Lunar Occultation Highlights for 2005

Nothing else in the sky beyond our atmosphere happens so fast. Perhaps you’ve watched in a small telescope as the edge of the Moon creeps up on a star. The point of light appears to sit on the Moon’s limb for a few seconds, then poof! — it’s gone. About an hour later, the star reappears just as abruptly on the Moon’s other side. The startling suddenness of these events proves that stars have very tiny angular sizes measured in milliarcseconds, smaller than could usually be measured any other way until recently.

All skywatchers should mark their calendars to catch the best of these occultations. Even more satisfying is timing them accurately, a task that’s easier than many observers think. You can make good timings by calling out an event as you see it to a tape recorder while time signals are playing in the background; this method can fix the time of an event to a few tenths of a second. Better timings can often be made just by pointing a camcorder into the eyepiece of your telescope while recording audio time signals; in this case we can identify the 1/30-second interval between two frames when the occultation happened. Some stars are so bright that you can zoom in on the Moon with a camcorder directly — you don’t even need a telescope.

Once again, we at the International Occultation Timing Association (IOTA) provide information about the events visible throughout the world in the coming year. The emphasis here is on those that can be seen from North America, Europe, Australia, and New Zealand, which are populated with many active observers. Only the brightest events can be mentioned, and a number of details (star's magnitude, lunar illumination, etc.) are not included in this Web story. The complete article appears in the January 2005 issue of Sky & Telescope, page 77.

Background Details

In 2005 the Moon will cover bright Antares, Spica, Mars, Venus, and Jupiter, as well as many 2nd- to 4th-magnitude stars. It will pass over the Pleiades several times. Regional tables that summarize the occultations of bright and double stars are available in the January 2005 issue of Sky & Telescope. (Tables listing the occultations of planets and the Pleiades can be found in this article on page 6.) However, it’s important to realize that a star’s disappearance or reappearance can occur up to two hours earlier or later than the stated hour, depending on your location; to create a 2005 timetable accurate for your site, you’ll need to write IOTA and ask.

A grazing occultation is visible within a mile or so (2 to 3 kilometers) of an occultation’s predicted northern or southern limit. There you may see the star wink off and on several times as it skims behind hills and valleys near the Moon’s north or south pole. Observers spaced across the graze path will time different sequences of events, which can be analyzed to map the lunar-limb profile. Visual timings are fine for grazes, since their scientific value depends more on knowing each observer’s geographical location accurately than on obtaining timings to better than, say, a half second. Grazes are important for mapping the Moon’s possibly ice-rich polar regions, because the laser aboard the US Naval Research Laboratory’s Clementine spacecraft did not reach those areas during its 1994 mapping mission from lunar orbit.

Grazes are the most dynamic, interesting, and valuable kind of lunar occultation. The year’s best grazes are plotted on the maps with this article.

Occultations of Bright Stars for North America in 2005

Occultations of Bright Stars for Europe in 2005

Occultations of Bright Stars for Australia and New Zealand in 2005

Special Events in 2005

First-magnitude stars. A four-year series of occultations of the red supergiant Antares begins this year, starting in the Northern Hemisphere. Antares’ 5th-magnitude companion was discovered during an occultation early in the 19th century.

Late in 2005, a short series of Spica occultations begins. Spica is a tight binary star with nearly equal components, but these are too close to resolve even during lunar occultations. However, a more distant 8th-magnitude companion to this pair is suspected from previous occultations; more about it might be revealed this year, especially during dark-limb southern-limit grazing occultations. The Antares and Spica occultations can be seen with a telescope during the daytime from some areas.

Eclipses. In 2003 and 2004, occultations of many faint stars could be seen during total lunar eclipses, but none will be visible during this year’s lunar eclipses on April 24th (penumbral) and October 17th (shallow partial). More interesting will be the annular eclipses of the Sun — lunar occultations of the brightest star of all! — on April 8th in Panama and northwestern South America, and on October 3rd in Iberia and Africa. IOTA encourages timing of Baily’s Beads phenomena on the Moon’s limb from locations near the edges of the paths of annularity during these eclipses. Information about planned IOTA expeditions to Panama in April and to Tunisia in October is at www.eclipsetours.com. European observers will also try to time Baily’s Beads during the October eclipse from Spain and Portugal.

To indicate the Moon’s brightness and whether the object will enter or leave on the dark limb, the lunar phase is listed in the planet and Pleiades occultation tables below as the percentage of the Moon’s disk that is sunlit, followed by “+” for waxing and “–” for waning.

