sun.

Answer 5

Dear Ret:

One of two possibilities exist for your problem...

A.) You are not looking at Mars.
Please observe it over a long period of time. If it stays
in the same place, it is a star that you are looking at.
See star charts for the present date and time to locate
and identify Mars...follow its path from hour to hour, and
look again.

B.) Your Eyepiece is not the right size for best viewing of
planetary objects. Change to a better eyepiece - higher
power which is smaller "mm."

My telescope is a 6 Inch Meade Refractor and I can see it
okay with that.

Were you desire to see planets "larger" and in more detail, I would go to an 8 Inch reflector telescope which will produce rather nice views of Jupiter and Mars.

Regards,
Zah

Answer 6

You should be able to see Mars as a disk with a 4.5 inch reflector. Maybe you need an eyepiece with a shorter focal length.

Answer 7

Most planets are non-stellar in binoculars. To see detail requires a telescope.

You should be able to see *something* in a 4.5 inch, even in a mediocre opposition like this one. The Valles Marineris region should be obvious in any telescope.

Answer 8

Mars for me is almost straight up at 2am est and with my williams optics 60mm ed refractor at 130x can see nice detail. I agree that betelgeuse could be mistaken for mars where it's now positioned. but mars does'nt twinkle and betelgeuse does.
You could try a 2x barlow to help a bit on the magnification.