Blog Image

Earthshine blog

"Earthshine blog"

A blog about a telescopic system at the Mauna Loa Observatory on Hawaii to determine terrestrial albedo by earthshine observations. Feasible thanks to sheer determination.


Control Software Posted on Oct 04, 2011 20:18

One of the scripts uses the MEDIAN ADJUST command – it adjusts the key word for exosure time so that a better guess is used, based on the previous exposure time and attained flux level. It seems to work in the DOMEFLAT_COMMANDED.csv script, except for B and VE2 filters, where the exposure times suggested is 180 seconds. This is the limit (to avoid wasting too much time) and the corresponding images are underexposed. This is basically because the CCD camera is RED-sensitive, not BLUE-sensitive, and because the paint on the inside of the dome at MLO is not very reflective at red wavelengths. The V, VE1 and IRCUT images are properly exposed to about 51000 counts as they should be.


Observing log Posted on Oct 04, 2011 19:51

Apparently managed to ‘unstick’ the previously stuck filter-wheel stage that caused blocking of the FOV by the edge of the aperture of the stage that holds the SKEs. This was done from the Engineering Mode by ‘finding the homes’. The Large Rotary Stage did not reset in such a way that the green light indicating success ever lit up. The Little Rotary Stage rotated, cleared the blockage, and its light lit up.

PSF in a Canon 35 mm camera

Exploring the PSF Posted on Oct 04, 2011 14:45

We decided to look at the scattered halo light around the moon in a conventional 35 mm Canon camera, out of sheer curiosity.

The field of view of the Canon of about 10 degrees across, with images of 3888×2592 pixels. There is a pincushion effect toward the very edges but otherwise the halo is well traced. 12 images starting from an exposure time of 1/2500 seconds and increasing exposure time by factors of two at each step were taken. The images were taken from Chris’ back garden in Sydney on a very clear night in September 2011.

Upper plot: halo around the saturated moon (seen at left) for the five longest exposures. The uniform separation of the profiles by 0.3 (in the log) is just as expected for factors of two increase in the exposure times, so the system appears to be linear. Lower plot: log-log plot of the halo flux versus distance shows a very closely followed power law with slope ~ -1: this we call a “Toto” profile (= r^-1). The earthshine camera instead shows a “Mitzi” profile, r^-3, which is as expected for a diffraction limited telescope. A 35 mm camera has a great deal more scattered light!

Papers we may need for reference

Relevant papers Posted on Oct 04, 2011 11:36

Andor camera test report, Darudi.

Darudi and Rodrigo report on Spectral Analysis of Earthshine telescope.

Astro-Physics v4.12 manual for Keypad:

SPIE paper by the team, on the telescope:

Dravins et al 1998:

Dravins et al 1997a (the scintillation figure is on p 186):

Dravins et al 1997b:

Bernstein 2007 (with table of PSF alfa’s):

Middlemass et al 1989 (interesting discussion of color-dependency in PSFs):

The Chae paper showing the alogorithm for calculating flat fields from dithered observations of extended sources.