Though stars are shining in the sky at all times, they are not visible during the day because the sun's brightness overpowers the dimmer stars. At night, without interference from the sun's rays, the other stars become visible.
In some areas, it is difficult to see stars at night because of light pollution. Too much light comes from buildings, parking lots, roadways and other structures. These sources throw excessive light into the sky and block star light. Though 15,000 Milky Way stars are visible in remote areas at night, some urban star watchers are only able to view fewer than 500 stars, even on a clear night.