Action pictures always bring it home. In this THEMIS visible light image, we see some towering
dust devils. These are truly monsterous twisters. The largest one is almost a mile high!
This picture was taken in the mid afternoon on a spring day. The majority of pictures returned
to earth of other planets show a landscape frozen in time. Even a recent occurance is often tens
of thousands of years old. But not this one. Ten or twenty minutes would have made a difference!
 To better understand what we are looking at, the
view of the Washington Monument at right is roughly the same perspective. Notice how we mostly
see the top of the monument. From above we would hardly know what it was. But there is a
clue in the photo - the shadow. If we know where the camera is that is taking the picture,
and where the sun is at the moment the picture is taken, then we can use simple math to
calculate the height of the monument. I don't know any of those things for the picture on
the right. I do know them for the picture on the left and it adds up to about a mile high
for the largest dust devil near the bottom.
Some links ASU page for this image ASU context Mars Global Surveyor / USGS context Other dust devil images |