Geek Trivia: A far side collection

How many man-made objects do we think reside on the far side of the moon, where even hypersensitive future Earthbound telescopes will never find them?

When so-called conspiracy theorists rattle off a patented rant about how the government faked all the Apollo moon landings on a movie soundstage at Area 51, many of us have no doubt wondered why NASA doesn't just point a big honking telescope at the moon to show the doubting Thomases exactly where all the leftover Apollo equipment resides. The simple answer is that we don't have any telescopes that perceptive.

As usual, it comes down to math. Astronomers have the unenviable task of dividing the infinite sky into measurable units of examination, and the finest of these general measures is the arc second. The full range of the sky visible from Earth is 360 degrees of arc. That means if you pointed a telescope straight up, it would cover 360 degrees in one day as the Earth completed a revolution. Each degree has 60 minutes of arc, and each minute has 60 seconds -- an arc second, 1/3600th of a degree.

For scale, the full moon spans about one-half of a degree of the night sky -- or roughly 1,800 arc seconds. The most powerful telescopes on Earth can resolve details as large as 0.02 arc seconds, so seeing major features on the moon isn't a problem.

However, the five-meter-wide lunar landers work out to span about 0.003 arc seconds -- far too small to make out with current telescopes. The same goes for the Hubble Space Telescope, which has a maximum resolution of 0.03 arc seconds.

While the Hubble is somewhat closer to the moon than terrestrial telescopes, the Apollo landers still wouldn't be more than 0.002 arc seconds in size from the Hubble's vantage point. The best Hubble could do is to render the landers as featureless, indeterminate dots.

The NASA Clementine lunar orbiter team has come closest to visually confirming evidence of moon landings. Clementine circled the moon in 1994, and scientists are still analyzing the various images it sent back.

In 2001, scientists identified a "regolith disruption" in the exact spot that Apollo 15 touched down, confirming, at the very least, that a rocket engine probably blasted the surface there. Still, that's not exactly indisputable photographic evidence of human moonwalkers.

That's not to say that future telescopes couldn't achieve the required sensitivity to view the Apollo artifacts from Earth or Earth orbit. It's simply a matter of technological improvement.

What we won't ever get is an Earthbound visual instrument that can identify all the man-made objects on the far side of the moon, which is never visible to terrestrial observers.


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