I finally saw how big the Whirlpool Galaxy really is compared to our moon

I was browsing the APOD site last night and found a photo that overlays the Whirlpool Galaxy (M51) against a full moon in the sky. Turns out that galaxy takes up about the same visual space as half the moon from Earth. Blew my mind because I always thought galaxies were tiny pinpricks in photos. Has anyone else run into a size comparison that totally surprised them?

3 comments

3 Comments

torres.thea18d agoMost Upvoted

I mean i gotta gently push back on "half the moon" because it's actually more like a third lol. If you look at the actual angular size M51 is about 11 arcminutes across while the moon is about 30 arcminutes, so it's closer to a third than half. Still ridiculously huge though. Like i remember seeing the Andromeda Galaxy comparison and it blows both of them away, that thing is six times wider than the moon in the sky. We just can't see it with our naked eyes because it's so dim and spread out.

william_garcia18d ago

Thea is out here with math facts while I'm still trying to figure out which blob in my telescope is actually a galaxy and not just a smudge on the lens. That Andromeda stat is wild though, six moons wide but invisible because it's basically a faint ghost in the sky. Guess my eyes are just not premium enough for cosmic real estate.

diana61718d ago

Wait is it really that serious though? I mean yeah the math is cool and all but does it really matter if someone says half the moon or a third when we're talking about something we can barely see anyway? @torres.thea has a good point about Andromeda being six moons wide but honestly my brain just can't process that kind of size, its like trying to imagine the number of grains of sand on a beach or something. And you're right about the smudge on the lens thing, I spent like twenty minutes once cleaning my binoculars just to realize the blurry spot was actually the Orion Nebula and not dirt. I guess what I'm saying is maybe we're overthinking this a bit, the universe is huge and our eyes are small and thats kind of the whole point.