I'm really interested here in getting the Subsim rank and file to understand some of the underlying principles happening in celestial navigation in a way that won't necessarily enable them to do it, but so that they don't feel like idiots whenever someone around them happens to mention it. Doing the chat wouldn't really accomplish that.
Now, is Greenwich Hour Angle the same as the Right Ascension of an astronomical object? I'm inclined to say close but no cigar, because astronomers use the Right Ascension to find an object. You use it for navigation.
So on an astronomical star chart, Right Ascension doesn't move for 25 or 50 years and then everybody changes charts. I imagine the Greenwich Hour Angles are real time adjusted for the very hour of calculation so the Greenwich Hour Angle of a star isn't the same two consecutive days at the same time.
Now there's a way to connect Hour Angles or Right Ascension with Longitude on Earth. Hour lines build to the west, starting at Greenwich. A star overhead at noon, will be 15 degrees away in an hour. So one hour in time is equal to 15 degrees of longitude on Earth. One degree of distance is equal to 4 minutes in time.
Let's say you are looking at the moon in a telescope with the perfect magnification to show the disk of the moon with no black space around. That means that roughly your field of view is half a degree. (notice how daintily I avoid saying 30 minutes, confusing angles and time. That would be bad.....) Now aim the telescope so the moon is just about to touch the field of view on one side. How long until it vanishes from view on the other side of your field of view?
Okay, the moon is half a degree wide. It's going to move half a degree to fill up your field of view and then another half degree to leave. So total movement to travel completely across your eyepiece is one degree. Moving 4 degrees takes one minute, so the moon will pass you completely by in a quarter of that time or 15 seconds! In 15 seconds you will go from seeing nothing to black space to seeing nothing but moon to seeing nothing but black space againi. It's hauling butt! Not really. Actually what you are seeing is the rotation of the Earth moving the aiming point of your telescope.
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