2Sirius

media type="custom" key="3517794"Stars
Basic Description Each star is an individual with its own personality. Thousands are visible on any clear night removed from city lights. Together, with the faint glow of myriad others, the tapestry of the celestial sphere is fashioned. Stars come in different colors, sizes, shapes and ages. One trait that makes a star unique is its brightness.

- Measuring Stars - Astronomers measure the brightness of a celestial object according to a system originally devised by Hipparchus in 120 B.C. Hipparchus ranked the brightness of stars in the sky on a scale of 1 to 6 as seen from the Earth. The brightest stars he could see were classified as first magnitude and the faintest were sixth magnitude. Centuries later we still use the magnitude scale of Hipparchus, although it has since been modernized. The magnitude scale is logarithmic; one magnitude difference is equal to a brightness difference of about 2.5 times. So a magnitude 1 star is about 100 times brighter than a magnitude 5 star. The brighter planets and stars have negative magnitudes. The Sun, being the brightest object in the sky, has a magnitude of 26, followed by the full Moon at magnitude 11. Objects with a magnitude of 6 or less can be seen without optical aid under ideal observing conditions away from all local lighting.

Sirius
Basic Description  Sirius resides in the constellation Canis Major. Sirius resides in the constellation Canis Major, the Big Dog, and is commonly called the Dog Star. In ancient Greek times the dawn rising of Sirius marked the hottest part of summer. This is the origin of the phrase "dog days of summer." - Quick Facts-   2. Greek word for "soaring" 3. About twice the mass of the Sun 4. Fifth closest star to the Sun 5. Best seen in favorable time during the winter 6. 8.6 light-years away 7. Binary Star System 8. Consist of a white main sequence star of spectral type A1V, termed **Sirius A** 9. Also a faint white dwarf companion of spectral type DA2, termed **Sirius B**. 10. Age : 2.3 x 10 million
 * 1) Brightest star in the sky

Scientific Information
 * At a visual magnitude of -1.42.[[image:Sirius_Star.jpg width="227" height="272" align="right"]]
 * Sirius is a binary star system consisting of two white stars orbiting each other with a separation of about 20 astronomical units and a period of just over 50 years
 * Sirius A has a mass of around 2.1 times that of the Sun
 * <span style="font-family: Georgia, serif;">Sirius B has a mass nearly equal to the Sun
 * <span style="font-family: Georgia, serif;">Sirius B is almost double the 0.5–0.6 solar mas average.
 * <span style="font-family: Georgia, serif;">Sirius B has a surface temperature of 25,200 K
 * <span style="font-family: Georgia, serif;">Sirius B will steadily cool as the remaining heat is radiated into space over a period of more than two billion years
 * <span style="font-family: Georgia, serif;">This star is primarily composed of a carbon-oxygen mixture that was generated by helium fusion in the progenitor star
 * <span style="font-family: Georgia, serif;">Sirius B is now almost pure hydrogen

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