Once the telescope has been acquired, it may well be necessary to construct a simple observatory or telescope housing. Telescopes are not elegant additions to domestic furnishings, and one with an. aperture above 150mm is likely to be awkward to manoeuvre. Local climatic conditions will to some extent dictate the type of observatory to be […]

The first decision must be: which type of telescope – reflector or refractor? The advantages and disadvantages can be summarized briefly as follows: Newtonian reflectors produce images that are free of chromatic aberration (false colour). They are relatively cheap, and it is fairly easy to re-align the optical system. Among the disadvantages are the need […]

Binoculars can be used for everyday observing, such as sporting events and nature study, as well as astronomy. They are classified according to their magnification and the diameter of the objective. A 10 X 50 pair magnifies 10 times (100 areas) and has objective lenses 50mm in diameter; note, however, that in cheaper binoculars the […]

The night sky Anyone with a keen interest in astronomy may want to acquire their own telescope. There is a large range of good telescopes on sale in most countries, with Europe and North America being particularly well supplied. The amateur astronomer can use a great variety of instruments and techniques, and even build an […]

Another coordinate system is sometimes preferred when astronomers are studying the structure of the Galaxy. This system uses the plane of the Galaxy as the reference plane and the centre of the Galaxy as the arbitrary reference point. The coordinates are both expressed in degrees. They are the GALACTIC LONGITUDE (1) and the GALATIC LATTITUDE […]

The right ascension and declination are defined relative to the plane of the Earth’s equator and to the vernal equinox. Unfortunately, neither of these is fixed in the sky because of precession. The Earth is not quite spherical but is slightly oblate. Because of this, the gravitational force between the Earth and the Sun produces […]

The plane of reference of this system is the equator of the Earth and the poles are at the points where the rotation axis of the Earth cuts the celestial sphere. The poles are called the NORTH AND SOUTH CELESTIAL POLES. The equatorial plane of the Earth cuts the celestial sphere at the CELESTIAL EQUATOR. […]

In this system the plane of reference is not the horizon but is a plane through the observing point parallel to the horizon. (If the observatory is at the top of a mountain, the horizon and the horizon plane defined here are different.) The line perpendicular to this plane, through the observer, passes through the […]

The accurate positions frequently needed in astronomy must be measured relative to a standard reference frame. To understand the coordinate systems used in astronomy, it is helpful to review first the familiar latitude-longitude system. It is convenient to measure positions on Earth in terms of LATITUDE and LONGITUDE. These two coordinates are determined relative to […]

Time It often happens that an astronomer needs to measure the precise position of an object in the sky. Accurate positions are required for many astronomical investigations. To determine proper motions, for example, positions measured over several months or years are needed. It is frequently necessary to compare the position of optically-visible objects with that […]