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OBSERVING
Sun, OBSERVING Moon & PlanetsApril’s
Sun, Moon & Planets
The Plunge of Venus
The brightest planet rushes toward the Sun in May.
People along a band from southern China
through southern Japan to parts of the
western U.S. can witness an annular
eclipse of the Sun on May 20th or 21st.
The partial aspect of this solar eclipse is
viewable over a huge surrounding area,
including much of Asia, the Pacifi c,
and North America (see page 50). And
observers worldwide can see Venus in its
last month of visibility before it makes a
historic transit across the Sun’s face on
June 5–6.
Seen from mid-northern latitudes,
Venus takes a steep, majestic fall in the
western twilight over the course of May,
appearing noticeably lower each evening.
Mars is high in the south to southwest in
early evening, and Saturn is moderately
high in the southeast to south.
Dusk, May 3 – 5
1 hour after sunset
10°
Lib
Saturn
Moon
May 5
Spica
Moon
May 4
Looking Southeast
48 May 2012 sky & telescope
Moon
May 3
DUSK AND EVENING
Venus is outstandingly conspicuous at the
beginning of May, shining at its maximum
brilliance of magnitude –4.7. This
is due to Venus achieving, on April 30th,
its “greatest illuminated extent” — the
largest area of sunlit surface in square
arcseconds. On May 1st Venus displays a
38″-wide disk that’s 27% illuminated.
At mid-northern latitudes, Venus is
also quite high as May starts. Viewers at
latitude 40° north can see it 36° high at
sunset and still 28° up when twilight is
deepening 45 minutes after sunset. And
Venus doesn’t set until fully 3½ hours
after the Sun, around 11:30 p.m. daylightsaving
time. But the fall of Venus during
the rest of the month is breathtaking.
Venus’s sunset altitude drops to 25° by
Dawn, May 7 and 8
1 hour before sunrise
Moon
May 8
Antares
Moon
May 7
SCORPIUS
Looking South-Southwest
These scenes are drawn for near the middle of North America (latitude 40° north, longitude 90°
west); European observers should move each Moon symbol a quarter of the way toward the one for
the previous date. In the Far East, move the Moon halfway. The blue 10° scale bar is about the width
of your fi st at arm’s length. For clarity, the Moon is shown three times its actual apparent size.
May 16th and just 6° or 7° by month’s end.
Venus’s brightness declines only a little
during the fi rst part of the month; it still
shines at magnitude –4.5 on May 20th,
when its crescent is 51″ long and 8% lit.
After that it changes rapidly, dimming to
magnitude –4.1 and less than 1% lit on the
American evening of May 31st, even as the
crescent lengthens to 57″. During the last
week of May Venus’s crescent should be
easy to see in binoculars, and may even be
visible to sharp naked eyes.
EVENING AND NIGHT
Mars is about 60° high in the south an
hour after sunset as May opens, so this
time is the best to observe it through a
telescope. Unfortunately, the planet is only
10″ wide at the start of May and shrinks to
Pollux
Moon
May 24
Moon
May 23
Betelgeuse
Dusk, May 21 – 24
30 minutes after sunset
Castor
Moon
May 22
Looking West-Northwest
Tau
Moon
May 21
Venus