Grimoire for the Apprentice Wizard

the position of the plane of the ecliptic, and the whole

thing can be rotated within a stationary frame marked

with the dates of the year. Hogwarts Headmaster Albus

Dumbledore has dozens of these all around his office.

You can make one yourself from the pattern in The

Great Sundial Cutout Book.

Orrery—this is a

small model of the So-

lar System, with the

Sun in the middle and

all the planets (sometimes including moons) set

up on arms or tracks to move around the Sun in circu-

lar orbits. Albus Dumbledore has a big one right in the

center of his parlor. You can easily make an Orrery as a

mobile, with a gold ball in the middle for the Sun, and

painted beads of various sizes representing the plan-

ets hanging by threads from struts of wire or bamboo

skewers. I made one of these for a science project in

school, and it hung from my ceiling for years.

Lesson 6. The Planets, etc.

Just remember that you’re standing on a planet that’s evolving,

And revolving at nine hundred miles an hour...

That’s orbiting at ninety miles a second, so it’s reckoned,

A sun that is the source of all our power.

—Monty Python, The Meaning of Life

Nine known planets circle our Sun, with over 100 sat-

ellite moons orbiting them. In order outward, these

are: Mercury, Venus, Earth, Mars, Jupiter, Saturn,

Uranus, Neptune and Pluto. The first four plus Pluto

are rocky planets, like the Earth, and are called terres-

trial (“Earth-like”) worlds. Venus and Mars also have

atmospheres, mountains, and other surface features.

The outer planets (except Pluto) are huge gas giants,

with no clear surface, just layers and layers of clouds,

many thousands of miles deep, getting ever denser,

and eventually becoming liquid, and finally solid.

In addition to the planets and moons, hundreds

of icy comets plunge in and out through the Solar

system on elongated orbits. And there are vast num-

bers of smaller objects, from tiny meteorites to aster-

oids the size of Texas. An estimated 100 billion of these

form outer “shells” of rocks, ice and debris surround-

ing our Solar System, and are the source of all comets.

These are known as the Kuiper Belt and the Oort

Cloud (named for Dutch astronomers Gerard Kuiper

and Jan Oort), and their outer edge is two light years

away! All these planets and objects are held within

the gravitational field of the mighty Sun in the center.

The Titius-Bode Rule

In the 18th century, two astronomers, Johann Titius

and Johann Bode, discovered a numerical formula for

the sizes of the planetary orbits. By using the distance

from the Sun to the Earth as a standard, called an

Astronomical Unit, or AU, astronomers can calculate

distances of the other planets in proportion to it. Titius

and Bode noticed the following pattern—they started

with 0, then took 3 and began doubling—0, 3, 6, 12, 24,

48, 96, 192, 384, 768. Then they added 4 to each num-

ber and divided by 10, and the result approximated the

actual planetary orbits in AU’s (see below).

In Titius’ and Bode’s time, the asteroid belt, Ura-

nus, Neptune and Pluto were as yet undiscovered.

However, the Titius-Bode Rule predicted a planet be-

tween Mars and Jupiter, which turned out to be right

where the asteroid belt is. Some astronomers believe

the asteroids were once a planet which exploded, and

have named it Krypton, after Superman’s mythical

homeworld. The Titius-Bode Rule also predicted an-

other planet out from Saturn, which turned out to be

Uranus, but Neptune falls a bit short of the pattern,

and Pluto doesn’t fit at all.

To get an idea of the scale of distances in the

Solar System, get a thin strip of wood (such as lath) at

least 40” long. Stick a big yellow thumbtack at one

end. Then, using the AU distances as inches, stick

colored pins into the lath at those distances. The Earth

will be a little blue pin 1” from the Sun-tack, and Pluto

Planetary Statistics

Planet Mercury V enus EarthMars Aster. Jupiter SaturnUranus Neptune Pluto

Distance from Sun 36 mm 67 mm 93 mm 142 mm 258 mm 484 mm 887 mm 1,784 2,796 3,676

Distance in AU 0.387 0.723 1.0 1.524 2.77 av. 5.203 9.539 19.18 30.06 39.44

Titius-Bode AU 0.4 0.7 1.0 1.6 2.8 5.2 10.0 19.6 38.8 77.2

Diameter (miles) 3,023 7,509 7,913 4,210 88,626 74,857 31,731 30,702 1,424

Mass : Earth 0.055 0.814 1.0 0.107 318 95.2 14.5 17.1 0.002

Gravity : Earth 0.25 0.85 1.0 0.36 264 117 0.92 112 0.059

Volume : Earth 0.06 0.92 1.0 0.15 1,318 736 64 60 0.178

Year : Earth 0.241 0.615 1.0 1.88 11.86 29.46 84 164.8 247.7

Year in days 87.66 224.6 365.25 694 4,383 10,592 30,681 60,266 90,582

Day in hours 1,416 5,832 24 24.6 9.8 10.2 15.5 15.8 153.6

Number of Moons 0012 403021111

100 lbs. Earth= 25 lbs. 85 100 36 264 117 92 112 6

264 Grimoire for the Apprentice Wizard

Corrected pages 3rd printing.2.p65 41 6/10/2004, 4:03 PM