This photo is actually 2 separate nebulae.
Even though these nebulae appear to be the same distance away from us (and part of the same "question mark" object), they are not.
The bottom nebula (SH2-170) is much further away from us (9,000 light years), while the top nebula (NGC 7822) is 3,000 light years away. It is just coincidental that they line up this way. (Or is it??!) Hah.
The top nebula is estimated to be 3,000 light years wide. Light travels about 6 trillion miles per year. This makes the nebula about 18 trillion miles wide. For context, we are 240,000 miles from the moon and 93 million miles from the sun.
Lots of stars are being created in the very middle of the photo (near the brightest star). These areas appear as cloudy pillars, shooting upward.
Full-size high resolution image available here: https://astrob.in/p0bjrx/0/
