Course Six: Spectrum, Part 2 265
will be 39.44” away!
Here is a chart of some basic statistics for the
nine Planets, plus the Asteroid Belt. Average Distances
from Sun are in millions of miles; AU is Astronomical
Units; Diameters at Equator are in miles; Mass, Vol-
umes, Length of Year (revolution) are compared to
Earth’s; Length of Day (rotation) is in hours. The num-
ber of moons listed is how many we know as of Jan.- And the last entry indicates how much a person
weighing 100 lbs. on Earth would weigh on those
worlds.
Pluto has an irregular orbit—it comes in closer
than Neptune at one point—and is askew from the
plane of the Ecliptic on which the other orbits lie. Most
astronomers now think that Pluto is not a proper planet
at all, but merely a stray body from the Kuiper Belt
that has been captured by the Sun into a closer orbit.
Some believe there may be a true 9th “Planet X” still to
be found at around 77 AU. Although it hasn’t yet been
discovered, it’s been dubbed Persephone (the Greek
Queen of the Underworld, wife of Pluto/Hades).
Our Moon
Astronomers believe that our Moon was formed
when a Mars-sized body smashed into the Earth, eject-
ing matter into orbit and lengthening our day to its
present value of 24 hours. This happened 4.5 billion
years ago, when the Earth was still in a molten state.
Therefore Luna is truly the “daughter” of Terra.Comets and Meteors
When comets come hurtling through our inner
Solar System, the frozen gasses that bind them together
boil off, creating the characteristic cometary “tail,”
which may be millions of miles long. The Great Comet of
1843 had a tail that would have reached from the Sun
past the orbit of Mars, nearly 200 million miles! Re-
leased from the melting ice, great quantities of rocks,
pebbles, and debris that had been held frozen together
fall off and are strewn in a wake along the comet’s orbit.
When the Earth passes through one of these cometary
wakes, we experience meteor showers. The rocks strike
the Earth’s atmosphere on the forward side (mostly af-
ter midnite) and burn up in bright fiery streaks. I think of
these as “bugs on the windshield.” Here are the peak
dates, names, and centers of the best annual showers:PEAK SHOWER CENTER LOCATION IN SKY
Jan. 3 Quadrantids* E—Between Bootes & head of Draco.
Apr. 22 Lyrids NE—Between Vega & Hercules.
May 5 E-Aquarids* E—SW of Square of Pegasus.
July 28 D-Aquarids SE—Aquarius
Aug. 12 Perseids* NE—Perseus.
Oct. 8 Draconids E—Draco. Only storm every 6½ yrs.
Oct. 21 Orionids E—Between Orion & Gemini.
Nov. 17 Leonids** E—Leo. Sometimes BIG storm!
Dec. 14 Geminids* E—Near Castor in Gemini.Best Prospects for Life
In addition to Earth, several other worlds in our
Solar System also have possible conditions for life. Of
course, we won’t know for sure until we can send life-
detecting probes to these planets and moons. Mean-
while, here are our best prospects, and the reasons
why life might exist there:Mars: Most Earth-like; much more so in the
past. Much water ice in soil underground.
Jupiter: Warm, plenty of water and many
complex organic chemicals.
Europa (a moon of Jupiter): Covered with ice,
liquid water beneath.
Enceladus (a moon of Saturn): Icy surface,
maybe liquid water beneath.
Ganymede (a moon of Jupiter): Maybe liquid
water beneath icy surface.
Callisto (a moon of Jupiter): May have liquid
water beneath icy surface.
Titan (a moon of Saturn): Complex chemistry
and surface liquids likely.
Io (a moon of Jupiter): Complex chemistry,
warmer than most moons.Lesson 7: Stars and Galaxies
The sun and you and me, and all the stars that we can see,
Are moving at a million miles a day.
In an outer spiral-arm at forty thousand miles an hour
Of the galaxy we call the Milky Way.
Our galaxy itself contains a hundred billion stars,
It’s a hundred thousand light years side to side.
It bulges in the middle, sixteen thousand light years thick,
But out by us it’s just three thousand light years wide.
We’re 30 thousand light years from galactic central point,
We go ‘round every two-fifty million years.
And our galaxy is only one of millions of billions,
In this amazing and expanding universe!
—Monty Python, The Meaning of LifeOur own Milky Way galaxy is about 100,000 light
years in diameter and contains around 100 billion star
systems. Our Solar System is located in the Orion Spur
of the Sagittarius Arm, about 27,000 light years out
from the galactic center—which is located in the con-
stellation of Sagittarius. At our speed of 135 miles per
second, it takes us 250 million years to make a com-
plete revolution around the galaxy.
To get an idea of just how really BIG the galaxy
and the universe are, I recommend an amazing little
Website called “Quarks to Quasars: Powers of Ten” at
http://www.wordwizz.com/pwrsof10.htm.
Galaxies are formed, driven, and stabilized by dy-
namic electromagnetic effects. At the center of every
galaxy lies a super-massive black hole. About a third
of all galaxies (including ours) have a flattened main- Spectrum 2.p65 265 1/15/2004, 9:31 AM