Jeff's Blog - Saturday, May 29, 2020 - Galaxies and a Comet

In the last couple weeks, I've enjoyed several clear evenings to photograph M81 and M82, two fairly bright galaxies in Ursa Major, from my light polluted patio under Bortle 5 skies. M81 is the galaxy on the left in the photo below, and M82 is on the right. You can click on the photo to make it bigger, then click on it again to put it back onto the page. The galaxies are physically close to each other in space, both being about 12 million light years away. So the light you're looking at in this photo left those galaxies 12 million years ago. This photo was built from 140 individual photographs: about half were 30 second exposures, the other half 60 second exposures, both series were shot on the night of May 20th-21st, 2020. About 40 other photos were involved to calibrate those 140 photos, then the result was heavily processed and extremely cropped to get this "best" photo. M81 is a "Grand Design Spiral Galaxy", one of the galaxies we deem to be pretty due to their symmetric spiral arms. M82, on the other hand, is a Starburst Galaxy in which an unusually high rate of star formation is currently happening (rather, it was happening 12 million years ago) possibly due to gravitational interaction with the more massive nearby M81 galaxy. The evidence of this burst of activity in my meager photo consists of the irregular red tendrils near its center.

The stars superimposed on the very distant objects in this photo and others on this page are stars in our own galaxy, named the Milky Way, which is 100,000 light years in diameter. Therefore, every star in this photograph is within 100,000 light years of the Earth, and there are 11,900,000 light years of empty space between the furthest of those stars and the next nearest things in the photograph, the M81 and M82 galaxies.

    
M81 on the left, and M82 on the right

I told you that the photo above was an extreme crop from the original photo taken in my camera. As evidence of this, below is the entire processed frame from the 30-second set of photos on May 20th, 2020. It's about 14 full-moons wide, by 10 full-moons tall, so about the size of the piece of sky you can cover with your hand when held as far from your face as possible.

    
The uncropped May 20th photo showing M81 and M82, as well as NGC 3077, NGC 2976, Comet Smol, and NGC 2959

M81 and M82 are just to the left of center in this original full-frame photo. But there's more here to see. Above and to the left of M81, in the 11 o'clock direction, is a fuzzy spot which is NGC 3077. I'd assume this galaxy is much further away from us than M81 and M82, but actually it's just a smaller galaxy in the same gravitationally-bound group as M81 and M82. A brighter fuzzy spot is located at 8 o'clock from M81, a little bit further away than NGC 3077 was. That slightly-larger fuzzy spot is the galaxy NGC 2976, also a member of this same so-called M81 Group of Galaxies.

But the real fun is still to come. I know you've seen it. That bright fuzzy splotch at 4 o'clock from M81, about 1/3 of the way across the frame. Total serendipity - I had no expectation of this - but it's actually a comet, identified with the prosaic name of "Comet Smol (C/2017 T2 PANSTARRS)". This one is a pretty faint comet and consists of a blue oblong coma (the head of the comet which is the icy snowball flying through space) with a very faint tail (the part of the icy snowball that the sun's heat has melted) which is pointing downward in the photo. Comets are members of our solar system, so they're quite close to us. This comet is in an orbit around the sun (just as our Earth is) but is in a very oblong elliptical orbit (rather than the Earth's nearly circular orbit). At the time of this photograph, it was about 200 million kilometers from my camera, which is about 0.00002 light years. It's closer to us than anything else in this photo, by far.

As you know, comets move across the sky, but very rarely at a speed you would notice. They just move a very small amount each day against the background stars because they're rarely close enough to Earth to have discernible motion to our eyes. The 3 photos below, taken on May 22, 24 and 25, clearly show the movement of the comet. In the photo above, on May 20th, the comet was well below the line from M81 to M82. In the first photo below, on May 22nd, the comet is nearly on the line from M81 to M82. In the second photo below, on May 24th, the comet is above M81 and M82, and on the third photo, May 25th, the comet is right at the top of the frame. (the fuzzy spots at the bottom of that last photo are just stars, but it was a hazy night with high clouds so they have a glow about them). In the first two photos below, you should be able to see that the comet has a very faint tail that points downward from the coma.

    
By May 22, the comet had moved up just a bit
    
By May 24, the comet had moved up considerably
    
By May 25, the comet had moved to the top of the frame

But before we leave, lets go back to the second photo on this page, the first full frame photo taken on May 20th, 2020. It's shown again as the first photo below. In the second photo below I've enlarged the region from M81 to NGC 2976 at 8 o'clock from M81. In the enlargement, at the center of the bottom of the photo is the very-small hard-to-see fuzzball of NGC 2959, which is much further away than anything else in my original photo, at 204 million light years. Though there's no detail to be seen in my photo of this galaxy, it still amazes me that light, travelling at 186,000 miles each second, for every second during 204,000,000 years, has managed to somehow reach my camera and now your eyes via this web site delivering ones and zeros to you from a computer in my basement.

    
Just another copy of the uncropped May 20th photo showing M81 and M82, as well as NGC 3077, NGC 2976, Comet Smol, and NGC 2959
    
NGC 2959 in the fuzzball at the center of the bottom of this blown-up part of the May 20th photo, 240,000,000 light years away

Ain't astrophotography grand?

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