SKYLIGHTS
Astronomy news for the week starting Friday, April 16,
1999.
Having just passed its new phase the night of Thursday, April 15,
the Moon will be readily visible in western twilight by the night
of Saturday, the 17th (just after it has passed perigee, its
closest point to the Earth) and will spend nearly the whole week as
a waxing crescent, reaching first quarter on Thursday, the 22nd,
just about moonrise in North America. The night of Saturday the
17th will present us with a spectacular sight, a combination of the
Moon appearing several degrees to the left of brilliant Venus and
the Pleiades, while at the same time occulting the bright star
Aldebaran in Taurus for much of western North America, the best
view from the Rockies, Pacific Northwest, and central and western
Canada. From the midwest the first magnitude orange star will
appear to hang beautifully in front of and above the crescent, the
occultation occurring very low in the sky just before moonset,
while from the east the event takes place after moonset. Whether
you can see the occultation or not, the sight will be well worth a
look.
As the Moon leaves the planet's vicinity, Venus continues both to
brighten and to set later, and is brilliantly visible in a fully
dark western sky well after twilight. The two great planets of the
Solar System, Jupiter and Saturn, are both too close to the Sun to
be seen, but over in the east, bright Mars rises just after sunset.
In the morning hours, Venus's companion Mercury passes through its
greatest western elongation on Friday the 16th, when it is as far
to the west of the Sun as it can get, the apparition unfortunately
not very good as the ecliptic (the apparent solar path) lies flat
to the horizon and the planet will be low in morning twilight.
In the evening, however, the ecliptic rises from the horizon at a
steep angle, allowing for fine viewing of the "zodiacal light," a
faint luminous band that runs through the constellations of the
zodiac caused by sunlight scattering from interplanetary dust
particles that come from comets and the debris of smashed
asteroids. To see the zodiacal light you need a very dark moonless
sky (which we will have early in the week) away from city lights.
After the end of twilight, the zodiacal light then rises like a
great cone from the horizon. Northern autumn affords the best
morning view, the delicate light sometimes called the "false
dawn."
Finally, if out in the early morning, watch for the Lyrid meteor
shower, which peaks the morning of Wednesday, the 21st, the shower
typically yielding 10 or so meteors per hour before dawn.
