<Tr> <Th> Second </Th> <Td> 1 / 60 minute, 1 / 3 600 hour, 1 / 86 400 circle </Td> <Td> </Td> <Td> 1 / 240 °, 1 / 4', 15" </Td> <Td> π / 43 200 rad </Td> </Tr> <P> The Earth's axis rotates slowly westward about the poles of the ecliptic, completing one circuit in about 26,000 years . This movement, known as precession, causes the coordinates of stationary celestial objects to change continuously, if rather slowly . Therefore, equatorial coordinates (including right ascension) are inherently relative to the year of their observation, and astronomers specify them with reference to a particular year, known as an epoch . Coordinates from different epochs must be mathematically rotated to match each other, or to match a standard epoch . Right ascension for "fixed stars" near the ecliptic and equator increases by about 3.3 seconds per year on average, or 5.5 minutes per century, but for fixed stars further from the ecliptic the rate of change can be anything from negative infinity to positive infinity . The right ascension of Polaris is increasing quickly . The North Ecliptic Pole in Draco and the South Ecliptic Pole in Dorado are always at right ascension 18h and 6h respectively . </P> <P> The currently used standard epoch is J2000. 0, which is January 1, 2000 at 12: 00 TT . The prefix "J" indicates that it is a Julian epoch . Prior to J2000. 0, astronomers used the successive Besselian epochs B1875. 0, B1900. 0, and B1950. 0 . </P> <Table> <Tr> <Td> </Td> <Td> This section needs additional citations for verification . Please help improve this article by adding citations to reliable sources . Unsourced material may be challenged and removed . (May 2012) (Learn how and when to remove this template message) </Td> </Tr> </Table>

What are the right ascension and declination of the autumnal equinox