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Unveiling the Moon's Hidden Gem: Mare Orientale

A serene night scene with a full moon over a calm eastern sea, reflecting soft moonlight.
Image: NASA / The Mare Orientale
Quick answer · as of 11 Jul 2026

Mare Orientale, a vast lunar impact basin, is revealed in this telescopic view thanks to favourable libration. Discover its history and significance.

The Mare Orientale, or Eastern Sea, is a captivating lunar feature that challenges our Earth-bound perspectives. Captured during a period of favourable libration on July 7, this image reveals the basin's concentric ripples, formed by an asteroid impact over 3 billion years ago. Despite its name, the Mare Orientale is situated on the Moon's western edge, a testament to historical naming conventions that predate the 1961 reversal of lunar map orientations.

The Science Behind the Mare

The Mare Orientale's formation is a classic example of planetary impact processes. Its nearly 1000-kilometre-wide basin is the youngest of the Moon's large impact sites, offering insights into lunar geology and the history of asteroid impacts in our solar system. The concentric rings visible in the image are akin to ripples in a pond, illustrating the immense forces at play during the impact. For those interested in observing the Moon's features, the Moon Globe on Orbital Radar provides real-time data on lunar phases and orbiters.

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Observing the Mare from Earth

Observing the Mare Orientale from Earth requires patience and timing due to its location on the Moon's limb. The phenomenon of libration, which causes slight tilts in the Moon's orientation, occasionally brings this region into view. For amateur astronomers, tracking these periods can be rewarding. The Orbital Radar's Pass Predictor can assist in planning your lunar observations by providing accurate timing for favourable viewing conditions.

Frequently Asked Questions

What is the Mare Orientale?
The Mare Orientale is a large lunar impact basin on the Moon's western edge, formed by an asteroid impact over 3 billion years ago.
Why is the Mare Orientale difficult to observe?
Its location on the Moon's limb makes it challenging to see from Earth, but favourable libration can bring it into view.
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