In the early 2000s, when I was having weekly clashes with people who believed the Apollo moon landings were faked, they brought up an argument they thought was their trump card: If NASA’s Hubble Space Telescope is powerful enough to see intricate detail in distant galaxies, why can’t we see the shoe prints of Apollo astronauts on Earth’s Moon?
Like most conspiracy theories, this argument seems plausible on the surface, but falls apart under a little investigation. Those who fall for it are left confused by the mechanics of the telescope and big Space is.
Many people think that the purpose of a telescope is to magnify an image. Indeed, manufacturers of inexpensive (i.e., shoddy) telescopes love to advertise it that way, printing “150x the Power!” in big letters on the box (along with very misleading photos taken with a much larger telescope). Magnification is important, but a telescope’s real strength is in its resolution. The difference is subtle, but important.
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Magnification is how much you enlarge an object to make it appear larger. This is important because even though celestial objects are physically large, they appear small in the sky because they are so far away. Magnification makes them easier to see.
Resolution, on the other hand, is the ability to distinguish between two objects that are very close together. For example, two stars orbiting each other (binary stars) may be perceived as a single star because they are too close for the eye to distinguish. solve But if we look at it with a higher-resolution telescope, we might be able to see the distance between them and realize that they are two separate stars.
But isn’t that just magnification? No, magnification only makes things bigger! This is easily illustrated with photography. You can magnify a photo as much as you want, but beyond a certain limit, you are just magnifying pixels and you don’t get any more information. To break through that limit, you need to increase the resolution, not the magnification.
A Hubble Space Telescope image of the Apollo 17 landing area in the Taurus-Littrow Valley on the Moon. This image does not have the resolution necessary to reveal any traces of the lunar module or astronaut surface activity.
NASA/ESA/J. Garvin (NASA/GSFC)
The problem is the resolution It is inherent to the telescope itself, This means that to get a significant improvement in resolution, you usually need to upgrade to a much larger telescope. But no matter how big a telescope gets, there’s a limit to how much resolution it can achieve. When light from a tiny point, like a distant star, passes through a telescope, it gets spread out a bit within the telescope’s optics (mirrors or lenses). This is a fundamental property of light called diffraction, and it can’t be avoided.
As mentioned earlier, the resolution of a telescope depends in part on the size of its mirrors and lenses. The larger the light-gathering optics, the higher the resolution. But the way light is spread out through the optics depends on the wavelength, and shorter wavelengths result in better resolution. So a telescope might be able to separate two blue stars that are close together, but not two red stars at the same distance. If astronomers build telescopes with cameras, they need to take into account the wavelengths they want to observe when deciding how big the camera pixels should be; otherwise they’ll just magnify noise, like in the zoomed-in example above.
All this leads to a surprising result: the Hubble Space Telescope’s mirror is 2.4 meters wide. NASA’s James Webb Space Telescope (JWST) mirror is 6.5 meters wide, so JWST Many It will have higher resolution. And at some wavelengths, it will. The shortest wavelengths JWST can see are about 0.6 microns (the wavelength the human eye perceives as orange light), and its resolution is technically much better than Hubble’s.
But JWST is designed as an infrared telescope. At its wavelengths, about 2 microns, its resolution matches what Hubble can see at visible wavelengths. In the mid-infrared, between 10 and 20 microns, JWST’s resolution is even lower. But because it’s the largest infrared telescope ever launched into space, it will provide some of the sharpest images ever at those wavelengths.
Astronomers measure resolution in degrees in the sky. There are 90 degrees from the horizon to the zenith, with 60 arc minutes per degree and 60 arc seconds per minute (an “arc” represents an angle in the sky). For example, the Moon spans 0.5 degrees on the sky, which is 30 arc minutes, or 1,800 arc seconds. So the maximum resolution of a telescope is the smallest distance at which it can distinguish two objects, expressed in degrees.
Hubble’s best resolution is about 0.05 arcseconds. very That’s a very small angle, but how much detail you can actually see depends on the distance and physical size of the object. For example, 0.05 arc seconds corresponds to the apparent size of a dime seen from about 140 kilometers away.
Back to conspiracy theorists and their frustration over finding shoe prints on the moon: Galaxies are typically tens of millions, or even billions, of light years away from Earth, at which distance Hubble can resolve objects a few light years wide. Trillion So, although Hubble’s spectacular images give us a seemingly incredible look at galaxies, even the smallest ones we can see are enormously large.
The Moon, on the other hand, is only 380,000 km away from us, and from the Hubble Space Telescope. At that distance, the Hubble Space Telescope’s resolving power is astonishingly low, allowing us to see only objects larger than about 90 meters in diameter. do not have Hubble Space Telescope images show the astronauts’ shoeprints, but not the Apollo Lunar Module, which was only about 15 feet (4 meters) in diameter.
An image of the Apollo 11 moon landing site taken by NASA’s Lunar Reconnaissance Orbiter (LRO). The LRO spacecraft uses much smaller optics than the Hubble Space Telescope, but its closeness to the lunar surface allows it to see incredible detail, including the Apollo 11 lander and the astronauts’ shoeprints.
NASA/Goddard Space Flight Center/Arizona State University
But you can see the lander and boot prints in images taken by NASA’s Lunar Reconnaissance Orbiter. The mission’s camera mirror is only about 20 centimetres wide, but the spacecraft is in lunar orbit and has only just passed over the Apollo landing sites at an altitude of 50 kilometres. It’s so close to the surface that it can see more detail on the moon than the Hubble telescope can. That’s why we send probes to planets – we get a much better view. Sometimes you don’t get much unless you’re there.
The lesson here is that the way things actually work is often subtle and not as you’d expect. Claims that sound reasonable fall apart when you learn a bit more about the underlying physics. And if you find a telescope being advertised based on its magnification, it’s probably best to walk away and look elsewhere. I know it’s hard, but it just takes a bit of determination.
