Venus 2012 transit |
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Show content only (no menu, header)OverviewThis document describes the observing plan for the Venus transit June 5th, 2012 from Mauna Kea. The goals of the observation are both scientific and outreach as detailed below.1. Goals1.2. OutreachA color movie of the event will be produced at high angular resolution (~0.3 arcsecond angular resolution if atmospheric seeing is below ~2 arcsecond). A high contrast greyscale video of the ingress will also be produced, showing sunlight refracted by Venus's atmosphere.1.3. Science
2. Observing plan2.1. SummaryTeam members: Guyon, Martinache, Clergeon
PROPOSED LOCATION: Mauna Kea, next to Subaru Telescope dome (South side) Schedule:
The hardware for the observation is:
2.2. Data acquisition details: DSLR cameraThe DSLR camera offers 0.057 arcsec per pixel scale. In the R and B channels, the effective sampling is 0.114 arcsec, close to 1.5x Nyquist. The sampling is finer in the G channel.
BEFORE AND DURING INGRESS: ISO 200 RAW camera mode 3 frames per second in AEB mode (EV step = 2): 1/125 sec, 1/30 sec, 1/8 sec
DURING TRANSIT: 3 frames per second ISO 200 1/125 sec exposure RAW camera mode
DATA VOLUME: 20MB per frame -> 60MB per second = 18 mn for a 64 GB card, 36 mn for a 128 GB card TOTAL DATA = 60MB x 3600 sec x 6hr = 1.3 TB (64800 shots) Data transfer speed M6500 card reader, 8GB SanDiskNOTE: Due to risk of camera shutter failure (mean time between failure = 90,000 shots, compared to 64,000 shots planned), a spare camera body will be ready for swapping within 1 min of failure. 2.3. Data acquisition details: Andor cameraThe Andor camera sampling is 86mas per pixel (approximately 2x Nyquist). Acquisition from 30mn before first contact to 30mn after first contact (1hr total)
DATA VOLUME: rate: 11 MB per frame -> 1.1 GB per second TOTAL DATA = 1.1 GB x 3600 sec = 4 TB (360,000 shots) Appendix: Initial hardware test (Apr 22, 2012, Hilo)The imaging system was tested on Apr 22 from Hilo to test hardware, calibrate exposure times and estimate the feasibility of science goals. Due to relatively poor seeing (light path to Sun went over a dark painted metal roof), the images are not very sharp, but the test was otherwise successful. The image below shows a single exposure acquired with the camera. The image is underexposed by a factor 4 (Sun surface contributes to 2000 ADU) compared to ideal settings, explaining the noise in the image. Unsharp masking was used to enhance small features.
Based on this test, the ideal exposure values are : ISO 200, exposure = 1/125sec Transit parameters: Sun diameter = 1891.500 arcsec Venus diameter = 57.8 arcsec Page content last updated: 27/06/2023 06:35:52 HST html file generated 27/06/2023 06:34:41 HST |