Feb 15, 2011

A Three-Planet Month

Jupiter, Saturn, and Venus are the only planets visible to the unaided eye in February.

As evening twilight
fades after February days, the sole bright planet visible is Jupiter, prominent
in the southwest. 
It sets a couple hours later, leaving the sky empty of any planets bright or
dim  for a little while. 
Then Saturn rises in the east, and it in turn is the only planet visible until
blazing Venus rises 2 or 3 hours before

Jupiter comes into view at dusk less than halfway up the southwest sky
(for observers around 40°north
latitude). It dims slightly in February, to magnitude 2.1, and its apparent
diameter dwindles a bit to 34.
Theres still much to check on its globe, however, including the status of 
the South Equatorial Belt and the 
Great Red Spot (SkyandTelescope.com/redspot). This is the last month 
until July when Jupiter will be high 
enough for good telescopic observations.

Jupiter crosses into the north celestial hemisphere on February 5th,
and late in the month it leaves Pisces 
for a brief journey through the northwest corner of Cetus. Jupiter sets 
around 9:30 p.m. as February opens
but around 8 pm as the month ends.

Uranus, faint at magnitude 6, had a close conjunction with Jupiter in
early January, but it begins February
almost 4° to Jupiters lower right. Jupiters swifter motion carries it to
6 from Uranus on February 14th 
and almost 8½°by months end.

Saturn rises in the east in Virgo around 10:30 p.m. on February 1st and
two hours earlier on February 
28th. The former is an hour after Jupiter sets, the latter only a half hour.
The ringed world brightens a l
ittle, from magnitude +0.7 at the beginning of February to +0.5 at month
Saturn was less than 8°from Spica in late January, but now the planet is
moving westward (retrograding) 
away from Spica.

The curved arrows indicate each planet’s movement during February, as if you were looking down on the solar system from the constellation Ophiuchus. The outer planets don’t change position enough in a month to notice at this scale.

Saturn culminates (is highest in the south) around 4:30 a.m. at the start of February and 2:30 a.m. at month’s end. The rings are getting a bit narrower during February, but they’re still close to 10° from

Venus rises while the sky is still fully dark throughout February, but the interval between Venus-rise and sunrise shrinks from 3 to 2 hours. Venus loses a bit of its tremendous luster this month, fading from magnitude –4.3 to –4.1. Its disk shrinks to less than 16″ in February, while its phase grows to  more  than 70% lit.
 Venus glides eastward across Sagittarius this month, passing several stars and deep-sky  objects.
 Pluto is also in Sagittarius, but it’s too faint to view when it’s so low in the sky. Interestingly, however, Pluto is only 2.3° north of Venus on February 9th. Pluto is usually far in the sky from the major planets, but it has been approaching the ecliptic in recent years and will cross it in 2018. So for the next decade, Pluto will have many encounters with
 Mercury, coming off a fine morning apparition in early January, rises only about 45 minutes before the  Sun on
February 1st (for viewers around 40° north). On that date, can you detect the planet with  binoculars just below the
crescent Moon very low in the southeast about 25 to 15 minutes before sunrise? Mercury is completely lost in the dawn
glow a few dawns later. It reaches superior conjunction with the Sun on February 25th.
Mars and Neptune also reach conjunction with the Sun this month, on February 4th and 17th,  espectively. So both
are unobservable.

The Moon is a very slender crescent a few degrees above Mercury at dawn on February 1st.  A waxing crescent Moon shines to the right of Jupiter on the evening of February 6th and above it on the 7th. The Moon is waning gibbous and rising in the late evening when it forms a triangle with Saturn and Spica on February 20th, and a vertical line with them on February 21st. The last-quarter Moon hangs to the left of Antares at dawn on February 25th. The waning lunar crescent is upper right of Venus at dawn on February 28th and lower left of Venus on March 1st.

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