All About Space




This is an alignment of objects at the same celestial longitude. The conjunctio­n of the Moon and the planets is determined with reference to the Sun. A planet is in conjunctio­n with the Sun when it and Earth are aligned on opposite sides of the Sun.

Right Ascension (RA)

Right Ascension is to the sky what longitude is to the surface of the Earth, correspond­ing to east and west directions. It is measured in hours, minutes and seconds since, as the Earth rotates on its axis, we see different parts of the sky throughout the night.

Greatest elongation

This is when the inner planets, Mercury and Venus, are at their maximum distance from the Sun. During greatest elongation, the inner planets can be observed as bright evening stars during greatest eastern elongation­s and as morning stars during western elongation­s.

Declinatio­n (Dec)

Declinatio­n tells you how high an object will rise in the sky. Like Earth’s latitude, Dec measures north and south. It’s measured in degrees, arcminutes and arcseconds. There are 60 arcseconds in an arcminute and there are 60 arcminutes in a degree.


An object’s magnitude tells you how bright it is from Earth. In astronomy, magnitudes are represente­d on a numbered scale. The lower the number, the brighter the object will be. So, an object with a magnitude of -1 is brighter than an object with a magnitude of +2.


This is when a celestial body is in line with the Earth and the Sun. During opposition, an object is visible for the whole night, rising at sunset and setting at sunrise. At this point in its orbit, the celestial object is closest to Earth, making it appear bigger and brighter in the sky.

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