APRIL 1999
APRIL STAR MAP |
INDEX
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APRIL 4, 1999: Eclipse Chasers Unite
- Now that the clocks have been set ahead and the sun doesn’t set until 7:30 p.m.,
many of us are going to begin contemplating summer vacation plans. If you’re
considering a trip to Europe, try making your travel plans coincide with the 11th
of August. One of nature’s rarest events, a total eclipse of the sun, will be
visible from both England and the European continent on that date. The moon’s
shadow first makes contact with the Earth at sunrise, about 325 miles east of
Montauk Point, Long Island. People there, as well as individuals in the Lehigh
Valley, will be able to observe a partial eclipse at sunrise with the proper
filters. The path of totality continues northeastward reaching Land’s End, in
England during mid-morning, crosses the English Channel, and then passes about
20 miles north of Paris. The moon’s shadow sweeps over Stuttgart and Munich,
Germany, then Salzburg and Graz in Austria. Hungary, Bulgaria, and Romania
also see totality before the moon’s umbra crosses the Black Sea. The maximum
duration in the shadow of the moon will be 2 minutes, 23 seconds. This occurs
northwest of Bucharest, Romania just after 1 p.m. local time. Interested in
seeing this eclipse? A local group of eclipse chasers have organized and are
flying to Greece on August 2. After a day and a half in Athens they will set
sail for exotic ports of call in the Aegean, and Black Sea. Totality will be
viewed from aboard ship on the Black Sea on August 11. The 14 day odyssey will
conclude with two days in Istanbul, Turkey. Follow the "’99 eclipse Black Sea"
link at the web addresses below, or call the ASD Planetarium at 820-2204. To answer
last week's question about when the moon was full; it happened on Wednesday,
March 31 at 5:49 p.m.
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- 137
APRIL 11, 1999: What Time Is It?
- We look at our watches, and our world is placed into an ordered framework
from which we manage our affairs. Time has always been an astronomical problem
based upon the spinning Earth and its ability to bring the sun back to a fixed
position. But it’s not quite that that simple. A properly working sundial
takes its queues from the sun, registering noon when the sun is due south on
the meridian. This is called apparent solar time. Each day, as Earth orbits
the sun, Sol moves approximately one degree to the east against the fixed
background of stars. But because our planet’s orbit is oval-shaped, Earth
travels faster in winter and slower in summer. This causes the sun’s eastward
motion to vary in a similar fashion, making the real sun cross the meridian
ahead of or behind a fixed arbitrary beat of 24 hours. Enter mean solar time,
which focuses upon a fictitious, uniformly moving sun which crosses the
meridian in precise 24 hour increments. However, every location on the planet
would have a slightly different mean solar time based upon its longitude east
or west of the Prime Meridian. Allentown, Bethlehem, and Easton would have
slightly different times because these cities are respectively eastward from
one another. So we standardize mean solar time into zones to make scheduling
more manageable. We further manipulate our clocks by jumping into the standard
time zones to our east in summer to make the daylight hours more consistent
with our waking hours. Does anyone know what time it really is? As you might
have already guessed, there are many different answers.
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- 138
APRIL 18, 1999: Lyrid Meteors
- The first major meteor shower of the year, the Lyrids, peak late Thursday
into Friday morning. The moon will be at first quarter Thursday, and should
have a minimal negative effect on the number of meteors seen. Meteor showers
are generally named after the constellation from which the shooting stars are
radiating. Meteors from the Lyrids, however, are actually emanating near the
eastern boundary of Hercules, a region of the sky devoid of bright stars except
for Vega, the principal star of Lyra, the harp. Blue white in luminescence,
and the sixth brightest star of the nighttime sky, Vega lies only 8 degrees
to the east of the radiant. It will be easy to spot by 11 p.m. in the
northeast, about two fists above the horizon. Don’t confuse it with reddish
Mars which will be higher in the southeast and about five times brighter than
Vega. Although observers are usually able to spot Lyrid meteors between April
16-25, concentrate your observations on Thursday morning, and especially Friday
morning. Your best viewing window will be after 2 a.m. until dawn. By 3 a.m.
Vega will be almost due east and more than half way up in the sky. Recline on
a lawn chair for comfort and observe about one fist (held at arm’s length) to
the right of Vega. That is the location from where the meteors will appear to
be radiating. On Friday morning you can expect to see about 5-10 Lyrids per
hour in suburban skies. However, in 1982 American observers recorded as many
as 90 per hour. Don’t expect rates like these in the Lehigh Valley, but
sometimes the Lyrids do impress.
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- 139
APRIL 25, 1999: Blue Moon Enigma Solved
- During the past several months this column has seen two articles about
blue moons (see the Earth/Moon section in the StarWatch Index at the web site below).
The term blue moon, meaning the second full moon of the month, seemed to have
originated during the 20th century. Little else was certain. Now it appears as
if our love affair with blue moons began as a mistake, some 53 years ago in "Sky
and Telescope" magazine. The use of the blue moon was traced to the 1937 edition
of the "Maine Farmers’ Almanac." However, the blue moon date occurred on August 22,
clearly not the second full moon of the month, since it takes 29.5 days for the moon
to complete its cycle of phases. What happened? The "Maine Farmers’ Almanac" used
a seasonal scheme for determining blue moons based upon a uniformly moving sun which
made the seasons of equal length. There were normally three full moons for each
season, and each of these was given a name. When a season contained four full
moons, the rule was to designate the third full moon of that particular season
as the blue moon. This allowed the other three named full moons to occur in
better step with the seasons. In other words, the blue moon to the "Maine Farmers’
Almanac" acted as a sort of "leap moon" to reset the seasonal calendar back into
step with the full moon cycle. The blue moon, as we use it today, resulted from
an interpretative error based upon an earlier July 1943 "S&T" article which
referenced the 1937 "Maine Farmers’ Almanac." The birthing month for the blue
moon was March 1946 (in "S&T"). Incidentally, the moon is full on Friday, but
it surely isn’t blue.
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