Saturn setting behind the Moon
yes this is real
Yes this is how it looks
When this picture by Andrew McCarthy was posted on Facebook, flerfs*, space deniers and other loonies claimed it was fake because Saturn was too big relative to the Moon. They also complained "where are the stars" but look at the larger image below for my reply to that.
So I did a rough measure of the diameter of Saturn in the picture and calculated the relative diameter of the moon from the curve we see in the picture** and found that the moon diameter appears roughly 112 times bigger than that of Saturn.
Using the current distance of Saturn from Earth of 1.567 billion km and the Saturn diameter of 120,500 km you can calculate that the moon diameter should appear about 117 times larger than that of Saturn.
Given the limited accuracy of taking measurements from the image and the uncertainty about when the image was taken (and so the distance to Saturn), this matches pretty well. I don't think we should conclude that this is fake from the size of Saturn in the image.
** You can estimate the apparent diameter of the moon in the picture if you draw a chord of the curve that we see and measure its length (2r in the diagram) and its "sag" (s in the diagram).
The radius (R) of the circle is then given by:
R = (r2 + s2) / 2s
Since the moon appears to span about half a degree when viewed from Earth, we don’t quite see it’s full diameter because we are too close, but we see 99.99905% of its diameter - I didn’t bother to account for this in my calculations.
Andrew McCarthy trekked to the top of the Hawaiian volcano, Mauna Loa, to get this picture of Saturn slipping behind the moon.
A reproduction of the original derivation that was actually done on the back of an envelope.
It's all about the exposure of course. They may be faint but they are there. Pictures of the night sky showing stars are long exposures - far too long for a picture of the moon and an extremely bright source like Saturn.
The obvious problem with this constant objection of "Where are the stars?" from flerfs*, is that if the picture was fake, fake stars could easily have been added.
*flerfs is an affectionate or sometimes derogatory name for flat earth believers
