HOLY FRAK! Moon transits Earth!

Bad Astronomy
The entire universe in blog form
July 17 2008 1:19 PM

HOLY FRAK! Moon transits Earth!

Regular readers know I am deeply impressed with astronomical imagery, and I tend to be a little over-the-top on occasion when describing it.

However, having said that, let me be very clear: the following is just about the coolest thing I have ever seen.

Phil Plait Phil Plait

Phil Plait writes Slate’s Bad Astronomy blog and is an astronomer, public speaker, science evangelizer, and author of Death From the Skies!  


First, the setup. The Deep Impact spacecraft was the one that smacked a chunk of copper into a comet so that we could see what materials were below the surface. After the impact, the spacecraft kept going (with the mission renamed EPOXI), and it's being used to do all sorts of interesting observations.

In late May, 2008, it turned its cameras back to Earth and observed us over the course of a several hours. During this time, from EPOXI's point of view, the Moon passed directly in front of the Earth! The images were put together (by my old boss, Don Lindler!) into, well, one of the most astonishing animations I have ever watched. Ever.

Now below is the same view, but this time the "red" you see is actually infrared; note that land masses which are warm, appear really red since they are emitting lots of IR compared to the oceans: appear bright in the IR due to vegetation and the ground being good reflectors (see note at bottom of post):

To my knowledge, nothing like this has ever been seen before. These are incredible. Higher-res versions of these videos can be found on the NASA EPOXI press release page.

Take a look at that, folks. It's us, seen from 50 million kilometers away. I've seen many images of the Earth and Moon together as taken by distant spacecraft, but this, seeing them in motion, really brings home -- if I may use that highly ironic term -- just where we are: a planetary system, an astronomical body, a blue orb hanging in space orbited by a desolate moon. This is a view that is literally impossible from the ground. Only a spacefaring race gets the privilege of this view from a height.

Stills from EPOXI animation of Moon transiting the Earth

While there is science galore in these animations, I think their real impact is the visceral one from simply seeing them. As Carl Sagan once said: everyone you have ever met, every human who has lived and died, lived out their lives on that blue ball. And yet here we are, in the 21st century, plains apes allowed to evolve and satiate their curiosity, now with the ability to lob metal proxies into deep space, look back, and see ourselves.

Science. I love this stuff.

A very big tip o' the solar panel to Don Lindler, for alerting me about these animations.

And oops: I originally said that the land is warm, and thus bright in the IR. That's wrong, at least in this case! That would be true if these were far (thermal) IR images, but they're actually near-IR, just outside the range seen by the human eye. At those wavelengths, plant and other objects are pretty good reflectors, so they appear bright. My thanks to R Simmons in the comments below for pointing this out.


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