Sally Langford of University of Melbourne's School of Physics, who conducted the study, said that brightness of the reflected earthshine varied as the Earth rotated, revealing the difference between 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," she added.
This is the first ever study to use Earth's reflection to measure the effect of continents and oceans on the apparent brightness of a planet. Other studies have used a colour spectrum and infrared sensors to identify vegetation, or for climate monitoring.
The three year study involved taking images of the moon to measure the Earth's brightness as it rotated, allowing 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, said a Melbourne University release.
"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," Langford said.
The paper was published in this week's edition of Astrobiology.
copyright 2009 by IANS.
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