| Astronomy
is the oldest of the sciences and every body can take an interest
in it. However before you can proceed with this science you have to know
some basic facts which are simple and interesting for everybody.
You
will find below some useful definitions for your reference:
What
is a star?
Our sun is a star. It is a great, glowing ball of hydrogen and helium
gas. All stars are suns, like our own but they are so far away that they
appear to us as mere points of light in even the most powerful telescopes.
Many stars have noticeable colors. The color of a star tells us its temperature.
The hottest stars of all appear blue while colder stars are red orange
in color.
Red
: up to 4000 deg cent
Orange :
up to 5000 deg cent
Yellow
: up to 8000 deg cent
White
: up to 10000 deg cent
Blue-White : up to 20000 deg
cent
Blue
: up to 50000 deg cent
A star brightness is called its magnitude. A star
of magnitude 0 is very bright. Stars of magnitude 5 are only just visible.
Really bright stars have minus magnitude. Sirius, the brightest star in
the sky, has magnitude of -1.5.
 Our Sun.
What
is a planet?
The basic difference between a star and a planet is that the stars
give out their own light but planets do not. Planets shine in the sky because
they reflect the light of the sun. Nine planets ,including the Earth orbit
the sun. These planets of our Solar system are: Mercury, Venus, Earth,
Mars, Jupiter, Saturn, Uranus, Neptune and Pluto.
 
Jupiter
Saturn
What is a Moon?
A moon like a planet shines by reflected sunlight. However a planet
orbits the sun while a moon orbits a planet. Most planets have moons. Saturn
has 19 moons, Jupiter and Uranus have 16 each, Neptune has 6, Mars has
2 and Pluto like our Earth has only one moon.
What
is a double star?
Most stars are not single as they appear to the naked eye, but have
one or more companion stars, a number of which can be seen trough small
telescopes and binoculars.
What
is a variable Star?
Not all stars are constant in brightness. Certain stars change noticeable
in brightness from night to night and some even from hour to hour.
What
is a constellation?
A constellation is a pattern of stars. Ancient astronomers found that
constellation were easier to recognize then individual stars.
Early civilizations such as the Greeks and Romans have named these
constellation patterns . 48 constellation have been recognized by these
greek astronomers of which we still use these names today.
Since then various astronomers have introduced new figures to fill gaps
between these constellations. There are now 88 recognized constellations
which can be seen during the year in different parts of the world. The
stars in a constellation are usually unrelated, lying at widely differing
distances from us and from each other.
What
are Comets?
Comets are snowballs of frozen gas and dust that move on highly elongated
orbits around the sun, taking from a few years to many thousands of years
to complete one circuit. The comet has a tail made up of gas and
dust which blows out from it in the solar wind sent out by the sun.
 Haley's Comet.
What are Asteroids?
There are thousands of pieces of rock, called asteroids in orbit around
the sun. Most of these asteroids are grouped together between Mars and
Jupiter. These large groups of rocks are known as the asteroid belts. Asteroids
are bigger than meteors and are like small planets.
 An
Asteroid.
What are shooting stars (Meteors):
Shooting stars are not stars at all! They are tiny pieces of
dust called Meteors. When a comet flies in the path of the earth, dust
from its burning tail falls toward earth. When these particles hit earth's
atmosphere at very high speed they burn up. When lots of dust hits Earth
atmosphere, it burn up and looks like lots of shooting stars. This is called
a meteor shower. A Meteorite is a meteor that has not been completely burnt
up in the atmosphere and has fallen to Earth.
What
is a galaxy?
A Galaxy is a group of millions of stars. The smallest Galaxies consist
of approximately a million stars, while the largest galaxies contain a
million million stars or more. Galaxies come in two main types: spiral
and elliptical. Spiral galaxies have arms consisting of stars and gas winding
outward from their star-packed centers, while elliptical galaxies have
no spiral arms. it is estimated that there are 100 billion galaxies in
our universe.
 A Spiral
Galaxy.
What
is the Milky Way? ?
The Milky Way is the name of our galaxy. It is a spiral galaxy and
our solar system is in one of its spiral arms. The Milky Way can sometimes
be spotted at night. It looks like a misty streak across the sky.
What is a Nebula?
Between the stars are vast clouds of gas and dust known as nebulae,
the latin word for mist. They are best seen in clear country skies away
from smoke and streetlights.
What is a star Cluster?
Many stars congregate in clusters, some of which are visible to the
naked eye. There are two sorts of star clusters: Open clusters and Globular
clusters. Open clusters are found along the spiral arm of our galaxy while
Globular clusters are found well away from the
plane of the Milky Way.
How do we measure large distances in space?
Stars are so far away that it is impossible to measure their distances
only in kilometers. Therefor Astronomers and scientists have found various
other methods to measure such huge distances .
1- An Astronomical Unit (AU):
The distance between the earth and the sun is used as a unit
of distance the (AU). This distance is equal to 150,000,000 km.
2- A Light Year (l.y.):
Light travels at the speed of 300 km per second. Therefor a light year
is the distance the light travels in one year which is equal to: 9460,000,000,000
km or 63,240 AU
3- A Parsec (pc):
The distance at which a star would have a parallax of one second of
arc. One parsec equals 3.2616 light years.
What Next?
If you become interested in astronomy ,the first step step should be
to learn how to recognize the stars and the planets. There are also many
books on astronomy, and if you do some careful reading you will soon find
out which branch of astronomy you find most interesting. The internet is
also a good place to find out about astronomy. Also it is a good idea to
join an astronomical society, and if you decide to make a serious hobby
out of astronomy then you should spend some money either on a good binocular
or a good size telescope. |
