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Credit & Copyright: Dan Long (Apache Point Observatory) -
Courtesy:
Tom Murphy (UC San Diego)
Explanation:
This is not a scene
from a sci-fi special effects movie.
The green beam of light and red lunar disk are real enough,
captured in the early morning hours of April 15.
Of course, the reddened lunar disk
is easy to explain as the image was taken during this week's
total lunar eclipse.
Immersed in shadow, the eclipsed Moon
reflects the dimmed reddened light of all the sunsets and sunrises
filtering around the edges of planet Earth,
seen in silhouette
from a lunar perspective.
But the green beam of light really is a laser.
Shot from the 3.5-meter telescope at Apache Point Observatory
in southern New Mexico, the beam's path is revealed as Earth's
atmosphere scatters some of the intense laser light.
The laser's
target is the Apollo 15 retroreflector,
left on the Moon
by the astronauts in 1971.
By determining the
light travel time
delay of the returning laser
pulse, the experimental team from UC San Diego is able to measure
the Earth-Moon distance to millimeter precision and
provide a test of General Relativity, Einstein's theory of
gravity.
Conducting the
lunar
laser ranging experiment during
a total eclipse uses the Earth like a cosmic light switch.
With direct sunlight blocked, the reflector's performance is
improved over performance when illuminated by sunlight during a
normal Full Moon,
an effect fondly known as The Full Moon Curse.
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NASA Web Site Statements, Warnings, and Disclaimers
NASA Official: Jay Norris. Specific rights apply.
A service of: LHEA at NASA / GSFC
& Michigan Tech. U.
Based on Astronomy Picture
Of the Day
Publications with keywords: lunar eclipse - apollo - laser
Publications with words: lunar eclipse - apollo - laser
See also:
- APOD: 2026 August 29 Á Eclipse Pair
- APOD: 2026 August 25 Á Earths Shadow Visualized with Lunar Eclipses
- APOD: 2025 November 3 Á A Double Helix Lunar Eclipse
- APOD: 2025 September 11 Á The Umbra of Earth
- APOD: 2025 March 25 Á A Blue Banded Blood Moon
- Eclipse Pair
- APOD: 2023 October 29 Á A Partial Lunar Eclipse