Stellar magnitude: An historic system
A star’s luminosity refers to its intrinsic brightness. However the phrase magnitude in astronomy often refers to how shiny a star (or different space object) appears. That’s what we’re speaking about on this submit: how shiny stars look and the way astronomers categorize the completely different brightnesses of the celebs.
The magnitude scale utilized by astronomers dates again a good distance. The early astronomers Hipparchus (c.190 – c.120 BCE) and Ptolemy (c.100 – c.170 CE) used this scale. Each males compiled star catalogs that listed stars by their obvious brightnesses, or magnitudes.
This method stays intact to this day, although with some modifications.
And possibly – to us at present – that’s why the magnitude scale doesn’t appear so simple as it may be. In accordance with this historic scale, the brightest stars in our sky are 1st magnitude. And the very dimmest stars seen to the attention alone are Sixth magnitude.
So a 2nd-magnitude star is modestly shiny. But it surely’s fainter than a 1st-magnitude star.
And a Fifth-magnitude star continues to be fairly faint. But it surely’s brighter than a Sixth-magnitude star.
So, the magnitude scale in astronomy is so much like a rating in golf, in that the decrease quantity means a higher brightness on the magnitude scale (and a greater rating in golf).
1st-magnitude stars, like Spica
Within the spirit of Hipparchus and Ptolemy, the modern-day charts of the constellation Canis Major above and the constellation Virgo beneath scale stars by magnitude. So, on star charts, the larger the dot, the brighter the star.
Take the star Spica, the only shiny star in Virgo. It serves as a main instance of a 1st-magnitude star.
In different phrases, though Spica’s magnitude is barely variable, its magnitude virtually precisely equals 1.
Stars and planets brighter than Spica
Loosely talking, the 21 stars that are brighter than magnitude 1.50 are known as 1st-magnitude stars.
Nonetheless, the 0-magnitude star Vega (magnitude = 0.00) is definitely one magnitude brighter than Spica (m = 1.00).
And the star Sirius with a detrimental magnitude (m = -1.44) is almost 2 1/2 magnitudes brighter than Spica.
One magnitude = 2.512 occasions brighter
Fashionable astronomy added precision to the magnitude scale. A distinction of 5 magnitudes corresponds to a brightness issue of a hundredfold. So a 1st-magnitude star is 100 occasions brighter than a Sixth-magnitude star.
Or, conversely, a Sixth-magnitude star is 100 occasions dimmer than a 1st-magnitude star.
So a distinction of 1 magnitude corresponds to a brightness issue of about 2.512 occasions.
Extending the magnitude scale
The sun and moon, plus the planets Venus and Jupiter, are a lot, a lot brighter than 1st magnitude. And trendy telescopes allow us to see stars which are thousands and thousands of occasions fainter than Sixth magnitude.
These days, the magnitude system contains not simply stars but in addition the sun, moon, planets, asteroids and comets throughout the solar system. In addition to, star clusters and galaxies that reside outdoors the solar system. Astronomers even listing the magnitudes of man-made satellites circling our planet.
As a result of a distinction of 5 magnitudes corresponds to a brightness issue of 100 occasions, then a distinction of 10 magnitudes corresponds to a brightness issue of 10,000 occasions (100 x 100 = 10,000). As well as, a distinction of 15 magnitudes corresponds to a brightness issue of 1,000,000 occasions, and a distinction of 20 magnitudes corresponds to a brightness issue of 100,000,000 occasions. Hipparchus and Ptolemy could be amazed!
Backside line: Stellar magnitude is a measurement of brightness for stars and different objects in space.
