Counting Stars: Images of the Deep Sky Above Swarthmore College

In March of this year, the Swarthmore Physics Society (SPS) bought a new telescope for astrophotography, using it to take pictures of galaxies and nebulae. Led by Wilber Dominguez ’22, Simon Ji ’23, and Caleb Scott-Joseph ’24, and under the guidance of Professor Rivera, the goal of the project was to introduce students to amateur star-viewing and generate more interest in astronomy throughout the campus community. On most clear nights, we and a handful of other interested students have been taking pictures with the telescope from the roof of the science center. We have also organized two trips to Cherry Springs State Park, a dark site in central Pennsylvania. In the article below, we present some of the best images we obtained so far.

Subject 1: Bode and Cigar

Bode’s galaxy (right) and the cigar galaxy (left) are interacting gravitationally, and their mutual influence is very noticeable. The cigar galaxy, being the smaller of the two, is much more strongly affected by the gravity of its large neighbor. Due to the gravitational pull of the Bode’s galaxy, the cigar galaxy forms stars at a rate hundreds of times higher than expected of a galaxy this size. The newly formed stars have immense stellar winds which eject a lot of gas from the galaxy, causing the red features seen in the center of the cigar. Bode’s galaxy, on the other hand, is a classic grand design spiral galaxy, about half the size of the Milky Way. This beautiful pair of galaxies was the first object we successfully imaged with our telescope, and thus it holds a special place in authors Ji and Scott-Joseph’s hearts, as it was the first object we observed with the astrophotography telescope in March 2022. This image is the result of about 2.5 hours of total integration, and boded well for our future astrophotography endeavors. 

Subject 2: Andromeda

The Andromeda Galaxy is the closest large galaxy to the Milky Way and was first recorded by the astronomer Abd al-Rahman al-Sufi in 964 AD, seven centuries before the invention of the telescope. Despite being 2.5 million light-years away, the Andromeda galaxy is clearly visible from a dark site and takes up a region of the sky five times wider than the full moon. Andromeda is a massive galaxy containing roughly one trillion stars, although the stars are so far away that you cannot resolve any of them individually. Andromeda is actually moving towards us at 300 kilometers per second and will in fact collide with the Milky Way in roughly five billion years.

We created this image from 320 three-minute exposures (16 hours in total) that were digitally integrated into one image. By stacking all of these exposures together, we were able to increase the signal-to-noise ratio of the image.

Subject 3: Triangulum

Sadly, unlike the name suggests, the Triangulum Galaxy is not shaped like a triangle. Instead, it is shaped like an elliptical blob with spiral arms. Charles Messier discovered it in the 18th Century, but he actually hated his own discovery because it was, to his great disappointment, not a comet. Triangulum has a high rate of star formation because it is being gravitationally perturbed by Andromeda, much like the cigar galaxy albeit on a smaller scale. All of the red regions, like the red spot in the lower right of the galaxy, are nebulae like the ones featured later in this article. These, however, are much bigger and brighter than the ones in the Milky Way, which is why we can see them even though Triangulum is so far away.

Subject 4: Pleiades

The Pleiades is one of the most famous star clusters in the night sky. Often used as an ancient eye test, you were considered to have good vision if you could see at least seven stars. You should probably get a new prescription for your glasses if you can’t see seven in a perfectly dark sky. The blue dust you see around the stars is actually behind them — the light gets scattered off the dust back towards the earth, allowing us to see it. Interestingly, it is thought that this blue dust is not actually associated with the Pleiades but is an unrelated cloud drifting behind them. This phenomenon is an example of a reflection nebula where dust is illuminated by nearby stars, causing a faint glow to appear.

Subject 5: The Heart Nebula

If you are in need of a good Valentine’s Day gift, consider sending a postcard containing the Heart Nebula. Discovered by William Herschel (who also discovered Uranus), the vividly red emission nebula is a hot spot for star formation. Located within the bright constellation of Cassiopeia (Big W), the Heart Nebula is called the Running Dog Nebula by some astronomers under the influence of special mushies. Scott-Joseph and Yerin Chang ʼ23 on the Science Center rooftop took this image during the fall equinox.

Subject 6: The Crescent Nebula

Also discovered by William Herschel, the brain coral-shaped Crescent Nebula glows brightly within a thin veil of dust emissions from the Sadr Region. Similar to the Heart Nebula, the Crescent Nebula is an emission nebula which emits light in frequencies corresponding to ionized hydrogen and oxygen. Because most of the light from the nebula is emitted at a few very specific wavelengths, we can use a special filter that only allows light of these wavelengths and blocks out most of the light pollution, enabling us to see faint details of the nebula even in the light-polluted suburban skies of Swarthmore.

Subject 7: The Eastern Veil Nebula

This nebula is known by many other names: the Bat Nebula, the Eastern Veil Nebula, and the Phallus Nebula (if you are Ji or Dominguez). The Veil Nebula is 2,400 light-years away and was formed from a supernova explosion over 20,000 years ago. Using a dual-bandpass filter, the camera detected brilliant streaks of red and blue, which correspond to H-Alpha and O-III emissions, respectively. This image is a 90-minute exposure, and it was taken in May 2022 by Ji and Dominguez during the first Society of Physics Students (SPS) astrophotography trip to Cherry Springs State Park. Professor Jesse Rivera subsequently stacked and edited the raw images.

Cherry Springs

Plagued by frequently cloudy skies and light pollution from nearby Philadelphia, Swarthmore is far from the ideal place for astronomy. Although the light pollution issue can be alleviated by using filters and stacking techniques, we cannot capture the level of detail that can be seen in a photo taken in a perfectly dark sky.

Luckily, one of the few remaining “dark sky spots” in the Eastern United States can be found within a few hours drive from Swarthmore. Sitting on top of the Allegheny Plateau in the Appalachian Mountain Range, the Cherry Springs State Park, unfortunately, has neither cherries nor springs. The Swarthmore Society of Physics Students (SPS) organized two successful trips to the park in May and September 2022. Many of the students who went on the trip saw the Milky Way for the first time with their naked eyes. With the help of Professor Jesse Rivera and Nate Fay (who drove all the way from UMass Amherst!), we took some wonderful photos of targets such as the Deer Lick Group and Iris Nebula, as well as wide-shot pictures of the dark sky. To learn more about the trip, you should read The Phoenix article from Chang! 

A wide-angle photo of the observation field at Cherry Springs. The combination of long-exposure and bright moonlight made the picture look more like daytime, even though the sun had already set.

Group photo for the second Cherry Springs Trip in September 2022. A total of 28 students, along with Professor Rivera, came to camp overnight at the park.

SPS Students setting up the telescope and learning about the process of polar alignment during the first Cherry Springs trip in May 2022.

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