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Sirius Facts for Kids. Kiddle Encyclopedia.
Sirius facts for kids
A simulated image of Sirius A and B using Celestia
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.
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Images for kids
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Sirius (bottom) and Orion (right). Together, the three brightest stars of the northern winter sky—Sirius, Betelgeuse (top right), and Procyon (top left)—can also be understood as forming the Winter Triangle.
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The image of Sirius A and Sirius B taken by the Hubble Space Telescope. The white dwarf can be seen to the lower left. The diffraction spikes and concentric rings are instrumental effects.
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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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An artist's impression of Sirius A and Sirius B. Sirius A is the larger of the two stars.
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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.