There are thousands, perhaps millions, of
asteroids
up there. When swinging close to Earth, they merely appear as
tiny
specs of light in backyard optical instruments. And, they are not
much different from the myriad background stars that are always
there.
But unlike stars, asteroids
move! Not as fast as satellites or meteors, but enough that
observations
a few hours apart will reveal their presence. That's the
key.
Look for little specs of light that move.
If you repeatedly scan a given celestial area, then
you will easily recognize an intruder. That's the method that
must
be used by comet-hunters, who simply don't know where the next comet
will
come from and therefore must rely on scanning "their" sky, night after
night. But asteroid hunters
usually know when and where an asteroid is about to make an appearance
so they merely sketch
the suspect area and return to it a few hours later to check on what
has moved. Unlike comets, which barely move from night to night,
an asteroid moves significantly in a matter of hours. So you see,
bagging an asteroid is easy and fun. Thousands of stargazers
enjoy
the hunt.
The first asteroid was discovered by Giuseppi
Piazzi,
a Sicilian monk, on January 1, 1801. He named it 1 Ceres.
Since
then, all asteroids get a number and a name. The number indicates
their order discovery. Three of the biggest are often binocular
sights
as they swing close to Earth.
1 Ceres is the largest known asteroid
at just under 1,000 kilometers. That's roughly the size
of England. It is darkish, and
may be frost-covered; but that is under dispute. It was once
thought to be football-shaped, but that has
since been discounted when the Hubble Space
Telescope clearly showed it to be a sphere
in 1998.
2 Pallas is about 525 kilometers
(about
330 miles) in size.
3 Juno, at 240 kilometers, is too
small
to be a binocular target.
4 Vesta, reported to be pinkish in
color, is about 500 kilometers and is often a fine binocular
target.
The Galilean Moons
The Galilean moons were discovered by Galileo in
1610 as he peered into a telescope of his
own making. He saw four moons, the "Galilean Moons", buzzing
about Jupiter.
Ganymede, the largest moon in the solar
system,
is larger than the planet Mercury and almost a big as Mars. It is
a glacial world consisting of ice and rock. Interestingly enough,
2,000 years
ago a Chinese astronomer, named Gan De, reported that Jupiter had a
moon. Presumably he
saw Ganymede -- way before the telescope was invented. Talk about
being eagle-eyed!
Callisto, the second largest Galilean moon,
is dark and dead -- a world of craters upon craters.
Io is bright yellow from all its active
volcanoes
spewing sulphurous ejecta all over the place. It
is the most geologically active body in the solar system.
Orbiting
closest to Jupiter, Io is constantly being torn asunder by the titanic
gravitational forces of Jupiter on one side and its sister moons (15 or
more) on the other. (Size-wise, our moon
fits here, between Io and Europa.)
Europa, the smallest of the Galilean moons,
resembles a bluish-white billiard ball. It is covered
by an ice-capped ocean believed to be hundreds of feet deep.
If there is life anywhere else in the solar system, scientists feel
Europa
is currently the best bet.
Observing the Moon
Contrary to popular opinion, the full moon
is not the best time to view Luna. The full glare of the Sun
washes
out all topographic detail but it does however present the best
opportunity
to delineate features of differential reflectivity (albedo). For
example, the maria (the seas) stand out clearly from the highlands
because
their contrast is at maximum. That is why macro-features such as
the "Old Man of the Moon" are best seen at full moon.
Veteran observers however view along the
terminator
-- the demarcation line setting off the sunlit side from the dark
side.
Here, the shadows are greatest and therefore the topography is best
accentuated.
Crater rims, for example, are especially sharp at the terminator.
If you think about it, the terminator creeps
just a bit each night. And, it will cross the entire surface
during
the lunar month. So there is your nightly viewing target.
All
you need now is a mosaic of the Moon for reference. Begin the
search
at your local library then check out the given
links to ALPO and NASA.
While you're out there keep an eye on the
craters Aristarchus, Gassendi and Alphonsus for Transient Lunar
Phenomena
(TLPs) -- reports of mysterious "... temporary appearances of coloured
patches on the surface or occasional obscurations of normally distinct
features." -- Norton 2000. Don't you just love the British?
Observing Planets
Our companion planets, with the exception
of
Pluto, are easy to view in binoculars or a small telescope. Some
are spectacular while others are quite dull. All, except Neptune
and Pluto, can
be spotted with the naked eye. They are listed here in order
of distance outward from the Sun.
Mercury is never far from the Sun and
can be downright dangerous to view because of this proximity.
Never
search for Mercury while the Sun is up. Serious and permanent eye
damage
can result from viewing the Sun, even for a moment, in binoculars or
telescopes. Mercury appears quite starlike -- a point of light --
sometimes easy to spot and yet quite difficult at other times.
Mercury
can sometimes be seen with the naked eye.
Venus, a strong bluish-white, is the
brightest of all planets. Its phases (yes it has phases, like
the Moon) are quite noticeable in good binoculars. Venus can
sometimes be so bright that it will cast a shadow.
Earth is situated here,
between Venus and Mars.
Mars, always ruddy-colored, is
dull and featureless except in big backyard telescopes. Its color
always makes it an easy naked-eye target. Mars has two much smaller
moons,
both
believed to be captured asteroids.
