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Glom
2004-Jan-11, 04:43 PM
I only bring this up now because I'm doing a question on the principles of this.

How far must two objects be on the moon to be resolved by the eye? Take the diameter of the pupil of the to be 5mm, the wavelength of the light to be 600nm, and the distance to the moon to be 380,000km.

Rayleigh criterion:

critical angle a = distance between objects *÷ distance to observe

a = 1.22 × wavelength ÷ aperture

distance between objects = 55.6km

How far must the objects on the moon be to be resolved by a telescope that has a mirror of diameter 4m?

distance between objects = 69.54m

Now with regard to HST claims, its mirror is about 2m. That means that the objects would have to be about 140m apart. It's in the physics, something that the HBers neglect to consider. In fact, to resolve an object of about 3m, the aperture would have to be more than 90m!

JayUtah
2004-Jan-11, 08:32 PM
That's the correct formula and the correct theory about diffraction limits. The HST's primary mirror is 2.4 meters in diameter. That's probably the maximum primary mirror size for the KH-11 spy satellites.

beck0311
2004-Jan-11, 08:39 PM
Yeah, I remember when I was taking physics in college we did the same problem in class. I was trying to remember the numbers the other days when I was talking to a freind at work about the possibility of looking at the moon with Hubble to shut up conspiracy theorists.

At the end of the day, even if it was physically possible to see the landing sites with a telescope and you did so, you would simply be identified as a disinformation agent. Conspiracy theories seem to have more to do with psychology than physics.

JayUtah
2004-Jan-11, 09:59 PM
Conspiracy theories seem to have more to do with psychology than physics.

Yes, amongst the "true believers". Conspiracist derives from a number of psychological conditions. But the kingpins of any conspiracy theory (who may or may not be true believers) are adept at putting a very slick veneer of plausibility over their pseudoscience. This occasionally traps otherwise reasonable people who may be intelligent and thoughtful, but who lack the specialized knowledge needed to see through the trickery.

Not everyone should be expected to know about Van Allen belts and the details of radiation exposure. In fact, radiophobia is fairly common. This makes the general public susceptible to arguments that rely on irrelevant comparisons (e.g., you wear a lead apron at the dentist's for only a small amount of exposure) and plain old fear-mongering (e.g., NASA states that radiation is a hazard for space travel). It is unfortunate that such paranoia persists in modern culture, but not everyone did well in science class. It's up to those of us who did to help out the general public, realizing that those of us who didn't do well in, say, economics really need people to help us with our taxes and investments. It's not always people's fault that they are fooled by slick pitches.

N C More
2004-Jan-12, 01:24 AM