Brilliant Sirius as a southern Pole Star
On January evenings, use the Belt of Orion to star-hop to Sirius, a future southern Pole Star.
Believe it or not, the brightest star in the sky – our sparkling night beacon, Sirius in the constellation Canis Major the Greater Dog – will someday serve as a very reasonable, and certainly very noticeable, South Star.
Unlike the Northern Hemisphere, the Southern Hemisphere currently doesn’t have a bright pole star. There’s not even a moderately bright star – like our North Star Polaris – to mark the south celestial pole, the point in the sky directly over the Earth’s South Pole.
The pole star – either north or south – is the point around which the entire sky turns. It’s like the hub of a great wheel.
But not for a long, long time
We found the information about Sirius as a southern pole star in the book “Mathematical Astronomy Morsels V” by the great celestial mechanist Jean Meeus. See pages 353 to 363. Meeus wrote that Sirius will take its turn as the southern Pole Star some 60 thousand years from now, around the year 66270. In that year, Sirius will come to within 1.6 degrees of the south celestial pole.
One precessional cycle later, in the year 93830, Sirius will miss aligning with the south celestial pole by only 2.3 degrees.
Sirius is the Brightest Star in the Sky
Sirius is known for being the brightest star in the night sky and is nearly twice as bright as the next brightest star, Canopus with a magnitude of -1.46. Sirius is also known as the ‘Dog star’ because it is part of the constellation Canis Major, which is Latin for “the greater dog.”
The name Sirius stems from the Greek word Seirios, meaning ‘scorching’ or ‘glowing’. Typically, the only objects that outshine Sirius in our night sky are the sun, moon, Venus, Jupiter, Mars, and sometimes Mercury.
Sirius’ brightness can be attributed to its luminosity and proximity at a distance of 8.6 light-years. There are few stars that are closer to Earth, but none of them can match Sirius’ magnitude.
Based on calculations from the European Space Agency’s Hipparcos satellite, Sirius will continue to increase in brightness over the next 60,000 years, as Sirius gradually moves closer. Eventually, the distance between Earth and Sirius will increase. Sirus will become fainter but will remain the brightest star in the sky for thousands of years.
Sirius is in the constellation Canis Major, a southern constellation bordering on Monoceros, Lepus, Columba, and Puppis. From mid-northern latitudes, Canis Major sits low in the sky and can be difficult to observe in its entirety.
Canis Major contains the following ten named stars: Adhara, Aludra, Amadioha, Atakoraka, Furud, Mirzam, Muliphein, Sirius, Unurgunite, and Wezen
This constellation includes many popular deep-sky objects including:
Sirius also forms the Winter Hexagon (or Winter Circle) asterism, which appears prominently in the northern sky between December and March and is also part of the Winter Triangle.
From the southern hemisphere, Sirius arcs high overhead. From the mid-northern latitudes, Sirius rises in the southeast, arcs across the southern sky, and sets in the southwest.
Any easy way to find Sirius in winter skies is to use the belt of Orion as a downward pointer following the three stars in Orion’s belt to the left.
Is Sirius the North Star?
Sirius, also known as the Dog Star or Sirius A, is the brightest star in Earths night sky. The name means “glowing” in Greek — a fitting description, as only a few planets, the full moon and the International Space Station outshine this star.
Because Sirius is so bright, it was well-known to the ancients. But the discovery of a companion star, Sirius B, in 1862 surprised astronomers. The star that you can see with the naked eye is called Sirius A, or sometimes just Sirius.
Sirius B is 10,000-times dimmer than Sirius, according to NASA (opens in new tab). Its so dim, and therefore so difficult to see from Earth, that astronomers couldnt estimate its mass until 2005, thanks to data from the Hubble Space Telescope.
Sirius is highly visible in the Northern Hemispheres winter night sky, because the star has a high luminosity, or intrinsic brightness, relative to other stars, and because its relatively close to Earth (8.6 light-years away). According to NASA (opens in new tab), Sirius has a mass thats two times that of Earths sun. If the star were placed next to our sun, Sirius would outshine it more than 20 times over, according to NASAs Astronomy Picture of the Day (opens in new tab).
