Sirius: Dog Star and brightest star
How to See It
Sirius is the sky’s brightest star. It’s nearly 3-and-a-half times brighter than Arcturus, the next-brightest star easily visible from northern latitudes. Most people notice Sirius in the southeast – south – or southwest on evenings from winter to mid-spring. It’s also fun to spot Sirius as it ascends in the east before dawn on late summer mornings.
Although white to blue white in color, it wouldn’t be unreasonable to call Sirius the “rainbow star,” as it often flickers with many colors.
The brightness, twinkling and color changes sometimes prompt first-time observers to report Sirius as a UFO. But these changes have nothing to do with Sirius. Rather, they are the result of variations in Earth’s atmosphere. The light from Sirius, which always appears fairly low in the sky from the mid-north latitudes, passes through a long column of air before it reaches our eyes. Changes in density and temperature of this air affect the light and cause the behavior we see. This happens for other stars, too, but it is more noticeable for Sirius because it is so bright, and because it appears low in the sky.
This X-ray image from Chandra satellite shows that the sky's brightest star - Sirius - is really two stars. The Sirius star system is located 8.6 light years from Earth. (NASA)
From the mid-northern latitudes such as most of the U.S., Sirius rises in the southeast, arcs across the southern sky, and sets in the southwest. In December, you’ll find Sirius rising in mid-evening. By mid-April, Sirius is setting in the southwest in mid-evening. Sirius is always easy to find. It’s the sky’s brightest star! Plus, anyone familiar with the constellation Orion can simply draw a line through Orion’s Belt, to the left. This line will point to Sirius, which is roughly 8 times as far from the Belt as the Belt is wide.
History and Myth
Sirius has been known since ancient times, and its name signified its nature as “scorching” or “sparkling.” It was associated with the Egyptian god Osiris and other gods. Ancient Egyptians noted that Sirius rose just before the sun each year immediately prior to the annual flooding of the Nile River. Although the floods could bring destruction, they also brought new soil and new life. Fittingly, Osiris, whom Sirius may have represented, was a god of life, death, fertility and rebirth of plant life along the Nile.
Sirius is also well known as the Dog Star, because it is the chief star in the constellation Canis Major, the Big Dog. Have you ever heard anyone speak of the dog days of summer? That phrase recalls Sirius’ role in predicting the summertime Nile floods.
In India, Sirius is sometimes known as Svana, the dog of Prince Yudhistira. The prince and his four brothers, along with Svana, set out on a long and arduous journey to find the kingdom of heaven. However, one by one the brothers all abandoned the search until only Yudhistira and Svana were left. At long last they came to the gates of heaven. The gatekeeper, Lord Indra, welcomed the prince but denied Svana entrance. Yudhistira was aghast and told Lord Indra that he could not forsake his good and faithful servant and friend. His brothers, Yudhistira told the Lord, had abandoned the journey to heaven to follow their hearts’ desires. But Svana, who had given his heart freely, chose to follow none but Yudhistira. The prince told the Lord that without his dog, he would forsake even heaven. This is what Lord Indra had wanted to hear, and then he welcomed both the prince and the dog through the gates of heaven.
Science
Magnitude is a star’s brightness expressed by a number. The smaller the number, the brighter the star. The visual magnitude of Sirius is -1.44, lower than any other star. It is 3.5 times brighter than Arcturus in Bootes, the next brightest star easily visible from the northern hemisphere. There are brighter stars in terms of actual energy and light output, but they are farther away and hence dimmer. Normally, the only objects that outshine Sirius in our heavens are the sun, moon, Venus, Jupiter, Mars and Mercury (and usually Sirius outshines the latter two!).
The next brightest star (Canopus) after Sirius, and the closest major star (Alpha Centauri) are both too far south in the sky to be easily seen from mid-north latitudes.
At 8.6 light years distance, Sirius is one of the nearest stars to us after the sun. (A light year is nearly 6 trillion miles!) In fact it is the nearest star easily visible to the unaided eye from most of the northern hemisphere. Classified by astronomers as an “A” type star, it is much hotter than our sun, with about surface about 17,000 degrees F (the sun is about 10,000 degrees F). With slightly more than twice the mass of the sun and just less than twice its diameter, Sirius still puts out 26 times as much energy. It is considered a normal (main sequence) star, meaning that it produces most of its energy by converting hydrogen into helium through nuclear fusion. As mentioned above, Sirius has a small, faint companion star appropriately called “The Pup.” That name signifies youth, but in fact “The Pup” is a dead star called a “white dwarf.” Once a mighty star, today it is an earth-sized ember too faint to be seen without a telescope.
The position of Sirius is RA: 06h 45m 08.9s, dec:−16° 42’ 58”.
HELLO. Iwould liki to ask ,is it that star which is known as SAGITOURIUS .
Nadeem,
No, Sirius and Sagittarius are not the same. Sirius is a star seen mostly in the evening sky of winter and spring (Northern Hemisphere). Sagittarius is a constellation, or group of stars, which is seen mostly in the evening sky of summer and fall (Northern Hemisphere). Interestingly, though, Sirius and Sagittarius are separated by about 12 hours in the sky, meaning that 12 hours after one appears (in the south, for example), the other other will appear in about the same place. They are not exactly opposite each other, but are best seen in opposing seasons. (Sirius is best in the early evening of early spring, whereas Sagittarius is best in the early evening six months later, in September.)
