نقل قول:
A guide to seeing and atmospheric transparency
by: Anton Vamplew
This article appeared in Sky at Night
THE BASICS
What Moving air in the atmosphere can spoil our views of the stars, making them shimmer and dance in the eyepiece
How toRate the stillness of the atmosphere and your view of the stars
Where Find observing locations with the stillest views
Tricks Techniques to create placid air around your scope
The weather is generally considered to be the biggest hindrance to astronomy. What’s the betting that the night you decide to use your Christmas telescope is the night that spell of fine weather changes for the worse? So you’d have thought that when the skies finally clear, your problems would be over. Surprisingly, though, even a clear night may not be the best time to go out and observe.
The issue is the ‘
seeing’.
In astronomy, this doesn’t mean how you look at something. It’s a term that describes how much the view you see through your telescope is disturbed by what’s going on in the atmosphere above you.
At moments of
good seeing, you’ll get sharp, steady views through your telescope. But
bad seeing produces turbulent, unstable telescope views of the Moon and shuddering, shaky images of stars. This is thanks to the layers of moving air between you and the object you’re looking at, the effects of which are magnified by your telescope. On the other hand, deep-sky objects like galaxies and nebulae aren’t that affected by bad seeing.
In the atmosphere, air at different temperatures is always moving around and mixing together. Light travels through hot and cold air at different speeds so it is continually bent this way and that before it finally arrives at your scope all shaken and stirred. Sometimes there are very few moments of clarity.
One of the best ways to see this distortion is to watch the Sun setting on a clear horizon. It will have a jagged appearance, thanks to the sunlight moving through layers of turbulent air.
to be continued...