Sky and Telescope - November 2017 - 51

Occultations of Aldebaran and Regulus
THE MOON IN NOVEMBER occults two
1st-magnitude stars for much of North
America just six days apart. The ﬁrst
event happens mostly in early-evening
darkness. The second takes place in
broad daylight.
* Aldebaran, November 5th. The
Moon will be just a trace past full
and shining in the eastern sky around
dinnertime when, for the eastern and
central parts of the continent, its bright
limb will creep up to and hide orange
Aldebaran - a telescopic "ﬁre on the
Moon" in its ﬁnal seconds. The star will
reappear on the other side from behind
the Moon's very thin dark sector (Luna
is only 5% unilluminated) up to an
hour or more later.
The farther west you are, the earlier
and lower it happens. From Texas
through Montana, the star will already
be behind the Moon at moonrise; you'll
only see the reappearance. Observers
farther west miss out altogether.
Northern Europeans will see the
occultation at a later hour: around the
middle of the night of November 5-6.
* Regulus, November 11th. The following Saturday, telescope users from
Georgia through British Columbia and
points father south and west can try for
the Moon occulting blue-white Regulus high in a (hopefully) blue sky. The
Moon will be a day past last quarter.
Again the star disappears on the bright
limb and reappears on the dark limb,
which will be invisible in the daytime
blue. Good luck.
Complete timetables for both stars'
occultations for hundreds of cities and
towns are at lunar-occultations.com/
iota/bstar/bstar.htm. Pay attention

USING A CHART WITH
YOUR TELESCOPE
º You know that to ﬁnd faint objects
with your telescope, you need
detailed, large-scale charts. But
you also need to know the size and
orientation of your eyepiece view
as it appears on the charts, so that

p On July 25th, Shahrin Ahmad in Kuala Lumpur, Malaysia, took a telescopic video of Regulus
emerging from behind the Moon's bright limb.

there to the altitudes listed for the Sun
and Moon. The daytime sky around the
Moon is deeper blue when the Moon
is higher than the Sun, giving your
telescope the best chance. The "CA"
column tells the cusp angle where the
star disappears or reappears: how many
degrees from the Moon's north or south
cusp the event occurs, so you'll know
exactly where to look. For each star,
the prediction page displays three long
tables with less-than-obvious divides:
for the disappearance, the reappearance,
and the locations of cities.
you can match star patterns in
your eyepiece to star patterns on
the paper or screen. Read how at
skyandtelescope.com/charts. Then
practice until it's routine.
If you know exactly where in your
ﬁeld of view a difﬁcult faint fuzzy
ought to be, you can detect things
at least a magnitude fainter!

Minima of Algol
Oct.

Nov.

21:22

10:18

18:10

7:07

14:59

3:56

11:48

0:45

8:36

21:34

5:25

18:22

2:14

15:11

23:03

12:00

19:52

8:49

16:40

5:38

13:29

Algol stays near minimum light, magnitude 3.4
instead of its normal 2.1, for about two hours.
These predictions are from the heliocentric
elements Min. = JD 2445641.554+ 2.867324E,
where E is any integer. For a comparison-star
chart, see skyandtelescope.com/algol.

s k y a n d t e l e s c o p e . c o m * N O V E M B E R 2 0 17

http://www.lunar-occultations.com/iota/bstar/bstar.htm http://www.lunar-occultations.com/iota/bstar/bstar.htm http://www.skyandtelescope.com/charts http://www.skyandtelescope.com/algol http://www.skyandtelescope.com

Sky and Telescope - November 2017

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