Jupiter, always bright white,
has many moons but four are easily seen in most binoculars.
Depending
on seeing conditions, these moons are always a challenge -- sometimes
clear
and
easy, at other times fading in and out -- but the dance of the Jovian
moons is always entertaining. Some viewers can tell which is
which,
but I can't do that yet; except for Ganymede, which is always a
standout.
Ganymede is the largest moon in the solar system.
Saturn, a creamy white,
resembles
the figure "o0o" in a small telescope because its rings are tilted to
our
view. That shape had Galileo forever baffled; he thought Jupiter
was braced by a
pair of stars. The largest of its 22(?) moons, Titan, can be
seen in a small telescope under good
conditions.
Uranus, with a very faint
greenish
tint, is visible to the naked eye as a tiny star on very dark
nights.
It merely looks like a bigger star in binoculars or telescopes.
Oddly,
it was never
mentioned by the ancient astronomers. It was discovered by
William
Herschel in 1781. He
thought he had spotted a new comet. Uranus may well turn out
to have the most moons of any planet. Two more have just been
discovered
(1999).
Neptune, never visible to the
naked eye, requires good binoculars or a small telescope. It
always
appears starlike. Its presence was surmised (it made nearby
planets
wobble) before it
was actually found in 1846 -- by searching where mathematicians
predicted
it would be.
Pluto, being hardly more than
a large red rock with a tiny grey moon, is visible only in big backyard
telescopes as a faint spot of light mixed in among a myriad of
background
stars.
It was found on a photograph in 1930.
Observing Satellites
I see many satellites when I'm out there mainly because
I go out early, about an hour after sunset. That,
incidentally,
is the best time to see those little buggers; because being high, they
are still in full sunlight and of course brilliantly reflective.
Unlike that autumn evening back in 1957 (I think it was) when I first
spotted
Sputnick and felt that rush of discovery, spotting satellites nowadays
is very routine. One night, I had three in my binocular field and
I didn't think anything about that.
Where to look? Look high overhead for
satellites going south to north or vice versa. They are mostly
polar-orbiting
buggers. With over 8,000 satellites up there (about 2,500 are
real
satellites, the rest is junk) it is almost a sure bet you will see at
least
one in 15 minutes. What do they look like? They often look
like slow-moving stars; but much faster and smaller than
aircraft.
NASA says: a typical low-orbit satellite circles the Earth 16 times
each
day, traveling 7.5 kilometers per second (27,000 km/hour). The
larger
satellites, like Russia's Mir and the USA's Space Shuttle, are as
bright
as the brightest star in the sky (Sirius). See "More Links"
for related sites.
While observing satellites you may see a
bolide.
Here's an old log entry . . .
"April 6, 1998 20:45 EDT Mostly clear,
tolerably warm. Gibbous Moon is high due south.
Eyeballing Orion in the southwest as I was coming home from work when
a huge bolide (fireball) appeared at the zenith. It was bright
emerald green, sputtering
white splotches, and leaving a short smoke trail as it plunged due
south;
passing just west of the Moon. As it entered a
cloudbank on the south horizon it broke up and suddenly disappeared
with a muffled sonic boom. Very much bigger and very much
brighter
than Venus at its very best - as bright as the Moon, I would say.
It was moving at the speed of a moderately fast meteor. The
length
of the smoke trail was about as wide as the Moon. It was a very
impressive
sight indeed."
Observing Novae
Stars explode at the end of their lives.
The
big ones blow themselves to smithereens in a violent cataclysmic
explosion
-- a "supernova". Smaller stars, lacking the oomph, blow up
in a less spectacular but much more common "nova". The tiny stars
flare up a bit and puff off a wispy mix
of gas and dust -- often circular in shape and known as "ring nebulae",
which are very common but not visible to the naked eye. When a
supernova
occurs, its flashy signature betrays it almost instantly to astronomers
world-wide. But when the more subdued nova happens, it is often
the
amateur who makes the discovery. One such amateur, the Reverend
T.D.Anderson of Edinburgh, Scotland, gained fame as the discoverer of
not
one but two nova -- Nova Aurigae on January 23, 1892 and Nova Persei on
February 21, 1901.
Amazingly, the Reverend spotted both with
the naked eye on his walk home after the evening service; which
attests
to his remarkable knowledge of the evening's starry panorama.
Obviously,
he had developed the habit of looking up on his way home to have
noticed
a faint star where none existed before. The moral is that
familiarity
with celestial star patterns is a prerequisite for the discovery of
such
things as nova, comets, variable stars, meteors, fireballs, etc.
As a matter of
fact, a suspected nova (Nova Bootis) was spotted in the vicinity of
Arcturus on the nights of April 10-11, 1860, by one Joseph
Baxendell.
It was never seen again but it is now reasonably certain that some nova
are recurrent. The so-called "dwarf nova" are known to be
recurrent
and are
characterized by an unusually rapid decline, which implies that prior
outbursts, if any, were probably missed. So keep an eye on
Arcturus,
which just might have a new neighbor
one of these nights.
Footnote: In late January 1892, the constellation Auriga
would have been high in the eastern sky; whereas, in late February 1901
the constellation Perseus would have been high in the western
sky.
It seems reasonable to suppose that the Reverend was probably traveling
the same road but in different directions at the time of his
discoveries.