Stars

Stars What are Stars? A star is a large ball of hot gas that emits huge amounts of energy. The closest star to Earth is the Sun. It looks like a big star because it is so close to Earth, but there are many stars that are bigger and brighter than the Sun. The Sun is 150 million km away from the Earth. To compare large distances in the solar system, astronomers sometimes use a distance measurement called the astronomical unit (a.u.), which is the average distance between the Earth and the Sun (1 a.u. = 150 million km)

Stars Units of Measurement in Space The astronomical unit is useful in describing distances between objects in our solar system, but it is too small to describe interstellar distances. Another unit called a light year is used to describe distances between stars. A light year is the distance that light travels in one year. Light travels at a speed of 300 000 km/s so in one year it can travel about 9.5 trillion km (9 500 000 000 000 km)! The closest star to us after the Sun is Alpha Centauri. It is 4.3 light years away from us!

There are lots of different colours and sizes of stars. The colours of stars tell us something about their temperature. A relatively cool star glows red. A very hot one glows bluish-white. Star sizes vary from dwarfs to supergiants.

Stars can also be classified by their brightness. About 2200 years ago, the Greek astronomer Hipparchus developed a system to classify stars based on their brightness. The brightest stars were said to be first magnitude stars The faintest stars were said to be sixth magnitude stars.

Astronomers now use the word “magnitude”: in two ways: Stars Astronomers now use the word “magnitude”: in two ways: Apparent magnitude refers to the brightness of the star as it appears to us from Earth. Absolute magnitude refers to the actual amount of light given off by a star at a standard distance.

Stars A group of stars that forms a pattern is called a constellation. Many constellations represent characters from Greek mythology

Stars EXAMPLE In Greek mythology, Orion was a great hunter, who was mistakenly killed by his wife. She placed him in the sky.

Stars During a night, constellations will rise in the East and set in the West. This is due to the rotation of Earth about its axis (which happens once every 24 hours). During a year, some constellations can only be seen during certain seasons. This is because the Sun blocks our view of some stars. As the Earth revolves around the Sun (this trip takes 1 year), new stars become visible, and others get hidden on the other side of the Sun. Some stars that are directly overhead can be seen during all seasons, and are never blocked by the Sun.

Stars Three of the most common constellations that we can see in the Canadian sky all year are shown in this picture. Polaris