One of the greatest thrills for an amateur is to look through the eyepiece and see one of those wispy clouds, one of those bright little donuts, one of those odd shaped multicolored little balls called nebulas. The first time I ever saw color in a non-planetary object was in the Lagoon Nebula. Later on I saw the Orion nebula and that was even better. Examples of these objects can be seen in almost any scope but to really get to know these objects, the bigger the scope, the better. Some of the objects I will be discussing can be seen even in a 60mm refractor but that little scope hardly does them justice, then again, you would be surprised what that scope can pick out with a sharp eye. I presently use a 16” Dobson, but cut my chops on an 8” reflector.

What is a nebula? A nebula is basically a cloud of gas floating around out in space. They come in all shapes, sizes, and colors, and are formed by several different processes. So the first type nebula we will discuss is the planetary.

A planetary nebula is formed when a star either explodes as in a nova, or when it ejects its outer shell. These objects are usually round, hence the name “planetary” because they are round like a planet. Planetaries are as varied as snowflakes. One classic example is the smoke ring shape of the Ring Nebula, also known as M-57. This little planetary is one of the easiest to spot and can even be seen with a 60mm refractor. An 8” scope or larger brings out the hollow center and a 16” or larger reveals the outer edge of the ring flaking slightly. To me, the nebula looks like a smoke ring someone just blew from a cigarette, except it never disburses. Another fine and easy to spot example is the Dumbbell Nebula, or M-27. Fainter and larger than the ring, it is still a spectacular object in an 8” or larger scope. This nebula is a solid ball but the density of the gasses in the center varies to form a dumbbell shape. The Saturn Nebula, or NGC-7009 is a solid bright blue ball with little extensions on each side that give it the appearance of a ring like Saturn. I know that in 10” or larger scopes, many of the more obscure planetaries show color, usually green or blue.

The next type of nebula is the diffuse nebula. This is an accumulation of gasses lit up by surrounding stars. It might be an area where stars are forming or where one exploded and external influences disbursed the gasses in a non circular pattern. It may just be a lump of random gas that is glowing, as can be the way with our random universe. In any case, some examples of these nebulae are spectacular. The grandest example is the Orion or “Great” nebula. This object often has a lime-green tint to it reminding one of anodized metal. The larger the scope, the more detail comes out and it will knock your socks off. Another good example is the Lagoon Nebula. This nebula is marked with several dark lanes and an open cluster. It is the first nebula I ever saw color in. In 1967 I saw it through a friends' 8” f/6 and saw a purple hue to it. I was much younger and my eyes were much sharper then. Today I can't see that color even with a 24”! I've heard that the lack of color may be because of atmospheric conditions which have worsened over the decades with air and light pollution and the still lingering effects of several volcanic eruptions throughout the world. My guess is a combination of sky conditions and my eyes.

The third type of nebula is the dark nebula. By far the most challenging, these objects are dark clouds that obscure background stars. So that brings up the point, how do you find them or see one against an already dark background? We'll get to that in a minute. The most popular example of a dark nebula is the Horsehead nebula in Orion. This challenging object is extremely hard to see on an average night and even on a good one, can be quite persnickety to deal with. Another example of a dark nebula is the coal sack and that one is a little easier to see, but is far less spectacular than the Horsehead. You can tell you are looking at it (the coal sack) because you are looking at a rich star field in the middle of the Milky Way and there seems to be several areas without stars. The stars are being blocked by the dark nebula. Another dark nebula that is even more challenging because of its large size is the Witch's Head nebula. This object is in Orion and is widespread so it is quite difficult to pick out amidst the background stars.

Now that we've covered the types of nebulae, what is the best way to observe them? I've learned a few things over the years that may help to get you started. There has been a huge marketing push for using filters. I'll have to admit that some of them help a lot. Then again, I was observing nebulas before there was such a thing as light pollution, O-3, or H-Beta filters. I'll have to admit that one filter in particular opened up a whole new world for me, and that was the O-3 filter.

