The Space Between the Stars: Astronomy Students Study Interstellar Medium

By Marcus Hughes ’18

The space between stars is emptier than any vacuum we can create on Earth, but it still contains dust, hydrogen, helium, more hydrogen, some carbon, and more hydrogen. This “interstellar medium” is a critical part of the galaxy because it’s where stars are born and die.

The main telescope in the observatory, the 24-inch telescope is the large white tube at the center. Light comes in the top of the tube, reflects off a mirror at the bottom, and then reflects off another mirror before passing through a filter and into the camera, the large blue and black parts at the bottom of the telescope. Around the main telescope there are other smaller telescopes that can be looked into with just your eye, no camera needed. These are used to get a second look or sometimes to look at the sun.

In Astronomy 402, we study the physical processes that govern the interstellar medium, from giant molecular clouds to superheated supernova remnants. For a project this semester, we were each asked to image a unique nebula, a cloud of dust and gas that is lit up for varying reasons. In the case of my nebula, the dust and gas was illuminated from other stars, like fog that can be seen because of light that reflects off it. In other nebulas, light shines from the gas itself, like a fluorescent bulb.

Other classes such as Astronomy 330 and Astronomy 111 also use the observatory. These students are required to complete various projects. One of the possible projects is taking images using the 24-inch telescope. This image is of M51, the Whirlpool Galaxy. Over the past several years students have taken nearly 200 pictures of it in the observatory. This image is the average of the best images taken.

Using the 24-inch telescope on the roof of the Thompson Physics Laboratory, we took images with different filters: red, blue, visible, H-alpha, and [O III]. Each filter is a piece of glass placed between the camera and the sky that only permits certain wavelengths through, providing different information about the physical conditions in the nebula.

The outside of the observatory dome located on top of Thompson Physics Building.

Narrowband filters like O[III] and H-alpha only let through very small wavelength ranges. The names O[III] or H-alpha refer to the fact that we’re looking at light from doubly ionized oxygen (O[III]) or ionized hydrogen (H-alpha) – in other words, these elements have lost one or two electrons. On the other hand, the blue, visible, and red filters let through a broader amount of light to produce a more general image.

M78, the reflection nebula I observed with MeiLu McDermott, is roughly 1,600 light years from Earth. The light you see in the center is light bouncing off of interstellar dust, little clumps of silicon, carbon, magnesium, sulfur, and other heavier elements.

Looking at the [O III] can indicate the presence of oxygen and constrain temperature models. This information is then combined to identify different temperature and ionization phases in the interstellar medium.

The control room of the observatory. The telescope is robotically controlled using the a program on the center monitor. Another program is then used to take pictures. The right monitor is used for spectroscopy and the left monitor is used to make sure the telescope is properly set up.


To learn more about the observatory or astronomy in general, you can attend a planetarium show (at the planetarium in Currier) every Friday. After each show, the observatory is open for public observing. The observatory is also open nightly, Monday through Thursday from 9 to 12, for students to complete their observing projects.