The needed telescope aperture

randa177

Hi,

In research, if you want to observe a certain galaxy or cluster, how do you decide to which big telescope to apply (in terms of aperture), how do you know what aperture you need for a certain project?

Thanks!

Drakkith

The visual magnitude of the galaxy determines the aperture needed to see it. Usually bigger apertures are better, as they allow more light to be collected at once, resulting in shorter observations times and greater accuracy and details.

russ_watters

Thats assuming a constant focal length. But you also need to pick the right focal length!

Drakkith

Yep!

turbo

Also, choosing a telescope for faint objects includes figuring in contrast. We really can't build and mount huge refractors inexpensively, but their lack of central obstruction, combined with good baffling and blackening can result in impressive performance on faint objects.

If you are doing research, and you have access to university-affiliated 'scopes, they will almost certainly be fixed with instrumentation, and not eyepieces. They will be large, and often Ritchey-Chretien designs meant to provide large flat fields for the instruments to exploit. If you are doing independent research and have to buy your own equipment, you're probably going to be settling for Newtonians of some sort unless you are independently wealthy.

As for design performance, aluminized mirrors never deliver the same throughput as well-coated glass, so contrast suffers, and degrades at about 1% a year. Catadioptric designs have a larger central obstruction than Newtonians, so although they are smaller and handier in some respects, resolution is generally not as good. Lots of trade-offs.

randa177

Thank you all for your reply, I am mostly interested in studying the Magellanic Clouds star clusters... I know that a 4m telescope would be best, but how would I find out the minimum aperture needed to observe these clusters? Is it just their apparent magnitudes?

russ_watters

For star clusters and the Magellanic clouds, there is no minimum and the field of view is much more critical.

randa177

What I mean is would I be able to observe it with a 2m telescope or a 1m telescope? How can I figure that out?

turbo

It is unclear what you wish to observe (at least to me). Do you want to observe the Magellanic Clouds or much smaller star clusters within them?

For example, if you want to observe the Magellanic Clouds in whole (or large parts of them at once), field-of-view is much more important than you might imagine, and that would drive you toward a telescope with a fast f:ratio. Also, you need to determine what you want to observe. Do you want to do spectroscopy, imaging in special bands, etc?

randa177

The spectroscopy of star clusters within MC.

turbo

OK, then that limits you to university or professional-grade telescopes with spectroscopes mounted on them. If you are planning on requesting grant-money for research you should get expert assistance from people who do this type of research. They can advise you on what types of telescope/instrument combinations are capable of fitting your needs, and hopefully can give you some guidance regarding what kind of hurdles you'll have to get over to get some time on an appropriate 'scope.

Telescope time on big equipment is in VERY short supply, so it's best if you can cogently make the case for your research with your adviser, AND your adviser has some pull with the time-allocation committee on an appropriate instrument, you might get a shot. Good luck!