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Look at the zoomed in images by the coast. Can you tell the peaks (that is, the ridges) from the valleys? It may seem easy, but you may be tricked by a common optical illusion in satellite images called relief inversion.

All Landsat images are designed to be morning views, so all of these images were taken in the morning. The Sun is to the east and south, so these images are lit from below and to the right. This causes the western and northwestern slopes to appear dark because they face the sun less squarely, and so are less illuminated.

However, we unconsciously expect to see images lit from above. This tricks the brain into believing that mountains are valleys or that craters are mountains. If you look at the image upside-down, with the sun angle generally from the top of the image, you will probably see the image differently.

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Aug. 1, 2011, Landsat 5 (path/row 165/35) — Elburz Mountains, Iran; north up, image lit from below
Aug. 1, 2011, Landsat 5 (path/row 165/35) — Elburz Mountains, Iran; north down, image rotated so it is lit from above

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