Astronomy with an online telescope
Astronomy with an online telescope

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Astronomy with an online telescope

Week 2: Telescopes and visual observing


We hope you enjoyed studying the first week of Astronomy with an online telescope. Course author Alan Cayless will now introduce the topics you’ll be studying in Week 2 of of the course...

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By now, I hope you're all getting used to using Stellarium, finding your way around the night sky, and learning some of the more prominent constellations. And I hope that some of you have had the opportunity to get outside and match those up what you've seen on the screen with the night sky outside. Now, at this stage, you don't need a lot of equipment. You don't need expensive telescopes.
There's an awful lot that you can do in astronomy just with your own eyes, and perhaps with a simple pair of binoculars. And in fact, when I started out in astronomy, for a long time, I just used a pair of binoculars. And it was some time before I started acquiring my first telescope which you need for photography, and so on.
As those of you who've had a look at the night sky from outside have probably found by now, more important is to find yourself a site that's nice and dark, away from streetlights, and finding clear weather can be a challenge as well. So, a good observing site at this stage is more important than equipment. And a particularly good choice is up the mountain side.
So here at Mount Teide, we're 2,400 metres up. We're well above the cloud layer. We've got beautiful clear air, and we're well away from the cities and any light pollution. So when night falls, we've got beautiful, clear, dark skies which are perfect for astronomy. And that's the reason that we've chosen this site for our COAST and PIRATE telescopes. And we're not the only ones who think this is a great place for an astronomical observatory.


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Now that you have installed the Stellarium software and started to navigate your way around the night sky it is time to consider the equipment that you can use to observe, and fully experience, some of the stunning objects the Universe has on offer.

The human eye is itself a remarkable optical system capable of amazing sensitivity under the correct conditions. You will therefore begin by considering how to make the most of your unaided vision for night-time observing. Some celestial objects are best experienced with the naked eye, but fainter objects will benefit from the use of binoculars or a telescope.

Whatever equipment you are using, one thing is certain: it is important to find the right place from which to observe the night sky. This week you’ll explore what makes a great observing site and you will get your first detailed look at the COAST facility on Tenerife.

By the end of this week you will be able to:

  • understand how the human eye adapts to dark conditions and how to make the most of your dark-adapted vision for astronomical observations
  • understand the need for telescopes with larger apertures and more sensitive detectors in order to collect more light and observe objects fainter than those that can be seen with the eye alone
  • explain how telescopes work and how the primary element of a telescope captures and focuses light to produce an image that can be magnified by an eyepiece or captured using a camera or sensor
  • understand how the Earth’s atmosphere can affect the quality of images formed by telescopes on the Earth’s surface and how the right choice of observing site can minimise these atmospheric effects
  • understand the purpose of COAST’s size and location.

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