7.6 Why don’t we just point a telescope at the landing sites?

IN A NUTSHELL: Because even the most powerful telescopes currently available on Earth can’t see such small features. Trigonometry and the laws of optics dictate that seeing any detail of the vehicles and equipment left at the Apollo landing sites from Earth would require a telescope with a mirror at least 45 meters (150 feet) in diameter. No current ground-based telescope comes even close.

THE DETAILS: The resolution of a telescope, i.e., the detail that it can see, is determined by the laws of optics, specifically by a formula known as Dawes’ limit, and depends essentially on the diameter of the main lens or mirror. Adding a lens to magnify the image acquired by this main telescope component will not yield more detail – only more blur.

The largest objects left on the Moon by the Apollo astronauts are the descent stages of the lunar modules, which measure approximately 9 meters (30 feet) across diagonally opposite footpads. A little trigonometry shows that at the minimum Earth-Moon distance, which is about 355,000 kilometers (220,600 miles), seeing the descent stage is equivalent to seeing a US one-cent coin from 740 kilometers (460 miles) away.

No current earthbound telescope can do that; not even the Hubble Space Telescope (Figure 7-6), which at the distance of the Moon can resolve nothing smaller than about 80 meters (262 feet).

Figure 7-6. The Hubble Space Telescope.

That’s an apparently counterintuitive fact. After all, telescopes can see incredibly distant galaxies, so why can’t they get a good picture of a 9-meter (30-foot) object on the Moon, which is in our back yard, astronomically speaking?

The reason is that galaxies are enormous, while the Apollo objects on the Moon are tiny, and their closeness doesn’t compensate for the difference in size.

For example, the Andromeda galaxy is two million light years away (19 million million million kilometers or 12 million million million miles), yet it’s bigger than the full Moon in our night sky; it’s hard to see with the naked eye because it’s very faint. That’s why large astronomical telescopes are designed more to collect light from these remote objects than to magnify them.

Dawes’ limit dictates that even in ideal conditions, seeing the Apollo lunar module descent stages on the Moon from Earth as nothing more than a bright dot would require a telescope with a primary lens or mirror at least 45 meters (150 feet) wide. Resolving any details of the spacecraft would require even more colossal telescopes.

The largest single-mirror telescopes on Earth are currently just over ten meters (33 feet) in diameter. Even the future record holder, the aptly-named European Extremely Large Telescope, which is scheduled for 2018, will be inadequate, because its composite primary mirror will only span 42 meters (138 feet).

A technique known as interferometry, however, allows astronomers to pair two telescopes to obtain a sort of “virtual” instrument that has a resolution equal to a single telescope with a primary mirror as large as the distance between the two telescopes. The Very Large Telescope in Chile, one of the best-equipped observatories for this kind of science, in ideal conditions could achieve a resolution of 0.002 arcseconds: enough to show the LM on the Moon as a handful of pixels (dots forming a digital image). That sounds promising, but there’s a catch.

Interferometry doesn’t produce directly viewable images, but only interference patterns, which require computer processing to extract meaningful information. This means that there’s no way to put a Moon hoax theorist in front of a massive telescope and tell him or her to peer into the eyepiece to see the Apollo landing sites in any significant detail.

However, it is quite possible to take a telescope close to the Moon, point it at the Apollo landing sites and view them with enough detail to make out the Apollo spacecraft. This is what several space probes of various countries have done, as detailed in Chapter 3 and below.