Occultations

2008 April 13,

Northern Virginia Astronomy Club meeting

David W. Dunham, IOTAAdopted from a similar talk given at the

2007 Virginia Association of Astronomical Societies, Crockett Park, 2007 Oct. 6

Types of High-Speed Celestial Phenomena

• Total lunar occultations

• Lunar grazing occultations

• Planetary occultations

• Asteroidal occultations

• Occultations by comets, natural satellites, and trans-Neptunian objects

• Lunar meteor impacts

IOTA = International Occultation Timing Association

• Occult – Latin for “to cover” – one astronomical body by another

• Lunar occultations of stars are most common• Timings used to be used to determine longitude and the

lunar orbit (now by laser ranging)• Then they were used to refine astrometric data until

Hipparcos data did most of that job better• Now timings used to map lunar profile, useful for solar

eclipse analysis & possible polar ice deposits (there’s new interest in grazes to refine the polar region data of lunar digital elevation models that will be used for planning observations by Lunar Reconnaissance Orbiter and other lunar missions that will be launched in the next few years)

• Many close double stars discovered during occultations; some stellar angular diameters measured

Lunar Profile from Graze of delta Cancri – 1981 May 9-10

Circled dots are Watts’ predicted limb corrections

Grazing Occultation Videos

 Graze, 5.7-mag. Arietis, Moon 10%-, Hockley, Texas, 2007 June 12 – c:\avi07626\MuArietis_N station.avi

Graze, 2.5-mag. close double star Scorpii, 8%+, Rockaway Beach, New York City, 2003 Dec. 21 –c:\avi07603\DeltaSco122103.avi

Graze, 1.0-mag. Spica, 37%-, w. of Delta, Utah, 2005 Dec. 25 –c:\avi07603\Spica122505seq2.avi (8 in. SCT & PC164C) andc:\avi07603\Spica_50mm122505_3.avic:\graze\muari612\Bob Sandy u Ari 070612\Bob . .avi

Occultations of Stars by Asteroids• Difficult to predict; 1st seen in Sweden in 1958• As orbits & astrometric techniques improved,

more observed in mid to late 1970’s• Predictions considerably more accurate in 1997

with release of Hipparcos space astrometry data• Observations determine the sizes, shapes,

satellites, and accurate positions of the asteroids• Accurate orbits allow mass determinations from

measuring perturbations of the orbits• Very close double stars and stellar angular

diameters resolved• Geometry shown in next figure• More distant objects (Trojans, Centaurs, TNO’s)

harder to predict but more valuable

Asteroidal Occultation Videos

Occultation of Regulus by (166) Rhodope, Montestirio, Spain, 2005 October 19 with 50mm telephoto lens – c:\avi\mp166reg.avi

Occultation of 9.5-mag. Star by Alstede, Oraville, MD, 2005 November 26 with 8-in. SCT & PC164C & f/3.3 focal reducer

Grazing occultation of 6.7-mag. Star by Thusnelda, Runyon, FL2007 Dec. 18 with 4” Meade & Collins I3 image intensifier – c:\asteroid\20071221\7FTALR41.asf

Later – Dike events, c:\avi\mp99xxx.avi

1999 Leonids Lunar Impactsrecorded Nov. 18 with 5” telescope at Mt. Airy, MD

Leonid Lunar ImpactRecorded 2001 Nov. 18, 23:19:15 UT, Laurel, MD

confirmed by Tony Cook at Arlington, VAand Roger Venable, Augusta, GA

Methods of Observing High-Speed Celestial Phenomena

• All methods need UTC time base (from VNG before shutdown, WWVH, WWVB, GPS, etc.)

