Sharing is Caring

[Branden]

Welcome, newcommers to the marvel of astronomy. As the title states, I just thought I would share some of the techniques I have acquired through the years and hopefully save some of the painstaking trial and error I have endured! (Though some, in hindsight, was rather comical!) I hope these help someone and remember, feel free to add to, evolve from, or developed a different method completely! Every person is unique, so what I find efficient you, the reader, may find not helpful.

First, a few terms I will be using:

TFL = Telescope Focal Length

OFL = Ocular Focal Length

xMAG = Magnification Power

A(mm) = Aperture in millimeters

A(in) = Aperture in inches

F/Rat = Focal Ratio

AFOV = Apparent Field of View

TFOV = True Field of View

E(pup) = Exit Pupil

PPI = Power per Inch

So now that that is out of the way, let's get started!

 For finding magnification, use the equation TFL/OFL=xMAG. For example: TFL=1650mm, OFL=20mm. So our magnification power is 1650mm/20mm which equals 82.5 xMAG. 

For finding your focal ratio, we use the equation TFL/A(mm)=F/Rat. For example: TFL=1650mm, A(mm)=355.6mm. So our focal ratio is 1650mm/355.6mm which equals a focal ratio of 4.6. 

For finding your true field of view when looking through a particular eyepiece, we use the equation AFOV/xMAG=TFOV. For example: AFOV=52 degrees (standard Plossl), xMAG=82.5. So our true field of view is 52 degrees/82.5 which equals a true field of view of .6 or approximately 38 arc minutes. 

The next one requires a little explanation and will really help out with not only selecting an eyepiece but also how much detail you will get when looking through the eyepiece in regards to how much light your eye is gathering. Were talking about exit pupil. Exit pupil is, in a nutshell, how much light is getting to your eye through your eyepiece. At full dark adaptation the human pupil dilates to about 7mm, so an eyepiece with an exit pupil greater than 7mm becomes useless, because 7mm is going to be your maximum detail. To find exit pupil we use the equation E(pup)=A(mm)/xMAG. For example: A(mm)=355.6mm, xMAG=82.5 power, so our eyepiece exit pupil is 355.6mm/82.5 power which equals 4.3mm E(pup).

To find out the power per inch of a particular eyepiece, we use the equation PPI=xMAG/A(in). For example: xMAG=82.5 power, A(in)=14" so our power per inch equals 82.5 power/14" which equals about 6 power per inch of aperture. 

That's it for the mathematics portion!

For finding objects in the night sky I recommend a good chart or computer software. I use a star atlas made by Michael Vlasov along with Starry Night Pro Plus 6 by Simulation Curriculum Corps out of Canada. Also, very important for me anyway, learn the constellations. They serve as extraordinarily useful landmarks in a massive sky! For finding objects that are at a certain angular separation from a particular star or other stellar object, I use the hand method in the image below. 

To preserve my night vision I use an eye patch to cover my right eye when I am looking at my laptop or looking through my charts. (Use a red-lens flashlight (or torch as my friends across the pond call it  ) to help maintain your natural night vision.) When I'm ready to view the object, I just flip up my eye patch. You'll be amazed at how much more detail you get! To keep record of my observations I use a simple log as shown below. 

Well, that's basically it! I hope this helps some of you guys out. As I said, feel free to modify or tweak, offer suggestions, or come up with an even better system altogether! Keep your eyes to the clear night skies and enjoy the marvels of our universe!

 

[Branden]

Something I forgot to mention, I have found that the longer you look at something, the more detail you will start to discern. Also, don't focus directly at the celestial. The optic nerve in our eye is about smack in the middle of our eye, directly behind the lens creating sort of a "blind spot" in our natural night vision. Instead, focus just slightly off to the side of the object you are looking at, letting the maximum amount of light hit our optic rods, the night vision portion of our eyes, which are located directly around the main optic nerve, allowing you to discern the maximum amount of detail when dark-adapted

[Branden]

