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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.


Mechanical design Posted on Oct 01, 2011 08:06

We have learned this about timings:

Color filters – it takes from 15 to 45 seconds to change a color filter. Mainly it takes 20 s, with exceptions.

SKE – it takes a full minute to set the SKE.

An image takes 0.3 s to be downloaded and written to disk.

Dome takes about 2 minutes to open.

One circuit of dome takes about 2 minutes.


Observing log Posted on Oct 01, 2011 07:44

Rain on MLO. Moon up.

Tested setting the SKE from a script – this failed. The values for cusp offset and cusp angle were taken from the System_Dataxxx.csv master spreadsheet rather than the script itself (“protocol”).

We actually have no, documented, proof that the setting of the SKE or KEDFs works, right?

Dome and telescope pointing

Observing log Posted on Oct 01, 2011 07:21

Ben has created a map of where the dome should be for a range of telescope pointings. Map works well so far! We are adding data points to it as we go along, and also mapping out the edges of the dome slit at various positions:

A better resolution version is available here:

Comparison of brute force and FFT methods for computing scattered light

Post-Obs scattered-light rem. Posted on Oct 01, 2011 02:11

Tested two methods for scattering light from an ideal moon. The Ideal image is shown upper left (log scale) with a completely dark sky, narrow BS crescent and ES.

Bottom left is the moon after scattering the light using our current PSF and a brute force method — simply add all the pixels in the ideal image multiplied by the PSF. Bottom right is the same, but using an FFT method instead. The scattered light at the edges of the frame is too high to simply use the 512×512 frame in the FFT, instead the idea moon is placed in the center of a 1536×1536 frame, the FFT carried out, and then clipped back to 512×512. Upper right is the ratio of these two methods. There is a lot of structure at a very low level — the display limits on the ratio are set at 0.9993 to 1.0009, and the ratio is with 0.1% of unity everywhere on the frame. This should be sufficiently accurate for our purposes, but we should double check!

The histogram of pixel values in the ratio image is shown below: