How and why does a day measured by the sun differ from a day measured by the stars?

Question

i need help u guys for my astronomy class

Answer 1

It is due the orbital motion of the Earth. If Earth were standing still, they two would be exactly the same. But since the Earth moves about 1/365th of the way around the Sun in a day, the Earth has to turn more than one full turn (by 1/365th) to face the Sun exactly, while it only has to turn exactly once around to face the same star exactly again. Think of it this way. If a year was only 2 days long, then by the end of one day Earth would be all the way on the other side of the Sun and have to turn an extra half turn to face it again, compared to how much it has to turn to face tome star that is always seen in the same direction. That is what is happening, but by a much smaller amount, every day.

Answer 2

If you want an easy-to-follow visualization, try this:

Imagine the face of a clock representing the Solar System. Imagine that the minute hand represents the rotation of the Earth, and the hour hand represents the orbit of the Earth around the Sun. (this is of course not an accurate scale, since there are only 12 hours on a clock, and 365 days in a year, but it's just a visualization).

Every time the minute hand passes the hour hand, that would be a full day . Notice that it takes another 7 minutes for the minute hand to pass the hour hand? The hour hand is moving while the minute hand makes its trip around, so when it gets back to twelve that first time, the hour hand is no longer there, but at 1.

The "day as measured by the stars" is also called a sidereal period, just in case you ever come across that term...

Answer 3

The Earth orbits the sun, so each day, the Earth has to turn a *little* bit more than 360 degrees to get the sun over the same spot of the Earth.  

But a far-away star, the Earth will always turn 360 degrees exactly for the star to get over the same point.  

Answer 4

earth's orbit makes up the difference.