• Visual, eye-and-ear• Visual, stopwatch (with assistants for multiple events)• Visual with tape recorder• Video, least expensive system• Video, airplane transport• High-speed photoelectric systems• CCD systems (drift scan method)• Remote sites (record more chords)

Visual ObservationNote on telescope box, WWV receiver (Timekube),

GPS receiver, eyepiece, tape recorder, cell phone

Items for video observation• PC164C camera, $130, www.supercircuits.com• PA3 microphone & tab adaptor• 12-volt battery & video connector• 1.25” to C – adaptor, $35, Adirondack video• RCA cable, Radio Shack• For SCT’s, recommend Meade f/3.3 focal reducing lens• Input-capable camcorder or portable 9-in. TV/VCR combo

unit (Sylvania unit on amazon.com for under $100 US)• Shortwave radio, WWV at 5 & 10 mHrtz, Radio Shack• GPS video time inserter (Kiwi has best error checking)• In USA, Europe, & Japan, GPS time can be checked with

clocks that set themselves with long-wave time signal (WWVB in USA, DCF77 in Europe)

The New Sensitive Cameras• The Watec 902H camera is over 4 years old, costs about $300, and has

been discussed at ESOP by A. Elliott and E. Bredner. It is excellent, seeing more than you can with an eyepiece, & is a little noisy.

• The PC164C, from www.supercircuits.com since 2001 Dec., has the same CCD chip as the Watec but 1/3rd inch rather than ½ inch; it is almost as sensitive with a 2/3rds smaller field, but at $130, it is less than half the price. It seems to be a little less noisy than the Watec.

• A small adapter tube from Adirondack Video for $35 screws into these cameras (C-mount) so they can be used with any 1.25-in. eyepiece holder, only about 1 inch long, the PC164C is 2 inches long and light.

• I believe there is a PAL version of the PC164C, but if it is hard to get, a similar camera for a similar price, CCTV Camera’s Model 2006X costs 69 pounds, with the same CCD chip as the PC164C. This British camera is PAL; see www.rfconcepts.co.uk/cctv-camera.htm .

• These cameras allow accurate timing of fainter star lunar grazes and asteroidal occultations, the latter especially important since visual timings of them have larger errors; there are more opportunities!

• Focal reducing lenses, esp. f/3.3 Meade, give much larger FOV.

Cheap Video SystemPC-23C, RCA TV/VCR combo, small 12-volt battery, optional f/6.3 focal reducer

Compact Video SystemWatec 902h, Meade f/3.3 focal reducing lens, small 12-volt

battery (not shown), camcorder

Air carry-on system (R. Nugent)

www.pfdsystems.com

Robust GPS video time insertion using the 1PPS signal from a Garmin 18 LVC GPS receiver

Station “B”, Sony Digital Camcorder

No Telescope, just an undriven good camcorder! I set the Moon just outside the field, above and left, 8 min. before the graze. This station had 5 D’s and 5 R’s, more than any other; although it had less than 1000th the aperture of the 1m telescope on Hokkaido, it was more successful!

Orion 8x50 finder scope video system

By Scott Degenhardt

The Pleiades recorded with the 8x50 finder system

Using PC164C camera and Mogg focal reducer, by Scott Degenhardt

Maps for the grazing occultation of Arietis on 2007 June 12

Showing locations of the expeditions, and of the observers at the expedition near Hockley, Texas

Path across Texas; total occultation is south of path

Our expedition

Rick Frankenberger

Path near Waller & Hockley, Texas (US 290 area)

Hockley

A

meet

Offsets are -0.7 and -1.7

Area shown in detailin next slide

Details of Hegar Rd./Imhof Rd. sites used n. of Hockley, Texas

met

R. Sandy

R. Nugent

P. Maley

Dunham N. remote/Cudnik

D. Dunham visual

D. Clark (2)

D. Stockbauer

D. Dunham S. remote

Light curve from Bob Sandy’s video recording of the

2007 June 12th grazing occultation of Arietis

Reduction Profile of Grazing Occultation of the Double Star Arietis (ZC 399) observed in Texas and Louisiana,2007 June 12

2007 Oct. 17 graze of ZC 2702

2007 Oct. 17 graze of ZC 2702

2007 Oct. 17 graze of ZC 2702

Remote Stations for Asteroidal Occultations• Separation should be many km, much larger than for grazes, so tracking times &

errors are too large• Unguided is possible since the prediction times are accurate enough, to less that

1 min. = ¼• Point telescope beforehand to same altitude and azimuth that the target star will

have at event time and keep it fixed in that direction• Plot line of target star’s declination on a detailed star atlas; I use the Millennium

