Earthshine reflects Earth's oceans and continents from the dark side of the moon

Apr 07, 2009

Researchers from the University of Melbourne and Princeton University have shown for the first time that the difference in reflection of light from the Earth's land masses and oceans can be seen on the dark side of the moon, a phenomenon known as earthshine.

The paper will be published this week, in the international journal Astrobiology.

Sally Langford from the University of Melbourne's School of Physics who conducted the study as part of her PhD, says that the brightness of the reflected earthshine varied as the rotated, revealing the difference between the intense mirror-like reflections of the ocean compared to the dimmer land.

"In the future, astronomers hope to find planets like the Earth around other stars. However these planets will be too small to allow an image to be made of their surface," she said.

"We can use earthshine, together with our knowledge of the Earth's surface to help interpret the physical make up of new planets."

This is the first study in the world to use the of the Earth to measure the effect of continents and oceans on the apparent brightness of a planet. Other studies have used a colour spectrum and to identify vegetation, or for climate monitoring.

The three year study involved taking images of the to measure the earth's brightness as it rotated, allowing Ms Langford to detect the difference in signal from land and water.

Observations of the Moon were made from Mount Macedon in Victoria, for around three days each month when the Moon was rising or setting. The study was conducted so that in the evening, when the Moon was a waxing crescent, the reflected earthshine originated from Indian Ocean and Africa's east coast. In the morning, when the Moon was a waning crescent - it originated only from the Pacific Ocean.

"When we observe earthshine from the Moon in the early evening we see the bright reflection from the Indian Ocean, then as the Earth rotates the continent of Africa blocks this reflection, and the Moon becomes darker," Ms Langford said.

"If we find Earth sized planets and watch their brightness as they rotate, we will be able to assess properties like the existence of land and oceans."

Source: University of Melbourne

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User comments : 5

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googleplex
2 / 5 (1) Apr 07, 2009
Smuh. What am I not understanding.
How can the earth be reflected on the dark side of the moon? Is earths light bouncing off other solar objects and arriving on the dark side of the moon?
Oh wait this is probably another physorg wrong headline. Or did the moon start rotating out of synch with the earth, but then it wouldn't be called the dark side of the moon?
Probably what they mean is that the reflection of the earth can be detected in the eclipsed portion of the moon that faces the earth.
h0dges
5 / 5 (1) Apr 07, 2009
This is true. The dark side of the moon is generally regarded as being the hemisphere that is facing away from the earth. What this article is trying to refer to, is in fact the portion of the moon that is unlit by sunlight giving us a cresent moon.

In summary, the title is a little misleading.
malapropism
3 / 5 (1) Apr 07, 2009
The title is not misleading at all. What else would you call it?

The dark side of the moon in the title is, as gooleplex suggests ("the reflection of the earth can be detected in the eclipsed portion of the moon that faces the earth") the *dark* part. The hemisphere with an absence of sunlight, regardless of whether or not it faces us. Not the side that is facing away from Earth, which would be the *far* side! (And on which hemisphere sunlight waxes and wanes just as on the near side, except we cannot observe it directly.)
Fazer
4 / 5 (1) Apr 08, 2009
Cool article. Not many details, like percentage change in light (and maybe spectra?) from land to water, but still a neat idea. Funny thing is that I dismissed the article and did not bother reading it right away. It sounded like such an obvious thing. It never occurred to me that it would apply to the study of extrasolar, non gaseous, planets. Doh!

When I was growing up, I used to draw interstellar spaceship designs, calculate travel time, including time dilation effects, and fantasize about taking the long journey. I never thought, in my lifetime, that we would actually be able to detect Earth type planets. I can't wait till they actually find one with (H2O) oceans!
googleplex
not rated yet Apr 15, 2009
The title is not misleading at all. What else would you call it?
The dark side of the moon in the title is, as gooleplex suggests ("the reflection of the earth can be detected in the eclipsed portion of the moon that faces the earth") the *dark* part. The hemisphere with an absence of sunlight, regardless of whether or not it faces us. Not the side that is facing away from Earth, which would be the *far* side! (And on which hemisphere sunlight waxes and wanes just as on the near side, except we cannot observe it directly.)

Ok thanks for clarifying.
http://en.wikiped...the_Moon