Admiring DSOs in the sky and finding new ones I haven’t seen before is one of my favourite things to do regarding visual astronomy. But how to know what to look for and where? How to make sure that what you’re looking at is actually what you searched for? Knowing a bit more about this class of items will make things a lot clearer.
In the simplest of terms they are non-stellar astronomical objects. Their classification began soon after the invention of the telescope. One of the first comprehensive catalogues is Charles Messier’s (1774) containing 103 “nebulae” and other faint fuzzy objects. As telescopes improved these objects could be broken into more descriptive scientific classifications such as:
- Star clusters
- Open clusters
- Globular clusters
- Bright nebulae
- Emission nebulae
- Reflection nebulae
- Dark nebulae
- Planetary nebulae
- Bright nebulae
- Supernova Remnants
All of these have different features and knowing them cand help you identify the object you’re looking at in the eyepiece. Star clusters for example are a “conglomeration” of stars with different densities. Nebulae have irregular form, but they can’t usually be “resolved” into individual stars, looking like bits of dust. Planetary nebulae on the other hand are recognised by their circular shape of light with a central star (when that central star is visible). About galaxies we know they’re really distant objects with different shapes (spiral, bars, irregular), some of them disposed edge-on (as we see them from Earth) giving us a great view in the telescope. Planetary remnants are a special class of objects – the remains of a dying star – clouds of gas blown away at some moment in time (also with an irregular shape) – Messier 1 and Veil Nebula are the leading examples that can be easily observed with amateur telescopes.
Some of these objects were given multiple names, according to the catalogues they got listed in. Of interest to us are Messier (M), NGC (New General Catalogue), IC (Index Catalogue) and maybe UGC, Abell, SH2 after a few months/years of experience – when a bigger telescope or/and an astro-photo setup becomes more and more intriguing.
Techniques to find DSOs
Star hopping using a Dobson telescope (or any altitude-azimuth mount)
This is the recommended way to start your journey. A Dob telescope is easy to use (pushing it left-right and top-bottom) and usually has the power to gather so much light (depending on the diameter of the main mirror). After you chose the target, let’s consider the Ring Nebula (M57) in Lyra you have to point the telescope to that region, most likely starting from the brightest star of the constellation – Vega. Star hopping technique is exactly like this: jumping from star to star (looking through a viewfinder) until you reach the place were the target object should be. Then, you move to the eyepiece with your eye and scan the area. If everything is aligned (viewfinder with the telescope tube for example) the object should be in the eyepiece field.
Using an equatorial mount
The mount needs to be assembled, polar aligned, the telescope securely mounted and properly balanced, and the finder scope aligned. Loosen your clutches to point to a bright star. Tighten the clutches and note the published right ascension (RA) of the star and set your RA circle to that. With many star charts, you can move to other objects by following the lines on the chart which correspond with the RA and declination controls on the scope.
Keep in mind that observing faint objects and amazing details in brighter ones you need mostly dark skies. There are filters that cut down light pollution and enhance contrast but these can’t compete with a good and dark observing site. Aperture is the second requirement for enhanced visual astronomy experiences – that’s why Dobson telescopes were built by enthusiasts with as big as possible mirror diameters – 16, 18, 20, 24 inches.