45 years ago next month, Apollo 17 astronauts Gene Cernan and Harrison Schmitt took three separate hikes and car rides on the lunar surface in the Taurus-Littrow Valley, a low spot tucked between the mountains that rim the southeastern “shore” of the Sea of Serenity. You can take a pair of binoculars, or better, a telescope and look at the spot tonight.
All that’s visible with earthbound telescopes is a location; the Apollo descent stage, rover and astronauts footpaths are below the limit of resolution even with the Hubble Space Telescope. People argue with me about that. They’ll point out rightly that Hubble can see see millions of galaxies, so why can’t we see the Apollo leftovers? Hubble’s highest resolution camera can resolve (picture) objects down to 0.03 arc seconds. One arc second is 1/60th of an arc minute and one arc minute is 1/30th the diameter of a full moon, so you see that 0.03 subtends a VERY tiny angle.
The biggest piece of hardware left on the lunar surface by the Apollo lunar landings was the descent stage, which measured 4.37 yards (4 m) across. At the moon’s distance, 4.37 yards is only 0.002 arc seconds wide, an order of magnitude and then some below Hubble’s limit. The only way we’ve been able to see the Apollo sites up close is through the eyes of NASA’s Lunar Reconnaissance Orbiter (LRO). Its orbit can be lowered to about 22 miles (35 km), close enough to take low res images of footpaths, the rovers, the descent stages and even a couple of the remaining flags.
Hubble can spot individual stars in relatively distant galaxies millions of light years away, stars that are way below the telescope’s resolution limit. How is that be possible? Easy. The star’s a brilliant point of light shining in the blackness of space. Hubble can’t see any details of the star, but the contrast makes it easy to see the thing itself.
The descent stage takes up only 0.15% of a pixel in a photograph. To fill just one pixel, the limit in terms of being able to say, “yes, it’s there,” we’d need to put a telescope with a 1,575-inch mirror (40-meter) into orbit. Hubble’s mirror measures just 94-inches (2.38-meters) across. No can do.
But I digress.
If you’re blessed with a clear sky tonight, the fat crescent moon will catch your eye in the southwestern sky. At six different places, our fellow humans have kicked up dust up on that rocky orb.
Cernan and Schmitt were the last people to leave their footprins. Indeed, it’s hard to believe so many years have passed since humankind launched a manned lunar mission. That may soon change but not without swallowing a bitter pill for some. The past administration made a manned mission to Mars a priority; the current administration instead wants NASA to focus on returning to the moon and establishing a permanent base there.
Although my heart belongs to Mars, refocusing on the moon has key advantages: it’s easier, faster and safer. Putting the moon first would delay a mission to Mars by 10 or 20 years. Supporters counter by offering that the experience gained there would be invaluable in making a trip to Mars and setting up a base there.
What do you think?