Thursday, September 29, 2011

Top 10 Brightest Start and the North Star

Stars are massive shining spheres of hot gas, the closest of which is our Sun. Stars are primarily made of hydrogen, smaller amounts of helium, and trace amounts of other elements. Even the most abundant of the other elements present in stars are only present in very small quantities. Those stars which you see with your naked eye in the night sky all belong to the Milky Way Galaxy, the huge system of stars that contains our solar system.
By: , former Guide

Here are the Top 10 Brightest stars as seen from Earth.

1. Sirius

Sirius, also known as the Dog Star, is the brightest star in the sky. Its name comes from the Greek word for scorching.
  • Distance: 8.6 LY
  • Spectral Type: A1Vm
Learn More: Sirius

2. Canop


Named either for an ancient city in northern Egypt or the helmsman for Menelaus, Canopus is the second brightest star in the sky.
  • Distance: 74 LY
  • Spectral Type: F0II
Learn More: Canopus

3. Rigil Kentaurus

Rigel Kentaurus, also known as Alpha Centauri, is the third brightest star in the sky. Its name literally means foot of the centaur.
  • Distance: 4.3 LY
  • Spectral Type: G2V
Learn More: Rigil Kentaurus

4. Arcturus

Arcturus is the brightest star in the constellation Bootes, which is one of the oldest constellations in the night sky. It is the 4th-brightest star in the entire sky.
  • Distance: 34 LY
  • Spectral Type: 5IIIFe-0.5
Learn More: Arcturus

5. Vega

Vega is the fifth brightest star in the sky. Its name comes from the Arabic for the swooping eagle. Vega is about 25 light-years from Earth.
  • Distance: 25 LY
  • Spectral Type: A0Va
Learn More: Vega

6. Capella

The sixth brightest star in the sky, Capella's name is from the Latin for little she-goat. Capella is a yellow giant star, like our own sun, but much larger.
  • Distance: 41 LY
  • Spectral Type: G5IIIe+G0III
Learn More: Capella

7. Rigel

The seventh brightest star in the sky, Rigel's name is from the Arabic for foot, indicating its place in the constellation Orion. It is a blue supergiant and part of a 4 star system.
  • Distance: 1400 LY
  • Spectral Type: B8Ia
Learn More: Rigel

8. Procyon

Procyon is the eighth brightest star night sky. It is a yellow-white star and at 11.4 light years, one of the closer stars to Earth.
  • Distance: 11.4 LY
  • Spectral Type: F5IV-V
Learn More: Procyon

9. Achernar

The ninth brightest star night sky is Achernar. It is a bluish-white white supergiant star that is about 69 light years from Earth.
  • Distance: 69 LY
  • Spectral Type: B3Vpe
Learn More: Achernar

10. Betelgeuse

Betelgeuse is the tenth brightest star in the sky. It is a red supergiant about 13,000 times brighter than our sun and over 1000 times larger. If you placed Betelgeuse in the place of our sun, it would extend past the orbit of Jupiter.
  • Distance: ~1400 LY
  • Spectral Type: M1-2Ia-Iab
Learn More: Betelgeuse

What is the North Star?
Source from: Essprtment

The North Star, also called the Pole Star or Polaris, is the star that the earth's axis points toward in the Northern sky. For many years, people have been fascinated with this star and the fact that it doesn't seem to move in the sky. Some have created legends explaining why the star stands still. As more detailed scientific instrumentation has become available, scientists have begun to study more about Polaris. Surprisingly, it is a rich subject consisting of a binary star system.

Why Do We Care about the North Star?
For many years, the North Star has been used as a navigation aid and to chart navigational maps. It has also been used to measure astronomical latitude since we map latitudes to the equivalent sky positions: the North Pole equates to +90 degrees latitude on Earth as does its projection into the sky. In addition to these functional uses, over time many cultures have built folklore around the North Star. Even people with little interest in astronomy or mapmaking know about the North Star, and some have created stories explaining why it seemingly never moves.