Larry Sessions
how many of our suns would fit inside the star sirius
Joseph,
It depends on what you mean. Let’s assume that both the Sun and Sirius are spheres. In reality, they aren’t. They are both “oblate spheroids,” but for our purposes it is OK to assume that they are spheres.
If you mean physically, how many spheres the size of our Sun would fit inside a sphere the size of Sirius, the answer is 1. Sirius is about 1.75 times the diameter of our Sun, and you simply could not fit more than one Sun inside Sirius.
However, if you mean how does the total volume of Sirius compare to the total volume of the sun, the answer is about 5.36. In other words, the volume of Sirius is about 5.36 times the volume of our Sun. This is because volumes vary by the cube of the radius. The radius of Sirius is about 1.75 times the radius of the Sun, and the cube of 1.75 is 5.359375.
I hope this helps.
Larry Sessions
Denver
thank you larry for responding back to me..the reason why i ask that question is i could of sworn i read that 100 of our sun can easily fit into the star sirius indicating how big the star sirius is bigger then our own sun
Joseph,
I suspect that you were thinking of another star, many of which are larger than Sirius. Betelgeuse, in Orion, for example, is about 600 times the radius of our Sun, meaning that 600 spheres the size of our Sun could fit, edge to edge, across the interior of a sphere the size of Betelgeuse (and a great many more besides). I don’t know the exact number right off because it involves something known as “packing density,” about which you can learn more here:
http://mathforum.org/library/drmath/view/55181.html
In terms of volume, Betelgeuse is 600 cubed times more voluminous than the Sun, which is 216 million times!
Larry S.
We are in Parker, AZ and at night we see this bright star or planet. I thouhgt after reading the first part of this page it was Sirius. At bottom of page it talks about Venus close to the Moon, so now I’m mixed up which one it is.
hi!
how does Sirius move??? does it orbit or what?
thanks Prue
The star Sirius is actullay Sirius A and B. Sirius A is the brightest star in our sky and Sirius B is it’s companion but is not a star. Both Sirius A and B revolve around each other at a distance of about 20AUs. Sirius A also rotates under 5.5 days not saying that Sirius B dosen’t.
i think that the stars are very intresting
what is the possible reason for the brightness of sirius??
will the sirius star always and forever be the brightest of all stars?
this is coOl
this is coOl
sigh
i am NOT an expert by ANY measure but without trying too hard…
PRUE: SIRIUS, being a star, does not ‘move’ or orbit. Just like our SUN, it is practically stationary and only travels along w/everything else in the expanding universe.
MEMOO: The 2 main reasons for SIRIUS’ brightness are: (1)its closeness to Earth and (2)its fuel mass. … i think. LOL.
DAMIEN: SIRIUS is not the the brightest star. Brightness depends a lot on distance, the more distant – the fainter it will shine regardless of its size… and vice versa. AND, NOTHING IS FOREVER.
CLEAR SKIES !
Is it true that sirius going to be just as bright as the sun in 2012? I have been doing some research and this is what most people are talking about. I know something major is going to happen involving this star in the near future. do you have any clue?
Sorry, but apparently I have not been getting the notifications on comments.
1) Sirius does move in an orbit, but it is about the center of the Milky Way Galaxy and takes more than 200 million years to go around once. As Ernesto said, its brightness in our sky is due to its closeness and energy. It is the brightest star to appear to the human eye from Earth, but far from the actual brightest star in the sky. Many others are brighter, but also so far away that they appear dimmer than Sirius. Sirius B is a dead star called a white dwarf. It is very small and faint and visible only telescopically.
And yes, I do have a clue about Sirius and 2012. The clue is that there is NOTHING out of the ordinary likely to happen to Sirius in 2012. Eventually Sirius and all other stars including the Sun will undergo major and even catastropic changes near the end of their lives, but there is no (0) reason to believe that anything will happen to Sirius out of the ordinary in 2012. Nor is it likely that anything out of the ordinary will happen astronomically in the year 2012. All those stories circulating around are male bovine excrement, to be civil. The people who circulate them are of the same ilk as those who circulate the garbage that claims Mars will be as big and bright as a full moon on August 27. Neither are true at all.
Hi, My family would like to know what star we“ve been noticing from Oklahoma around mid-night to 3 am coming up from the south east thats like 10 times more brighter than all the other stars?June 28-09
Hi, My family would like to know what star we“ve been noticing from Oklahoma around mid-night to 3 am coming up from the south east thats like 10 times more brighter than all the other stars?June 28-09
Johnny,
That super brilliant “star” rising in the southeast at late night in June of 2009 is actually the planet Jupiter. Jupiter is the 4th brightest celestial object to light up the sky after the sun, moon, and the planet Venus. By the way, you can see Venus in the east during the dawn and predawn hours.
I send a preview of our upcoming July 9 EarthSky Tonight show:
Moon and Jupiter from late night till dawn
Bruce