5. So
why is there no South Star?
Actually, there is a South Star, but unlike its northern
counterpart it is a small, faint star. It is Sigma Octantis, in
the very dull southern constellation of Octans, the Octant.
It is, in essence, the "Polaris of the Southern Sky" (some texts
even refer to it as "Polaris Australis"), although at magnitude
5.5, this South Star is only 1/25 as bright as the North Star.
Northerners might wonder how those in the Southern Hemisphere
find their way around without a bright benchmark near their
pole. For that they can rely on Crux, the Southern Cross, whose
longer bar points almost precisely toward the south pole of the
sky.
6. Can
artificial satellites be seen with the unaided eye?
Most definitely they can! In fact, many people are surprised
that an object orbiting hundreds of miles above our heads can be
readily seen without the use of binoculars or a telescope.
From the launch of the first Sputnik in 1957 to the present, the
number of satellites in space has grown at a spectacular rate -
there are now more than 10,000 good-sized hunks of metal
orbiting the Earth, though not all are functional satellites. In
fact, the total number of active satellites is about 600. From
the days of the old Soviet Union, countless hundreds of
discarded rocket casings and cylinders from their Kosmos program
alone were left in orbit. Some of these can shine like a
moderately bright star.
British astronomer Desmond King-Hele once noted that a satellite
"looks like a star that has taken leave of its senses and
decided to move off to another part of the sky."
If you go out and carefully study the sky near dusk or dawn, the
odds are that you should not have to wait more than 15 minutes
before you see a satellite. Most are too faint to be seen with
the unaided eye. But a few hundred are large enough (over 20
feet in length) and low enough (100 to 400 miles, or 160 to 640
kilometers above Earth) to be visible.
Satellites are seen at night because they are illuminated by the
Sun. A satellite entering the Earth's shadow immediately
vanishes from view and pursues an unseen path until it again
emerges into full sunlight.
The International Space Station ("Alpha") and the Space Shuttle
are by far the brightest. Orbiting the Earth at an average
altitude of 240 miles (380 kilometers), they can appear to move
as fast as a high-flying airliner;
sometimes taking about three to four minutes to cross the sky.
They can easily be confused with aircraft lights, though at
their brightest they can sometimes appear to rival Jupiter in
brilliance.
u ever seen the Moon whiz across your line
of sight
like a meteor? Ev
the Earth at more than 2,000 mph (3,200 kilometers
perceptible.
7. Must
I wait centuries to see a total solar eclipse?
Not if you don't mind doing some traveling. On average, a total
solar eclipse is visible about every 18 months somewhere on the
Earth's surface. Unfortunately, the tracks of total solar
eclipses seem to have this perverse habit of occurring over
sparsely populated regions of the Earth or out over the open
oceans. The planet is two-thirds water, after all.
And even though a typical eclipse track can run for several
thousand miles or more, the width of that track is likely to be
less than 100 miles. So, the odds are that any one particular
spot on the Earth will have to wait a very long time - about 375
years) - between total solar eclipses.
But that nearly four-century wait is merely a statistical
average. Indeed, the paths of different eclipses sometimes will
criss-cross over a specific place, so in some cases the wait
isn't so long at all.
For example: a forty-mile stretch of
the Atlantic coast of Angola, just north of Lobito, experienced
a total solar eclipse on June 21, 2001 and will be treated to
another later this year (December 4) after a wait of less than
18 months. On the other extreme, we can cite the case of the
islands of Bermuda. Their last total eclipse was on August 30,
1532 with the next one
scheduled for February 16, 2352!
A comet moves across
the sky in the fashion of the Moon (or the planets for that
matter). Not in the fashion of g mete
