I had so many things going on when I got home that I didn't have much time to post any more Stellafane photographs after I posted that one of the memorial with all the lights. So this is late in the day, before it gets dark enough to observe. I love how strange this looks. What are all those silver ghosts doing on the observing field? These are all telescopes which need to cool down before observing. They are covered with this aluminized mylar because the telescopes sit out in this field all day and the mylar keeps the sun from warming them up.
4 comments:
At first glance, I thought you were jumping ahead to Halloween. I learn something new everyday. Joan
They do look like silver ghosts! Didn’t know that the telescopes have to cool down before observing at night!
Good question and I was going to explain in the text but the explanation is too long. So here it is here: These telescopes under the mylar are "Newtonion" telescopes, which means they use a mirror as the "optical element." rather than a lens, at the bottom of the telescope.. So, in my 8" telescope which I built, the mirror is made of optical glass and it is 8" in diameter, and 2" thick! It has to be that thick so as not to distort as you move the telescope around. So, about the temperature. You how a road gets hot in the sun and when you look down a road on a hot day, all the heat rising from the road distorts cars a long way down the road? Well, if the mirror is much hotter than the surrounding air, the heat from the mirror will warm the air above it, and that air rising from the hot mirror will distort the moon and planets and stars that you look at. So the mirror wants to be at the same temperature as the air, for perfect views of the night sky. So, protect the mirror from the sun with mylar during the day and when the sun goes down, take the cover off and the mirror will slowly cool for a couple of hours and by the time it is really dark, maybe 2 hours after sunset, it will be at the same temperature as the air, and things will be much clearer because there are no air currents rising up through the telescope. Cool, huh?
Thank you so much for explaining all of this. It is so interesting and makes sense now. Joan
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