Now, for the next section, I wanted to discuss the actual logging of your observations because there will be some important terms in regards to atmospherics that I would like to share. Now, in the image of my log (which I am posting again to save you the trouble of scrolling back and forth from the first post to here) I have several details written down. I log the date, time, and location of my observations along with latitude and longitude of my location. You can use whatever format you prefer. For example I use the Gregorian date but if you want to use the Julian date, by all means. Its whatever your personal preference is. Same with time. I use Greenwich Mean Time but if you prefer, use your local time. Then of course I log the object, (Messier 81, NGC 8631, Crab Nebula, etc) its right ascension and declination. I log my telescope, which is an Orion SkyQuest xx14i intelliscope, and its aperture, which is 355.6mm. I then log what eyepiece I am using, whether it be a Plossl or wide field or what have you, and the magnification power of the eyepiece/telescope combination along with the true field of view and what filter I am using if applicable. The next two lines are the two I'd like to discuss. Seeing and Transparency. Seeing and Transparency deal with Earth's current atmospherics. Seeing relates to the amount of turbulence in the atmosphere. This same air current that causes aircraft to "bounce" through its flight has a visible effect when peering through it. I've found the easiest way to measure seeing is by looking at a bright object such as the moon or one of the planets at a relatively high power and note how much "air" moves across your field of view. A turbulent atmosphere will kind of make the object look as if you are peering through heat waves causing your image to kind of "shimmer". This effect is magnified if the object you are viewing is close to the horizon as you are looking through much thicker, more turbulent air. To log the seeing conditions I use a scale of 1 to 8, with 1 being no turbulence, 8 being very turbulent. Transparency is how clear the Earth's atmosphere is, or how much detail you can make out of dim objects. Things such as moisture content in the air affect transparency. If you look at a bright planet or star, or the moon and it has sort of a " halo" then the transparency is horrid. Lol. But a good way to measure transparency is to look at the Whirlpool Galaxy about 5 degrees from the tip of the tail of Ursa Major. There are two galaxies in view and appear to be colliding, however this is only an illusion. The "smaller" galaxy is much further away than the "larger" one. Both galaxies are fairly bright. To gauge the transparency, see how much detail you can discern from the two galaxies. If you can make out a distinguished bright core and spiral arms in both galaxies, then your transparency is approximately 1, again using the 1 to 8 scale. If they appear as fuzzy puffballs then your transparency is closer to 4. If you can barely make out the galaxies at all, you've got yourself an 8! Keep in mind that light pollution will have an effect on the transparency conditions, so transparency isn't entirely an atmospheric condition. The final detail is atmospheric pressure. I log mine in kilopascals (kPa) but again, personal preference. Feel free to log yours in millibars or inches of mercury (inHg) or not at all if you feel! Then I have a space for any notes I feel like taking, lunar phase or what have you. Again, as before, feel free to leave comments or suggestions. There is always more to learn so if you have a better method you feel like sharing, please, by all means!

[Dave In Vermont]

Have you heard of and/or used Stellarium? It is the planetarium-program we usually suggest to new folks to get and try. It is completely free - whereas Starry Night, which is an excellent program, costs money.

Here's a Cut & Paste:

On this link is the main page for downloading Stellarium. Choose which version is correct for your computer. Here you go:

http://www.stellarium.org/
 
As for instructions, the most current one's are posted in Wiki due to there being new features & functions being created almost daily. There is also a Pdf. that's almost up-to-date, absolutely enough 'up-to-date' in all needed ways. Here's the Wiki-Link:
 
http://www.stellarium.org/wiki/index.php/Stellarium_User_Guide
 
And the Pdf. is here:
 
http://barry.sarcasmogerdes.com/stellarium/stellarium_user_guide-new.pdf

And I tend to remember to drop in a screenshot:

Click image for full-size.

And on that note -

Good night,

Dave

[Branden]

Yes. Thank you for that, Dave. I do have Stellarium (I'd have to look at which version) however I don't often use it, with the exception of the telescope/eyepiece function that shows you how the celestial body you are looking at should appear through a particular lens/Barlow combination. The fact that I don't hardly use it is why I failed to mention it. Thank you for adding that! Yes, Stellarium is freeware, whereas my planetarium software cost me well over $200. Lol. So, yeah, Starry Night may not be the preferred choice. 

[Mak the Night]

Don't forget Cartes du Ciel

Which also runs on Ubuntu and other Linux distros.

And can be used to print out observing charts (if you have a printer that hasn't exploded recently lol).

CDC is also freeware.

Then there is the old fashioned way of finding stars. Seen here; my decades old and slightly battered Phillips' Planisphere with a newer David Chandler Night Sky Planisphere.

At just 13cm long this rechargeable Pellor dark adaptation red light torch is surprisingly powerful. It has different brightness settings but can be a bit overpowering, to the point where it will probably reheat microwavable pasties on its highest setting lol. Useful though for finding pieces of kit in pitch blackness and reading planispheres.