Overview

This 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. Goals

1.2. Outreach

A 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

(1) Observation of the Aureole to constrain Venus atmosphere properties (see description on this link ). Data will be acquired in 3 colors simultaneously, and at higher cadence / sensitivity with an unfiltered detector. All data will be published for analysis by other groups. Our group is in contact with the Venus transit group to arrange data sharing.
(2) High precision light curve in 3 color will be produced, serving as a template for evaluating the prospects of detecting exoplanetary atmospheres during transits
(3) Use Venus disk to probe small scale features on the solar disk (down to few mas scale on solar disk). This is made possible thanks to the high speed camera.

Fig 1: Venus image during the 2004 transit (TRACE spacecraft). The Aureole is visile. Credit: Glenn Schneider, University of Arizona, TRACE mission (NASA).

2. Observing plan

2.1. Summary

Team members: Guyon, Martinache, Clergeon

PROPOSED LOCATION: Mauna Kea, next to Subaru Telescope dome (South side)
Hardware requires acces to AC power

Schedule:

JUNE 4 (2pm - Sunset): Hardware test on Sun
JUNE 4 (Sunset - 10pm): Perform mount alignment on stars and thus facilitate tracking during the event. Leave hardware at summit during the night
JUNE 5, 9am: Arrive at summit
JUNE 5, 7pm: Leave summit

The hardware for the observation is:

355mm diameter telescope (C-14) with computerized mount [link to manufacturer description] . See this picture for idea of scale. Weigth = 110kg without accessories.
Photographic full aperture solar filter , ND3.8 (not safe for viewing by eye - but allows short exposures at high magnification to freeze turbulence and vibrations)
4x Barlow lens, giving 15.6m focal length
Desktop computer
color camera: Canon 550D DSLR (18 Mpix, 14 bit per pix, ~10 e- RON), capturing in RAW mode at 2 frames per second (fps)
greyscale high speed camera: high dynamical range Andor Zyla (5.5 Mpix, 16 bit per pix, 1.2 e- RON), capturing at 100 fps

2.2. Data acquisition details: DSLR camera

The 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 SanDisk

NOTE: 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 camera

The Andor camera sampling is 86mas per pixel (approximately 2x Nyquist).

Acquisition from 30mn before first contact to 30mn after first contact (1hr total)
full frame, 100fps, 16 bit per pix

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.

Fig 2: Sample Sun limb image acquired from Hilo on Apr 22, 2012. Exposure time = 1/250sec at ISO 100. The apparent size of Venus on June 5 is shown as the green circle.

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