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The surface of the Earth is the only place we know of where a natural satellite appears exactly the same size as the primary / only star.

dmurray 4y ago
This can't be true: you can choose a point behind any sufficiently round satellite where it appears the same size as the star. Perhaps it's the only place we know of on a planet's rocky surface. But most of our solar system's planets with moons don't have rocky surfaces, and we can't detect moons in other systems, so you really mean it's not true from the surface of Mars, Pluto or Charon. Additionally, the moon varies in apparent diameter by about 13% from apogee to perigee, and the sun by about 3%. So while it might appear "exactly" the same size at some point in its orbit, mostly it's just within 5%.
- TheSpiceIsLife 4y ago
  Yes, sorry, I should have also wrote "where one can stand".
  - zaarn 4y ago
    The Moon Kerberos of Pluto is actually very very close to the size of the sun in the sky (of by being 0.0099° compared to the suns 0.0089°, around 11%), so the earth isn't the only planet (if you count Pluto as planet, otherwise, but it's still a solar body you can stand on where a moon is roughly the size of the sun).
    - sidewndr46 4y ago
      Doesn't Pluto have some weird elliptical orbit? Does it not matter enough to change the apparent size of the sun as seen from Pluto's surface?
      - zaarn 4y ago
        I used the current values, they should be valid for a reasonable timeframe. Edit: only by a few percents; the distances are too large to appreciably change the visible size of the sun in the sky.
- mtlmtlmtlmtl 4y ago
  We are actually pretty close to having found "exomoons"(natural satellite orbiting an exoplanet), with several promising candidates having been identified already. David Kipping's Cool Worlds lab at Columbia has done some promising research on this, some of which is detailed in excellent videos on their youtube channel.

dmurray 4y ago

This can't be true: you can choose a point behind any sufficiently round satellite where it appears the same size as the star. Perhaps it's the only place we know of on a planet's rocky surface. But most of our solar system's planets with moons don't have rocky surfaces, and we can't detect moons in other systems, so you really mean it's not true from the surface of Mars, Pluto or Charon. Additionally, the moon varies in apparent diameter by about 13% from apogee to perigee, and the sun by about 3%. So while it might appear "exactly" the same size at some point in its orbit, mostly it's just within 5%.

TheSpiceIsLife 4y ago
Yes, sorry, I should have also wrote "where one can stand".
- zaarn 4y ago
  The Moon Kerberos of Pluto is actually very very close to the size of the sun in the sky (of by being 0.0099° compared to the suns 0.0089°, around 11%), so the earth isn't the only planet (if you count Pluto as planet, otherwise, but it's still a solar body you can stand on where a moon is roughly the size of the sun).
  - sidewndr46 4y ago
    Doesn't Pluto have some weird elliptical orbit? Does it not matter enough to change the apparent size of the sun as seen from Pluto's surface?
    - zaarn 4y ago
      I used the current values, they should be valid for a reasonable timeframe. Edit: only by a few percents; the distances are too large to appreciably change the visible size of the sun in the sky.
mtlmtlmtlmtl 4y ago
We are actually pretty close to having found "exomoons"(natural satellite orbiting an exoplanet), with several promising candidates having been identified already. David Kipping's Cool Worlds lab at Columbia has done some promising research on this, some of which is detailed in excellent videos on their youtube channel.