The Sun looks to be in perpetual motion, rising on one side of the sky, travelling across it, and setting on the other. The apparent motion across the sky is caused by the Earth's rotation. Because we are on the surface of a rotating body, everything around us appears to be moving relative to the fixed stars. During a day, the Sun rises every morning over one part of the earth and sets every evening over another.
This is called "the solar eclipse". The Moon stops directly between the Sun and the Earth, blocking most of the sunlight from reaching us. Only a small amount reaches where it can pass through the shadow of the Moon and reach it again. This area of the planet is now in darkness, so they are called "shadow zones".
As the Earth continues to rotate, the next place where the Sun will rise again will be over another part of the shadow zone. So, the location where the eclipse starts and ends depends on where you are standing on Earth at the time it happens.
An eclipse of the Sun can only happen at full moon because that is when the Moon is closest to the Earth. If it was closer or farther away, then it would not be able to block out all the sunlight.
The Sun travels through the sky in the same direction; but, the Sun's position along the route at any one moment varies from day to day; it rises or descends to a higher or lower point in the sky at different times of the day. This is because the axis around which the Earth rotates is not fixed, but rather is inclined with respect to the orbit plane of the Earth around the Sun. Thus, the angle between the Earth's equatorial plane and its polar axis changes over time.
This phenomenon has two important effects on the appearance of the Sun: north and south poles of the Sun appear to move across the sky at different speeds, causing days to become shorter at the poles and longer at the equator; also, the angle between the Earth's equatorial plane and its orbital plane changes throughout the year, so that the location of the Sun at any given time throughout the year is not exactly at the vernal equinox (the point in space where the equatorial and orbital planes are parallel).
The effect of solar rotation on the length of a day is very small, about 1 part in 2,400. The reason is that the radius of the Sun is large compared to the distance between the Earth and the Sun.
As the Earth rotates eastward on its axis, we move with it, generating the appearance that the Sun travels across the sky during the day. During a full rotation, the Sun appears to rise someplace new and set somewhere else, just as if someone were walking around it.
This is not actually moving, but rather appearing to move because of how far away we are from the Sun. If we were closer, we would see it rising in the East and setting in the West, just like our planet does.
Closer to the Earth are the stars that make up the Milky Way Galaxy. From outside the galaxy, you would see only these stars.
Inside the galaxy, there are many other objects besides stars. Gas clouds within galaxies form planets such as Earth, while dark matter makes up most of the mass of galaxies. Galaxies are held together by gravity, which is why they need dark matter to keep themselves together.
Outside of galaxies, there are even more stars than inside them. The Milky Way is just one of hundreds of millions of galaxies in the Universe. There are so many galaxies that if we looked closely enough, we could see everywhere light, invisible dark matter.
The apparent motion of the sun, produced by the Earth's rotation on its axis, alters the angle at which the direct component of light strikes the Earth. The sun seems to move across the sky from a stationary place on Earth. This apparent solar motion is called "ecliptic latitude." The closer an observer is to the equator, the greater will be this apparent motion.
On average, the north pole is tilted toward the Sun by about 53 degrees, while the south pole is tilted away from it by about 51 degrees. Because the plane of Earth's rotation is perpendicular to the plane of its orbit around the Sun, each hemisphere experiences both winter and summer, but at different times of year. In winter, the far side of Earth is dark; in summer, it is not. The interval between these two periods is called an "earth day."
An earth day is 24 hours for those places near the Equator, but it is longer at higher or lower latitudes. For example, at the North Pole, the sun is up for only 9 hours due to darkness during the other 15 hours. At the South Pole, the sun is up for only 3 hours due to darkness during most of the other 12 hours.
At the Equator, the entire celestial sphere is visible all at once, so there is no such thing as night and day for observers there.
The Sun, Moon, and planets appear to travel through the sky in the same way as the stars do. Because of the Earth's rotation, everything in the sky appears to move in unison, spinning once every 24 hours. Similarly, every point on the celestial equator is directly above from some point on Earth's equator. At any given moment, therefore, all points along the equator are pointing directly at the Sun or the Moon.
Because the Earth spins on its axis, we experience night and day. The plane of the Earth's orbit around the Sun is called the ecliptic; it is this that determines when we can see the Sun and when not. If the Earth were exactly perpendicular to the line of sight between us and the Sun, then neither could be seen. But because of the Earth's axial tilt, we get seasons: winter here on Earth means that the Sun is never far from being completely hidden by our own planet!
The time it takes for the Earth to rotate so that each part sees the Sun rise twice per year is called a solar cycle. Since 1755, when astronomers first began to record such things, the average length of a solar cycle has been about 11 years. But there are times when the Sun seems to shine more brightly than usual, causing global temperatures to rise. This is because even though it may take the Earth 12 years to circle the Sun, during these extra-warm periods it does so in only 10 years or less.
ROTATION If you look up in the night sky for a few hours, you'll notice that the stars appear to rotate around a fixed point in the sky (which happens to be near the pole star, Polaris). This movement is caused by the rotation of the Earth. But they're actually standing still while we watch them go by.
ORBITS Many stars are part of a binary system which means they have a companion star orbiting them. These stars appear to orbit each other instead of the center of mass that defines a single star. Astronomers can tell how many stars are in a binary system by looking at their spectra; the lines in these spectra are shifted slightly due to the gravitational pull of the companion star.
Some binary systems consist of two identical stars that are attracted to each other but not enough to form a single star. Instead, they stay separate even though they share the same gas cloud from which they formed. Such pairs of stars are called "binary stars," or sometimes "twins." They can be found in the centers of galaxies where they play a role in creating new elements within those galaxies.
Stars also can be found in groups known as open clusters. These large aggregates were created when a large number of similar stars collapsed together under their own weight.