When the Moon is waxing (on its way to full), stars almost always disappear on the Moon’s dark limb, where they are easy to watch. The reappearance happens on the bright limb, which overwhelms most stars with its glare and makes them too hard to watch or time.

When the Moon is waning, the sequence is reversed: disappearances happen on the bright limb and reappearances on the dark limb. Reappearances always require more care, since you need to be looking at just the right moment at the right part of the Moon’s limb.

Planets. The three brightest major planets will be occulted in 2005. There is probably little new that can be learned from these events in this age of space exploration, but they’re still interesting to watch. The controversial “ashen light” that some observers have reported on Venus’s dark side might be observed briefly during a lunar occultation, but both of this year’s events occur at night only in polar regions where there are few observers. And for both events Venus is mostly sunlit.

Jupiter and its Galilean satellites are occulted most often. These events come during the first half of 2005, concluding the series that started late last year. Almost all of the lunar occultations of planets this year occur in the Southern Hemisphere.

Planets Occulted in 2005
Date	UT (h)	Planet	Mag.	Diameter	Moon (%)	Area of Visibility
Jan. 4	1	Jupiter	-1.6	36"	47-	Africa, SW Australia
Feb. 27	14	Jupiter	-1.9	42"	89-	S Australia, Antarctica
Mar. 26	15	Jupiter	-2.0	44"	99-	SW Australia, Antarctica
Apr. 22	17	Jupiter	-2.0	44"	97+	Africa, Antarctica
May 19	22	Jupiter	-1.9	42"	82+	S. America, S. Africa
May 31	10	Mars	+0.5	7.8"	40-	S S. America, Africa
June 16	6	Jupiter	-1.7	38"	62+	N Australia, NZ
July 13	18	Jupiter	-1.5	36"	41+	S. America, Antarctica
Aug. 8	5	Venus	-3.4	13"	9+	Alaska
Sept. 7	8	Venus	-3.5	13"	12+	Africa, Antarctica
Dec. 12	4	Mars	-1.1	15"	87+	E Siberia

The Pleiades. A highlight of 2005 will be occultations of the Pleiades cluster, the start of a four-year series. As the table below shows, most of these are in the Southern Hemisphere, but late in the year Hawaii and southern Asia will be treated to Pleiades events.

Pleiades Occultations in 2005
Date	UT (h)	Moon (%)	Visibility area
Apr. 11	23	10+	Chile
July 2	19	12-	New Zealand
July 30	2	31-	W Australia, Indonesia
Aug. 26	7	53-	South America
Sept. 22	18	75-	Hawaii, E Australia
Oct. 20	4	92-	South America, N Africa
Dec. 13	20	96+	Africa, S Asia

Also occulted will be the much smaller and fainter clusters NGC 2331 in Gemini and NGC 6520 in Sagittarius with about 30 stars each, all of them 9th or 10th magnitude or fainter.

For More Information

Japanese photographer Akira Fujii caught the crescent Moon's very close approach to Spica on November 29, 1994. A new series of events involving Spica begins late this year.

Timetables of lunar occultations for 17 North American stations are given in the 2005 Observer’s Handbook of the Royal Astronomical Society of Canada. About 30 occultations of stars as faint as 5th magnitude are listed for each location. The handbook also has maps of northern and southern limits for 248 occultations of stars to magnitude 7.5 for the US, Canada, and northern Mexico.

IOTA’s Walt Robinson (515 W. Kump, Bonner Springs, KS 66012; [email protected]) will compute a custom 2005 lunar occultation timetable for you if you send him accurate geographical coordinates and an e-mail address or a long, self-addressed, stamped envelope. European residents should instead contact Hans Bode, Bar-told-Knaust Strasse 8, D-30459 Hannover, Germany; [email protected].

The International Lunar Occultation Center in Tokyo collects and analyzes timings; your observation reports can be sent to them at [email protected] using forms available from IOTA’s Web site.

Annual membership in IOTA costs $30 in North America ($35 overseas) and includes free graze predictions for stars brighter than 9th magnitude, local circumstances for the approaches of asteroids to stars, descriptive materials, and a subscription to the Occultation Newsletter (available separately for $20, more overseas). A Web-based membership is available for $15.

Also visit Sky & Telescope's occultation page where you can learm more about occultations in general. Details about specific major events are usually posted on the page about one month before the occultation occurs.