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Deepsky Observer's Companion

Published: 2008 November. Updated: 2009 June 17. Revision number: 13

An introduction to deep sky observing

"Astronomy is a typical monastic activity: it provides food for meditation and strengthens spirituality."

Paul Couteau

Two hundred years ago astronomers were mainly preoccupied with the globe on which they lived and the solar system of which it was a member. Consequently, only nineteen objects outside the solar system were known. Today, hundreds of thousands of objects have been discovered that lie beyond our solar system and are known collectively as deep sky objects. This appellation covers clusters of stars, nebulae and the galaxies. These distant worlds are the objects of study for the deep sky observer.

For the beginner, observing the deep sky requires time, patience and a willingness to learn. A small telescope will reveal hundreds of objects to the skilled observer, and many thousands are within reach of a modest telescope.

Through practice and experience, anyone can master the art of deep sky observing. There are a wealth of deep sky objects awaiting your scrutiny.

Observational astronomy is to a great extent an aesthetic pursuit. Enjoy the view as you explore the night sky, but in doing so, do yourself one favour: don't rush. As you move from one target to the next, pause a while.

Don't just look at the universe – see the universe. Hopefully this tutorial will point you in the right direction as you start your journey of discovery.

1. Deep sky observing for the beginner

Some thoughts on taking up astronomy as a hobby.

2. Observing equipment

Some form of optical aid, either binoculars or a telescope, is needed if you want to observe the deep sky. Both types of instruments have pros and cons: binoculars are very portable, easy to use, offer wide-field views and are comparatively inexpensive. Telescopes, although more cumbersome, have greater light gathering power, allowing fainter objects to be seen.

3. Planning your observing

Planning and preparing for an observing session.

4. Observing techniques

Star-hopping, directions in the sky, measuring the field of view, and keeping observing notes.

5. The art of visual observing

The eye and dark adaptation; sky brightness; seeing and transparency; prolonged observing; averted vision; sketching; choice of magnification.

6. Astronomy and vision

Dark adaptation, averted vision, Troxler phenomenon; the role of magnification; the role of contrast; deliberate image motion; observing at the limit; colour vision; are two eyes better than one?

7. The atmosphere, weather and seeing

The atmosphere which blankets us greatly influences our view of the universe. Weather conditions, too, play an important role in the quality of observing. Not to forget the growing problem of light pollution. Some of these complex topics are discussed here.

8. Selecting an observing site

When selecting an observing site, various criteria should be considered. I've collected the points of view of a few authors, summarising the properties they think are important.

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