An image purportedly showing the Andromeda Galaxy next to the moon circulated in May 2016, along with the claim that it was taken from Finland and without the aid of a telescope.
However, this picture is actually a composite of two separate images, and the Andromeda Galaxy appears far smaller in the night sky to the naked eye — almost identical to a garden-variety, somewhat fuzzy star, as this photograph illustrates (the galaxy is in the top center):
Hot stars burn brightly in this new image from NASA's Galaxy Evolution Explorer, showing the ultraviolet side of a familiar face.
At approximately 2.5 million light-years away, the Andromeda galaxy, or M31, is our Milky Way's largest galactic neighbor. The entire galaxy spans 260,000 light-years across -- a distance so large, it took 11 different image segments stitched together to produce this view of the galaxy next door.
Andromeda is so bright and close to us that it is one of only ten galaxies that can be spotted from Earth with the naked eye. This view is two-color composite, where blue represents far-ultraviolet light, and orange is near-ultraviolet light.
In 2015, Reddit user Tom Buckley took the GALEX image and added it into a photograph of the moon that had been taken by Flickr user Stephen Rahn. Buckley said that his composite showed "Andromeda's actual size if it was brighter":
Most versions of this size comparison paste the moon (rather poorly) onto an existing picture of the galaxy. But I couldn't find any the other way round, where the galaxy is pasted onto an existing picture of the moon. I think you get a much more realistic sense of what's 'hidden' in our night sky like this.
Oh yes and original credit to (Stephen Rahn):
“The GALEX image of Andromeda is in the ultraviolet, and the extent of this image is close to the size of the optical image of Andromeda that everyone is familiar with,” says astronomer Alan McConnachie of the National Research Council Herzberg in Victoria, Canada. “The moon is about 0.5 degrees in diameter; the Andromeda galaxy, measured on its longest axis, is approximately 2-3 degrees long.”
Thus, if possible for Andromeda to be more luminous, it would appear roughly six times larger than our moon. But at 2.5 million light-years from Earth, the galaxy is not as easily seen as the crescent in our sky—which is only 238,900 miles (384,400 kilometers) from Earth.
While Buckley provided the source images when he first shared his composite, and while the image circulated along with an explanation in 2015, some only encountered the picture when it was attached to the erroneous claim that it was a real photograph of the Andromeda Galaxy and the moon.