21 deepsky tips
by John Baars
A list of 21 deepsky tips that will make you a better observer
1. You have to make sure that the viewfinder and telescope are aligned with each other. But almost everyone will undoubtedly have done that already and we assume that. There are also amateurs who swear by a Red Dot Finder: a small red dot is projected onto the sky through a screen. No magnification is used. Some even use both: viewfinder and RDF. Very experienced wide-field observers sometimes nothing at all. Everything is allowed as long as it serves its purpose: find.
2. A good atlas. It is not that you can just put your telescope outside and no matter where you point it, the objects dance through your field of vision. Searching for and finding deep sky objects is more difficult than people think. You do not just 'smooth' an object into the picture. Outside, under the stars you can use a good atlas and a small red light. The illuminated screen of a laptop or telephone must be screened with tight red foil (double is better) otherwise it will spoil your night vision. The fainter the red light, the better. The Pocket Sky Atlas (PSA) is a great atlas that can be bought at all telescope stores for a few tens. A great App that is used by more and more observers is SkySafari Plus or Sky Safari Pro.
3. You search on the App, with a planisphere or with the PSA a bright star (which is reasonably close to the object being searched for) and you put it into view with the help of your viewfinder. You put the RDF dot on the bright star. That is already an art in itself with the seeker. After all, you see more stars in the viewfinder than with the naked eye. Sometimes even more stars than in the atlas. Do not immediately search with the main telescope. Because of the amount of stars, the small field of view and the 180-degree rotated image, you can hardly orientate yourself.
4. If you have a known bright star in the viewfinder / at the RDF point, check the atlas to see how many viewfinder image fields you have to move in which direction to reach the desired object. You pay attention to the direction, the field of view and the pattern of fairly bright stars that can be found in both your atlas and the viewfinder. Difficult, because the viewfinder again gives a 180 degree wrong image. Takes a few sessions before you can translate the Atlas-image to “the real thing” and vice versa. You can also rotate your atlas 180 degrees. On a phone app or I-pad you can often rotate or flip the image, according to the image in your viewer. The well-known automatic straightening of the cellphone must be better off. With the RDF, you must continue to use stars that can be seen with the naked eye. There is no other way.
5. To execute the previous tip, make a ring (cardboard, clear plastic) the size of the field of view of your viewfinder in the used atlas. This makes it easier to estimate the number of image fields that you have to move. This tip does not apply to RDF owners.
6. You jump in small-viewfinder- image-field steps from star to star until you are at the position of or near your object. Only then do you look through your main telescope. This is called star hopping. This is difficult the first few times. Look back often in your viewfinder. Watch a lot in your atlas. Translating the image in the viewfinder to the image in your atlas and vice versa is difficult. After a while it becomes second nature. So practice a lot.
7. The minimum magnification is the one which gives you get an exit pupil of approximately 7 mm. That is the same size as the pupil of your eye in the dark. In practice, this appears to result in a clear sky background with little light pollution. With such in a light polluted background, the larger and misty deep sky objects fade into the sky background. So you are looking for a sky background that is considerably darker. Usually an exit pupil (* 1) of about 1-2 mm appears to be enough to reduce the LP sky background and thus get darker. Many deep sky objects pop up under those circumstances. A zoom eyepiece comes in handy here. As the magnification increases, the faint deepsky object appears to loom. With even greater magnification, it disappears again. Except for the very large objects, because you look through them with such a higher magnification. Even very small planetary nebulae then remain difficult because with that magnification they still look like stars.
8. If you are sure that you are in the right place in the sky and you do not see it yet, you can still "play" with various magnifications. (read: making the sky background darker or lighter) In the 120mm and 150 mm telescopes of the compiler of these tips, he initially searches at 35x and quickly switches to 100x. Then we look if the object might tolerate even more magnification. Higher magnifications generally make a large object more difficult to see. But small objects pop up!
9. But ... feel free to experiment with magnifications. Often with higher magnifications, more details become visible if the air is stable and transparent enough. Keep in mind that faint parts of nebulae and the galaxy will appear even fainter because the light is smeared over a larger surface at higher magnifications. Sometimes you will see more detailed darker regions though.
