Announcement

Collapse
No announcement yet.

Really dumb but quick question for astronomers

Collapse
X
  • Filter
  • Time
  • Show
Clear All
new posts

    Really dumb but quick question for astronomers

    I didn't want to soil the excellent other thread.

    How is it when I'm sat in my garden right now with the sun right behind me I'm looking at a half moon in the sky above me - literally 180 degrees apart in our sky?

    #2
    What's the issue?

    Comment


      #3
      Why am I not looking at a full moon when the sun is behind me and the moon is in front of me? I have the sun on my back and my shadow is directly pointing at a half-moon, high in our evening sky.
      Last edited by Rogin the Armchair fan; 14-05-2019, 17:17.

      Comment


        #4
        Originally posted by Rogin the Armchair fan View Post
        Why am I not looking at a full moon when the sun is behind me and the moon is in front of me? I have the sun on my back and my shadow is directly pointing at a half-moon, high in our evening sky.
        Because it's not on the horizon, so isn't at 180 to the Sun?

        Comment


          #5
          Yeah, so I need someone cleverer than Guy to still explain that to me then.

          Comment


            #6
            If you can see the sun in the sky, it's above 0 degrees from the horizon. If you can see the moon in the sky it's above zero degrees from the horizon. Therefore they can't be 180 degrees to each other. They usually have to be substantially less for you to see both.

            Comment


              #7
              Originally posted by Rogin the Armchair fan View Post
              Why am I not looking at a full moon when the sun is behind me and the moon is in front of me? I have the sun on my back and my shadow is directly pointing at a half-moon, high in our evening sky.
              How can your shadow be pointing at something high in the sky, Rogin? Shadows run along the ground and therefore can only point at something on the horizon. That is the source of your misunderstanding (shorter, more technical reply - it's vectors, mate)

              Comment


                #8
                Originally posted by Rogin the Armchair fan View Post
                I didn't want to soil the excellent other thread.

                How is it when I'm sat in my garden right now with the sun right behind me I'm looking at a half moon in the sky above me - literally 180 degrees apart in our sky?
                A half moon is when the line between the centre of the earth and the moon is at ~90 degrees to the line between the centre of the earth and the centre of the sun, so the face that's facing the earth is 50% sunlit.

                as others have said, the angle must be less than 180 degrees if both are above the horizon, but if it's a half moon it has to be ~90 degrees (with some variance due to eliptic orbits). It's not quite exact because the moon orbits in a different plane to the earth's solar orbit - which is why we don't get solar/lunar eclipses every month)

                Comment

                Working...
                X