Red Giants coming soon
The Magnitude Scale
The brightness of stars and other objects is given as their magnitude. The magnitude scale of brightness had its beginning centuries ago. Ptolemy, the Egyptian astronomer, gave the approximate magnitude of stars in his catalogue, which appeared in the 2nd century. The brightest stars wer called first-magnitude stars. Dimmer stars were of the second magnitude, and so on to sixth magnitude--the dimmest stars that could be identified.
When instruments to measure light became available, it was possible to determine differences in brightness exactly, rather than extimating them as Ptolemy had done. It was found that the degree of difference between successive magnitudes amounted to a value of 2.512. A first-magnitude star is about 2.5 times dimmer than a 0-magnitude star; a second-magnitude star is about 6.3 (2.512 X 2.512) times dimmer, and so on.
In some of the tables below, magnitude values are given. Those objects having the highest magnitudes are the dimmest; those with smaller numbers are brighter. In some cases the object is so bright it has a negative magnitude. Such objects are much brighter than the brightest stars.
Spectrum Classification
One way of classifying stars is by the light spectra they produce. These are then put in order, form the very hottest stars to the coolest, and categorized by letter designations.
Initially, A type stars were thought to be the hottest stars; B type stars the second hottest; and so on. Improved measuring techniques and greater knowledge resulted in a rearrangement of classes-thus the departure from alphabetical order. Examples of each spectral type, including range in temperature and some of the principal materials found, are given below.
| Type |
Name |
Temp. Range (K) |
Abundant Materials |
Color |
| O |
Naos |
30,000 - 60,000 |
Helium |
Blue-white |
| B |
Spica |
12,000 - 25,000 |
Helium |
Blue-white |
| A |
Vega |
8,000 - 11,000 |
Hydrogen |
White |
| F |
Procyon |
6,200 - 7,200 |
Hydrogen, metals |
Yellow-white |
| G |
Sun |
4,600 - 6,000 |
Hydrogen, metals |
Yellow |
| K |
Arcturus |
3,500 - 4,900 |
Calcium |
Orange |
| M |
Antares |
2,600 - 3,500 |
Titanium |
Orange-red |
| R |
Variables |
2,000 - 3,000 |
Zirconium |
Red |
| N |
Alpha Cygni |
2,000 - 3,000 |
Carbon |
Deep red |
The 25 Brightest Stars
The 15 Nearest Stars
