Sidereal Year

• The Sidereal Year is the time taken for the Earth to complete one full orbit around the Sun, in relation to the fixed stars.
• This is shorter than the Solar year by 20 minutes due to the Precession of the Equinoxes. One Sidereal day is 4 minutes shorter than a Solar day.

The Difference between a Tropical and Sidereal Year

• Tropical Year
  • Also known as the Solar Year, is the time taken for the Sun to return to the same position after the cycle of Seasons is complete. For example, from one Summer Solstice until the next Summer Solstice.
• Sidereal Year
  • The Sidereal Year is the time taken for the Earth to complete one full orbit around the Sun, in relation to the fixed stars.
  • However, due to the Precession of the Equinoxes, discovered by Hipparchus (c.190-120 BCE), the Tropical Year is 20 minutes shorter than the Sidereal Year, in relation to the fixed stars.

Other Sidereal Measurements

• Sidereal Compass
• Sidereal Hour Angle
• Sidereal Time