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What is the red in this picture of earth? At first we thought it might be pollution, but Jupiter also has red.

Picture source: https://education.seattlepi.com/primary-movements-motions-earth-4701.html

enter image description here

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    $\begingroup$ Land mass? I guess a good question would be why does this appear red ... so the question might need to be rephrased a bit? $\endgroup$ – Tosic Dec 3 '20 at 10:59
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    $\begingroup$ The "red" areas are North and South Africa, and Arabia, so desserts. $\endgroup$ – Steve Linton Dec 3 '20 at 11:07
  • $\begingroup$ That link (seattlepi) continues to be blocked (it has happened before) due to a bad cert error which Firefox will (sensibly) block a site as it is not valid for that website and the site and pages from it cannot be authenticated. $\endgroup$ – StephenG Dec 3 '20 at 12:41
  • $\begingroup$ I think your image is a bit saturated; that's why it looks red. $\endgroup$ – fasterthanlight Dec 3 '20 at 13:38
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    $\begingroup$ Even when I ignore the certificate warning, the linked webpage is not available due to legal reasons here (geoblock?) $\endgroup$ – planetmaker Dec 3 '20 at 18:26
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tl;dr: This is the famous "Blue Marble" image taken by one of the Apollo 17 astronauts. This particular rendering is labeled in Wikipedia as

Image redone with colors

From Wikipedia's The Blue Marble:

The Blue Marble is an image of Earth taken on December 7, 1972, from a distance of about 29,000 kilometers (18,000 miles) from the planet's surface. It was taken by the crew of the Apollo 17 spacecraft on its way to the Moon, and is one of the most reproduced images in history


The question asks for:

Source of red in earth's photographs

What is the red in this picture of earth?

This is not asking what land mass appears red, it asks for the source of the red color.

That's a good question and I think it has a disappointing answer in (at least) two parts:

  1. This is an old image and has been reproduced many times. Below are another versions of it. As it continues to be reproduced and "color corrected" each time the original colors may be lost in reproductions.
  2. If the image was from a weather or other Earth-observation satellite, they would be false colors generated for coding the real wavelengths that the satellite imaged into human interpretable colors, since rarely if ever is a space-based Earth-imaging camera fitted with regular RGB color filters that match Human's sensitivities. Instead, filters are optimized to tell the scientists that will be reviewing each satellites data best whatever it is that those particular scientists are looking for. Very often "red" in images is used to code infrared wavelengths, but since some satellites have several or even a dozen or more wavelength channels, anything can happen.

The link from the article is: https://l.hdnux.com/350x235p/photos.demandstudios.com/getty/article/41/249/87467861_XS.jpg

Here's a bigger one: https://images.unsplash.com/photo-1564053489984-317bbd824340?ixlib=rb-1.2.1&ixid=eyJhcHBfaWQiOjEyMDd9&auto=format&fit=crop&w=2014&q=80

Here it is again at https://www.innovatorsmag.com/enter-earth-school/ and the credit says "Photo by The New York Public Library on Unsplash" and while they are amazing I didn't know that The NYPL has a branch in Space!

and here it is cropped below, and then analyzed. It looks like the center of the image is roughly 29 degrees South latitude, and 37 degrees East longitude.

It's not from a geosynchronous weather satellite, it's from something that's far from Earth but in an unusual orbit.

Earth's axis is tilted 23 degrees to the ecliptic, and for example DSCOVR's halo orbit around Sun-Earth L1 is big and Wikipedia tells us that it

orbits the L1 point in a six-month period, with a spacecraft–Earth–Sun angle varying from 4 to 15°

so that means that at about 1.5 million km from Earth it could have easily taken this image.


enter image description here enter image description here

Click for larger sizes. left: credit: The New York Public Library and CC BY right: approximate subsurface point of spacecraft is at -27 degrees latitude, so not from a geosynchronous spacecraft.

But it wasn't taken by DSCOVR!

