Two or three times a year, NASA's orbiting Solar Dynamics Observatory observes the moon travelling across the sun - but the images show the moon as a black shadow.

Two NASA technicians used data from another NASA satellite, the Lunar Reconnaissance Orbiter, to show the surface of the moon as it passed the sun.

The technicians used six billion measurements of the moon to ensure it was in the correct position - so while the image has been made digitally, it's totally accurate, and composed of photographs.

The moon's crisp horizon can be seen against the sun, as the moon has no atmosphere. (At other times of the year, when Earth blocks SDO's view, the Earth's horizon looks fuzzy due to its atmosphere.)

[Related: Moons, not planets, could be best place to look for ET]

The crisp edge of the moon in the SDO images inspired two NASA visualisers to overlay a 3-dimensional model of the moon over the image.

Such a task is fairly tricky, as Scott Wiessinger who works with SDO imagery and Ernie Wright who works with LRO imagery had to precisely match up data from the correct time and viewpoint for the two separate instruments.The end result is an awe-inspiring image

To start the process, the visualizers took the viewing position and time from the SDO image. This information was dropped into an LRO model that can produce the exact view of the moon from anywhere, at any time, by incorporating 6 billion individual measurements of the moon's surface height from LRO's Lunar Orbiter Laser Altimeter instrument.

The model had to take many factors into consideration, including not only SDO's distance and viewing angle, but also the moon's rotation and constant motion. Wright used animation software to wrap the elevation and appearance map around a sphere to simulate the moon.

The two images were put together and the overlay was exact. The mountains and valleys on the horizon of the LRO picture fit right into the shadows seen by SDO.

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NASA satellites capture the moon passing the sun