Tuesday, 5 August 2014


Antares can appear red or
    If you live in Australia, go out on a clear evening and look up. You will see the constellation of Scorpius straight above you, its tail stretched out in a hook behind it. In the center of Scorpius is the twinkling red star Antares, a massive red giant.
     We see stars as tiny shining specks of light. If you zoom in with a telescope or binoculars, you can see many more stars, but the stars look the same.

Epsilon Lyrae, the 'Double Double'
     A star you can see in the constellation Lyra, where the bright star Vega exists, is Epsilon Lyrae. If you look closely, you can see it is a double star, or two stars so close together in the sky they look like one. If you look through a telescope, you can find out each star in the double star is a double star itself, making Epsilon Lyrae a quadruple star.
     Double stars are all over the sky. The brightest star in the night sky is Sirius B. Sirius A, a very small white dwarf, is so close to Sirius B that it makes a double star called Sirius. Sirius has a magnitude of -1.46 and can be seen in many places in the southern hemisphere.
     People say Sirius is the brightest star in the night sky, but it isn't the brightest thing. The only times the moon is less bright than Sirius are during a new moon and a total lunar eclipse. The planets can also be brighter.

The Sun, merely a yellow dwarf star
     Nor is Sirius the brightest star in the sky. The sun is only 149,600,000km away and has a magnitude of -26.74, so high that you cannot look straight at it.
     The sun is a nuclear fusion machine. Its immense weight makes its atoms so hot that their electrons are stripped from the nucleus and they go around at high speed. The positively charged atoms then crash into other atoms. When a heavy form of hydrogen, Deuterium, crashes into a heavier form of hydrogen, Tritium, It yields a Helium nucleus. The Helium is unstable, so it splits into one stable helium atom and one neutron. This process creates heat and light.
     In this way, the sun is constantly converting hydrogen into helium. The helium is heavier than hydrogen, so helium is always accumulating in the core of the sun. In a few billion years, the sun's core will be heavy enough to start converting helium into heavier elements. You should be thankful it hasn't started doing that yet, because it will expand into a red giant and swallow up Mercury and Venus.
     After that it will fuse heavier and heavier elements until Iron, the heaviest element that can be produced by nuclear fusion. Then It will explode, creating a Supernova. Luckily all of this will happen after all life on Earth is extinct.
     That happens to every star. They get formed in a nebula, where another star has exploded, then they form heavier and heavier elements, explode, and form a nebula that gives birth to new stars.
     The night sky- star charts, constellations, and shapes- is our view of the visible cosmos. It has been helpful. In the old library of Alexandria sat the famous star charts of Ptolemy that has guided sailors for years.
     Ptolemy was an astronomer and mathematician. In his star charts he included for each star latitude, longitude, hemisphere, and part of the sky.

The calendar. There used to be only
360 days in a year, because there are 
360 degrees in a circle.

     During the Renaissance the sky was split into twelve parts, each labelled by a constellation. These constellations include Gemini, Pieces, Cancer, Aries and eight more. At some time, the zones of the sky determined times of the year, judging by which zone was highest at that time of year. This led to the modern calendar and the twelve signs of the zodiac.
     We picture the sky as a sphere around the earth, but this idea was around for a long time. Before the Renaissance people thought the earth was the center of everything, and that the Universe was created just for them. They thought of the night sky as a crystal sphere, with nothing outside it. This thought probably led to the making of celestial globes, as they are the sky, seen as a sphere.
     There is a problem with celestial globes. In the real sky, we see it from the inside, but in a globe, the user sees it from the outside. If the manufacturer chooses to put the stars on their real positions on the globe, the globe will look backwards compared to the sky. One way to solve this problem is to have the globe backwards. Another way is to make the globe transparent so that the user looks through it, just like we look through the imaginary giant celestial globe from earth.
     There are ways to find both the north celestial pole and the south celestial pole. To find out the south, you find the southern cross, or Crux Australis. Then you extend it by three or four times. That point is the south celestial pole.

Finding Polaris
     To find the north celestial pole, you have to find a famous constellation. That constellation is Ursa Major, or the Big Bear. If you look at the brightest stars of it near the tail, you can see a part of Ursa Major called the Big Dipper. Find the two stars at the side of the 'cup' of the big dipper, then make an imaginary line going through those stars. Follow that line and you will come to a bright star called Polaris, or Alpha Ursa Minor(stars are labelled by brightness in the constellation, using the Greek alphabet. For example, Alpha Lyrae is the brightest star in the constellation Lyra). Polaris is at the tip of the tail and the brightest star of the 'Little Bear'. It is also the tip of the Little Dipper and a good definition of the north celestial pole.
     There are thousands of stars you can see through binoculars, many constellations, many wonders of the sky. From Barnard's loop, which takes up most of Orion, to the Hubble deep field, a tiny spot of sky where the Hubble Space telescope found thousands of very young galaxies, there is an uncountable number of things you can find by looking at a clear sky with a telescope or binoculars.

No comments:

Post a Comment