Thursday, January 16, 2014

Part-Time Lunatic!

So what is an amateur astronomer hungry to do some observing to do when it is at or near full Moon?  Well, I guess that it is time to look at the Moon!  Normally it is absolutely the worst time to observe it - not only is it extremely bright, but also with the sun directly behind us (on Earth), nothing on the Moon casts a shadow.  As a result, there are not many fine details to be seen - only differences in albedo (reflectivity) can be discerned.  But there are a few things that are of interest to see, even when full!

Shown at left here is a picture of the Moon with my Celestron 14" telescope 2 nights ago - the night before the full moon.  Now realize that the C14 has a 4,000mm focal length and the entire orb won't fit in the field of view.  Those following the blog lately know that isn't a problem - I have the Microsoft ICE software that will easily assemble a set of pictures into a mosaic.  That is what this is - a 6 frame mosaic, with overlap on each to make assembly easier.

What I had planned to post about is color on the moon.  While the above picture looks like it is B&W, it is, in fact, a color picture.  Visual observers will tell you that color is really subtle on the Moon, and it doesn't show in photos either.  However, you can see some differences - especially in the Sea of Serenity, the dark area just right of center above in the mosaic.  Shown here at left is that part of the frame, but in Photoshop, the saturation is cranked up a bunch.  In this one you can easily see color differences.  What causes it?  Well, it is generally known now that the "seas" on the Moon were caused by asteroid impacts, and the color indicates composition differences, likely from different chemical abundances of the asteroids that caused them.  Most striking in this frame is the blue color of the Sea of Tranquility, which indicates a higher abundance of titanium, compared to the orange tint of the Sea of Serenity at upper left with less titanium.  I had planned to process the upper mosaic the same way to show the color differences, but the mosaic program evidently makes subtle color shifts - I got the prettiest paisley color charts when cranking up the saturation on it!

The other thing I read about the full Moon yesterday (the 15th) was that it was a "tiny" full moon.  Though you rarely think about it, nothing in the solar system orbits in a circular orbit - all planets and their moons move in elliptical orbits, and it happened that yesterday's full moon happened with the moon near its apogee - the furthest point of its orbit from Earth.  Interestingly, I recalled about 20 months ago that I photographed a "Supermoon" taken near perigee (closest point of its orbit).  The image at left is a full Moon at each time with the same telescope (a 5" Celestron) and same camera, cropped in half and assembled next to each other at the same scale.  The date and distance from the Earth's center is noted on each, and you can easily detect the approximately 14% change in diameter caused by the Moon's elliptical orbit.  While 14% sounds like a lot (about 1/7th), in practice, it is difficult to discern very accurately without instrumentation.  Similarly, the Earth's orbit around the sun is elliptical too, though only by a few percent.  Interestingly, we are closest to the sun in January, the middle of northern hemisphere Winter!  Obviously, the Earth's season's aren't driven by distance, but rather the tilt of the earth's axis!  Perhaps a lesson for another day...

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