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Eclipses of Saturn's Satellites Titan and Rhea


Eclipses of Titan in 2009.         Transits of Titan's Shadow.         Eclipses of Rhea 2008 and 2009 | 2010

Events of Saturn's Satellites Rhea and Titan

Eclipses of the satellites of Saturn only occur for a year or two near the time when Saturn's rings are edge on to the Sun. This next occurs on 2009 August 10.

Saturn's satellites are a lot fainter than the four Galilean satellites of Jupiter, only eclipses of the two brightest, Titan (magnitude 8.6) and Rhea (magnitude 9.9) are likely to be observable through a small telescope. The inner satellites are fainter still and eclipses will occur close to Saturn's disk, making them difficult events.

Eclipses of Rhea started in July 2008 and occur at intervals of approximately 4.5 days. Those of Titan, which is considerably further from Saturn than Rhea, do not start until 2009. They occur at intervals of approximately 16 days. The tables show times of eclipses of both these satellites. All eclipses are shown, whether they are visible from New Zealand or not.

The dates and times of events are in Universal Time (UT). To convert from UT to NZST add 12 to the hours if they are less than 12. If the hours are 12 or more, subtract 12 from them and add 1 to the date. During NZDT add 13 to the hours if less than 11, else subtract 11 and add 1 to the date.

Saturn is at conjunction with the Sun on 2008 September 4 and again 2009 September 17. It will be too close to the Sun for observation about a month either side of those dates.



Table of eclipses of Titan during 2009

The first eclipse of Titan occurs at the beginning of March just 3 days before Saturn is at opposition. As a result of the Sun, Earth and Saturn being almost in line, Saturn's shadow will be cast almost directly behind the planet as seen from the Earth. Titan will disappear into Saturn's shadow while very close to the planet. It will emerge from eclipse while still behind Saturn so Titan will not be visible from the Earth until it emerges from behind the planet itself.

Subsequent eclipses will take place with Titan at increasing distances from Saturn, especially when it comes out of eclipse, so being more readily observable from the Earth. Most of these events are visible from New Zealand up to the time of conjunction in September. After conjunction the situation is reversed with the disappearances into eclipse taking place further from Saturn than reappearances. The eclipses after conjunction are not observable from New Zealand as they occur either during the hours of daylight or when Saturn is set. Eclipses unobservable from New Zealand are shown in red.

The table gives the times of all eclipses except for a few weeks when Saturn is too close to the Sun and conjunction to observe. Also shown is the distance of Titan from Saturn's limb in arc seconds and the position angle of Titan with respect to Saturn, at the time of the event. The equatorial diameter of Saturn (without the rings) ranges from just on 20" at opposition to 16" close to conjunction.

At an eclipse it will take Titan 15 minutes or so to move completely into or out of Saturn's shadow. So fading, or brightening, will occur over a period of a few minutes either side of the predicted time. The exact time at which the satellite will disappear from, or reappear into, view will depend on the size of the telescope used, the observing conditions and the closeness of Titan to Saturn itself. Reappearances will be easier to observe than the disappearances as the latter take place when Titan is close to Saturn's lit limb. After May the disappearance stage will occur before sunset in New Zealand, so after that date only the reappearance will be visible.

Times of events are adapted from those given by Dave Herald's OCCULT 4 program.


