-7

I was reading today that, in research published in The Astrophysical Journal, molecular oxygen has been discovered in the Markarian 231 galaxy, 561 million light-years from Earth. A light-year, which measures distance in space, equals about 6 trillion miles.

And yet we can't photograph the Apollo landing equipment 243,000 miles away.

Why is it that we can better observe this far-away oxygen than stuff nearby on the surface of the Moon?

GrapefruitIsAwesome
  • 2,339
  • 14
  • 35
user31866
  • 11
  • 1
  • 5
    But the Moon landing stuff has been photographed. – ProfRob Feb 22 '20 at 16:42
  • 5
    This appears to be an invitation to discuss, rather than a question to answer. Please take the [tour] to see how this differs from a discussion forum. – James K Feb 22 '20 at 19:27
  • 4
    One has nothing to do with the other. The molecular oxygen was discovered by spectroscopy. – David Hammen Feb 22 '20 at 21:48
  • 2
    We have absolutely nothing to image anything in that galaxy, not even a star system. The molecular oxygen was discovered by spectroscopy (we have seen photons what is given out exclusively by molcular oxygen). – peterh Feb 23 '20 at 00:10
  • 1
    "Thoughts?" is not a proper Stack Exchange question, therefore voting to close because answers to this question ("Thoughts?") will tend to be almost entirely based on opinions. If you are curious how they are able to detect molecular oxygen so incredibly far from Earth, then please feel free to ask a new question! As long as your question is on-topic and can have a fact-based answer, it might be much better received. Thanks! – uhoh Feb 23 '20 at 03:10
  • 5
    as for "Good luck getting Excel to calculate that!": https://i.stack.imgur.com/cc7My.png – uhoh Feb 23 '20 at 03:27
  • 1
    False fact, followed by false fact, followed by rampant bad logic, followed by false fact, concluded with snide remark. Congratulations. YOu must be so proud of your achievement – PcMan May 22 '21 at 00:13
  • I thought even the original version was a semi-reasonable question (or it is at least clear what an answer should look like). – ProfRob Aug 09 '23 at 12:36

1 Answers1

10

The Moon landing sites have been photographed, but from orbit around the Moon. For example: https://www.nasa.gov/mission_pages/LRO/news/apollo-sites.html It is legitimate to ask why not from the Earth?

A lunar module has a diameter of about 4m. At a distance of 400,000 km, this subtends an angle of 0.002 arcseconds.

The absolute best angular resolution you can obtain from the surface of the Earth, using massive telescopes and adaptive optics imaging is about 0.1 arcsecond.

i.e. You cannot resolve anything on the Moon's surface, using a telescope on Earth, that is much smaller than about 200 m in diameter.

The observations you refer to (see Wang et al. 2020) are of a galaxy, taken at microwave wavelengths (so hardly comparable). A galaxy is far away, but very big. The observations were able to resolve emission from the central 20 kpc (about 60 thousand light years) diameter region of this galaxy. The galaxy itself is at a distance of about 180 Mpc (about 600 million light years), so the angular resolution involved, using a bit of basic trigonometry, was about 22 arcseconds, which is set by the instrumentation they were using (i.e. the signature they found could be more concentrated than that). Thus this central region in Markarian 231 subtends an angle of 22 arcseconds at the Earth, which is roughly 10,000 times the apparent size of a lunar module on the surface of the Moon.

ProfRob
  • 151,483
  • 9
  • 359
  • 566