In the previous articles in this series, we started by considering observing techniques and expectations from your equipment. The beginner to astronomy is unlikely to have a large telescope and may have no equipment at all. This does not mean that observations cannot be carried out. The October article gave advice on purchasing and using binoculars and November gave some hints on getting started. This article is intended to give the newcomer to astronomy some indication of what can be seen through various instruments.
Let us assume we have set ourselves up in the darkest corner of the garden, shielded ourselves fro any bright lights and allowed about ten minutes for our eyes be become adjusted to the dark. If we then look up into the night sky and it is a clear moonless night it will be possible to see about 5000 stars with just naked eyes. It is also possible to see some of the brightest deep space objects. The Orion Nebula, M42, can be seen as a small faint smudge of light. The Great Andromeda Spiral Galaxy M31 can also be seen as a faint smudge of light. Some other objects including some open clusters can be seen. In particular M45 The Pleiades also called ‘The Seven Sisters' and located in Taurus can even be counted by those with keen eyes.
Binoculars of about 50mm aperture will increase the light directed into the eye by about 40 times therefore enabling the observer to see objects 40 times fainter. Many more stars will be seen including those of the Milky Way. These appear as a cloud of stars stretching across the sky. Quite a number of the brighter Messier objects will become visible but not the galaxies, all these except M31 are all too faint. The brighter planets will be seen as bright spots but no detail will be seen. It might be possible to see the four brighter moons of Jupiter in a pair of 10x50 or 12x50 binoculars. These will appear as a line of four ‘star like' points of light positioned to either side of Jupiter. It may even be possible to sketch the positions of the moons and follow their movements over a few hours through the evening or from night to night. The Moon will show some detail of the 'Seas', craters and mountain ranges.
A telescope of 60mm aperture will increase the light directed into the eye by about 60 times and increase magnification to about 100 times. This will allow some stars in the brighter clusters to be resolved as individual stars. The moons of Jupiter will be seen clearly and one or two cloud bands may even be seen on the surface of Jupiter. It might just be possible to see the rings of Saturn but the image will be quite small. Some study of the Moon will be possible.
A telescope of 150mm aperture will increase the light directed into the eye by about 350 times and increase magnification to about 200 times. With an instrument such as this the astronomer will be able to see nearly all of the 110 objects in Charles Messier's catalogue although some will still be very difficult to see. The views of the larger and brighter planets will be quite rewarding. Cloud bands on Jupiter and just possibly Saturn will be possible to make out. The moons of Jupiter and even some of brighter moons of Saturn will be seen. With a 150mm telescope some of the nebulae and even some of the brighter galaxies will be available for observing. Views of the Moon will be breathtaking.
It should however be appreciated that even a 150mm telescope will not produce the spectacular images that can be seen in text books and magazines. No objects, except the brighter planets, will show colour and the images will be small. However the real reward is in finding these objects and sensing the light from them with our own eyes.