Skylights featured three times on Earth Science
Picture of the Day: 1
, 2
, 3
, 4
.
Photo of the Week.. A quiet sunrise, the Sun
reflected in gentle waters, begins another day filled with wonder.
Astronomy news for the week starting Friday, April 15, 2005.
The Moon passes its first
quarter on Saturday the 16th somewhat before its daytime
Moonrise in North America, and then waxes through
gibbous as it heads to its full phase next week. Only four
hours after it passes the quarter, it also passes apogee,
where it is farthest from the Earth.
Tides are caused by
both the
Moon and the Sun,
which act independently of each other. (Their gravity "stretches"
the waters of the Earth, so that as our planet rotates beneath the
tidal bulge, the water at the shore goes up and down.) At the
quarters, the weaker solar tide fills in the lunar, so the tides
(called "neap tides") are neither as high nor as low as they are at
full and new Moons. Tides are also very sensitive to distance, and
with the quarter Moon at apogee, this neap tide will be especially
weak.
The night of Friday the 15th finds the not-quite-quarter in central
Gemini, just up and to the right
of Saturn,
the two, along with the constellation's bright Castor and Pollux, making a fine sight. The
following night, with the Moon to the east of Saturn, will be
almost as good. By the night of Tuesday the 19th, the Moon will
have arrived in central Leo. Near
the end of the week, the night of Thursday the 21st, the
brightening Moon will lie just to the west of Jupiter,
which itself is now just east of Porrima (Gamma Virginis) in Virgo. The ringed planet now
crosses the meridian to the south well before sunset, and sets
around 2 AM daylight time, leaving the morning to Jupiter (which
crosses the meridian around midnight and does not set until dawn
begins to brighten the eastern sky) and Mars. Slowly
brightening, while moving quickly to the east against the
background stars, the red planet (along with Neptune,
in Capricornus) rises just before
4 AM (Daylight Time).
Among the naked eye planets, that leaves us with Mercury
and Venus. On opposite sides of the sky, Mercury rises midway
through morning twilight and is quite difficult to see. Setting
shortly after the Sun, Venus is virtually impossible to find
against the bright sky. By next month, it will begin to make an
appearance.
Spring chases Orion and Canis Major (with brilliant Sirius) westward. Down and to the
left of the Great Dog is the broken ship Argo, which is separated into Puppis (the Hull) immediately southeast of Canis Major,
Vela (the Sails) farther to the
southeast, and Carina, the Keel,
which contains the second brightest star of the sky, Canopus, and extends far to the
south, its limit only 15 degrees from the southern pole.
