Modifies a noun

• zodiac: The vernal point reached 0 Aries in the sidereal zodiac in AD 221.

• clock: Once in every two seconds a similar mark was made by a current sent by means of the standard sidereal clock of the Observatory.

• day: Instead we let the Earth's rotation sweep the telescope beam across the sky, once each sidereal day.

• period: The sidereal period is the time taken by a planet to execute a single orbit around the Sun.

• time: The local hour angle of an object is the local apparent sidereal time minus the apparent right ascension.

• rate: My original application was for stepping at a sidereal rate.