Sky and Telescope - October 2017 - 47

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December
solstice

PR E- DAW N A N D DAW N
Venus comes up about 2 hours before
the Sun on October 1st, with much
dimmer Mars following about 3° below
it. The pair should be on best display a
little more than an hour before sunrise,
low in the due east, but for Mars especially, optical aid will help. Both planets
are almost at their dimmest, with Venus
at magnitude -3.9 and Mars at magnitude 1.8. They're also almost at their
smallest, Venus appearing 11″ wide and
Mars 3.7″. Coincidentally, Mars is the
same apparent width as distant Uranus
this month!
Venus and Mars pass very close to
each other at dawn on October 5th.
They stand only about 10° high but
just ¼° apart an hour before sunrise
for North Americans at mid-northern
latitudes - high enough for Mars to
be potentially visible to the unaided
eye in the early twilight glow under
very good conditions. But a better view
comes with binoculars or a telescope
at medium power: meager Mars is fully

Uranus

Venus
Sun
Saturn

Neptune

June
solstice

ORBITS OF THE PLANETS
The curved arrows show each planet's movement during October. The outer planets don't
change position enough in a month to notice at this scale.

lit but a tiny, blurry speck, and more
vibrant Venus is almost fully lit but also
lacks sharpness.
Venus appears lower and Mars higher
each morning thereafter; by the end
of October Venus rises about 1½ hours
before the Sun and Mars more than 2½
hours before the Sun. By month's end,
Venus is deep in advancing dawn and
Mars is 16° upper right of it.
Mercury goes through superior
conjunction with the Sun on October

Dusk, Oct 22 -24
1 hour after sunset

LEO

OPH IUCHUS

Moon
Oct 24
Saturn
Moon
Oct 23

Moon
Oct 16

Moon
Oct 22
Antares

Denebola

Mars
Moon
Oct 17

VIRGO
Venus

Looking East

Sept.
equinox

Mercury

Dawn, Oct 15-17

Moon
Oct 15

Earth

March
equinox

Jupiter

1 hour before sunrise

Regulus

Mars

Looking Southwest
t 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 fist at arm's length.
For clarity, the Moon is shown three times its
actual apparent size.

8th, passing from the morning to the
evening sky, but it's too poorly placed
for observation from mid-northern latitudes this month. Look for it to become
visible at dusk once again around the
17th of next month.

M O O N PAS SAGE S
The fairly fat waning gibbous Moon
rises late on the evening of October 8th
and creeps closer to Aldebaran for the
rest of the night and into dawn on the
9th. The Moon hangs about 5° lower
right of red Aldebaran before sunrise on
October 9th.
The waning crescent Moon occults
Regulus just before or during dawn on
October 15th for much of the United
States and part of Canada. Look for the
1st-magnitude star to disappear behind
the Moon's bright limb, then reappear
at its dark limb about an hour later. See
pages 50-51 for timing for major cities
and advice on timing the occulation.
A thinner lunar sliver hangs left or
lower left of dim Mars on October 17th;
the pair is about 8° above vivid Venus.
Back in the evening sky, the waxing
crescent Moon beams about 6° right
of Saturn fairly low in the southwest
on October 23rd. The next evening the
Moon is about the same distance to
Saturn's upper left.
¢ Contributing Editor FRED SCHAAF
welcomes your letters and comments at
fschaaf@aol.com.
s k y a n d t e l e s c o p e . c o m * O C T O B E R 2 0 17

47
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Sky and Telescope - October 2017

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