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Comet 41p is ideally placed.

IF YOU HAVEN'T STARTED watching it yet, now's the time. Periodic comet 41P/Tuttle-Giacobini-Kresak may be reaching 6th or even 5th magnitude very high in the northern evening sky. Comet T-G-K, as it's being called, will probably remain about the same brightness from late March through the beginning of May. As the charts here show, the comet skims the lip of the Big Dipper's bowl (Alpha Ursae Majoris) near the end of March, sails past the Little Dipper's bowl and the head of Draco in April, and moves past Vega through Hercules in May. You can follow it with a small telescope or perhaps even good binoculars.

In May it's likely to fade from magnitude 6 to 8, then in June from 8 to 12.

As mentioned last month, the Planetary Science Institute has put out a call for high-quality amateur images of this comet. The goal is to ensure continuous monitoring of fast-changing activity in the inner coma. The comet is passing near Earth; its closest approach is 0.14 a.u. on March 27th. Read more about the campaign, and how to join it, at https://is.gd/4pcometcampaign.

Don't get your hopes too high, but during its 1973 return this comet flared by an astounding 10 magnitudes--a factor of 10,000 in brightness--twice. Each outburst lasted many days. That year the comet was having an unfavorable return, so it jumped from only about 14th magnitude to 4th, rather than the Jupiter-bright spectacle we would get if the comet were to do the same thing now.

And in 2001, two more outbursts brightened it by 4 and 6 magnitudes.

Action at Jupiter

JUPITER REACHES opposition on April 7th, remains 44" wide all April, and shrinks only a little to 41" by the end of May. Meanwhile it becomes more convenient to observe, passing high across the southern sky in the evening. See our telescopic guide to Jupiter in last month's issue, page 48.

Any telescope shows Jupiter's four big Galilean moons. Identify them at any date and time using the diagram at far right (where north is up).

The interactions in May between Jupiter and its satellites and their shadows are tabulated on the facing page.

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 Daylight Time is UT minus 4 hours.

April 1, 2:10, 12:05, 22:01; 2, 7:56, 17:52; 3, 3:47, 13:43, 23:39; 4, 9:34, 19:30; 5, 5:25, 15:21; 6, 1:17, 11:12, 21:08; 7, 7:03, 16:59; 8, 2:54, 12:50, 22:46; 9, 8:41, 18:37; 10, 4:32, 14:28; 11, 0:24, 10:19, 20:15; 12, 6:10, 16:06; 13, 2:02, 11:57, 21:53; 14, 7:48, 17:44; 15, 3:40, 13:35, 23:31; 16, 9:26, 19:22; 17, 5:18, 15:13; 18, 1:09,11:04, 21:00; 19, 6:56,16:51; 20, 2:47, 12:42, 22:38; 21, 8:34, 18:29; 22, 4:25,14:20; 23, 0:16, 10:12, 20:07; 24, 6:03, 15:58; 25, 1:54, 11:50, 21:45; 26, 7:41, 17:37; 27, 3:32, 13:28, 23:23; 28, 9:19, 19:15; 29, 5:10, 15:06; 30, 1:02, 10:57, 20:53.

May 1, 6:50, 16:46; 2, 2:41, 12:37, 22:33; 3, 8:28, 18:24; 4, 4:19, 14:15; 5, 0:11, 10:06, 20:02; 6, 5:58, 15:53; 7, 1:49, 11:45, 21:40; 8, 7:36, 17:32; 9, 3:27, 13:23, 23:18; 10, 9:14, 19:10; 11, 5:05, 15:01; 12, 0:57; 10:52, 20:48; 13, 6:44, 16:39, 14, 2:35; 12:31, 22:26; 15, 8:22, 18:18; 16, 4:13, 14:09; 17, 0:05, 10:00, 19:56; 18, 5:52, 15:47; 19, 1:43, 11:39, 21:34; 20, 7:30, 17:26; 21, 3:21, 13:17, 23:13; 22, 9:08, 19:04; 23, 5:00, 14:55; 24, 0:51, 10:47, 20:42; 25, 6:38, 16:34; 26, 2:30, 12:25, 22:21; 27, 8:17, 18:12; 28, 4:08, 14:04, 23:59; 29, 9:55, 19:51; 30, 5:46, 15:42; 31,1:38, 11:34, 21:29.

