Astronomy Software and FOV

The Skywatcher Avant mount is a manual one: it cannot be controlled via any type of electronic or computerised equipment, and only recently a small simple motor drive has been available. However, we owners of the SkyMax-102 AV can use the computer to run very helpful and sophisticated amateur astronomy programs. This is of a great help: when out in the hills watching dark skies, instead of looking at maps and printouts, we can find out exactly what is in the sky at that moment in that direction by just looking at the screen of our laptop, or even our smartphone. I will mention only the programs I am using at present, and I can testify about their quality, but not their superiority: some users prefer other programs that have similar functionality.

STELLARIUM

This is a free software that runs in any Windows or Mac computer and also has an Android version for tablets and smartphones. Stellarium starts up in a split second and is very useful to find out your target up there in the sky.
[It also allows direct computer control for computerised mounts].

                    

STARRY NIGHT 7 ENTHUSIAST

The Starry Night (“SN”) program is payware, but worth every cent of it. It runs in any Windows or Mac computer, and can do the same as Stellarium but also much more: it is both a complete astronomy educational package and a fully-fledged planetarium. SN comes in four variants:

1. CSAP 7: This is meant “for beginners who want an easy to understand starting point into both astronomy and software simulation.” If amateur astronomy will be a hobby important enough for you to get a telescope, even a relatively small one such as the SkyMax-102, this variant is not for you.
2. Enthusiast 7: This is “designed for the serious amateur astronomer who wants an entry-level program that also includes advanced observing features and binocular databases”. This version is relatively affordable (US$ 80).
3. Pro 7: “The premium go-to solution for advanced stargazing ... for research and ... professional observatories." At almost twice the price of Enthusiast 7, this is only worth for owners of telescopes that are quite important.
4. Pro Plus 7: “fully featured ... for the astronomer ... best ... astronomy software and telescope control experience.”

For SkyMax-102 AV users the obvious choice is Starry Night Enthusiast 7 (“SNE7”).

            

You can always upgrade years later if you wish.

I got SNE7 three years ago in the DVD version, and these are my impressions.

Few and inessential "cons":

• Downloading the latest version took quite a while (1.2Gb). Careful comparison with the DVD showed that, although the main program was the same, the data files were not: the ones in the download were remarkably more complete. Accordingly, I installed the download.
• SNE7 took about 20 sec. to start (it loads lots of data and starts by default a fully-fledged sky simulation). With my hard disk drivers now substituted by SSDs, this time is now about 7 sec.
• Sometimes it is not easy to change an option or to do some action amidst the plethora of menus and options.
• There is no user-customisation of its menus and toolbars.

Many "pros":

• It updates automatically when new versions of either program or data become available.
• It is a very complete program.
• It includes a very long series of tutorials so that you can learn Astronomy from the ground up.
• It is “relatively” easy to use, although there is quite a significant learning curve in such a complete package.
• You can change your location and any observation time (including the remote past or future) in a breeze.
• You can customize SNE7 to your telescope and your eyepieces (see below).
• You can save location, time and other customisations, so you can return to them automatically when needed.

STARRY NIGHT AND YOUR FIELD-OF-VIEW

Even if you have a manual-control-only telescope such as the SkyMax AV, you can still customise Starry Night so that it includes onto its simulated sky the accurate circles that show exactly the “Field of View” (“FOV”) that you get when you watch the sky through your telescope and eyepieces. To achieve this you should enter (once only) the apparent diameters obtained with the different eyepieces of your telescope. Let us see in detail how you enter this data to SNE7.

FOV. This is an angle—typically less than 1 degree—expressed in minutes and decimals, showing the size of what you will later see in real life with your telescope. [Note: the FOV is not the “Apparent FOV” or AFOV found in eyepieces' specs, which is your eye's perspective inside the eyepiece, typically a value from 50º upwards.]

Eyepieces and Lenses. The SkyMax-102 came with its bundled 25mm and 10mm eyepieces, but the set I recommend replaces the latter with a 9mm and includes also a 14mm and possibly a 5.5mm as well.

FOV Formula. SNE7 requires that the user enters the FOV of each combination of eyepiece and lens. This can be found using different online calculators. With the following abbreviations,

FOV : Eyepiece Field of View in minutes
TFL : Telescope Focal Length in mm
EFL : Eyepiece Focal Length in mm (*)
AFOV: Eyepiece Apparent Field of View in degrees

(*) including the effect of Barlow or Focal Reducer if any

all the calculators use the—intuitively easy to deduce—general formula, valid for all telescopes and eyepieces:

FOV = 60 * EFL * AFOV / TFL 

For our SkyWatcher Maksutov 102/1300, with its TFL = 1300mm, the above formula becomes

FOV = EFL * AFOV/ 21.67

To introduce FOVs in SNE7, you perform a “Search” for “FOV”, click on “Circular” and the program lets you add a new FOV item. In this way you enter, one after the other, the following data by typing the required “Indicator Name” and “Diameter” (the FOV value given by the above formula). These are the data I entered:

Indicator Name    Diameter

SM102-25m           60.0'
SM102-14m           40.1'
SM102-09m           25.8'
SM102-05.5m        15.7'

After selecting a colour for each of the circles, “presto!”, when looking at a sky object in SNE7, you can see the field of view of the different eyepieces. The pictures below, obtained with SNE7's File-Export function, shows what I see when looking at either the Moon or the Andromeda Galaxy.

                              

                              

The only issue is that SNE7 has no function to enable/disable the FOV circle functionality: you have to search for “FOV” and enable or disable each circle.