The Earth rotates on its own axis, but as we live on its surface we don't actually notice this motion and we get the impression that it is the stars that move around us. We can only see the Sun and the Moon during the day. At night we can see the stars. On a really clear night, when there is no light pollution, we are able to enjoy the breathtaking view of the Milky Way which consists in billions of stars of our galaxy.

Another spectacular vision that the night sky has to offer is when meteorites penetrate the earth's atmosphere. These are materials that orbit in space and due to friction with the surrounding air become incandescent and emit light.
During the year the Earth slowly moves around the Sun.
This means that the stars we can see in the sky at a specific time of the day, at a specific moment of the year, will be different from the ones we can see at the same time of the day, at a different moment of the year (fig. 1).
Let's now take a brief look at how the stars move in the sky. Their apparent motion (defined in this manner because - as we have stated - it is the Earth that moves) is very different when observed from different locations at different latitudes.
Fig. 2 illustrates three different cases:
- the North pole
- an intermediate latitude location
- the equator
It is clearly seen how, at the North pole, all the stars move along paths that are parallel with the horizon. On the equator the stars move along paths that are perpendicular to the horizon. At intermediate latitudes the stars move along paths which are inclined compared to the horizon. At intermediate latitudes there are stars close to the celestial pole (the North celestial pole is very close to the Polar Star) that never rise and never set...



  The motion of stars in the sky
  Learning about the sky
  Sky map

... These are the so-called "circumpolar stars" (fig. 3). Stars that are farther from the celestial pole, however, rise and set; or more precisely during their motion they spend a certain amount of time below the horizon.

The more distant a star is from the celestial pole, the more time it spends below the horizon. Beyond a certain limit, stars never rise as they are always located below the horizon. At the North Pole, all the stars in the visible half of the sky are circumpolar. On the contrary, no stars are circumpolar on the Equator.