Planetary nebulae are some of the easiest to see because they are relatively dense and concentrated compared the other nebulae. There are literally hundreds of planetaries within range of a 10” scope and almost as many available to an 8”. The larger and brighter ones such as the Ring and Dumbbell nebulae require only a star chart and a little searching. Once you've found them, there is no mistake! But there are many smaller planetaries that at first appear as an out of focus star and are very easy to miss. One technique I found for detecting the smaller planetaries is to make sure the scope is sharply focused on known stars. Then using your star chart, aim for the target area and start sweeping slowly. Look for anything with a blue or green color or anything that looks out of focus. You will know you've found something if the “star” is fuzzy but the surrounding stars are sharp. Then if you have a filter, especially an O-3, plug it in and take another look. You may be surprised at what jumps out! An example is this one planetary in Gemini I passed over multiple times with my 16” (can't remember the number). When I obtained an O-3 filter, I popped it in and scanned the same area and there it was! It practically slapped me in the face! Then I took out the filter and looked again and could see why I kept missing it. It was still visible but so faint against the background that it was easy to miss as I scanned. I must mention that I also tried an UHC light pollution filter before the O-3 and still missed it.

Another example of what the O-3 filter can do is on nebulae like the Dumbbell and the Owl. Without the filter, the dumbbell is round with a faint dumbbell shape in the middle. Add the filter and wow! The dumbbell shape and mottling in the center jumps out. When observing the Owl nebula, if you cannot see the eyes without the filter, try it and the eyes jump out. One drawback of the O-3 is that is it lousy for general scanning of the skies and will not work on galaxies. The O-3 darkens the background too much for general searching and also blots out some of the fainter background stars. Stars may look purple or even green.

Probably the most touted filter out there is the light pollution filter. They come in several different versions and I have tried most of them. Before the O-3 filter, the LPR, as they are called, impressed me on certain nights. In fact, I used two different versions for several years before I tried the O-3. After that, the LPR pretty much gathered dust in my eyepiece box! So why the O-3? The band of light this filter lets through is much narrower than the LPR and is specifically designed to bring out the O-3 or oxygen light frequencies. This is the most prominent light emitted by planetary and emission nebulae. The LPR is designed to cut out light pollution that will make the sky background darker and bring out dimmer objects. Does it work on nebulas? Of course! But does it cut through the O-3 band? No. For general applications, the LPR is fine but for emission nebulae like most planetaries and diffuse nebulae, the O-3 is much better.

Diffuse nebulae are for the most part, easy to pick out. The classics of the summer skies are the Lagoon, Triffid, and Omega nebulae. Each is readily visible in an 8” or larger scope. Here is where the O-3 really shines. Find the Triffid nebula and you will see a faint cloud around a small cluster. The cloud stands out against the darker background and almost looks like a hazy open cluster instead of a nebula. Put in the O-3 filter and wow! The dark lanes of the nebula jump out. The same goes for the Lagoon nebula. The dark area of the nebula really stands out when the O-3 cuts through the mix. The Omega appears as a wedge shaped blotch until you put in the filter, and then it looks more like a comet as the tail gets longer and longer.

Okay, so what if you don't have or cannot afford an O-3 filter? As I said before, I was observing these same objects long before those filters existed. The key to observing nebulae is to use good star charts, know the limitations of your scope, and take your time. Once you have the nebula in the field, use averted vision to pick out details. Lower power works much better. Many planetaries can take magnification, but the detail is much better if you don't crank the power up too high. Remember, the higher the power, the dimmer the object and hence, the less detail is visible! Now what if you have other filters, say planetary types? For the most part, they do not seem to help much, and in fact deteriorate the image significantly.

We've talked about the easy objects, the planetary and diffuse nebulae. But now we come to the most difficult to observe, the dark nebulae. It is a forgone conclusion that unless you have a 24” or larger scope, the only way you'll see the Horsehead nebula is with an H-Beta filter. This highly specialized filter is only good for basically two nebulae in the northern hemisphere, the Horsehead and the North American nebulae. Does the $80.00 price tag justify the reward of maybe seeing one of these two objects? I obtained an H-Beta at an Okie-Tex star party in Oklahoma from a vendor, and I got it very cheap. We had what some people call a “Horsehead night.” That term has come to mean the skies are superb. On that night, I tried my filter and barely, and I mean “barely” glimpsed the Horsehead in my 16”. It took an hour of trying but I finally nailed it. I saw it earlier in a 25” and then it disappeared in even that big scope. That was the same weird night a guy with a 28” could not see it yet another with a 10” Dobson did! I did not believe the 10” man and looked for myself and there it was! This object has been the bane of many an amateur and the ultimate challenge. Here in Las Vegas with the altitude, it may be a realistic goal, but with massive light pollution from the strip, the jury is still out. I have yet to see the North American nebula so I cannot comment on that. I have seen the coal sack several times but have never tried it with the H-Beta filter so don't know if that filter helps or not.

In summary, nebulae are some of the most interesting and varied objects in the sky. So no matter what sized scope you have, get out there and try a few. You will not be disappointed!