Earlier in a question on this website, I saw the following picture:

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If you look to the right side of the moon, you will see a massive yellow transparent area.

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I am wondering what caused the yellow, anyone have ideas?


1 Answer 1


IINM, the EPIC camera on the DISCOVR spacecraft takes several images through different filters, which are then combined to get a "true color" image. There's enough of a delay between taking the first image and the last image that the Moon moves through the field of view a little bit, such that you see a "shadow" of where the Moon was in one of exposures (first or last, not sure which).


The first EPIC image, released by NASA on July 6, 2015, shows the full sunlit Earth from 916,651 mi (1,475,207 km) away, centered on the Americas. The Earth Polychromatic Imaging Camera (EPIC) takes images of the sunlit side of Earth for various Earth science monitoring purposes in ten different channels from ultraviolet to near-infrared. Ozone and aerosol levels are monitored along with cloud dynamics, properties of the land, and vegetations.

EPIC has an aperture diameter of 30.5 cm (12 in), a focal ratio of 9.38, a field of view of 0.61°, and an angular sampling resolution of 1.07 arcseconds. Earth's apparent diameter varies from 0.45° to 0.53° full width. Exposure time for each of the 10 narrowband channels (317, 325, 340, 388, 443, 552, 680, 688, 764, and 779 nm) is about 40 ms. The camera produces 2048 × 2048 pixel images, but to increase the number of downloadable images to ten per hour the resolution is averaged to 1024 × 1024 on board. The final resolution is 25 km/pixel (16 mi/pixel).

This means that the color images we see are not reconstructed from three RGB filters that simulate human color perception, but are rebuilt from three or possibly more narrow-band filter channels, and there's more than one way that that could be done.

The EPIC website itself says:

These images were created using the bands from EPIC that are within the human visual range. They have been color and brightness adjusted to represent what a conventional camera would produce.

Note that the natural color imagery was fully reprocessed earlier this year, resulting in a new collection of imagery. The filenames and timestamps for those images have changed as well to reflect the difference in processing. The new processing has allowed for an expansion of available imagery as well. Updated lists of available images and file names can be retrieved using the EPIC API.

On the site's EPIC page you can read more:

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Figure 6. The EPIC double filter wheel

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Figure 7. Shutter wheel assembly showing 3 shutter positions, 1) Narrow, 2) Medium, and 3) wide.

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Figure 4. Schematic of the EPIC telescope.

  • $\begingroup$ I had a similar idea when reading the question. $\endgroup$
    – Uwe
    Nov 21, 2019 at 22:36
  • $\begingroup$ Answers are always better if they can cite or link to sources or references that support factual information that's stated and provide readers with additional reading material. I've added some relevant info and a bit more, please feel free to roll-back or edit further. $\endgroup$
    – uhoh
    Nov 21, 2019 at 23:47
  • $\begingroup$ The movement of the moon! Genius! It hadn't occurred to me that the layers could've been snapped that far apart from each other. I wonder how short you'd need the exposures to be to avoid it completely. I also wonder if the ordering could minimize it... $\endgroup$ Nov 22, 2019 at 14:33

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