Punching Past Pollution

What’s in the sky over New York? Most of the city’s residents are proud of the fact that you can find almost anything in Gotham, but if you’re reading this you’re aware of some of the things we can’t have: The Milky Way, Nebulae, Galaxies, and the other features of our universe that can be seen from dark places – but not from here.

I’m done with this. Well, actually I’m obsessed with this. After edging into astrophotography from more routine backyard observing, I’ve been surprised and impressed at every stage with the amount of sky that can be revealed by leveraging the technology advances of the past 20 years. The silicon revolution – including extraordinarily sensitive imaging chips and computer processing power available to consumers – have enabled me to image deep space objects right over my own house, in the suburban “red zone” 18 miles north of Times Square. I can’t match the images of faint galaxies or dark nebulae that can be achieved from the darkest locations, but I already have my own portfolio of pretty good renderings of many Messier objects and more – from the City of Yonkers, just above the Bronx. While many of my colleagues in the AAA’s Astrophotography Group are eager to travel away from the city in pursuit of magnificent dark site skyscapes, I’m more inclined towards seeing how far we can get using different techniques to punch through the city’s light pollution in order to make the invisible visible for New Yorkers.

How well does it work? You can be the judge. Here are several versions of the Great Orion Nebula, M42. This is an object that is just bright enough to be viewed from the city under good conditions as the middle star in Orion’s sword. Through a medium power telescope, you can see the core of the nebula and it was one of my favorite backyard targets long before I tried long exposure astrophotography. It should look something like this:

photo credit Mauri Rosenthal
M42 looks like this through a small scope in the city.

This image was taken with a “planetary camera” on an unguided mount, using similar techniques that can be used to get nice images of Jupiter, Saturn, or the moon from just about anywhere including the city.

I was truly surprised, once I learned how to generate longer exposures with a cooled astro-cam, that this is only a small fraction of the magnificent nebula. The next image is my first serious stab at it from Westchester. In this case I used a guided Questar 3.5” telescope with a focal reducer and a Starlight Xpress CCD camera to shoot about 90 minutes worth of 2 and 4 minute exposures plus another 60 short exposures. The varied exposure lengths allow “HDR” (High Dynamic Range) processing so that both bright and faint details come through in the finished image.

photo credit: Mauri Rosenthal
Guided long exposure with HDR processing reveals elaborate nebula structure. From Yonkers, NY.

The full nebula is an extraordinary mass of interstellar dust and gas which resembles a bat or butterfly; and when the image is properly color balanced, it displays extensive regions of red, blueish gray, and brown.

Wow! So what about the city? Last spring I was able to shoot at M42 shortly after sunset from one of the AAA Highline Stargazing Parties. I’ll show two versions here; the first is very similar to the “live view” on my laptop for the portable imaging rig I carry in a backpack down to the High Line. I’ll describe my equipment in more detail in a future column.

photo credit: Mauri Rosenthal
Laptop view of M42 from HighLine Stargazing Party, April 2017. Borg 55FL lens; Starlight Xpress SX-694 CCD camera; iOptron CubePro mount.

The city’s lights generate the splotchy gradients in the image. The breadth, colors, and detail of the nebula do come through on the laptop, affording a view that is difficult to obtain via visual observation through a telescope of any size, let alone a scope we might haul on the subway. But the gradients make a mess.

photo credit: Mauri Rosenthal
M42 from HighLine, April 2017. Same data as previous image with additional processing to remove gradients.

Using image processing software which has been optimized for deep space astrophotography, I removed the gradients to generate this image, which is a not too bad rendering of M42 from Manhattan. It’s not the finest astrophoto you’ll ever see, but it does demonstrate that we can shoot through the city’s light pollution and bring the deep sky to New York.

Next issue: Ultraportable imaging equipment for city and suburban use.

You can view my deep sky images at http://www.fluidr.com/photos/124244349@N07 or https://www.instagram.com/mtrastronyc/