North celestial pole
- Altitude
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Polaris and latitude
The altitude of the north celestial pole equals the latitude. South of the equator that altitude is negative, and the pole is below the horizon. Polaris is not the pole. It is a small offset from it.
The left circle is the meridian. North is on the left. The brown line joins the two poles, and the north celestial pole sits at an altitude equal to the latitude. The circles on the right are the view facing each pole. Facing north, the stars turn anticlockwise. Facing south, they turn clockwise. The northern circle is enlarged: its rim is 3° from the pole, so Polaris can be seen on its ring. On the meridian that same offset is smaller than the pole mark. The dots move so the direction can be seen. The real turn takes a sidereal day.
- Meridian and the north celestial pole
- Polaris, and the axis
- Below the horizon
South celestial pole
- Altitude
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Polaris
- Offset from the pole
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What this page shows
The primary number is the altitude of the north celestial pole. It is the latitude you chose, in degrees. A place at 59° N has the pole 59° above the northern horizon. On the equator the pole is on the horizon. South of the equator the pole is below the horizon by the same number of degrees as the southern latitude.
The south celestial pole is opposite that. Its altitude is minus the latitude, so it is above the southern horizon only when the north pole is below the northern one.
Polaris, α Ursae Minoris, is the bright star near the north celestial pole. It is not on the pole. At epoch J2000.0 its declination was +89° 15′ 50.8″, so it stood 0° 44′ 9.2″ from the pole. That is 0.7359°, and about 0.7° is the same offset in the usual round figure. Through one turn of the sky the star stays within that angle of the pole. Its altitude is the pole’s altitude, plus or minus at most that offset. This page does not offer the star’s altitude as the latitude.
Assumptions
- Altitude is measured from the geometric horizon, positive above it. There is no refraction. Refraction lifts a star that is close to the horizon; it is not in these numbers.
- The north celestial pole is due north. Its altitude equals the geographic latitude. That is the definition used here, not an approximation that brings in Polaris.
- South of the equator the latitude is negative. The north celestial pole is then below the horizon.
- The offset of Polaris is the J2000.0 catalogue distance, 0.7359°. Precession has moved the star since that epoch. The page does not compute another year.
- The drawing is a meridian and two pole-on views. It is not a planetarium. The enlarged ring is so the offset can be seen. The cards, not the ring, are the angle.
- Stars turn westward. Facing north, that is anticlockwise around the north celestial pole. Facing south, it is clockwise around the south celestial pole.
- The map requests tiles from OpenStreetMap. The latitude is used only in this browser.
Sources
- ESA (1997). The Hipparcos and Tycho Catalogues, ESA SP-1200. Polaris is α Ursae Minoris, HIP 11767. The declination used here at epoch J2000.0 is +89° 15′ 50.8″. The angular distance from the north celestial pole is 90° minus that declination.
- Smart, W. M. (1977). Textbook on Spherical Astronomy, 6th ed., revised by R. M. Green. Cambridge University Press. The altitude of the celestial pole is the observer’s geographic latitude.
- Map tiles © OpenStreetMap contributors.