Double and Multiple Stars: And How to Observe Them by James Mullaney

My rating: 4 of 5 stars

“The amateur astronomer has access at all times to the original objects of his study; the masterworks of the heavens belong to him as much as to the great observatories of the world. And there is no priviledge like that of being allowed to stand in the presence of the original.”
-Robert Burnham, Jr. (my emphasis)

One of my goals this summer has been to spend more time with the fleet of telescopes I have access to through my university. I teach about the night sky and I research scientists who spent their lives studying the night sky, but I find I’ve had very few opportunities myself to get to know the sky outside the simulated confines of the planetarium dome.

Double stars are an ideal target for starting out. Unlike nebula, galaxies, and other deep sky targets, double stars are bright and fairly easy to spot. They’re like tiny gems hidden up there in the sky. The sky is a map, and sometimes it’s hard to learn. It’s often difficult to tell whether the star you have in your sights is actually the star on your charts that you think you might be looking at. Yet if your resources tells you it’s supposed to be a tight, nearly equal double with a separation of six arcseconds, and if you see it staring back at you like a pair of distant celestial headlights, then you know you’ve found it. They’re targets that are immediately rewarding, bright enough to spot on moonlit nights or in light polluted skies, and varied enough to be interesting.

Take separation, for instance. My six-inch reflecting telescope hasn’t had any troubles on the evenings I’ve been observing splitting pairs down to a separation of about four arcseconds. Izar in Bootes, with a separation of just under three arcseconds, shows a hint of the bluish companion star elongated from the edge of the brighter orangish primary. Depending on the viewing conditions each night, my scope should theoretically be able to distinguish even closer pairs, but the challenge of realizing this is part of what makes these targets rewarding.

Then there’s color contrast. You view an image from the Hubble Space Telescope, and it seems like space is vibrant with color. Yet actually viewing a nebulae or galaxy with the eye in a telescope eyepiece reveals perhaps a hint of greenish glow at best. With double stars though, the color contrast in star pairs is often quite dramatic. Different people observe different colors, which are artifacts of both intrinsic color differences in the stars and contrast between them.

Finally there’s simply the conceptualization of what you’re actually looking at. Most very close doubles are binary stars, which means systems of two (or more) stars rotating around a common center of mass. These are the objects John Herschel and others were studying in the early 1800s in order to directly calculate stellar masses. (They’re still the only method we have for directly measuring the mass of stars.) These star pairs, I argue in my dissertation, were instrumental in changing the way people thought of the stars: seeing them as vast physical systems. They continue to inform our popular stellar conceptions; recall the iconic scene of the double sunset on Tatooine in Star Wars.

Fortunate for the enthusiast like me there are a host of guides and resources regarding showcase double stars to observe. The Cambridge Double Star Atlas is a great place to start, and banking on the usefulness of that resource I purchased this observing guide by one of the authors of that atlas: Double and Multiple Stars and How to Observe Them. This slim guide is an ideal introduction to the topic, exploring in an overview the practical aspects of observing these objects but also going into some detail on the real scientific contributions an amateur could pursue. Mullaney’s enthusiasm for the topic is contagious, from the introductory physical descriptions of double stars as astrophysical objects (reminescent of the language popularizers were using to describe them in the 19th century) to his own advice on keeping observing journals.

Though the prose is good, I had two big complaints with the work. The first is the quality of printing. It was clear as soon as I cracked the cover that this was a print-on-demand title by Springer, with the pages consisting of scans of a PDF or other electronic image. The text is not crisp or clear, and on many pages there is grey stippling in what should be the white space between letters and lines. It’s not bad enough to make the text illegible, but it is annoying. The second is that Mullaney says the work is really two resources in one: a background or overview on double stars and observing them, along with an observing guide of locations and descriptions for one hundred showcase double stars. Yet– though I haven’t compared it star to star– this list seems to duplicate the list provided in the Cambridge Double Star Atlas. So if you’re looking for a lot of new double stars to admire, you might be disappointed.

“What we need is a big telescope in every village and hamlet and some bloke there with that fire in his eyes who can show something of the glory the world sails in.”
-Graham Loftus (my emphasis)