3towers Observatory Moon

Mosaic of the Full Moon on December 23, 2007

The major features on the Moon are labeled

The 12-inch f/10 Meade LX 200 telescope at the 3towers Observatory has been used for extensive Lunar photography. The earliest images were taken at prime focus with an f/6.3 focal reducer effectively operating at f/6.5 producing an 80-inch (2000 mm) focal length.  Current Lunar imaging uses either the f/10 prime focus (focal length 120-inches, 3000 mm) or a 2x Barlow system coupled to the f/10 prime focus of the telescope. This later technique gives a focal ratio of f/20 with a 240 inch (6000 mm) focal length. 

For Lunar and planetary imaging, the telescope is equipped with a variety of interchangeable web cameras.  Initial imaging was performed with a Philips ToUcam Pro PCVC740K web camera.  More recent imaging uses either a Lumenera SKYnxy 2-0 monochromatic camera or a Lumenera SKYnyx 2-1 color camera. Monochromatic or color images are obtained depending on the sky conditions and the result desired.  In general, color images are produced with the Philips ToUcam and the SKYnyx 2-1, because they are usually more pleasing. However, it is unpredictable with a given web cam file whether processing it in a color or monochromatic mode will produce a better result. 

The characteristics of the Meade 12-inch LX 200 system and these cameras are as follows:

General Formula:
D = (W x 3438) / (F) 

Where D is field of view in arcminutes, F is focal length, and W is the size of a chip dimension length or width (pixel size x # pixels).  F and W have to be in the same units.

For the Meade LX 200 telescope:

f/6.5 = 80 inches ~ 2000 mm or 2,000,000 microns. 

f/10 = 120 inches ~ 3000 mm or 3,000,000 microns

f/20 = 2X Barlow = 240 inches ~ 6000 mm or 6,000,000 microns

I.  The Philips ToUcam Pro PCVC740K web camera contains a CCD chip with 640 x 480 5.6 micron pixels. 

f/6.5 = 6.15  x  4.62 arcminutes         0.58 arcseconds/pixel

f/10 =  4.11  x  3.08 arcminutes         0.39 arcseconds/pixel

f/20 =  2.06  x  1.54 arcminutes         0.18 arcseconds/pixel

II.  The Lumenera SKYnyx 2-0  contains a CCD chip with 640 x 480 7.4 micron pixels: 

f/6.5 = 8.14 x 6.11 arcminutes           0.77 arcseconds/pixel

f/10 =  5.42 x 4.07 arcminutes           0.51 arcseconds/pixel

f/20 =  2.71 x 4.04 arcminutes           0.25 arcseconds/pixel

 III.  The Lumenera SKYnyx 2-1 contains a CCD chip with 1392 x 1040 4.65  micron pixels.

f/6.5 = 11.1 x 8.3 arcminutes             0.48 arcseconds/pixel

f/10 =  7.42 x 5.5 arcminutes             0.32 arcseconds/pixel

f/20 =  3.71 x 2.75 arcminutes           0.16 arcseconds/pixel

K3CCDTools runs the cameras and is set up to produce standard 8 bit video AVI files. The Philips camera is usually operated in automatic exposure mode running at 5 frames per second. The SKYnxy 2-0 camera is operated at 60 frames per second, and the exposure times and gain are manually adjusted.  The SKYnxy 2-1 camera is run at 10 frames per second, and the exposure times, the color balance, and the gain are manually adjusted. 

Registax (2006) version 4.0.1.1 is currently used for processing the raw AVI files.  For Lunar imaging, 1200-2000 individual frames are taken and analyzed.  The best 300-1000 frames are registered and stacked using the default settings in Registax. Mild wavelet sharpening is next performed on the individual images, which are saved as JPG files. The JPG files are often enhanced using Photoshop CS (Adobe Systems, Inc., San Jose, CA) to improve the contrast and brightness.
 

To check the accuracy of this system for Lunar measurement, the widths of selected Lunar craters were measured with the Philips ToUcam. The diameter of the craters were calculated using the small angle formula as shown below. Each feature width was measured in pixels with Maxim DL Version 4.01 (Diffraction Limited, Ottawa, Ontario). This pixel value was converted into arcseconds using the factor 0.58 arcseconds/pixel for the Philips ToUcam working at f/6.5. The date each image was obtained was correlated with the Moon’s distance from the Earth for that date as shown in LunarPhase Pro. To estimate the accuracy of this methodology, the following features were measured and compared to their sizes (LunarPhase Pro):

*Calculations: Philips web cam CCD chip 640 x 480 pixels. Pixel size = 5.6 microns, 0.58 arcseconds/pixel

Small Angle Forumla: D = (a x d) / 206265

D = Linear Size in kilometers; a = Angular size in arcseconds; d = Moon distance in kilometers.

These measurements show this method for determining the size of a Lunar feature from the images obtained at the 3towers Observatory is reasonably accurate.   The Table below lists standard formations found on the Moon.  Various representatives of these Lunar features are shown in the web cam images displayed on this web site.

Table  – Lunar Formations*

* Taken from Rukl 2004