Hi, Asher,
I have some problems with that synopsis.
I start by quoting the basic issue:
Radial longitudinal lines on the Moon are fine, linear features that appear to extend outward from the lunar poles.
Yet later the synopsis says:
Impact Cratering: The Moon's surface is heavily cratered due to impacts from asteroids and comets. These impacts can create radial patterns, especially around larger craters, where ejecta is thrown outwards.
This does not seem to follow the stated basic issue.
I am not able to understand this:
Lunar Libration: The Moon exhibits a phenomenon called libration, which allows observers on Earth to see slightly different hemispheres at different times. This can affect how features appear in photographs, making lines seem more pronounced.
Can you tell us a little more about the mechanism that is referred to here? I am not yet able to recognize why libration should make lines radiating from the lunar poles "seem more pronounced" in photos.
Thanks.
Best regards,
Doug
Doug,
I have never been on the moon or even taken a course in moon history, or meteor impact in sculpting the surface. So I asked Gemini, the Large Language, so-called, AI model to figure out answers from the Wikipedia-derived text I shared.
“
Critique and Explanation of Lunar Radial Lines
The text you provided offers a good foundation for understanding linear features on the Moon, correctly identifying that impact cratering causes radial patterns. However, the core premise—that these specific fine straight lines radiate from the
lunar poles—is a common visual misunderstanding of the Moon's most dramatic geological features.
Here is a critique of your text and the reality of the phenomenon visible in your photograph (IMG_0080.jpeg).
Critique of the Explanation
| Section | Assessment | Factual Reality in the Image |
|---|
| "Radiating from the lunar poles" | Incorrect focus. | The lines clearly radiate from the central point of a major impact basin in the Moon's southern hemisphere (Crater Tycho). |
| Impact Cratering | Correct principle. | This is the true cause. The lines are ejecta material thrown out during the impact that created a young crater. |
| Lunar Libration | Observational factor, not a cause. | Libration only changes the viewing angle; it does not create or cause the radial pattern itself. |
| Geological Features | Mix-up of features. | Rilles (grooves from collapsed lava tubes) and grooves are different features (tectonic/volcanic) and are not the bright, long rays seen here. |
The Reality: Lunar Ejecta Rays (Tycho)
The prominent, fine straight lines visible in your photograph are known as
lunar rays or
ejecta rays. They represent the clearest signs of relatively recent, large-scale impacts on the Moon.
- Source Crater: The brightest and most extensive ray system visible, especially in the lower half of the image, originates from the massive crater Tycho (named after astronomer Tycho Brahe). This crater is located in the southern high-lands and is about $85$ kilometers ($53$ miles) in diameter.
- Composition and Formation: The rays are bright streaks composed of pulverized, fine-grained rock and dust that were blasted out during the impact. This material traveled at high speeds and settled back to the surface in ballistic trajectories, creating the radial patterns.
- Why They Are So Bright: Tycho is considered a young crater, formed only about $108$ million years ago. Because of its youth, the ejected material has not been significantly darkened by space weathering—the constant bombardment by solar wind and micrometeorites. Older craters have rays that have mostly faded.
- The Pole Misconception: The rays from Tycho are exceptionally long, stretching for thousands of kilometers and literally covering the entire Moon. In the image, because the rays extend outwards from the southern region, they inevitably pass near or even over the visible poles, which creates the visual impression that they might originate there.”
I hope Pao you don’t mind us focusing on on the details of your fine photograph of the Luna surface.
I never imagined we’d see here such a detailed picture that allows this discussion.
I do hope you find it fascinating as much as I do!
Asher