Atlas• From the RA difference and event time for the area of observation, calculate

times along the declination line• Adjust the above for sidereal rate that is faster than solar rate, add 10 seconds for

each hour before the event• Can usually find “guide stars” that are easier to find than the target• Find a safe but accessible place for both the attended & remote scopes• Separation distance limited by travel time & total tape record time• Roger Venable uses VCR’s with timed starts, allows larger separation• Better to have remote sites attended for uncovering telescope (dew prevention)

and starting equipment later (allows larger separations), and security

Finder chart for occultation of 10.3-mag. star by (1685) Toro on 2004 August 10

Finder chart for remote station for occultation by (1685) Toro on 2004 August 10

Please do not disturb -

 Precisely Pointed AutomaticAstronomical Station toRecord the eclipse of the star TYC 0483-01460-1 by the asteroid 491 Carina at 4:28 am PDT this morning If you have any questions or concerns, call my cell phone, 301-526-5590, I’m nearbyDavid Dunham,International Occultation Timing Assoc.

Successful Remote + Attended Positive Observations from 2 or more stations

• 2001 Sept. 7, 9 Metis, northern California, D. Dunham• 2002 April 21, Oriola, Washington, S. Preston• 2003 Jan. 17, Bathilde, Georgia, R. Venable• 2004 July 1, Nanon, s. Calif., D. Dunham, but D. Stockbauer was at “remote” site, turned on recorder without changing

pointing• 2004 Oct. 6, Ute, North Carolina, D. Dunham• 2004 Oct. 29, Flora, New Mexico, D. Dunham• 2005 Mar. 12, Bathseba, Georgia, R. Venable • 2005 May 13, Dufour, New South Wales (AU), D. Gault (home “remote” & mobile)• 2005 Dec. 1, Laurentia, Georgia, R. Venable• 2005 Dec. 1, Dike, Maryland & Virginia, D. Dunham (3 positives, star close double)• 2005 Dec. 3, Europa, California, D. Dunham• 2006 Jan. 28, Veritas, North Carolina, D. Dunham • 2006 Feb. 24, Turandot, Indiana, D. Dunham• 2006 Feb. 26, Abnoba, Florida, R. Venable• 2006 June 12, Pallas, Georgia, R. Venable (4 positives! Widest separation)• 2007 Jan. 10, Nysa, Georgia, R. Venable• 2007 Feb. 21, Thisbe, Florida, D. Dunham• 2007 Feb. 28, Nemausa, California, D. Dunham• 2007 Apr. 13, Fortuna, Virginia and N. Carolina, D. Dunham (2 +, 1 miss, my widest separation)• 2007 Apr. 22, Dike, Florida, R. Venable• 2007 May 24, Papagena, Maryland and Pennsylvania, D. Dunham (3 positives)• 2007 Sept. 11, Senta, New South Wales (AU), D. Gault• 2007 Nov. 20, Amalia, Georgia, R. Venable• 2007 Dec. 18, Thusnelda, Florida, D. Dunham• 2008 Jan. 14, Sicilia, Alabama, R. Venable (star close double)• 2008 Feb. 10, Dynamene, North Carolina, R. Venable• Many other cases where 2 stations were run and 1 had an occ’n & the other a miss, especially by Roger Venable; example was

my observation of Rhodope occulting Regulus on 2005 October 19

The video files are In c:\avi\mp99*.avi

Klotilde occultation

May 8th graze

May 12th graze

Oct. 6th graze

For More Information about IOTA and observing occultations:

• http://iota.jhuapl.edu - my web site; /iotaindx.htm for items of recent interest; /exped.htm for Mid-Atlantic occultations

• Updates by e-mail – dunham@starpower.net • http://www.lunar-occultations.com/iota – the main IOTA web

site• http://www.asteroidoccultations.com - asteroidal occultation

updates• http://www.poyntsource.com/New/Global.htm - asteroidal

occ’n maps, station & star lists• http://www.asteroidoccultations.com/observations/NA -

Results of asteroidal occ’n observations, etc.• http://www.pfdsystems.com – Kiwi video time inserter