Page:Astronomy for Everybody.djvu/178
the orbit of the earth, or the ecliptic, as the horizontal or standard one. As each orbit is centred on the sun it will have two opposite points which lie on the same horizontal plane as the earth's orbit. More exactly, these are the points at which the orbit intersects the plane of the ecliptic. They are called nodes.
The angle by which an orbit is tipped from the plane of the ecliptic is called its inclination. The orbit of Mercury has the greatest inclination, more than 6°. The orbit of Venus is inclined 3° 24′; those of all the superior planets less, ranging from 0° 46′ in the case of Uranus to 2° 30′ in the case of Saturn.
Distances of the Planets
Leaving out Neptune, the distances of the planets follow very closely a rule known as Bode's Law, after the astronomer who first pointed it out. It is this: Take the numbers 0, 3, 6, 12, etc., doubling each as we go along. Then add 4 to each number, and we shall hit very nearly on the scale of distances of all the planets except Neptune, thus:
| Mercury, | 0 + 4 = | 4; | actual distance | 4 |
| Venus, | 3 + 4 = | 7; | actual„ distance„ | 7 |
| Earth, | 6 + 4 = | 10; | actual„ distance„ | 10 |
| Mars, | 12 + 4 = | 16; | actual„ distance„ | 15 |
| Asteroids, | 24 + 4 = | 28; | actual„ distance„ | 20 to 40 |
| Jupiter, | 48 + 4 = | 52; | actual„ distance„ | 52 |
| Saturn, | 96 + 4 = | 100; | actual„ distance„ | 95 |
| Uranus, | 192 + 4 = | 196; | actual„ distance„ | 192 |
| Neptune, | 384 + 4 = | 388; | actual„ distance„ | 300 |
On these actual distances we remark that astronomers do