Aperture - Size Matters

When using telescopes for viewing space, there are some important things to consider. Space is a dark place, and looking at objects in a dark space can be difficult without the proper tools. For that reason, one important aspect of a telescope is the size of its aperture or opening. The aperture is the side of the telescope that is open and gathers light. This part of a telescope can be fairly compared to the pupil of the human eye. Here we'll explain.

When a person walks into a dark room, they usually can not see anything. As the person stays in the room with their eyes open, however, objects in the room tend to become more visible. This is because the pupil of the eye dilates, or expands, allowing more light to reach the receptors in the eye. A telescope works similarly. As more light enters the telescope (ie it has a larger aperture) the more faint an object can be seen. This does not mean that the object will appear bigger than with a telescope with a smaller aperture or that the telescope can see "further." This does mean that the telescope will gather more light and you will be able to view fainter objects. Bare in mind that simply because a celestial body is further away, does not mean it is going to be dimmer. There are plenty of stars that are closer to us than others, but can not be seen very well simply because they are not very bright. This would be comparable to a 10 watt bulb that is 10 feet away versus a 100 watt bulb that is 11 feet away. The 10 watt bulb is closer, but you'll probably be able to see the 100 watt bulb considerably better.

Magnification & Clarity

It’s easy to get hung up on the magnification power of your telescope and its eyepieces--new amateur astronomers do it all the time. And magnification is important. That’s the only way you’ll see any details in the objects you aim your telescope at. But it’s very important to remember that magnification has its limits. You could blow something up to 1,000 times its regular size when viewed by the naked eye, but if it’s just a fuzzy blur, what good is that? Your ability to magnify with clarity is what’s really important, and is mostly dependent on the aperture size of your telescope.

If you put a high-power eyepiece on your telescope, the aperture is still taking in the same amount of light, but now it’s trying to get that light to do more work and show more detail. So, as you zoom in, your view will become dimmer. At some point, there is a limit to how large a given aperture can magnify any object. A good rule of thumb is to multiply the aperture size of your telescope by 50 if the aperture is measured in inches and by 2 if it’s measured in millimeters. That will give you the approximate largest power magnification that will be useful with your telescope. So, the maximum useful magnification for a 50mm telescope is about 100x.

Automatic Controls

When you first get a telescope, it takes a while before you become good at finding things in the sky. It really is a special skill! If you’d rather be able to easily observe many objects on your first night with your telescope, you may want one with automatic controls. Referred to as go-to, computer-controlled, or automatic telescopes, they have a built-in computerized mount system that will aim the telescope for you. The mounts come equipped with a library of thousands of space objects for you to choose from. Many of these automatic systems also teach you about astronomy and give you facts on the objects you observe.

Many automatic telescopes do require a short alignment, but it’s nowhere near as complicated as setting up a manual EQ mount. Usually, you just aim the telescope at the North Star, enter your coordinates, and the go-to mount does the rest. From there on out, you’ll just have to push a button on the controller when you want to view a new object.

The most advanced amateur telescopes have both automatic controls and GPS. GPS telescopes are amazing! You don’t even have to align them because they automatically know where they are, just like the GPS in your car.

• Automatic Go-To Telescope Buying Guide
• GPS Telescopes Buying Guide

Glossary

Glossary is coming soon.