Sirius

* A
* B

## Kurzgesagt

### **First appearance**

The Largest Star in the Universe – Size Comparison

### **Latest appearance**

The Largest Star in the Universe – Size Comparison

## General Information

Sirius is the brightest star in the night sky. Sirius is a binary star system consisting of a main-sequence star of spectral type A0 or A1, named Sirius A, and a white dwarf, Sirius B. The distance between the two varies between 8.2 and 31.5 astronomical units as they orbit every 50 years.

Sirius appears bright because of its intrinsic luminosity and its proximity to the Solar System. At a distance of 2.64 parsecs, the Sirius system one of the nearest systems to Earth. Sirius is gradually moving closer to the Solar System.

Sirius A is about twice as massive as the Sun. It is 25 times as luminous as the Sun, but has a significantly lower luminosity than other bright stars. The system is between 200 and 300 million years old. It was originally composed of two bright bluish stars. The initially more massive of these, Sirius B, consumed its hydrogen fuel and became a red giant before shedding its outer layers and collapsing into its current state as a white dwarf around 120 million years ago.

### History

Ancient Greeks saw Sirius as the morning star, portending a hot and dry summer and fearing that the star would cause men to weaken, women to grow aroused, and plants to wilt. Because of its brightness, Sirius would have been more visible to twinkle during the erratic early summer weather.

Edmond Halley found the proper motion of the previously assumed fixed stars in 1717 by comparing contemporaneous astrometric observations with those from the second century AD published in Ptolemy's Almagest. Significant motion was observed in the bright stars Aldebaran, Arcturus, and Sirius; Sirius had advanced approximately 30 arcminutes (almost equivalent to the diameter of the Moon) to the southwest.

Christiaan Huygens calculated the distance to Sirius in his book Cosmotheoros in 1698 to be 27,664 times that of the Earth to the Sun, or approximately 0.437 light-years, or nearly 7.5 arcseconds of parallax. Jacques Cassini, some astronomers (including Nevil Maskelyne) using Lacaille's observations made at the Cape of Good Hope, Piazzi, using Lacaille's observations made at Paris, more numerous and certain than those made at the Cape and Bessel were among the unsuccessful attempts to measure the parallax of Sirius.

Scottish astronomer Thomas Henderson used his observations made in 1832–1833 and South African astronomer Thomas Maclear's observations made in 1836–1837, to determine that the value of the parallax was 0.23 arcsecond, and error of the parallax was estimated not to exceed a quarter of a second, or as Henderson wrote in 1839, "On the whole we may conclude that the parallax of Sirius is not greater than half a second in space; and that it is probably much less."45] For the most of the 19th century, astronomers used a value of 0.25 arcsecond.[46]- Its parallax of over 0.4 arcseconds is now recognized.

Friedrich Wilhelm Bessel concluded that Sirius had an invisible companion based on variations in its proper motion, as stated in a letter dated August 10, 1844. On January 31, 1862, Alvan Graham Clark made the first observation of the dim companion. This occurred during testing of a big refractor telescope for Dearborn Observatory with an aperture of 18.5 inches, which at the time was the largest telescope in the United States and one of the largest refracting telescope lenses in use. On March 8, the discovery of Sirius B was verified using smaller telescopes.

### Properties

Sirius, with an apparent magnitude of 1.46, is the brightest star in the night sky, about twice as brilliant as Canopus, the second-brightest star. From Earth, Sirius is always brighter than Jupiter and Venus, and at times brighter than Mercury and Mars.