Photo of the Week.A rare double sundog seen from an airplane
at an altitude of about 30,000 feet. The top one is
caused by direct sunlight refracting through ice crystals in clouds. The
lower is caused by refraction of light from the
reflection of the Sun off a lower deck of icy clouds, a subsun.
Both the Sun and the subsun are off the picture to the right, 22 degrees to
the right of the sundogs.
Astronomy news for the week starting Friday, April 26, 2002.
We begin the week with the full Moon, the phase reached on Friday,
the 26th, just about the time of moonrise in North America, causing
the Moon to rise almost exactly at sunset, which is now taking
place rather late in the evening. The remainder of the week sees
the Moon wane through its gibbous phase far to the south as it
transits through and above the constellation Scorpius.
The real eye is not on the Moon,
however, but on the Great Gathering of the planets in the early-
evening western sky. Near month's end, look first for brilliant Venus,
which shines to the right of Aldebaran in Taurus. Down and to the right, find Venus's brother
planet Mercury
, which will lie just to the left of (and be in conjunction
with) Taurus's Pleiades (Seven
Sisters) star cluster. A line upward from Mercury through Venus
leads to
href="http://pds.jpl.nasa.gov/planets/special/saturn.htm">Saturn,
which itself lies just above and to the left of
now-second-magnitude reddish Mars.
Better yet, find Saturn (above Aldebaran),
and draw the line downward from Saturn through Venus to find more
elusive Mercury. Be sure to have a clear twilight horizon, as
Mercury sets close after the Sun. Watching the whole show from a
much higher vantage point is very-bright Jupiter
, which now courses easterly through the bright stars of Gemini. Early May sees a series of
planetary conjunctions, Mars with Saturn on May 4, Venus with
Saturn on the 7th, Venus with Mars on the 10th. Jupiter will not
get into the act until June 3, when it will make a fine pair with
Venus.
The morning sky is not without interest. Comet
Ikeya-Zhang climbs higher to the west of southern Cepheus heading toward the head of Draco, though the bright Moon will
render it rather difficult to see. Toward the end of the week we
also begin to see a few meteors of the
Eta Aquarid shower, which results from the debris of
Halley's Comet. The Moon will make rather a mess of these
too.
We are now at prime "Leo-viewing-
season," the mythical Lion seen due south in late twilight. Below
Leo winds the immensely long and thin constellation of Hydra, the Water Serpent, the longest
constellation in the sky. On his back lie two classical
constellations. A rather obvious box makes Corvus, the Crow, whose top two stars point eastward to
Spica in Virgo. To the west of Corvus is one of the dimmest of
all the ancient figures, Crater, the
Cup, which moonlight completely washes out. Above Leo, however, is
one of the grandest figures the sky has to offer, the Big Dipper, which for those in mid
norther latitudes courses the sky nearly overhead.
