The first photo of the Andromeda galaxy, then thought to be a nebula, was taken by engineer and amateur astronomer Isaac Roberts #OTD in 1888.
The image, captured with his 20" reflector, revealed a clear spiral structure. But scientists assumed M31 was a gas cloud in our galaxy.
Image: Isaac Roberts
The most interesting part of this story is why.
Why did they think it was a nebula, a gas cloud?
I didnt know why, until I read this. Fascinating. Wonderful.
Answer next if anyone wants it.
The answer for why, despite a good photo of Andromeda, they thought it must be a nearby nebula, because:
Its so big!
Andromeda is HUGE - and I don't mean150,000 light years across, but thats not unusual, our galaxy is even bigger.
No, its huge, but its huge in THE SKY.
Andromeda in our sky is ten times the size of the moon.
No one thought a galaxy could be that close. But its faint. With the eye just the centre is seen, as a smudge.
Without space dust it would look like this.
Andromeda
Robert McNees
Kevin Russell
Drew