To find Sirius, use the belt of Orion as a pointer. The belts three stars point downward toward Sirius to the left. To be more precise, the position of Sirius is:
Today, Sirius is nicknamed the “Dog Star” because it is part of the constellation Canis Major, Latin for “the greater dog.” The expression “dog days” refers to the period from July 3 through Aug. 11, when Sirius rises in conjunction with the sun, Space.com previously reported. The ancients felt that the combination of the sun during the day and the star at night was responsible for the extreme heat during mid-summer.Related articles
The star is present in ancient astronomical records of the Greeks, Polynesians and several other cultures. The Egyptians even went so far as to base their calendar on when Sirius was first visible in the eastern sky, shortly before sunrise. According to Joe Rao of Space.com, the Egyptians called Sirius the “Nile Star,” because it always returned just before the river rose and so announced the coming of the floodwaters that would nourish their lands.
In 1718, English astronomer Edmond Halley discovered that stars have “proper motion” relative to one another, according to the Quarterly Journal of the Royal Astronomical Society (opens in new tab). This means that stars, including Sirius, move across our sky with a predictable angular motion with respect to more-distant stars.
More than 100 years after Halleys finding, in 1844, German astronomer Friedrich Wilhelm Bessel published a scientific note in the Monthly Notices of the Royal Astronomical Society (opens in new tab) describing how Sirius had been deviating from its predicted movement in the sky since 1755. Bessel hypothesized that an unseen companion star affected Sirius motion. Alvan Graham Clark, a U.S. astronomer and telescope maker, confirmed Bessels hypothesis in 1862, when the U.S. researchers spotted Sirius B through Clarks newly developed great refractor telescope.
Sirius B is a white dwarf star, which is the last observable stage of a low- to medium-mass star. White dwarfs get dimmer and dimmer until they eventually stop burning and go dark, thus becoming black dwarf stars— the theoretical final stage of a stars evolution. Scientists study white dwarfs like Sirius B in hopes of gaining a better understanding of the stellar cycle. Eventually, Earths sun will cycle to the white dwarf stage as well.
The mass of a star is an important factor in the objects stellar evolution, because it determines the stars core temperature and how long and hot the star will burn. Astronomers can calculate the mass of a star based on its brightness, or luminosity, but this was challenging for Sirius B. The luminosity of Sirius A overpowered ground-based observations, making it impossible to isolate the much dimmer luminosity coming from Sirius B, according to the Astronomical Society of the Pacific (opens in new tab).
It wasnt until 2005, when a team of astronomers assembled data collected by the Hubble Space Telescope, that scientists were able to measure the mass of Sirius B for the first time. They found that the star has a mass that is 98 percent that of Earths sun.
In April, 2018, NASA launched the Transiting Exoplanet Survey Satellite (TESS), with the aim of its primary mission being to find exoplanets orbiting bright stars. Because Sirius is a young star, its not likely to have planets orbiting it. TESS discovered 66 new exoplanets, according to NASA Exoplanet Exploration (opens in new tab), but none have been discovered orbiting Sirius.
You can read about Hubble Space Telescopes of Sirius A and its companion Sirius B on the European Space Agency (ESA) website (opens in new tab). To learn more about the Canis Major and Canis Minor constellations, watch this video from Lowell Observatory (opens in new tab).
“Edmond Halley– a Commemoration”. Quarterly Journal of the Royal Astronomical Society, Vol. 34 (1993). https://adsabs.harvard.edu/full/1993QJRAS..34..135H (opens in new tab)
“On the variations of the proper motions of Procyon and Sirius”. Monthly Notices of the Royal Astronomical Society. https://adsabs.harvard.edu/pdf/1844MNRAS…6R.136B (opens in new tab)
“On the Luminosity of the Companion of Sirius”. Publications of the Astronomical Society of the Pacific. https://adsabs.harvard.edu/full/1930PASP…42..155V (opens in new tab)
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Ailsa is a staff writer for How It Works magazine, where she writes science, technology, space, history and environment features. Based in the U.K., she graduated from the University of Stirling with a BA (Hons) journalism degree. Previously, Ailsa has written for Cardiff Times magazine, Psychology Now and numerous science bookazines.