Eclipses of Titan
Disappearance of Titan into eclipse Reappearance of Titan from eclipse
Date UT Time UT Distance PA Date UT Time UT Distance PA
2009 Mar 4 11:41 1" 212° 2009 Mar 4 14:56 From Occultation 147°
Mar 20 10:24 2" 186° Mar 20 14:04 5" 132°
Apr 5 09:18 3" 165° Apr 5 13:40 11" 122°
Apr 21 08:18 5" 151° Apr 21 13:12 16" 117°
May 7 07:22 7" 144° May 7 12:41 19" 114°
May 23 06:29 7" 139° May 23 12:07 20" 112°
Jun 8 05:38 7" 137° Jun 8 11:31 20" 109°
Jun 24 04:50 5" 137° Jun 24 10:52 18" 107°
Jul 10 04:03 2" 138° Jul 10 10:12 16" 105°
Jul 26 00:03, Occultation 215° Jul 26 09:30 13" 102°
Aug 10 23:35, Occultation 239° Aug 11 08:45 9" 97°
September 17, Saturn at conjunction with Sun
Disappearance of Titan into eclipse Reappearance of Titan from eclipse
Date UT Time UT Distance PA Date UT Time UT Distance PA
Oct 13 23:50 7" 294° Oct 14 05:25 from Occultation
Oct 29 23:13 10" 296° Oct 30 04:27 2" 342°
Nov 14 23:38 14" 298° Nov 15 03:27 6" 330°
Nov 30 22:07 17" 300° Dec 1 02:23 9" 323°
Dec 16 21:41 18" 302° Dec 17 01:12 11" 319°
2010 Jan 1 21:26 18" 305° 2010 Jan 1 23:51 13" 316°


Shadow Transit Events of Titan

A number transits of Titan's shadow across the face of Saturn occur during 2009. These should be visible as a black spot on Saturn's disk in a moderate telescope. Predictions of times of the transits are in the table. The predicted time of the start and and of all events are shown except 2 close to the time of Saturn at conjunction in September. Events in red are unobservable from New Zealand as they occur either during the hours of daylight or when Saturn is set. No stages of any transits are observable from NZ after conjunction.

The first shadow transit occur near Saturn's north pole (lower pole as seen from the southern hemisphere. Subsequent transits gradually move south so that by August they occur close to the rings. After conjunction the events continue to move southwards, until the final shadow transit on 2010 January 9 occurs close to the planet's south pole.

Shadow transits are likely to be fairly difficult to observe and will require a medium sized telescope.

Transits of Titan itself across Saturn occur during parts of the first two transits in February and March and again from mid July to early October. The times of Titan's transits mostly overlap part of the times of the shadow transits. Transit of Titan will be very difficult to observe as there will be little contrast between the satellite and background planet.

Times of events are adapted from those given by Dave Herald's OCCULT 4 program.



Shadow Transits of Titan
Start of Shadow Transit End of Shadow Transit
Date UT Time UT Date UT Time UT
2009 Feb 24 10:49 2009 Feb 24 13:19
2009 Mar 12 09:32 2009 Mar 12 12:58
2009 Mar 28 08:21 2009 Mar 28 12:29
2009 Apr 13 07:22 2009 Apr 13 11:56
2009 Apr 29 06:23 2009 Apr 29 11:20
2009 May 15 05:28 2009 May 15 10:42
2009 May 31 04:34 2009 May 31 10:02
2009 Jun 16 03:42 2009 Jun 16 09:20
2009 Jul 2 02:52 2009 Jul 2 08:37
2009 Jul 18 02:03 2009 Jul 18 07:52
2009 Aug 3 01:15 2009 Aug 3 07:06
2009 Aug 19 00:28 2009 Aug 19 06:17
September 17, Saturn at conjunction with Sun
Start of Shadow Transit End of Shadow Transit
Date UT Time UT Date UT Time UT
2009 Oct 5 22:13 2009 Oct 6 03:39
2009 Oct 21 21:30 2009 Oct 22 02:42
2009 Nov 6 20:50 2009 Nov 7 01:42
2009 Nov 22 20:11 2009 Nov 23 00:39
2009 Dec 8 19:35 2009 Dec 8 23:33
2009 Dec 24 19:03 2009 Dec 24 22:21
2010 Jan 9 18:42 2010 Jan 9 21:00
End of sequence of shadow transits of Titan

Table of eclipses of Rhea, December 2008 and through 2009

Between conjunction in September 2008 and opposition in Mar 2009 and again after conjunction on 17 September 2009, only disappearances of Rhea from eclipse are visible, the reappearance taking place while it is behind Saturn as seen from the Earth. For these the times of occultation reappearance, when Rhea emerges from behind Saturn are shown instead of the eclipse times. After opposition on Mar 8, the situation is reversed with only the reappearances of Rhea being visible, the satellite disappearing into eclipse while behind Saturn. For these the time of the start of the occultation is shown instead of the eclipse times. In both cases the background for occultation events is in grey.

