There’s nothing that compares with your first outing with your new telescope – what astronomers refer to as first light. What amazing things you will see and what great discoveries you will make!
But often the reality is very different, and people see very little, usually because they are too eager to get going and don’t puzzle over the instructions.
But here are some steps to get you started, and which will overcome most of the hurdles that people encounter. Take the first step by daylight if at all possible.
Step 1 (by daylight)
Align the finder. People often wonder why they need a little finder scope attached to the side of the tube. It’s there because the magnification of the main telescope makes it very hard to pick out individual objects, particularly in the night sky where there are no big landmarks to get started on. Some finders are small refracting telescopes, while others show you a red dot against the stars when you look from some distance behind them. Both types have adjusters that enable them to be lined up precisely with the main telescope.
The secret is to do this job by day, so that you can find a distinctive and distant object easily through the main telescope (but not the Sun, which will blind you). It’s easier to focus on daytime objects because there is more to see. Once you have found something with the main scope, adjust the finder so that its crosswires point exactly to the same object.
What if nothing is in focus or visible at all? If you are using a refracting telescope, you may need to use the star diagonal supplied in order to get the telescope to focus. Always use the lowest magnification first (see Choosing the magnification). The focus position for nearby objects is slightly different from that for astronomical objects, but it should be similar, so leave the telescope focused on the most distant object you can observe by day.
If nothing is visible, look through the telescope in the light without an eyepiece. You should see a circle of light, but if not try to work out where the obstruction lies – is everything uncapped? Check that the star diagonal if you have one is working properly and that nothing has been dislodged inside it. Look through it in the light – you should see a circle of light with objects mirrored at 90° from the direction you are looking.
TIP: If your finder is a small telescope with single adjusters and you are having trouble adjusting it, make sure that the telescope tube is gripped properly by the mounting. If it slops around, insert a sheet of plastic to help as a washer to grip it.
Step 2 (at night)
Find a bright object (star, planet or the Moon) using the finder and use the lowest magnification on the main scope (see Choosing the magnification). You should see the object in the middle of the main field of view. Even if the view is out of focus, a star will appear as a large disc which you can focus down to a point of light. That’s it – you have made your first-light observation.
Notice how bright this star appears compared with its appearance in the sky with the unaided eye and through the finder. Get to know the field of view of the finder compared with the main scope by looking at groups of stars. Don’t be tempted to increase the magnification until you have had a bit of practice with moving the telescope around and looking at different objects.
Choosing the magnification
Always begin your observations with the lowest magnification – that is, the eyepiece with the highest number on it, such as 20 mm or 25 mm. This usually gives the widest field of view and the brightest image. Even experienced astronomers do this – rarely will they start using a high magnification.
As you increase the magnification (often referred to as power), four things happen. One, the field of view decreases, so an object which was not dead central at low power might now be outside the field of view. Two, if your telescope is not accurately set up and motorised to follow the stars, objects will drift through the field of view more quickly than at low power. Three, the focus position may change, so if there is no bright object in the field of view you may see nothing at all, or just faint discs of light which are the defocused images of faint stars. Four, the images of anything other than stars will get dimmer, so again you may not see anything at first glance.