The planets, the stars, the moon and other bodies in the sky are known as celestial bodies. Astronomy is a branch of science that studies celestial bodies and their associated phenomena. The change in the shape of the moon every day is one of the observations of celestial bodies that we can make. The day on which the whole disc of the moon is visible is known as the full moon day, while the day on which only a small portion of the moon is visible is known as the new moon day. Various shapes of the bright part of the moon seen during a month are known as the phases of the moon. The phases of the moon occur as we can only see the part of the moon that reflects the light of the Sun towards us.
A constellation is a group of stars forming a recognisable shape. A few of the constellations known to us are:
- Ursa Major – Seen during the summertime in the early part of the night
- Cassiopeia – Visible during the winter in the early part of the night
- Orion – Seen during the winter in late evenings. Sirius, the brightest star in the sky is located close to Orion.
The solar system is comprised of sun, planets and celestial bodies like comets, meteors and asteroids. The gravitational attraction between the celestial bodies and the sun is what keeps them revolving around the sun. Let us look at a few members of the solar system.
- Meteors and meteorites
- Artificial Satellites
A few important points of the celestial members of the solar system are:
- Sun continuously emits a huge amount of heat and light. The Sun is the source
of almost all energy on the Earth.
- Planets, unlike the stars, do not have a light of their own. Planets revolve around the sun in a definite path known as orbit. The time taken by a planet to complete a revolution is known as the period of orbit. There are eight planets in the solar system as follows:
- A large number of small objects that revolve around the sun is known as asteroids. They are found in the large gaps between Mars and Jupiter.
- Comets are celestial bodies with a bright head and a long tail. They revolve around the sun in elliptical orbits.
- Moon is the natural satellite of the earth. The artificial satellites revolve around the Earth and are much closer than the moon. They are used for long-distance communication, weather forecasting and remote sensing.
Important Questions of Class 8 Science Chapter 17
- What is a constellation? Name any two constellations
- Do all the stars in the sky move? Explain.
- Why is the distance between stars expressed in light years? What do you understand by the statement that a star is eight light years away from the Earth?
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