The distance of Rhea from the limb of Saturn at eclipse is just over 8" at a maximum, eg at the end of May, considerably less than for Titan. In addition Rhea is about 1.6 magnitudes fainter than Titan. Both these factors will make observation of Rhea's eclipses more difficult.

Before opposition on March 8, eclipses of Rhea take place to the west of Saturn, between opposition and conjunction (September 17) eclipses of Rhea take place to the east of Saturn. If Saturn is allowed to drift through a telescopes field of view, it moves to the west.

Transits of the shadow of Rhea are difficult events due to the small size of Rhea's shadow on the face of Saturn. They occur close to mid way in time between pairs of eclipses.

Times of events are adapted from those given by Dave Herald's OCCULT 4 program.


Eclipses of Rhea
Date Time UT Date Time UT
Disappearance Reappearance Disappearance Reappearance
2008 Nov 22 09:04 14:05 2008 Nov 26/27 21:30 02:34
Dec 1 09:56 15:04 Dec 5/6 22:22 03:32
Dec 10 10:48 16:00 Dec 14/15 23:15 04:27
Dec 19 11:41 16:54 Dec 24 00:07 05:20
Dec 28 12:33 17:46 2009 Jan 2 01:00 06:11
2009 Jan 6 13:26 18:35 2009 Jan 11 01:52 06:59
Jan 15 14:19 19:21 Jan 20 02:45 07:44
Jan 24 15:12 20:06 Jan 29 03:38 08:27
Feb 2 16:05 20:48 Feb 7 04:32 09:08
Feb 11 16:59 21:28 Feb 16 05:25 09:47
Feb 20 17:52 22:06 Feb 25 06:19 10:24
Mar 1 18:46 22:43 Mar 6 07:14 11:01
Mar 8 Saturn at opposition, eclipses move from west to east of the planet
Date Time UT Date Time UT
Disappearance Reappearance Disappearance Reappearance
Mar 10 19:41 23:23 Mar 15 08:03 11:52
Mar 19/20 20:24 00:20 Mar 24 08:46 12:48
Mar 28/29 21:08 01:17 Apr 2 09:30 13:45
Apr 6/7 21:52 02:14 Apr 11 10:15 14:42
Apr 15/16 22:38 03:11 Apr 20 11:02 15:39
Apr 24/25 23:25 04:08 Apr 29 11:50 16:36
May 4 00:14 05:05 May 8 12:39 17:33
May 13 01:04 06:02 May 17 13:30 18:30
May 22 01:55 06:59 May 26 14:21 19:27
May 31 02:47 07:56 Jun 4 15:14 20:25
Jun 9 03:41 08:53 Jun 13 16:08 21:21
Jun 18 04:36 09:50 Jun 22 17:04 22:18
Jun 27 05:33 10:47 Jul 1 18:01 23:15
Jul 6 06:31 11:44 Jul 10/11 19:01 00:12
Jul 15 07:31 12:40 Jul 19/20 20:02 01:09
Jul 24 08:32 13:37 Jul 28/29 21:04 02:05
Aug 2 09:36 14:33 Aug 6/7 22:08 03:01
Aug 11 10:40 15:29 Aug 15/16 23:13 03:57
Aug 20 11:47 16:25 Aug 25 00:20 04:53
Sep 17Saturn at conjunction with Sun, eclipses move from east to west of the planet
Date Time UT Date Time UT
Disappearance Reappearance Disappearance Reappearance
Oct 13 18:02 22:24 Oct 18 06:29 10:55
Oct 22 18:57 23:27 Oct 27 07:25 11:57
Oct 31/Nov 1 19:53 00:28 Nov 5 08:20 12:57
Nov 9/10 20:48 01:27 Nov 14 09:15 13:56
Nov 18/19 21:43 02:24 Nov 23 10:10 14:53
Nov 27/28 22:38 03:20 Dec 2 11:06 15:48
Dec 6/7 23:33 04:14 Dec 11 12:01 16:41
Dec 16 00:28 05:07 Dec 20 12:56 17:34
Dec 25 01:23 06:00 Dec 29 13:51 18:25

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