Why do we have sunrise and sunset

All rights reserved. Mystery Class. As the Earth rotates toward the east, it looks like the sun is moving west. Learning Standards. Exploring the Earth's Daily Cycle Here's what scientists say about "sunrise" and "sunset": The sun stays in its position at the center of our solar system. Uranus is another, which not only rotates westward, but is inclined so much that it appears to be sitting on its side relative to the Sun.

Pluto also has a retrograde motion, so for those standing on its surface, the Sun would rise in the west and set in the east. In all cases, a large impact is believed to be the cause. In essence, Pluto and Venus were sent spinning in the other direction by a large impact, while another struck Uranus and knocked it over on its side!

With a rotational velocity of 1, This means, in essence, that a sidereal day is less than 24 hours. But combined with its orbital period see below , a solar day — that is, the time it takes for the Sun to return to the same place in the sky — works out to 24 hours exactly. This means that every four years in what is known as a Leap Year , the Earth calendar must include an extra day.

Figure 7. The daily or diurnal paths of the Sun during the solstices 21 December and 21 June and the equinoxes 21 March and 21 September as seen by an observer at the equator.

Solid lines are daytime, dashed lines are night-time. At all seasons on the equator, the daily paths of the Sun are divided equally above and below the horizon. On Summer Solstice, you would see the Sun rise on your "horizon" at the eastern point of the longest track. It would follow the track high in your sky, and eventually set on the western horizon.

It would be up for about 17 "hours", thus making summertime days long and warm. On the Winter Solstice, you would observe the Sun rising at the western end of the smallest track. It wouldn't rise high in the sky, and would be up for only about 6 or 7 hours, making your days short on daylight and cold. At the Spring and the Fall equinoxes, the Sun would rise at the east end of the middle track and set at the west end.

Build your own Sun Track Diorama What about the stars? The rising points of the stars don't change as much as the Sun's because they are so very far away. So the rising points of stars on the horizon were not as critical to ancient cultures.