Lunar surface feature size visible from Earth

[rod]

A note I make here about surface feature size that can be seen on the Moon from Earth.

From earth, telescopes can resolve features about 0.5 miles across (about 0.8 km), ref - The How And Why Wonder Book of The Moon, p. 26, 1963. Telescopes like I use can see features about 1.86 km diameter or so (close to 1.16 miles), this is 1 arcsecond size when the Moon is near its mean distance, 384401 km. Modern radar images of the Moon from Earth today show surface features about 5 meters size. Ref - GREEN BANK TESTS NEW PLANETARY RADAR, https://skyandtelescope.org/astronomy-news/green-bank-tests-new-planetary-radar/, Feb-2021. "This may look like an ordinary visible-light image . . . in reality, it’s anything but. The image was constructed using a new 70 kilowatt transmitter installed at the Green Bank Observatory in West Virginia, which sent the radar signal to the Moon. A network of radio telescopes caught the reflected signal to create the image of the Hadley Rille feature snaking near the Apollo 15 landing site. The image shows features as small as five meters across; for context, the base of the descent stage — the largest piece of hardware left on the lunar surface during the Apollo missions — is just shy of five meters..."

So in summary, my telescopes can see objects perhaps 1.8 to 2 km size on the Moon, better telescopes can see 0.5 mile across size (about 0.8 km), and newer radar imaging shows objects 5 meters in size on the Moon. Today, there is much more detail visible on the Moon from Earth than in the old days

 

[COLGeek]

Green Bank is a great place to visit if you ever get the chance. Beautiful location and fascinating folks and science being conducted there.

 

[Space Dust]

So it's just like LOLA done with radar instead of lasers.

 

[rod]

FYI. Radar imaging of the Moon apparently got started shortly after WWII ended by the US Army. Here is a quote from the 1926-1951 Naval Academy book, Navigation And Nautical Astronomy by Dutton, Benjamin.

"864. Physcial characteristics of the moon. - When the Army, early in 1946, announced that it had made radar contact with the moon, interest in the possibility of some day making a trip to the moon increased...", page 275-276.

There is a long history of using radar to measure the Moon and distance. There are many examples at NASA ADS Abstract site. High-resolution radar maps of the lunar surface at 3.8-cm wavelength, https://ui.adsabs.harvard.edu/abs/1974Moon...10...17Z/abstract, May 1974.

"The entire earth-facing lunar surface has been mapped at a resolution of 2 km using the 3.8-cm radar of Haystack Observatory. The observations yield the distribution of relative radar backscattering efficiency with an accuracy of about 10% for both the polarized (primarily quasispecular or coherent) and depolarized (diffuse or incoherent) scattered components. The results show a variety of discrete radar features, many of which are correlated with craters or other features of optical photographs. Particular interest, however, attaches to those features with substantially different radio and optical contrasts. An anomaly near 63° is noted in the mean angular scattering law obtained from a summary of the radar data."

Radar imaging of the Moon is improving apparently because the Green Bank showed some surface features about 5 meters across now.

LOLA, Lunar Orbiter Laser Altimeter (nasa.gov)

 

[Space Dust]

The images can only ever be computer generated. Love to see a radio telescope image of an Apollo landing site.

 

[billslugg]

Here is a frame from the most detailed radar image of the Moon ever made, this from a beam sent by the Green Bank dish, bounced off the Moon and received by the Very Long Baseline Array in New Mexico. The location of the Apollo 15 landing is covered by a dot.
5M-small-1024x640.png (1024×640) (greenbankobservatory.org)

Here is the image without the dot.

https://public.nrao.edu/wp-content/uploads/2021/01/5meterSAR_Apollo15-copy.jpg

I can't see anything at the location.

Here is a closer, optical view. The bright spot looks to be "many"pixels wide and high. Should be visible in the radar image, BUT radar probably is not able to see the difference in color. It all looks the same to the radar. The remains of the lander itself might affect one pixel in the radar image. That's a tough sell.

I am sure there are still optical retroreflectors there, so they have a real good way of measuring exactly how far away it is. I set up a tent just outside the laser ranging station in the Andes at Arequipa, Peru in 1986. I was photographing Halley. The telescope there sent out a green beam every few seconds, pointed straight at the Moon.

 

[Space Dust]

It seems very pixelated and not very good IMO.

It probably cost millions to upgrade, not money well spent as the image looks shoddy.

 

[billslugg]

These are 15 meter pixels from 250,000 miles away with a radar signal that penetrates several feet into the ground, telling us its properties are. It is not supposed to be optical quality. They don't really care what it looks like, they have 100% coverage from close orbit with resolution of inches. What they very much want to learn are the properties of the upper few feet of soil. The wavelength must be long in order to penetrate the surface. Being a long wavelength cuts way down on the picture sharpness. Nothing can be done about that.