Constellation position?

Can you explain why a constellation appears to change position from hour to hour during the night . Also is it at a different location at the same time on different nights?

Also would there be any difficulties in using stars to indicate direction while travelling? Would any one star bemore useful than any other? The North Star ?Maybe?Constellation position?Hi Hard Rock!



That's an easy one! It's because the earth is rotating.



Think of yourself looking up into space. The earth is spinning beneath you. As it rotates, the stars above seem to drift from east to west.



You're right that stars also shift their position from night to night, looking up at the same hour. The stars make one full circuit around the sky in 23 hours 56 minutes, four minutes less than a 24-hour day. During that extra four minutes, they drift a bit further west each evening



The North Star is certainly the best one to use for finding your directions at night. It always points almost exactly north.



It isn't the only one, though. If you're in the Southern Hemisphere or the tropics, the Southern Cross always points to where the South Pole should be.



Many constellations can be used to indicate directions with a little practice. For instance, the brightest constellation in the skies is Orion. When Orion is rising, I know that it is in the eastern sky. When it's going down, it is in the west. At its highest point, Orion marks the south (in the Northern Hemisphere, or north if you happen to be in the Southern Hemisphere).Constellation position?The rotation of the earth and the orbit of the earth around the sun cause the constellations to change in the sky. If you know the time and date, there are ways of using the positions of the stars to navigate. You can buy an ephemeris which is a book that gets published every year that has the major star positions for every second of the year. The North Star (Polaris) stays in the same apparent position in the sky all year long. You can use Polaris to find your latitude. Your latitude will be the same as the angle from the horizon to the Polaris. This only works in the Northern Hemisphere. You can't see Polaris from South of the Equator.Constellation position?The constellations' positions shift as the Earth rotates. The Earth does a complete turn in 24 hours, so the constellations will appear to do a complete circle in our sky in that time. Since the Earth also moves a bit in its orbit in 24 hours, the constellations actually are back in the same position 4 minutes earlier every night. At the end of a year, voila, back where they started, same time same place.

Polaris, a/k/a/ the North Star, has been used to point to the North for over two millenia. When you locate North and face it, you know South is behind you, East to the right and West to the leftt. Also, if you can measure how many degrees Polaris is above the northern horizon, this is your latitude.