Sirius facts for kids
Sirius is the brightest star in the night sky. It is a binary star system in Canis Major, near Orion. It has an apparent magnitude of −1.46. The system is between 200 and 300 million years old. It was originally composed of two bright bluish stars.
Sirius appears bright because of its intrinsic luminosity and its position (it is relatively close to Earth). At a distance of 2.6 parsecs (8.6 ly), the Sirius system is one of Earth's near neighbours.
The Egyptians called this star 'Sopdet'. They relied on it to predict when the flood season would start. Sirius is sometimes called the Dog Star. The phrase the dog days of summer means the hottest days of summer.
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Sirius A
Sirius A is about twice as massive as the Sun and has an absolute magnitude of 1.42. It is 25 times more luminous than the Sun, but has a significantly lower luminosity than other bright stars such as Canopus or Rigel.
Sirius B
Originally, Sirius B had about five times the mass of the Sun. and was a B-type star (roughly B4–5) when it still was on the main sequence.
Sirius B used up its resources and became a red giant. Then it shed its outer layers and collapsed into its present state as a white dwarf, about 120 million years ago. Its mass now is about the same as the Sun.
Related pages
Images for kids
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Sirius in space
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Sirius is the brightest star in the constellation of Canis Major
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Hubble Space Telescope image of Sirius A and Sirius B. The white dwarf can be seen to the lower left. The diffraction spikes and concentric rings are instrumental effects.
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Sirius (bottom) and the constellation Orion (right). The three brightest stars in this image – Sirius, Betelgeuse (top right), and Procyon (top left) – form the Winter Triangle.
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The orbit of Sirius B around A as seen from Earth (slanted ellipse). The wide horizontal ellipse shows the true shape of the orbit (with an arbitrary orientation) as it would appear if viewed straight on.
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A Chandra X-ray Observatory image of the Sirius star system, where the spike-like pattern is due to the support structure for the transmission grating. The bright source is Sirius B. Credit: NASA/SAO/CXC.
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Comparison of Sirius A and the Sun, to scale and relative surface brightness
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Comparison of Sirius B to Earth
