Page 37 - Astronomy - October 2017 USA

RISINGMOON

See the Moon in a new light Aristoteles and Protagoras

Most skywatchers observe between the snaking Serpentine
during the evening and shun Ridge and Mare Serenitatis.
the morning hours except From there, jump halfway
Protagoras
for special events. That’s why to the pole and find the large
lunar observers tend to focus crater Aristoteles. The low Sun
on the Moon’s waxing phases angle transforms its apron of
visible after sunset and ignore impact splatter into a finely Mare Frigoris Aristoteles
the waning phases best seen textured expanse. Check out
before dawn. But this month the shadow cutting across
provides a nice opportunity to Aristoteles’ middle and trace the
N
view the waning gibbous Moon huge “divot” of light back to the
before midnight. You might be small crater that breaches the
E
surprised at what the different western flank and allows sun-
lighting reveals. light to reach the floor. Two distinctive craters show up on the frozen lava of Mare Frigoris
Target Luna around 11 P.M. Farther to the northwest lies on October 9’s gibbous Moon. CONSOLIDATED LUNAR ATLAS/UA/LPL; INSET: NASA/GSFC/ASU
local daylight time October 9. As the crater Protagoras, which
you scan along the terminator resembles a golf hole in the flow came right up to the west- suspect this unusual feature was
— the dividing line between putting green formed by the ern lip of Protagoras, so there’s hiding in plain sight.
day and night — features may solidified lava of Mare Frigoris. no rim to catch the Sun’s rays. The shadows intensify on
look odd because you’re view- Normal craters are surrounded Under the more familiar lighting the 10th as the Sun drops lower
ing lunar sunset and not sunrise. by a raised rim whose western conditions of a waxing crescent in the lunar sky, though the
The reverse lighting makes it flank glows brightly in the set- Moon on the evening of Moon doesn’t climb to a decent
easy to see the relationship ting Sun. But an ancient lava October 25, you might never altitude until midnight.

elongation October 13. It then METEORWATCH
lies 8' from Saturn and shows
up nicely through 4-inch and
larger scopes. The same Dark skies for the Orionid meteor shower
instrument reveals a trio of Aldebaran
similarly bright moons — Hunter’s show TAURUS
Tethys, Dione, and Rhea —
that circle the planet inside Halley’s Comet last appeared in GEMINI Radiant
Titan’s orbit. our sky more than 30 years ago, Castor ORION
As Saturn prepares to but it still makes its presence Pollux Betelgeuse
set, turn your attention to known. Every October, Earth Rigel
plows into debris left behind by
Neptune. This distant ice
giant reached opposition the periodic comet during its trips LEPUS
through the inner solar system.
and peak visibility in early As this dusty debris burns up in
September, but the view in Procyon
our atmosphere, we see flashes
October barely suffers in of light known as meteors. The Sirius 10°
comparison. It appears in the
flashes appear to radiate from the CANIS MAJOR
southeast as darkness falls constellation Orion the Hunter,
in early October and climbs which lends its name to the October 21, 2 A.M.
highest in the south around Orionid meteor shower. Looking southeast
11 p.m. local daylight time. (It Conditions this year should be With the Moon absent for this Orionid meteors
reaches the same position two ideal. The shower peaks before month’s premier shower, Active dates: Oct. 2–Nov. 7
hours earlier by month’s end.) dawn October 21, just two days observers can expect to see Peak: October 21
Neptune glows at magni- after New Moon. Observers under up to 20 meteors per hour. Moon at peak: New Moon
tude 7.8, so you’ll need bin- a dark sky can expect to see 20 meteors per hour in the Maximum rate at peak:
20 meteors/hour
oculars or a telescope to see close to the maximum rate of hours before dawn.
it. The planet resides in
Aquarius, less than 1° from
magnitude 3.8 Lambda (λ) OBSERVING The zodiacal light glows in the predawn sky for Northern Hemisphere
observers at dark sites from October 17 to November 2.
— Continued on page 42 HIGHLIGHT
WWW.ASTRONOMY.COM 37