Apparent Magnitude A Star example essay topic

1. a) What is a constellation? A constellation is a group of stars that appears to form a pattern in the sky. b) What are circumpolar constellations? Give examples. They appear to move around Polaris the star located almost exactly above Earth's North Pole. Ursa Major, Ursa Minor and Cassiopeia are examples of circumpolar constellations. c) Describe and explain the apparent motions of the stars in our sky? The apparent movement of circumpolar constellations is caused by earth turning on its axis.

Earth turns from west to east. As a result the whole sky appears to turn from east to west. That is why the sun, the moon, and the stars are said to rise in east and set in the west. 2. a) Name some constellations that can be seen in summer. The 1st star is Vega in the small constellation Lyra, The Lyra of Harp. The 2nd star is Altair in the constellation Aquila, The Eagle. The 3rd star is Deneb at the top of Northern Cross, which is part of Cygnus the Swan. b) Identify some constellations that can be seen in winter.

One of them is Orion the Hunter. And to the left Sirius (brightest), part of Canis Major, the Large Dog. To the right Taurus the Bull and the famous Pleiades star cluster. c) Explain why the constellations that are visible change with the season. The changes are caused by the changing position of earth in its orbit around the sun. d) Why will the shapes of constellations be different in the future? Each star move toward or away from the other stars at high speed. Because stars are so far away it takes thousands of years before they appear different. 3. a) what is an astronomical unit?

How many kilometers equal an astronomical unit? The astronomical unit is an average distance between Earth and the sun, which is about 150 million km. b) Name the star nearest the sun. How far is this star? It is Alpha Centauri, which is about 40 trillion km away-nearly 300000 times as far from Earth as a sun. c) What is a light-year? How many kilometers equal a light- year?

A light-year is a distance that a ray of light travels in one year. The speed of light is about 300000 km / sec. At this rate light can travel about 9.5 trillion km in 1 year. 4. a) What are the sun's diameter, density and mass? Its diameter is about 1380000 km.

Its average density is about 1.4 times that of water. Its mass is about 300000 times that of Earth. b) Describe how stars vary in size, density and mass. The smallest star is maybe smaller that Earth and the largest star known is more than 2000 times the diameter of the sun. Betelgeuse is one ten-millionth as dense as sun. Sirius has a neighbor so dense that one teaspoonful of it would weight more than a ton on Earth. Masses are larger than 50 times that of a sun are very rare.

The smallest star is about one hundredth the mass of the sun. c) How is the color of a star related to its temperature? Give examples. Cool stars are redder in color. Hot stars are bluer in color. Stars radiate all colors, but hotter stars emit blue and less red. Betelgeuse is red, the sun is yellow and Sirius is blue. 5. a) What are two most abundant elements in stars?

Stars are mostly made of hydrogen and helium. b) Identify two factors that determine the spectrum of a star? The temperature and its composition. 6. a) what does apparent magnitude tell about a star? The apparent magnitude is how bright the star appears to an observer on Earth. b) How is apparent magnitude written for stars brighter than a first magnitude? Give examples. They are expressed as values less than 0 magnitude and have negative values. The apparent magnitude of Sirius is - 1.43. c) What is luminosity?

The actual brightness of a star is its luminosity. d) What is absolute magnitude? Absolute magnitude is the apparent magnitude a star would have if placed at a distance of 32.6 light-years from a sun. e) Compare the apparent magnitudes, absolute magnitudes and luminosities of the sun and Rigel. The sun's absolute magnitude is 4.8, and Rigel's is -6.4. That's why Rigel is more luminous than a sun and its brighter than a sun because it has a negative magnitude.