Thursday, July 26, 2012

Nebulous Comparisons

My post yesterday comparing the Lagoon and Orion Nebulae got me to thinking: how would they look compared to each other? I can say that the Lagoon Nebula (Messier 8) is about 110 light-years across while the Orion Nebula (Messier 42) is only 24, but those are just numbers. Being the visual person I am, I decided to see what they would actually look like if compared. So this afternoon I sat down and put together the two pictures seen below.

This picture shows the two nebulae side-by-side just as they appear on the sky:

Left: M8, the Lagoon Nebula. Right: M42, the Orion Nebula. North is up in both pictures.
These two nebulae are the biggest and brightest on the sky, and pretty much the only ones that can really be seen with the naked eye. The Orion Nebula looks a little bigger here due to its much closer distance (the Lagoon Nebula is about two-and-a-half times further away). Also note the difference in star density between the two pictures.

This next picture shows what they would look like if M42 was was at the distance of M8:

M8 and M42 as they would be if they were the same distance away.
Quite the difference, no? To be more realistic I should also have dimmed M42 by about 7 times to accurately reflect how it would look being ~2.5 times further away, but my first attempt at a rough approximation made M42 so dim it could barely be seen. I opted instead for the slightly-less-realistic but more visually interesting picture.

As I mentioned in my last post, despite their differences M8 and M42 are more similar than not. Both are star-forming regions, both are large cavities of gas (mostly hydrogen and helium) and dust being blown open from the inside by young stars, both would probably appear boring and dark from the other side. The main differences are their size, as seen, and their location: M8 is situated nearly directly towards the galactic core from us, while M42 is located almost directly away. That's why there are a lot more stars visible around M8 than around M42.

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