Jupiter's Moons

The wavy lines represent Jupiter's four big satellites. The central vertical band is Jupiter itself. Each gray or black horizontal band is one day, from 0" (upper edge of band) to 24h UT (GMT), UT dates are at left. Slide a paper's edge down to your date and time, and read across to see the satellites' positions east or west of Jupiter.

Caption: Symbols at 0:00 Universal Time every three days show the comet's position, and the orientation of its gas tail if any, as it sails high across the northern sky from late March through June.
Phenomena of Jupiter's Moons, May 2017

May 1      6:38     II.Tr.I
           7:43     II.Sh.I
           9:02     II.Tr.E
          10:10     II.Sh.E
          10:35     I.Tr.I
          11:07     I.Sh.I
          12:46     I.Tr.E
          13:19     I.Sh.E

May 2      7:44     I.Oc.D
          10:31     I.Ec.R
          18:18    III.Oc.D
          20:33    III.Oc.R
          20:34    III.Ec.D
          22:57    III.Ec.R

May 3      1:28     II.Oc.D
           5:02     I.Tr.I
           5:02     II.Ec.R
           5:36     I.Sh.I
           7:12     I.Tr.E
           7:47     I.Sh.E

May 4      2:11     I.Oc.D
           4:59     I.Ec.R
          19:47     II.Tr.I
          21:02     II.Sh.I
          22:12     II.Tr.E
          23:28     I.Tr.I
          23:29     II.Sh.E

May 5      0:05     I.Sh.I
           1:39     I.Tr.E
           2:16     I.Sh.E
          20:37     I.Oc.D
          23:28     I.Ec.R

May 6      7:51    III.Tr.I
          10:07    III.Tr.E
          10:25    III Sh I
          12:47    III.Sh.E
          14:36     II.Oc.D
          17:54     I.Tr.I
          18:19     II.Ec.R
          18:33     I.Sh.I
          20:05     I.Tr.E
          20:44     I.Sh.E

May 7     15:04     I.Oc.D
          17:57     I.Ec.R

May 8      8:56     II.Tr.I
          10:20     II.Sh.I
          11:22     II.Tr.E
          12:21     I.Tr.I
          12:46     II.Sh.E
          13:02     I.Sh.I
          14:31     I.Tr.E
          15:13     I.Sh.E

May 9      9:30     I.Oc.D
          12:25     I.Ec.R
          21:40    III.Oc.D
          23:58    III.Oc.R

May 10     0:33    III.Ec.D
           2:55    III.Ec.R
           3:45     II.Oc.D
           6:47     I.Tr.I
           7:30     I.Sh.I
           7:36     II.Ec.R
           8:58     I.Tr.E
           9:41     I.Sh.E

May 11     3:57     I.Oc.D
           6:54     I.Ec.R
          22:07     II.Tr.I
          23:39     II.Sh.I

May 12     0:33     II.Tr.E
           1:14     I.Tr.I
           1:59     I.Sh.I
           2:05     II.Sh.E
           3:25     I.Tr.E
           4:10     I.Sh.E
          22:24     I.Oc.D

May 13     1:23     I.Ec.R
          11:15    III.Tr.I
          13:34    III.Tr.E
          14:24    III.Sh.I
          16:44    III.Sh.E
          16:54     II.Oc.D
          19:41     I.Tr.I
          20:27     I.Sh.I
          20:53     II.Ec.R
          21:51     I.Tr.E
          22:38     I.Sh.E

May 14    16:51     I.Oc.D
          19:51     I.Ec.R

May 15    11:17     II.Tr.I
          12:57     II.Sh.I
          13:43     II.Tr.E
          14:07     I.Tr.I
          14:56     I.Sh.I
          15:23     II.Sh.E
          16:18     I.Tr.E
          17:07     I.Sh.E

May 16    11:17     I.Oc.D
          14:20     I.Ec.R
May 17     1:05    III.Oc.D
           3:27    III.Oc.R
           4:32    III.Ec.D
           6:04     II.Oc.D
           6:53    III.Ec.R
           8:34     I.Tr.I
           9:24     I.Sh.I
          10:10     II.Ec.R
          10:45     I.Tr.E
          11:35     I.Sh.E

