Grazing star occultation by the Earthmoon on October 21, 2008
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On October 21, 2008 at about 04h24 UTC the Earthmoon grazed the star SAO 79660 in a height of 31 degrees above the southwest horizon with the dark area of the moon southpol. Thereby the star was occulted and became visible several times by the moon mountaines and moon valleys on the moon horizon. It is remarkable that despite of very dense ground fog ten occultation events could be recorded on video due to the use of an infrared pass filter.
|The earthmoon grazes the star SAO 79660|
Diagram created with Guide 8 from Bill J Gray
|The moon profil at the calculated graze point|
Diagram created with Occult 4 from Dave Herald
This grazing star occultation on the dark moon area was captured with my equipment with a relative high accuracy of some milliseconds and evaluated later.
|Diagram of equipmennt setup|
|The path of the grazing star occultation runs cross through Europe|
|The calculation of the observation point was done in a self made table sheet|
|Position elevation and moon profil require a double parallel shifting of the observation point (OP)|
Correction of observation point = (-224m) + (-2026m) = -2250m shift to the green line for 0m above sea level
|Aerial image of the calculated observation place southwestt from Schirnes - in northern Woodquarter|
Observation position 48° 51´ 05.9" North, 15° 15´ 08.3" East
|The observation place and all the region around was covered by dense ground fog|
When I started to drive to the observation place dense ground fog was around. After arriving at the observation place I could see that the fog was more dense there. No star was visible through the ground fog. Also not the bright Sirius with -1mag. Only the moon was visible but dimmed and with a halo around due to the waft of mist. But I had done all the preparation work for this observation until this moment so I decided to setup my station just to get a confirmation that this observation was impossible through the dense fog.
But because of the use of an Astronomik Planet IR Pro 807 filter and the high IR sensitivity of the WAT-902H2 Ultimate camera the star SAO 79660 with +7.6mag really could be hold visible on the bright and outshined moon limb. A short change to the filters RG850 and RG1000 made the result more worse. Then with the Astronomik Planet IR Pro 807 filter ten events of this grazing star occultation could be recorded.
|The visibility on the ground was only few meters also in the light of the lamp|
Date Observer Position - 3842 Schirnes Observer 2008/10/21 48° 51´ 05.9" North (WGS84) Gerhard Dangl Star 15° 15´ 08.3" East (WGS84) 3830, Nonndorf 12 SAO 79660, +7.6mag 521m (MSL), 565m (WGS84) AUSTRIA
TELESCOPE: Type: Newton Focal length: 1200mm Aperture: 254 mm Magnification: video/primary focus/FOV 16.5'x13.7' (640x576, 1.56"x1.43" per pixel) Mount: Equatorial EQ6 with EQMOD Motor drive: Yes TIMING & RECORDING: Timekeeping: GPS 1PPS Garmin18 LVC + KIWI-OSD Sensor/Camera: WAT-902H2 Ultimate, CCIR, 1/2" Sony CCD-Sensor ICX419ALL Mode of recording: It=20ms (50 Img/s), Video CCIR, AVI, YUY2, Huffyuv, Device of recording: Xpert V-Stream Videograbber USB2.0, Notebook Harddisk Time insertion: KIWI-OSD OBSERVING CONDITIONS: Atmospheric transparency: very bad (dense ground fog) Wind: No Star image stability: fair Temperature: 276 Kelvin (+03 deg Celsius) ADDITIONAL COMMENTS: Predictions with Occult4 WAT-902H2 Ultimate with Astronomik Planet IR Pro 807 Filter and manual cable gain control. Video evaluation accomblished with VirtualDub1.8.5 Only clear glass filter (Astronomik) for CCD protection was used 3-D position and timing with Garmin GPS18 LVC receiving 10 satellites Horizontal dilution of precision 1.1, geoidal separation 44.5m Position shift calculations: Correction for MSL 517m: - 224 meters (path calculated for Mean Sea Level=0m) Correction for profile : -2026 meters Observation point (OP) : -2250 meters
Grazing Occultations near Nonndorf_0m_25cm, Austria E. Longitude 15 14 8.4, Latitude 48 47 13.5, Alt. 0m; Telescope dia 25cm; dMag 0.0 day Time P Star Sp Mag Mag % Elon Sun Moon Cusp angle Distance Azimuth Path formula y m d h m s No D v r V ill Alt Alt o km 08 Oct 21 4 25 7 Gr 79660 K0 7.6 6.8 53- 94 -11 63 ** GRAZE: CA 9.9S; Dist. 9km in az. 20deg. [Lat =48.88-0.25(E.Long-15.24)]
Table with results of the video measurement Phenomen Cause hh:mm:ss.sss Comment ====================================================================== Video start 04:19:09.539 First video frame D1 moon limb 04:24:53.335 (+/- 20ms) R1 moon limb 04:25:05.734 (+/- 20ms) D2 moon limb 04:25:07.334 (+/- 20ms) R2 moon limb 04:25:15.214 (+/- 20ms) D3 moon limb 04:25:15.654 (+/- 20ms) R3 moon limb 04:25:15.774 (+/- 20ms) D4 moon limb 04:25:24.014 (+/- 20ms) R4 moon limb 04:25:26.134 (+/- 20ms) D5 moon limb 04:25:57.054 (+/- 80ms) R5 moon limb 04:26:51.933 (+/- 20ms) Video end 04:30:05.171 Last video frame
Because of the dense waft of mist a low signal/noise ratio exists in the records. Therefor the evaluation of the videos was not operated automatically with Limovie but manually with VirtualDub in single frame modus.
|Video R1, D2
|Video R2, D3/R3|
A report with data of this measurements was created with Occult4 and transfered via email to the relevant autority in Japan for evaluation and further use.
|The reduction of the measurement data to the moon profil|
Created with Occult 4 from Dave Herald
January 26, 2009
Questions and suggestions to => Gerhard Dangl