The most famous story about the North Star is the Native American myth explaining why the North Star stands still. In this story, a brave son Na-Gah tried to impress his father by climbing the tallest cliff he could find. Through difficult conditions he persisted until he found himself at the top of a very high mountain. The mountain was so tall that Na-Gah looked down on all the other mountains. Unfortunately, there was no way down. When his father came looking for him, he found Na-Gah stuck high above. Not wanting his son to suffer for his bravery, he turned Na-Gah into a star that can be seen and honored by all living things.

Polaris: The Current North Star
Today the Earth's axis points within one degree of Polaris, the brightest star in the constellation Ursa Minor (also called the Little Bear or the Little Dipper). Polaris appears to be in a fixed position in the sky throughout the year. All other stars and constellations seem to revolve around the North Star.

To find Polaris in the sky, locate the Big Dipper and follow the two stars at the end of the basin upward. This should lead you directly to Polaris. It is the last star in the tail of the Little Dipper.

Why isn't the North Star Fixed?
Over the course of time, the North Star changes. Right now Polaris is within one degree of true north, but at other times the North Star has been and will again be Thuban (the brightest star in the constellation Draco), Vega (the brightest star in the constellation Lyra), and Alpha Cephei (the brightest star in the constellation Cepheus).

The North Star changes over time because the direction of the earth's axis changes slowly over time. Since by definition the North Star is the star most closely aligned with the earth's axis, as the axis moves the nearest star changes too.

This type of axis movement is similar to that of a spinning top. As the top slows, the axis of rotation changes as the top draws out each rotation; that is to say that the stem of the top itself traces out a circular pattern rather than pointing at a single spot or staying mostly still. If you draw an imaginary line of the earth's axis and continue it up to the sky, it will make a similar path. This type of axis rotation is called precession.

In the case of the earth, precession is caused by the gravitational pull of the sun and the moon. The earth's axis makes one complete rotation over the course of approximately 26,000 years. If you trace the path of the axis in the sky, you will find that Polaris, Vega, Thuban, and Alpha Cephei all fall on or very close to it. So when the earth's axis is at a point on the path near Vega, Vega becomes the North Star while Thuban is the North Star when the axis is near it on the path. Five thousand years ago, Thuban was the North Star. Five thousand years from now, the North Star will be Alpha Cephei. Seven thousand years after that, it will be Vega. Nine thousand years after that, Thuban will be the North Star again. At these dates, the various stars will be at the closest to absolute north. For some time before, the relevant star will be approaching due north and it will be receding for some time after the time listed. In these interim times, the North Star is whichever star is closest to north.

What is the North Star?
Posted in: Astronomy

Were you wondering about the North Star? Firstly, you might expect one of the most famous stars in the night sky to be one of the brightest, but it isn't; not by a long shot. That honor belongs to Sirius and many less bright stars besides. The North Star shines with a humble brightness that belies its navigational importance.

Polaris, or the North Star, sits almost directly above the North Pole; therefore, it is a reliable gauge of North if you find yourself lost on a clear night without a compass. Stars that sit directly above the Earth's North or South Pole are called Pole Stars. Interestingly, the North Star hasn't always been, nor will it always be the Pole Star because the Earth's axis changes slightly over time, and stars move in relation to each other over time.

You can also approximate your latitude by measuring the angle of elevation between the horizon and the North Star. There is no equivalent star in the South Pole, but Sigma Octantis comes close. It isn't very useful for navigational purposes as it isn't very bright to the naked eye. Instead, navigators use two of the stars in the Southern Cross, Alpha and Gamma to determine due South.

The North Star is easy to find if you can first locate the Little Dipper. The North Star lies at the end of the handle in the Little Dipper (Ursa Minor). For a point of reference, The Big Dipper (Ursa Major) lies below the little dipper and their handles point in opposite directions. The two stars in the end of the ladle of The Big Dipper point to Polaris. Also, both The Big Dipper and The Little Dipper remain in the sky all night long, rotating in relation to the Earth's axis.

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