SIRIUS THE DOG STAR IS THE BRIGHTEST STAR IN THE NIGHT SKY & IT HAS A PUP.

SIRIUS THE DOG STAR IS THE BRIGHTEST STAR IN THE NIGHT SKY & IT HAS A PUP.

SIRIUS THE DOG STAR IS THE BRIGHTEST STAR IN THE NIGHT SKY & IT HAS A PUP.

Photo By: NASA/ESA Hubble Space Telescope. CLICK for full size photo and a link below.

Located a close 8.6 light years distant in the constellation Canis Majoris the “Great Dog” is the white/blue Dog Star, Sirius. It’s the brightest star in the night sky and at an apparent magnitude of -1.44 it’s almost twice as bright as Canopus (The next brightest star) and only twice the mass of the Sun though it’s 25 times more luminous. The name Sirius is derived from the ancient Greek word “Seirios”, meaning “glowing” or “scorcher”.

A great twist on the old Dog Star is that it has a companion. Sirius is termed Sirius-A while the Pup Star as the companion is called is Sirius-B. It’s a white dwarf which was once the larger of the two that after using up all of its fusion fuel expanded into a red giant and shed its remaining material leaving the small, almost undetectable white dwarf with a mass of the Sun and the size of the Earth.

The ancient Egyptians called Sirius the ‘dog star’, after their god Osirus, whose head in pictograms resembled that of a dog. In Egypt, Sirius shines for most of the summer, and since it is such a bright star, the Egyptians actually believed that the additional light from this nearby star was responsible for the summer heat. This of course is not true. However the origin of the phrase ‘the dog days of summer’ comes from this ancient belief — the ‘dog star’ being the root of this common saying.

A mystery surrounds Sirius as well……history records Sirius as a reddish star. In 150AD Cladius Ptolemy described Sirius as reddish along with 5 other stars; Betelgeuse, Antares, Aldebaran, Arcturus and Pollux. Others including poets and artists cited and painted the star red. It is widely rejected that Sirius A or B and the evolution of either one could be responsible for this and today the mystery is still unsolved.

NAME: Sirius, the Dog Star, SAO 151881, HD 48915.

WHAT IS IT?: Binary star system consisting of Sirius-A (type-A star) and Sirius-B (white dwarf).

HOW FAR AWAY IS IT?: Approximately 8.6 light years distant or 2.6 parsecs.

HOW BIG IS IT?: Sirius-A is about twice the mass of the Sun and approximately twice the radius. Sirius-B is about the mass of the Sun packed into the radius of Earth.

AGE: Approximately 250 million years old.

APPARENT MAGNITUDE?: A very bright -1.46.

WHERE IS IT? (General): Constellation Canis Majoris the “Great Dog” & one of the three stars in the Winter Triangle asterism with Procyon and Betelgeuse as well as one of the 6 stars in the Winter Hexagon asterism. Another location method is to follow the line of Orions belt down to it.

WHERE IS IT? (Exact RA/DEC J2000): RA: 06h 45m 08.9s, dec:-16° 42′ 58″.

NASA Hubblesite page for this photo: http://hubblesite.org/gallery/album/pr2005036a/

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Image | This entry was posted in Astronomy (Learning), Astrophotography (DSOs), Images, Stars (Non-Sun Related), Telescopes & Detection Equip. and tagged , , , , , , , , , . Bookmark the permalink.

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