Orion consists of seven major stars: two for his shoulders, two for his feet,and three for his belt. Each star has a name. Also, astronomers havemeasured bright and how far away each star is.
Astronomers measure how bright a star is with a number calledmagnitude. The brighter the star, the lower the magnitude. Also,magnitude changes very fast. A difference of 5 in magnitude means a factor of 100 difference in brightness.
The stars to the left are magnitude 13 and 18, so they differ by a factor of 100. Similarly, a magnitude 1 star is 100 times brighter than a magnitude 6 star. This might seem confusing to you, but astronomers have used magnitude for thousands of years.
Astronomers measure distance in light-years. One light-year is the distance light travels in one year: 9,458,000,000,000 kilometers. A light-year is a long way: to go one light-year in the Space Shuttle would take you about 40,000 years!
The table below shows magnitudes and distances for the seven stars that make up
Orion. What can you learn about the stars from these numbers?
| Star Name | Part of Orion | Magnitude | Distance (light-years) |
| Betelgeuse | Left shoulder | 0.45 | 427 |
| Saiph | Left foot | 2.07 | 720 |
| Bellatrix | Right shoulder | 1.64 | 243 |
| Rigel | Right foot | 0.18 | 773 |
| Alnitak | Left belt | 1.82 | 815 |
| Alnilam | Center belt | 1.69 | 1,350 |
| Mintaka | Right belt | 2.41 | 916 |
Even though the stars look similar to your eye, they are all very different. They have different brightnesses and are at different distances from Earth.