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Alphonsus

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description Alphonsus Overview

Alphonsus is a large lunar impact crater approximately 119 kilometers in diameter, located in the central highlands south of Mare Imbrium. Its relatively flat floor contains dark halo craters, evidence of volcanic gas eruptions, making it a notable site for lunar geology studies. Alphonsus was the target of the Ranger 9 probe in 1965, which transmitted close-range images before impact.

help Alphonsus FAQ

Where is Alphonsus crater on the Moon?

Alphonsus lies in the lunar highlands between Ptolemaeus to the north and Arzachel to the south. The three large craters form a striking chain visible through modest backyard telescopes.

What are the dark patches on the floor of Alphonsus?

Several are dark-halo deposits surrounding small vents or craters and are widely interpreted as pyroclastic volcanic material. They make Alphonsus an important site for studying volcanism that occurred after the original impact.

Why did Ranger 9 target Alphonsus?

NASA's Ranger 9 spacecraft transmitted close-up television images while descending toward Alphonsus in 1965. It then struck the crater as planned, ending the final mission of the Ranger lunar-probe program.

How large is Alphonsus crater?

Alphonsus is about 119 kilometers in diameter and has a relatively flat, fractured floor surrounding a central peak. Its worn rim shows that it is older than sharply defined craters such as Copernicus.

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