Observing the Sky

Observing the Sky

1. A sidereal day is the time taken for the earth to spin once

   • If you looked at the night sky youd see distant stars appear to cross the sky from east to west. Astronomers have known for years that its not the stars that move but in fact its the earth spins on it saxis. For a star to get to the same position in the sky the earth needs to spin 360 degrees: this is called a sidereal day
   • A sidereal day is the time taken for a star to return to the same position in the sky. Its about 23 hours and 56 minutes

2. The Sun and Moon Appear to Cros the Sky at Different Speeds

   • The sun and moon also appear to move from east to west. The sun seems to more more slowly across the sky than distant stars - it takes 24 hours to get to the same position this is called a solar day
   • A solar day is the time taken for the Sun to appear at the same position in the sky. Its 24 hours
   • The earth orbits the Sun in the same direction as it spins so the earth needs to spin slightly more than 360 degrees for the Sun to appear in the same position in the Sky. The moon seems to go more slowly than the Sun taking 25 hours this is because the ,oon orbits the earth in same direction as the earth is rotating

3. The Stars you can see in the sky change during the year

   • As the earth moves around the sun, the direction we face changes slightly every day, this means we can see a slightly difernt patch of sky each night. We can see the same stars on the same day each year