Sky and Telescope - January 2018 - 50

JANUARY 2018 OBSERVING
Celestial Calendar

Action at Jupiter
TWO MONTHS PAST solar conjunc-

Regulus Puts on a Show
THE SAME WANING gibbous Moon that
interferes with the Quadrantid meteor
shower offers a spectacle the very next
night. An occultation of 1st-magnitude
Regulus occurs over northern North
America on the night of January 4-5.
Optical aid will help you catch the star's
disappearance behind the Moon's bright
limb, but reappearance at the dark limb
will be easier. For those on the southern
edge of the event path, Regulus only
just meets the Moon, producing a grazing occultation. The graze line extends
from southeast Alaska, across central

Canada through northeast Ontario, and
on past the Maritimes. A good graze offers a dramatic light show, with the star
blinking on and off as lunar peaks and
valleys pass in front of it. Some timings: Anchorage, disappearance, 9:42
p.m., reappearance, 10:22 p.m. AKST;
Juneau, d. 9:47 p.m., graze 9:58 p.m., r.
10:14 p.m. AKST; Whitehorse, d. 10:45
p.m., r. 11:22 p.m. PST; Yellowknife, d.
11:54 p.m., r. 12:36 a.m. MST; Churchill,
d. 1:12 a.m., g. 1:27 a.m., r. 1:45 a.m.
CST; St. John's, NL, d. 4:39 a.m., g.
5:05 a.m., r. 5:18 a.m. NST.

Alaska for Aldebaran
FAR NORTHWEST North America will

see the gibbous Moon, its face 80%
sunlit, occult Aldebaran on Saturday,
January 27th. Alaska, Canada, and the
Paciﬁc Northwest see the event during
the early morning hours, while much of
central and southern Asia see a daylight

Minima of Algol
Dec.

UT

Jan.

UT

2:27

1

15:28

3

23:16

4

12:17

6

20:05

7

9:06

1

9

16:55

10

5:56

12

13:44

13

2:45

15

10:33

15

23:34

18

7:22

18

20:23

21

4:11

21

17:13

24

1:00

24

14:02

26

21:49

27

10:51

29

18:39

30

7:41

These geocentric predictions are from the recent
heliocentric elements Min. = JD 2445641.5540+
2.86732400E, where E is any integer. For a comparison-star chart and more info, see skyandtelescope.
com/algol.

50

JA N UA RY 2 018 * SK Y & TELESCOPE

occultation. Prime evening visibility
happens over north-central Asia.
It may be winter, it may be early hours
for North America, but at least dark-sky
occultations are easy to observe. This is
especially true when the star disappears
behind the Moon's dark limb, as it does
whenever the Moon's in a waxing phase,
as it will be on the 27th.
The Moon travels through an angle
roughly equal to its own diameter in
an hour, so the longest duration of an
occultation (the time between the disappearance of a star at one lunar limb
and reappearance at the opposite limb)
is also about an hour. For this occultation, observers at the western edges of
the visibility zone will see only the disappearance of the 1st-magnitude star,
as the Moon sets only a few to some 30
minutes afterward. Viewing conditions
are best for Alaskans, who can watch
the disappearance and reappearance
before the Moon sets around 5:40 a.m.
local time.
Some timings: Anchorage, disappearance, 1:53 a.m., reappearance, 2:50
a.m. AKST; Vancouver, d. 3:11 a.m. PST;
Seattle, d. 3:13 a.m. PST; Edmonton, d.
4:04 MST.

tion, Jupiter opens the year in Libra,
where it lingers with Mars in the early
morning hours. The duo comes together
for a close conjunction on the mornings of January 6th and 7th. Jupiter
rises earlier and earlier each morning,
brightening just a bit over the course
of the month, from magnitude -1.8 to
-2.0, and increasing from 33″ to 36″ at
its equator.
Any telescope shows Jupiter's four big
Galilean moons, and binoculars usually show at least two or three. Use the
diagram on the facing page to identify
them at any date and time.
All of the January interactions
between Jupiter and its satellites and
their shadows are also tabulated on
the facing page. Find events timed for
when Jupiter is at its highest in the early
morning hours.
And here are the times, in Universal
Time, when the Great Red Spot should
cross Jupiter's central meridian. The
dates, also in UT, are in bold. (Eastern
Standard Time is UT minus 5 hours.)
January 1, 5:46, 15:42; 2, 1:38, 11:34,
21:29; 3, 7:25, 17:21; 4, 3:17, 13:12, 23:08;
5, 9:04, 19:00; 6, 4:55, 14:51; 7, 0:47, 10:43,
20:38; 8, 6:34, 16:30; 9, 2:26, 12:21, 22:17;
10, 8:13, 18:08; 11, 4:04, 14:00, 23:56; 12,
9:51, 19:47; 13, 5:43, 15:39; 14, 1:34, 11:30,
21:26; 15, 7:21, 17:17; 16, 3:13, 13:09, 23:04;
17, 9:00, 18:56; 18, 4:52, 14:47; 19, 0:43,
10:39, 20:34; 20, 6:30, 16:26; 21, 2:22,
12:17, 22:13; 22, 8:09, 18:04; 23, 4:00,
13:56, 23:51; 24, 9:47, 9:43; 25, 5:39, 15:34;
26, 1:30, 11:26, 21:21; 27, 7:17, 17:13; 28,
3:09, 13:04, 23:00; 29, 8:56, 18:51; 30, 4:47,
14:43; 31, 0:38, 10:34, 20:30.

These times assume that the spot will
be centered at System II longitude 285°.
If the Red Spot has moved elsewhere, it
will transit 12/3 minutes earlier for each
degree less than 285° and 12/3 minutes
later for each degree more than 285°.
Features on Jupiter appear closer to
the central meridian than to the limb for
50 minutes before and after transiting. A
light blue or green ﬁlter slightly increases
the contrast and visibility of Jupiter's
reddish and brownish markings.
http://skyandtelescope.com/algol http://skyandtelescope.com/algol
Sky and Telescope - January 2018

Table of Contents for the Digital Edition of Sky and Telescope - January 2018