Going to NPYL at unsplash: https://unsplash.com/@nypl then searching for "earth from dscovr" I found https://unsplash.com/photos/yEauzeZU6xo and the caption reads:

Full Disk Earth, Apollo 17, 1972

So after all this hullabaloo about narrow band filters from satellites this turns out to be a hand-held photograph from a large format 70-millimeter Hasselblad camera by an Apollo 17 astronaut using Kodachrome or whatever!

So the image is nearly 50 years old and has been reproduced a zillion times in a zillion ways, and the exact colors seen reproduced today on some random website are meaningless!

From https://commons.wikimedia.org/wiki/File:The_Earth_seen_from_Apollo_17.jpg#/media/File:The_Earth_seen_from_Apollo_17_(AS17-148-22727).jpg

Image redone with colors 2,400x2,400 (3.33 MB)

"The Blue Marble" is a famous photograph of the Earth taken on December 7, 1972 by the crew of the Apollo 17 spacecraft en route to the Moon at a distance of about 29,000 kilometers (18,000 statute miles). It shows Africa, Antarctica, and the Arabian Peninsula.

From NASA Johnson Space Center's https://eol.jsc.nasa.gov/SearchPhotos/photo.pl?mission=AS17&roll=148&frame=22727

Image Caption: This classic photograph of the Earth was taken on December 7, 1972. The original caption is reprinted below:

View of the Earth as seen by the Apollo 17 crew traveling toward the moon. This translunar coast photograph extends from the Mediterranean Sea area to the Antarctica south polar ice cap. This is the first time the Apollo trajectory made it possible to photograph the south polar ice cap. Note the heavy cloud cover in the Southern Hemisphere. Almost the entire coastline of Africa is clearly visible. The Arabian Peninsula can be seen at the northeastern edge of Africa. The large island off the east coast of Africa is the Republic of Madagascar. The Asian mainland is on the horizon toward the northeast.

enter image description here

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    $\begingroup$ Appreciate the correction. Could you condense this answer a bit? $\endgroup$ – Mike G Dec 3 '20 at 15:03
  • $\begingroup$ @MikeG agreed! Yes this was written in real time and reads chronologically, and I ran out of time. I'll tidy this up in the next few hours. $\endgroup$ – uhoh Dec 3 '20 at 22:44
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    $\begingroup$ @MikeG I've made a first pass, I'll try to do more at some point soon... $\endgroup$ – uhoh Dec 4 '20 at 3:19
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If you look closely at the central part of Africa, which is mostly covered with clouds, you may seem some greenish color between clouds. Equatorial Africa is mostly lush and and green. Most of Northern Africa is the Sahara Desert, and there are also large deserts in Southern Africa.

So if the clouds weren't in the photograph, one could see all of africa clearly, with desert in the north and south and greenish vegetation in the center.

So the "red" color, which is actually some combination of reddish, orangish, yellowish, brownish, tawney, and sandy shades, is the various colors and shades of desert regions seen from outer space.

Since that photo has been copied, and copied, and copied many times since it was taken, it is quite possible that the copy you saw has somewhat different shades than the original photo. It is possible that the copy you saw exaggerated the redness of the desert regions and the actual colors were less red.

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Where is there red in your image? If you mean the yellow/orange-ish parts of land masses, these are deserts. Your Blue Marble image is a bit darker; the original image is black-and-white while the colored version is this one, it's a bit brighter than your image and the deserts are clearly yellow: enter image description here

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  • $\begingroup$ The original image is in color. $\endgroup$ – Mike G Dec 3 '20 at 15:00
  • $\begingroup$ @MikeG I think it was black-and-white and it's actually upside down. commons.wikimedia.org/wiki/… $\endgroup$ – Greenhorn Dec 3 '20 at 15:03
  • $\begingroup$ @Greenhorn your link shows a link to a NASA database where we see that it is film magazine number 148. You can see all of the 70mm Hasselblad images from that film magazine are color. $\endgroup$ – uhoh Dec 11 '20 at 14:50

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