Sky and Telescope - October 2015 - 49

Learn how to use detailed star charts to ﬁnd
the faintest things with your telescope: skypub.com/charts.

period comet that currently rounds the
Sun about every 6.6 years. Most displays
have happened in years close to the
comet's perihelion; the comet last passed
nearest to the Sun in February 2012. That
would suggest not much will happen in
2015. But you never know.
Nor is the timing of a possible shower
very predictable. Recent activity suggests
that if we see anything this year, its brief
peak could arrive anytime from 21h Universal Time on October 8th (Thursday
afternoon in North America) to 14h UT on
the 9th (midday Friday).
The shower's radiant is at the head of
Draco, which is circumpolar. The radiant
is highest in the evening, rather than in
the morning as for most showers, so start
watching at dusk. The Draconids appear
exceptionally slow-moving as meteors
go - partly because they are catching up
to Earth from behind, and also because
their short-period orbit means they don't
fall sunward from very far out.
This year we'll have no problem with
moonlight; the Moon is a waning crescent.

Vesta, the brightest asteroid, isn't getting much attention lately - not since
NASA's Dawn spacecraft dumped it in 2012
and ﬂew away to take up with Ceres, which
Dawn is now orbiting and becoming ever
more photographically entranced with.
But Vesta remains the leading asteroid date for amateurs. It's easy to see in
binoculars at magnitude 6.2 for a couple
weeks around its September 29th opposition, and it's still as bright as 6.8 on
November 1st, 7.5 on December 1st, and
8.0 at the end of the year. On its path at
left, the ticks are for 0:00 Universal Time.
PISCES

Path of
Vesta
ι
ζ

ψψ
-

η
CETUS

γ
0

β
-

Alan MacRobert

A Blue-Sky Occultation
Dawn

Day
Reappearance
at moonrise

Night

Occcu
cult
ltaat
ati
tiio
on of Aldebaran
Ald
deb
ebar
bar
aran
an
n
Occultation
Octobe
Oc
tobe
ber 2
October

Disappearance
at moonrise

On the morning of October 2nd, the newly risen waning crescent Moon occults Aldebaran for
most of North America in daylight, and for the West Coast as dawn brightens before sunrise.
(The dividing lines between day, dawn, and night are drawn for the center of the occultation,
halfway between disappearance and reappearance.)

Have you ever seen the Moon occult a
star in the clear blue sky of a sunny day?
For the second time in two months, the
Moon will cover 1st-magnitude Aldebaran
for parts of North America. The Aldebaran
occultation of September 4-5 was written
up in last month's issue, page 51. The one
coming up on the morning of October 2nd
will be rather diﬀerent.
First, it happens well after sunrise for
most of the continent. Westerners are the
exception; most of them will see the Moon
cover Aldebaran while dawn is brightening.
Along much of the West Coast, it won't
quite be sunrise even when Aldebaran reappears out from behind the Moon.
Second, the Moon will be waning gibbous, 74% sunlit. When the Moon is waning, an occulted star disappears on the
bright, sunlit limb and reappears from
behind the dark limb. The bright limb's
glare will be greater than during September's occultation, when the Moon was last
quarter, so it will interfere a little more with
Aldebaran's orange ﬁrespark in the last seconds before the star snaps out.
Most important will be the clarity of your
daytime sky. If the sky is hazy blue-white,
the Moon itself may be hard to spot. Once
you've got it, though, even a small telescope is likely to show the 1st-magnitude
star, especially if you switch to medium-

high power (see S&T: Oct. 2014, p. 36).
Aldebaran will snap back into view from
behind the Moon's invisible dark limb up to
an hour or more later.
Here are some predicted times; all are
a.m.: Montreal, disappearance 9:56, reappearance 10:52 EDT. Central Massachusetts,
d. 10:00, r. 10:56 EDT. Toronto, d. 9:56, r.
10:55 EDT. Washington DC, d. 10:03, r. 11:00
EDT. Atlanta, d. 10:09, r. 11:01 EDT. Miami,
d. 10:32, r. 10:56 EDT. Winnipeg, d. 8:35, r.
9:41 CDT. Chicago, d. 8:53, r. 9:55 CDT. Kansas City, d. 8:53, r. 9:54 CDT. Austin, d. 9:18,
r. 9:43 CDT. Edmonton, d. 7:14, r. 8:23 MDT.
Denver, d. 7:41, r. 8:44 MDT. Vancouver, d.
6:02, r. 7:17 PDT. Berkeley, d. 6:17, r. 7:17 PDT.
Los Angeles, d. 6:39, r. 7:15 PDT.
Interpolate between cities near you to
estimate the times for your location. Set
up early; the Moon and star won't wait.
Detailed timetables for western locations where the sky will be somewhat
dark are at lunar-occultations.com/iota/
bstar/1002zc692.htm. (The table has three
long sections: disappearance times, reappearance times, and the cities' coordinates.)
In the West, also watch for occultations
of Hyades stars, 4th magnitude and fainter.
Timetables for the brightest Hyades, for
sites where the sky may be suﬃciently dark,
are at lunar-occultations.com/iota/bstar/
bstar.htm.

Sk yandTelescope.com October 2015

http://www.skypub.com/charts http://www.lunar-occultations.com/iota/bstar/1002zc692.htm http://www.lunar-occultations.com/iota/bstar/1002zc692.htm http://www.lunar-occultations.com/iota/bstar/bstar.htm http://www.lunar-occultations.com/iota/bstar/bstar.htm http://www.SkyandTelescope.com

Sky and Telescope - October 2015

Table of Contents for the Digital Edition of Sky and Telescope - October 2015