Dogon People -- The Sirius Star System: Astronomical Facts
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| Property |
Value
|
| Common name |
Sirius; the Dog Star; Alpha Canis Majoris
|
| Distance from Earth |
Approximately 8.6 light-years -- one of the closest star systems
|
| Apparent magnitude |
-1.46 -- brightest star in the night sky after the Sun
|
| Spectral class |
A1V (main-sequence, hydrogen-burning)
|
| Mass |
Approximately 2.063 solar masses
|
| Luminosity |
Approximately 25.4 times the Sun
|
| Surface temperature |
Approximately 9,940 K
|
| Visibility |
Easily visible to the naked eye; the brightest stellar object in the night sky
|
| Property |
Value
|
| Type |
White dwarf -- the remnant of a star that exhausted its hydrogen fuel
|
| Spectral class |
DA2 (hot white dwarf; hydrogen atmosphere)
|
| Mass |
Approximately 1.018 solar masses -- roughly equal to the Sun
|
| Radius |
Approximately 0.0084 solar radii -- roughly the size of Earth (~5,900 km radius)
|
| Density |
Approximately 3 x 10^6 g/cm3 -- a teaspoon of material would weigh approximately 5 tonnes
|
| Luminosity |
Approximately 0.056 times the Sun (faint despite large mass)
|
| Surface temperature |
Approximately 25,200 K
|
| Orbital period |
50.1284 years
|
| Orbital eccentricity |
0.5914 -- a distinctly elliptical orbit
|
| Visibility |
Not visible to the naked eye; apparent magnitude approximately +8.44; requires a telescope of at least 150 mm aperture
|
Sirius B's invisibility is specific: it is overwhelmed by the brilliance of Sirius A, the brightest star in the night sky. Even with a large amateur telescope, Sirius B can only be glimpsed when it is near its maximum separation from Sirius A. Casual naked-eye observation would never detect it under any circumstances.
| Date |
Event |
Person
|
| 1844 |
Friedrich Bessel detects gravitational perturbations in Sirius A's proper motion; infers an unseen companion |
Friedrich Bessel, German astronomer
|
| 1862 (January 31) |
Alvan Clark first directly observes Sirius B while testing a new 18.5-inch refractor at Dearborn Observatory |
Alvan Graham Clark, American optician
|
| 1914 |
Walter Adams measures the spectrum of Sirius B; discovers it must be extraordinarily dense |
Walter Adams, astronomer
|
| 1925 |
Arthur Eddington calculates Sirius B's density; confirms white dwarf physics |
Arthur Eddington, astrophysicist
|
| 1970 |
First detailed photographic documentation of Sirius B; visual separation from Sirius A achieved photographically |
Various observatories
|
| 2005 |
Hubble Space Telescope obtains precise measurements of Sirius B's mass and radius |
NASA/HST team
|
The Dogon's Emme Ya Tolo -- a third star in the Sirius system -- has been searched for by Western astronomers. In 1995, French astronomers Daniel Benest and J.L. Duvent published a paper in Astronomy and Astrophysics proposing a faint red dwarf companion (Sirius C) based on astrometric data. Most astronomers do not consider this confirmed; Hubble observations have not revealed a third stellar-mass object. Whether a very faint companion exists remains technically open; the consensus is that the system is a binary.