May 18     5:44     I.Oc.D
           8:49     I.Ec.R

May 19     0:28     II.Tr.I
           2:16     II.Sh.I
           2:55     II.Tr.E
           3:01     I.Tr.I
           3:53     I.Sh.I
           4:42     II.Sh.E
           5:12     I.Tr.E
           6:04     I.Sh.E

May 20     0:11     I.Oc.D
           3:18     I.Ec.R
          14:43    III.Tr.I
          17:05    III.Tr.E
          18:24    III.Sh.I
          19:14     II.Oc.D
          20:43    III.Sh.E
          21:28     I.Tr.I
          22:22     I.Sh.I
          23:27     II.Ec.R
          23:39     I.Tr.E

May 21     0:32     I.Sh.E
          18:38     I.Oc.D
          21:46     I.Ec.R

May 22    13:39     II.Tr.I
          15:34     II.Sh.I
          15:55     I.Tr.I
          16:07     II.Tr.E
          16:50     I.Sh.I
          18:00     II.Sh.E
          18:06     I.Tr.E
          19:01     I.Sh.E

May 23    13:05     I.Oc.D
          16:15     I.Ec.R

May 24     4:35    III.Oc.D
           7:00    III.Oc.R
           8:24     II.Oc.D
           8:32    III.Ec.D
          10:22     I.Tr.I
          10:51    III.Ec.R
          11:19     I.Sh.I
          12:33     I.Tr.E
          12:44     II.Ec.R
          13:29     I.Sh.E

May 25     7:33     I.Oc.D
          10:44     I.Ec.R

May 26     2:52     II.Tr.I
           4:49     I.Tr.I
           4:54     II.Sh.I
           5:19     II.Tr.E
           5:47     I.Sh.I
           7:00     I.Tr.E
           7:19     II.Sh.E
           7:58     I.Sh.E

May 27     2:00     I.Oc.D
           5:13     I.Ec.R
          18:15    III.Tr.I
          20:39    III.Tr.E
          21:35     II.Oc.D
          22:22    III.Sh.I
          23:16     I.Tr.I

May 28     0:16     I.Sh.I
           0:40    III.Sh.E
           1:27     I.Tr.E
           2:01     II.Ec.R
           2:26     I.Sh.E

          20:27     I.Oc.D
          23:41     I.Ec.R

May 29    16:04     II.Tr.I
          17:44     I.Tr.I
          18:12     II.Sh.I
          18:32     II.Tr.E
          18:45     I.Sh.I
          19:54     I.Tr.E
          20:37     II.Sh.E
          20:55     I.Sh.E

May 30    14:55     I.Oc.D
          18:10     I.Ec.R

May 31     8:10    III.Oc.D
          10:37    III.Oc.R
          10:47     II.Oc.D
          12:11     I.Tr.I
          12:32    III.Ec.D
          13:13     I.Sh.I
          14:22     I.Tr.E
          14:51    III.Ec.R
          15:18     II.Ec.R
          15:24     I.Sh.E

Every day, interesting events happen Between Jupiter's satellites
and the planet's disk or shadow. The first columns give the date
and mid/time of the event, in Universal Time (which is 5 hours ahead
of Eastern Standard Time). Next is the satellite involved: I for lo,
II Europa, III Ganymede, or IV Callisto. Next is the type of event:
Oc for an occultation of the satellite behind Jupiter's limb, Ec for
an eclipse by Jupiter's shadow, Tr for a transit across the planet's
face, or Sh for the satellite casting its own shadow onto Jupiter.
An occultation or eclipse begins when the satellite disappears (D)
and ends when it reappears (R). A transit or shadow passage begins
at ingress (I) and ends at egress (E). Each event is gradual, taking
up to several minutes. Predictions courtesy IMCCE /Paris
Observatory.
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Title Annotation:OBSERVING: Celestial Calendar
Publication:Sky & Telescope
Date:May 1, 2017
Words:2048
Previous Article:Saturn has a southern apparition: with rings still tipped invitingly open, Saturn invites your most careful scrutiny.
Next Article:Napoleon's comets: the world took notice when two "great comets" appeared four years apart in the 19th century.
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