Globulars, small planetary nebulae and double stars are the deep sky objects that can withstand very high magnifications. 2X Diameter objective in mm. for globular clusters, 3XD in mm. for small planetary nebulae and even 4XD in mm for very narrow double stars. You can try it out. The highest magnification in the series (only for the difficult double stars) requires the utmost of viewer optics, mount, seeing and observer. But in 1910 they already did it with 10 cm refractors. Under normal conditions increasing 400X on a deepsky object is the maximum. Also with much larger (mirror) telescopes than the 10 cm refractor. "Cracks" will sometimes go further, with specialist targets that are unfathomable for a starter, but most often they will stay at lower power.
10. When the Moon is above the horizon, all deep sky objects fade.
11. Looking above or next to the object helps. (Averted vision) Let your eye circle through the image field. Do not fix on the middle of the field or your eye. The middle of your retina contains less light-sensitive rods, the peripheral area of your retina is much more sensitive to faint light. That is why tapping the telescope also helps, so the image moves. A moving faint spot of light is more noticeable. Slewing the object through the image also works great. If you have got a zoom-eyepiece: zooming in helps sometimes too. If possible observe the object at its highest point above the horizon. (Culmination) Less atmosphere to look through. Amazing how in the last split-second of time it takes for the light to reach the eye, after a journey of light-years, the image is ruined by the atmosphere or the turbulence in the instrument itself!
12. Certainly do not give up too quickly. Sometimes it can take minutes to more than half an hour (about the time to completely adjust the eye to dark conditions) before a hint of an object looms up. Experienced observers consider an object as found when it pops up only a few times a minute. Less experienced ones need more and feel less sure about their observation. If you are a beginner, don’t let an experienced observer next to you discourage you. He or she will notice the object long before you will. Experience is doing that. You will be there where he / she is within six months.
13. You can also think of a deepsky filter, but do not expect the difference of day or night. Usually it is a subtle difference. And sometimes surprising. UHC filters and OIII filters are commonly used. Be sure the exit pupil of your telescope to be at least 2-3 mm. Those filters eat light. Sometimes even 5 mm is necessary.
14. The best deepsky filter is the jokingly called "gasoline filter": a long drive to a place where it is really dark. After several hours in complete darkness the sky looks less dark than when you started. It is not the sky. It is you own completely adapted eyes that take care of that. A look at the limiting magnitude of your telescope will prove it. A long forgotten ability of our eyes from the times we were hunters.
15. Keep all stray light out of your eyes and therefore far away from you. A large hood, towel or something similar over your head may be crazy (who sees it?), but this really makes the difference between a yes or seeing nothing - amazingly much difference even. Make sure that heat from the face / breath can escape, otherwise your eyepiece will irrevocably cover.
16. Pressing your eye against the eyepiece also covers the eyepiece. The eyepiece will be dewed. Keep some distance. You take the slightly smaller field of view for granted. That is why that hood is so important. You keep eyepieces above the dew point in your jacket pocket, close to your own body.
17. Do not try to switch on your red light for each wiping wash, such as changing eyepieces or anything else that can do without light. You can often do without. If you have ever seen a time-lapse of observing amateur astronomers: nice, even funny, but for visual perception all that light is hardly needed.
18. Sitting while observing allows you to concentrate better than standing.
19. When you sit still you get cold. Provide extra warm clothing (the more layers the better), footwear, gloves in winter. You will not be the first to stop the session because your toes fail ( heated shoes! ) while you yourself are still in the mood. Summer nights also get surprisingly fresh by the morning.
20. Also take care of your inner person! Food, hot tea. However, alcohol and nicotine deteriorates your night vision. Extra for the summer: Deet, against the mosquitoes.
21. In a lonely dark location, remember that people and animals are more afraid of you than you are of them. After all, YOU are that "scary creep" yourself! People hardly see you. Once a cough from the author was enough to give unsuspecting passers-by almost a cardiac arrest. Most animals have already heard, seen and smelled you from miles away. Long before you did. Going out there with the two of you feels more comfortable. Always nice to have some company. Nevertheless every now and then I read about encounters. Be aware that you are the guest and not the ruler out there.
Reflection: Think of it as a joke if you stand outside there on your own: Many are outside with you too. Wherever it is clear. So you are alone, but in fact you are not ...
*1) Exit pupil: the diameter of the light cone that comes out of your telescope. Calculated by dividing the diameter of your telescope through the magnification. For example: a 150 mm telescope with a magnification of 100X gives an exit pupil of 150/100= 1,5 mm.