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Visual Deep Sky Observing Part 2

By Edited Apr 15, 2016 0 0

Crescent Nebula

Introductions aside, now its time to get down to the nitty gritty details of starting an observing program. Many people do not know this but you can start doing observational astronomy by just using your eyes (yes you heard that right!). Of course observing with a binocular or telescope helps you look deeper. However many project can be undertaken using only the naked eye. For instance you can spot meteors with the naked eye. This is best done from a rural setting where the skies are darker. One can also learn the constellations (grouping of stars) using just your eyes.

Visual astronomy is a learned skill however. Like any other skill, the more you practice, the better you get at it. Its no wonder so many beginners poo poo small scopes in favor of bigger and bigger scopes. They think that by going bigger, they can see more. While that is very true, deep sky objects would not look very much different between say a 3 inch versus 6 inch scope. Most deep sky objects appear as dim grey smudges anyway. If they don't hone their observing skills, they soon grow weary of lugging that big scope out on not so perfect nights. As they say a small scope gets used more than one that so big, it becomes a chore. Its easier to just turn the telly on. So what skills are required for visual astronomy? I will discuss some of these in the next few paragraphs.

The Art of Seeing

Seeing detail in deep sky objects is an art in itself. A good example of this is comparing notes at the eyepiece of a telescope. A seasoned astronomer would start discussing the detail he sees in the spiral arms of a galaxy, while the beginner would be left scratching his head, wondering if that dim smudge he had just seen was the same object. As they say the more you practice, the better you become. A good way to hone this skill is to make pencil sketches of the deep sky objects you observe. This forces you to take the time to drink in the view rather than to go hopping from one object to another. You don't have to be an artist to make pencil impressions of these deep sky objects you see either. All that is needed is a clip on red flash light (so as not to ruin your night vision), a spiral bound sketchbook, preferably with a hard back and a few pencils of different hardness. A blending stump is great for smudging, as is a rubber putty so you can mold it to whatever thickness you want. Also you might want to experiment with different eyepiece combinations. Most season astronomers use different magnifications to eke out minute details. You can even make use of special deep sky filters. These filters work by filtering out certain wavelengths of light. While not a magic bullet, these will improve the view of deep sky objects such a nebulae, which emit light at a certain wavelength.

Proper observing techniques and tricks of the trade

Averted Vision

Have you ever noticed when stepping out from a brightly lit room into the dark of night you are suddenly not able to see much at all? After standing in the dark, your pupils dilate and you start to see better? This is what you call night vision. Our eyes are built such that there are two cell type, the rods and the cones. For bright daylight vision, we use the cone cells in our eyes. The cells of the cones are packed at a point in the eye called the fovea centralis. These are for photopic vision, best for color and resolution. Under dim or dark conditions, we use the rods, which are located at the periphery. These cells help us see in the dark, what is called scotopic vision. When we step into the dark, a chemical reaction also takes place and rhodopsin is formed in the rods. This is photochemically sensitive and breaks down when exposed to light. We are usually fully dark adapted by 20 to 30 minutes.

Astronomers exploit this by allowing their eyes to fully dark adapt. At the start of the session, you try to look at brighter objects such as star clusters, before taking n the dimmer fare. We also practice the art of looking away but keeping your attention on the object. This is know as averted vision in astronomy. Basically all you are doing is positioning the object so its dim light falls on the rods in the periphery. That is the reason why most if not all of the deep sky objects will appear in different shades of grey. Only the very brightest of these deep sky objects will be able to stimulate the cones and hence will appear green, blue and even subtle shades of reds and pink.

Movement to see better

Another trick that seasoned astronomers use to study faint deep sky objects is to deliberately tap the tube of their telescope, or the tripod to induce slight movement. This can sometimes make the difference between spotting the object and not at all. This trait is inherited from our ancestors. We tend to see objects better when they are moving. This probably came from detecting movement in the shadows to avoid become the prey of other larger mt eating animals.

Proper Breathing Techniques

Another trick of the trade is to get sufficient oxygen to the brain and eyes. Many people tend to subconsciously stop breathing when concentrating on seeking out the dimmest of details in a deep sky object. You should be doing the opposite and trying to take in as much oxygen as you can. A good way to do this is to hyperventilate for short periods of time when observing, but not to the point of passing out. This will greatly aid in enabling you to see more at the eyepiece.

Relaxing the eyes to see more

Most people also do not realize that you need to be relaxed in order to peer deeper into the universe. One of the worst things you can do is to stand while you observe and attempt to block ambient light with one hand and to cover one eye with the other. I have conducted the best and most productive observing sessions when I am most relaxed. This means sitting down comfortably in a camping chair (or an observing chair with adjustable heights for dobsonian users). Also, the use of an eye patch an greatly reduce eye fatigue. You can get these at a pharmacy. Just try not to walk around in the light or someone might mistake you for a pirate.

Yet another trick to help you relax and see more is to use a monks hood whilst observing, a trick used by photographers in the past. These are simply thick dark cloth that you can drape over your head to shield your eyes from the glare from street lamps etc.

In summary, I hope this primer has given you tips on how to improve your observing sessions and to really see the deep sky. In my next few articles, I will focus on the brighter deep sky objects that will hopefully whet your appetite and serve as a jumping off point  to other denizens of the night sky!

 

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