Stars and Star Names
- A few thousand stars are visible to the naked eye from a dark location on a moonless night.
- the actual number depends on the brighness of
your sky and the acuity of your vision.
- Note that there are few hundred billion stars in our Galaxy! We see just a fraction.
- the brighter stars that we can see are some combination of the nearest and intrinsically brightest stars.
- Stars span a range of apparent brightness (apparent meaning how they appear to us here on Earth - as opposed to their intrinsic/absolute luminosity (that is, how much energy they radiate)).
- Astronomers use a "magnitude" system to compare the brightness of stars.
- The system ranks stars by brightness (1st, 2nd, 3rd, ...)
- This ranking system can even be extended to negative numbers for very bright stars.
- A difference of 5 magnitudes = a factor of 100 difference in brightness.
- An example
- The brightest star in the night sky (Sirius) is -1.5 magnitude.
- The Hubble Space Telescope permits observations of stars as faint
as 30th magnitude.
- The difference between the two is roughly 30 magnitudes.
- 30 = 6 x 5, so the stars observed by the Hubble Telescope are six factors of 100 (100x100x100x100x100x100 = (100)6 = one trillion) times fainter than the bright 0th magnitude stars in the night sky.
- Every star visible to the naked eye has at least a dozen names
- Vega = Alpha Lyrae = 3 Lyrae = HR7001 = ...
- The brightest stars have names which derive mainly from Arabic
- Rigel (Beta Ori) -- The left leg of the giant
- Sheliak (Beta Lyr) -- The Tortise
- Aldebaran (Alpha Tau) -- The Follower (of the Pleiades)
- Antares (Alpha Sco) -- The Rival of Mars
- Stars are named within a constellation by Greek letter in order
of brightness (alpha, beta, gamma).
Updated February 04, 2000