Magnitude – N. A reference to the brightness of an object in the night sky.
2,300 years ago when the Greeks looked up in the night sky, they described the brightest stars they saw as First magnitude. The faintest stars they could make out they described as Sixth magnitude. The rest fell somewhere in between.
Today, we still describe stars such as Sirius, Aldebaran, Vega and the like as first magnitude but we have refined the scale to decimal points and beyond. It is interesting that with our unaided eyes we still call the faintest stars 6th magnitude, in a very dark sky, but now with telescopes and cameras, we have expanded our reach to view stars as faint as 20th magnitude. Even binoculars and simple telescopes can bring objects as faint as 12th magnitude easily into the view of amateurs.
We have also applied that magnitude scale to objects other than stars – like planets, galaxies and nebulae. With my own telescope viewing I loved to find my favorite group of 15th magnitude galaxies – Stephan’s Quintet- as a test of the night’ seeing conditions.
On November 19, 2020 we have a great trio to give us a lesson on magnitude because the Moon will align with Saturn and Jupiter. Saturn is, at this point, Magnitude 1. Planets can vary because their distance to us and to the sun varies as they travel. Mighty Jupiter is brighter than Mag 1 so we say it is Mag -2 at this particular time. The slender crescent of the Moon is -9 on this night. Our sun, by the way, is Mag -26.74!
Looking up at this lovely composition it is easy to see it as a primer on stellar magnitude, or it can simply be seen as the universe’s gift for the evening. And that’s reason enough to look up!