The globe spins 360 degrees in **around 24 hours**, which equates to 15 degrees each hour or one degree every four minutes. When it is noon at Greenwich, the time at 15 degrees east of Greenwich is 15 x 4 = 60 minutes, or one hour ahead of Greenwich time. However, at 15 degrees west of Greenwich, the time will be one hour behind Greenwich time. The planet's rotation creates **a daily cycle** of light and darkness, which we call day and night.

The angle that the Earth makes with the Sun varies throughout the year because it orbits the Sun. In January when the Earth is on the same side of the Sun as Mars, they travel together in an orbit that is almost exactly perpendicular to **one another (85 degrees**). By June when the Earth is on the opposite side of the Sun from Mars, they travel together in an orbit that is almost parallel to one another (90 degrees). The distance between them decreases during this time so by the end of June the Earth is getting closer to the Sun than it was in January.

As a result, in June and July the Earth enters into a period where there is no sunset or sunrise. For us on the ground, this means that it gets dark at some point during these months, but from up in space it looks like the whole world is illuminated all the time.

This is called "Summertime". During summertime, the amount of daylight traveling across the country varies depending on where you are located.

This spin is a whole 360 degrees. So, in one hour, the world will be 15 years old! The earth rotates **one degree** every four minutes. So, if it took 24 hours to rotate completely, then the earth would be alive today that time span.

There are 60 minutes in an hour and 60 seconds in a minute. So, if we want to know how many radians the earth turns in one hour, we can use the formula: 1 radian = 180 degrees. So, the answer is 1 radian = 90 degrees.

A radian is a measure of angle, equal to 1/180 of a circle. One rotation is called a full turn or complete rotation because there are 360 degrees in a circle. So, one hour equals **15 full turns** or 45 partial turns of the earth.

The earth orbits the sun at about 30 miles per second, or 55,000 miles per hour. That's about 16 million feet or half a mile deep. If you went straight up on Earth, you'd reach orbit within **about 8 minutes** 40 seconds. But actually moving around the surface of Earth takes more time because of **all the terrain** and gravity.

In reality, the planet revolves 360 degrees in 4 minutes less than 24 hours. This effect is caused by the Earth's orbit around the Sun, which moves one degree every day. The sidereal day refers to **the 360-degree rotation**. The solar day is actually about 24 hours because of atmospheric effects but we can consider it as being exactly equal to the sidereal day.

For example, if you were standing on the North Pole and watched **the night sky**, you would see all the stars again in the morning. This is because the Earth has rotated 180 degrees while they were out watching the night sky.

Stars that appear in the east after midnight will reappear in the west the next morning. Stars that rise due north do not move across the celestial sphere, they just remain in the same place relative to earth. They are still rising due north even though we cannot see them from over land masses.

Stars that rise due south do not move across the celestial sphere, they just remain in the same place relative to earth. They are still rising due south even though we cannot see them from over land masses.

Stars that set west of Greenwich will eventually set back over land again. However, since the rotation of the Earth is not exact, some stars do not return to **their original position** but wander within the constellation.