Another talk by our learned group member Angus Idle featured his great interest in astronomy. His first point was that his subject did not exclusively concern stars but amongst others, constellations, planets, asteroids, comets, Messier objects, galaxies and the universe.
Constellations can be considered to be groups of stars which are visible from the earth. Names are given to the patterns made by the stars, such as Orion or Leo but the individual stars may be of varying distances from the earth. The area in the sky which these patterns occupy is also refered to as a constellation. To find these areas in the sky it is necessary to look at a map. The map varies according to one's position on the earth and the time of the year. The base line for mapping celestial bodies is called the ecliptic. This is the perceived path the sun takes across the sky during the year. When trying to identify stars by using the correct map, this is the starting line around which the bodies are shown.
Asteroids are small objects orbiting planets within our solar system. Comets are bodies within our solar system but appear to have a tail because of the effects of solar radiation upon the comet's nucleus. A comet's nucleus may consist of loose collections of ice, dust and small rocky particles. Their size may vary between be a few hundred metres and tens of kilometres across.
Planets are those celestial bodies which orbit a sun and have their own gravitational system. Within our own solar system there are planets that comprise either gas or rock. Those made of gas tend to be the larger. Some of these planets can be seen quite readily from earth, there are 5 which can be viewed comparatively easily by the naked eye. Angus told us that in Tanzania the planet Venus, the brightest planet in the sky was so apparent that it cast a shadow. Mercury, he said is best viewed at twilight and is difficult to find. It has a strange orbit and one side never receives any sunlight. Jupiter we were told has a great red spot that can be seen from earth and numerous moons. Jupiter is the second brightest planet. Saturn has a number of rings consisting of ice particles, rocks and dust. To view these rings from earth binoculars or a telescope is needed. The fifth planet which may be viewed without help is Mars.
Asteroids are small objects orbiting planets within our solar system. Comets are bodies within our solar system but appear to have a tail because of the effects of solar radiation upon the comet's nucleus. A comet's nucleus may consist of loose collections of ice, dust and small rocky particles. Their size may vary between be a few hundred metres and tens of kilometres across.
Messier objects are other bodies which can be seen in the sky initially catalogued by a French astronomer called Messier. These objects are indexed using an "M" prefix and include M31 the Andromeda Galaxy, M6 the Butterfly Cluster, an open cluster of stars in the constellation Scorpius and M8 the Lagoon Nebula a giant interstellar cloud in the constellation of Sagittarius.
Angus also pointed out some of incorrect perceptions of celestial bodies. The first was the use of the image of the crescent moon shown on many flags of the world. This view of the moon is wrongly observed and does not exist. Secondly the astrological star signs of the Zodiac are those constellations through which the sun seems to pass through the astronomical year. As Angus pointed out only 12 of these signs are used in astrology, Ophiuchus which is between Sagittarius and Scorpius is missed out.
Thanks go to Angus for his engaging talk and I hope during warmer weather our group may have someof his practical instruction on astonomical phenomena during the coming year