Want to buy a home telescope? Tips from a professional astronomer to help you choose

• While the unaided eye or binoculars can reveal much of the night sky, a telescope reveals so much more.
• Seeing Saturn’s rings or the Moon’s craters with your own eyes can be an “oh wow” moment.
• Telescopes also come in a range of sizes, with a trade-off between light-gathering power, portability and price.

How big should the aperture be?

Aperture is fundamental for telescopes. The bigger the light-collecting lens or mirror, the fainter the objects you can see. Double the aperture from 50mm diameter to 100mm diameter, and the light-collecting area quadruples.

• Again, bigger is better – a larger aperture telescope will produce sharper images than a smaller aperture telescope of comparable design.
• Earth’s turbulent atmosphere also blurs images, which can limit the detail seen when the aperture is more than 150mm.

Refractor or reflector?

• Refracting telescopes Refracting telescopes can be good for viewing objects on Earth and in the sky.
• While 70mm aperture refracting telescopes can be quite affordable, bigger refractor telescopes are often more expensive than comparable reflecting telescopes.
• Reflecting telescopes Reflecting telescopes use mirrors to focus light.

How do I find things in the sky? Depends on the mount

• To do this, a telescope needs a mount, which is often sold with the telescope but can also be bought separately.
• Equatorial mounts have an axis aligned with Earth’s axis, so a single motor can compensate for Earth’s rotation.

• With the advent of cheap computing, they can now be used to automatically point at and track celestial objects.
• A completely manual telescope will be cheaper than a telescope with automation, but you will need to navigate the sky yourself.

Do I need a finder scope?

• A finder scope with a wider view and crosshairs simplifies things.
• Even telescopes with goto electronics often need to be calibrated with bright stars and locating them is easier with a finder scope.

What about the eyepiece?

• Sometimes decent telescopes are sold with quite cheap eyepieces, but it can be relatively inexpensive to upgrade to a better one.
• More complex eyepieces that provide better views are also available, and far cheaper than they once were.

What if I want to take astro photos?

Taking basic astronomical photos has become much easier with smartphones. While you can hold a phone to the telescope eyepiece for a photo of the Moon or a planet, you will get better results with an adapter that holds your phone securely in place.

• For long exposures, automatic tracking of celestial objects is essential, and that adds to a telescope’s price.
• However, you do lose the experience of seeing the universe directly with your own eyes through the eyepiece.

Try before you buy!

• There should be plenty of telescopes, and owners happy to wax lyrical about them.
• A specialist shop can also give a direct experience of a telescope: its size and how it works (with limitations during daytime).
• For example, you may find a telescope is too bulky or technical for your needs.

Michael J. I. Brown receives research funding from the Australian Research Council and Monash University.