Constellation - An area of the sky containing a pattern of stars. There are 88.

Asterism – A pattern of stars in the sky, e.g. the Plough

Open cluster – a group of young stars, e.g. the Pleiades

Globular cluster – a group of old stars tightly packed around the galactic nucleus that resemble a fuzzy ball, e.g. M13

Nebulae - a dense cloud of gas and dust that appear like faint fuzzy patches of light

Double Stars – Stars that appear close to each other. Some are binary stars that are close and orbit each other. Whereas others just appear close because of the angle we see them at.

Labelling Constellations

Drawing Constellations

Pointer Stars

Seasonal Stars

Observing the Night Sky

Right Ascension & Declination

Right Ascension is measured from the vernal equinox (were the sun appears to cross the celestial equator) in a similar way to longitude. Right Ascension is sweeps eastward like bearings on a compass. It is measured in hours, minutes and seconds with 15 degrees equal to one hour.

Declination is measured from the celestial equator in a similar fashion to latitude. It is measure in degrees.

The Right Ascension and Declination of stars, nebulae and galaxies are fixed but the Sun, moon and planets are not due to their orbits.


The declination of Polaris is 90 degrees this means that it appears to stay in a fixed position in the sky. The angle of Polaris is equal to the latitude of the observer.

Circumpolar Stars

Circumpolar Star – A star that does not dip below the horizon from the perspective of the observer

You can find out if a star is circumpolar using the following formula:

Declination of Star >= 90 – latitude

This is because the latitude is the distance the horizon is away from Polaris and as long as the stars declination is higher than this then it will be circumpolar.

Any constellation that is not circumpolar is a seasonal constellation. This means that they might only be visible for a few months of the year like Orion.

Messier Catalogue

Created by Charles Messier, a list of 110 indistinct objects in the night sky that are not comets. Made as he was fed up of discovering objects that looked like comets but were not. Contains fine examples of star clusters, nebulae and galaxies but was limited to objects that could be seen from France.



Physical Properties of Stars


M = m + 5 - 5 log D

M = Absolute Magnitude
m= apparent magnitude


Cepheid Variables

Binary Stars