We’re all familiar with light. On Friday evening, March 1, 2019, at Pupin Hall, Rose Gibson, graduate student in astronomy at Columbia University, surveyed the electromagnetic spectrum, and how we detect and make use of each part of it to learn about the cosmos.
Gibson started by reminding her audience of the various components of the spectrum, from radio waves to gamma rays, with an emphasis on the relationship between a photon’s energy and its wavelength. She then proceeded to a discussion of spectroscopy—measuring an object’s spectrum—and photometry—measuring its broadband brightness—and how each is used in astronomy.
First up were radio waves, the lowest-energy form of light. NASA’s Deep Space Network, which is a worldwide network of space communication facilities, uses dishes in California, Spain and Australia to provide 24/7 two-way communication capabilities with our interplanetary spacecraft.
Next she discussed microwaves. As an aside, Gibson gave her audience a useful tip: when heating food in a microwave oven, it’s better to place the food off-center to ensure even heating of the entire dish, as the microwaves in the oven tend to focus in the same spots for the duration of the cooking session (take that, Marie Kondo!) More to the point, Gibson recounted the history of the discovery of the Cosmic Microwave Background Radiation (CMBR), the stretched-out, ubiquitous leftover radiation from the early universe, by Arno Penzias and Robert Wilson in the 1960’s.
Moving on to infrared, Gibson showed images from the Spitzer Space telescope. Infrared light is particularly useful in examining stellar nurseries, where nebulae swaddle their star-forming regions in dust, which infrared light has the ability to penetrate.
For visible light, Gibson focused on the use of the transit method used by the Kepler and Tess satellites to detect exoplanets. In addition to being the sole form of light which human eyes can see, visible light has the distinct advantage over other wavelengths of using equipment which is considerably cheaper to build.
Gibson then discussed X-Ray astronomy, particularly the study of pulsars. She compared optical and X-ray images of arguably the most famous pulsar of all, that of the Crab Nebula, the supernova remnant from 1054 AD. It is X-ray astronomy which enabled the measurement of the central pulsar’s spin rate of 33 milliseconds.
Finally, Gibson mentioned LIGO and gravitational waves. Although gravitational waves are an entirely separate phenomenon not directly related to light, such observations can provide an alternate form of astronomical observation, complementary to those using light, thereby adding to our understanding of the universe.
A lively Q&A discussion ensued, particularly as concerns the CMB, which clearly piqued the Columbia audience’s curiosity.