262
A VOYAGE IN SPACE
"squint," or parallax, which we dealt with in the second lecture. He found the distances very different indeed; so that the actual sizes of the stars must be also very different.
| Name of Star. | Brightness compared with an exactly first magnitude star. |
Parallax or "Squint." |
Distance in "Light Years." |
Diameter of star compared with α2 Centauri. | |
| Sirius | 13½ | 0.37 | 9 | 6 | |
| Canopus | 6½ | 0.00 | ? | > | 140 |
| Rigel | 2½ | 0.00 | ? | > | 75 |
| α2 Centauri | 2½ | 0.75 | 4 | 1 | |
| α Eridani | 1½ | 0.04 | 80 | 18 | |
| β Centauri | 1½ | 0.03 | 100 | 20 | |
| α Crucis | 1½ | 0.05 | 64 | 11 | |
| Spica | 1½ | 0.00 | ? | > | 55 |
In the first column is the name of the star: Sirius, or the Dog Star, I expect you have heard of, even if you don't know the others. In the next column you see that Sirius is not exactly a first magnitude star, it sends us actually thirteen times as much light as the standard which has been adopted as first magnitude, and others in the table are brighter than first magnitude. In the next column you see the amount of parallax or "squint"; but I expect you prefer to look at the column after that which shows that Sirius is nine "light years" away, meaning that light, travelling as we know at 186,000 miles per second, actually takes nine years to come to us from Sirius! Can you now tell how many miles away Sirius is? Remember that there are 30 million