Posts Tagged ‘celestial sphere’


Literally, equinox means “equal night”.

In other words, at the Spring (Vernal equinox) or Autumn (Autumnal equinox) the daylight hours are equal to the darkness hours i.e 12 hours each. Technically speaking, the equinox is the point at which the ecliptic and celestial equator intersect.


The angle north or south of the celestial equator to a star. It is one  of the two co-ordinates used to describe the position of an astronomical object on the so-called celestial sphere. Together with Right Ascension, declination describes where in the sky an object can be found.

GoTo telescopes are programmed with thousands of celestial co-ordinates and make it extremely easy to find an object. But where is the satisfaction in that? For an amateur astronomer, finding a faint object for yourself is extremely satisfying, users of telescopes with the RA and declination pre-programmed are missing out on half of the fun and can only really be called stargazers, not astronomy enthusiasts. Sadly, the marketing machine of telescope manufacturers suggests otherwise – they just want to get as much of your cash as they can. Cynical, aren’t I?


A pattern of stars named after an object, animal or mythical person. The stars in a constellation have no physical connection, they are a line of sight effect. Sometimes, people confuse the term asterism with constellation.

Celestial Sphere

This does not actually exist. Early humans believed that stars were fixed to a crystal sphere in the sky, at a great distance from Earth. This is because there is no sense of distance in the night sky and the stars always seemed to be fixed in position relative to each other. The idea is a handy one when dealing with positioning and angles between objects in the sky. See also celestial latitude, longitude, azimuth.

Celestial Longitude

The angle that is measured eastward along the ecliptic, from the vernal equinox, to the foot of a circle that is perpendicular to the ecliptic and passing through the object.

Celestial Latitude

The angle north or south of the ecliptic to an object. Used to help to describe the location of a star on the imaginary celestial sphere.

Celestial Equator

A great circle on the celestial sphere that is midway between the two poles of rotation. It really amounts to the projection of the Earth’s equator onto the sky. It can be thought of as an imaginary ring, 90 degrees from either pole in the sky.

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