Tag Archives: stars

November Skywatch

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Cass

This month starts with us relaxing our clocks back into a more natural rhythm with the Earth’s diurnal cycle, as we conclude Daily Saving Time the first Sunday of November and fall back one hour to Standard Time. This means our evenings get darker sooner, and the stars come out earlier for sky-watchers. It also means clock noon and solar noon once again roughly coincide. With evening arriving earlier, this month we’ll continue our series of looking more closely at sky objects that can be seen through sidewalk telescopes even from the streets and backyards of Kankakee.

The bright planets are still mostly grouped in the pre-dawn sky, but evening begins with the constellation Cassiopeia high in the northern sky. This recognizable, easy-to-find constellation hosts a pair of impressive multiple-star systems. Nearby are some lovely clusters and the famous Andromeda Galaxy (often unfortunately washed out by the light pollution in the skies above town).

Cassiopeia is shaped by turns as a 3, a W, an E, or an M depending on its orientation in the northern skies. In the early evening skies of November, it looks like an angular number 3, its bottom pointed down toward the northeast, with five bright stars marking the ends and each angle of its zig-zag shape.

To find our first double star, η (eta) Cassiopeiae, look for a fairly bright star halfway down the second “zag” of the zig-zag number three. This star is one of the most famous binary stars of the night sky. Though it looks like a single star, through a telescope it’s revealed as two stars—a bright yellowish star with a dimmer, reddish companion nearby. Measures of the relative positions of these stars over decades have revealed that this system is actually gravitationally bound, with an orbital period of about five hundred years. The system itself is about 20 light years away, but the two component stars are separated from each other by a distance of only 70 times the distance between the Earth and the Sun,

Once you’ve tried your hand at finding and viewing η Cassiopeiae, the next target in Cassiopeia is ι (iota) Cassiopeiae, a moderately bright star just below the constellation’s southernmost “zag.” Drawing a line through the southernmost two stars of Cassiopeia’s zig-zag, extending again about as far as the distance between the stars, will get you there. Through a telescope, ι Cassiopeiae will look like a smaller version of η Cassiopeiae. In fact though, it’s not a double but a triple system, with the brighter component actually itself a very close double star. Under high magnification and clear viewing, you may be able to just barely spot a small blue companion close to the yellow primary star. This entire triple system is about 160 light years from Earth.

If we go east from the bottom of Cassiopeia, toward the constellation Perseus, we’ll run into the Double Cluster (NGC 869 and 884). Visible with the naked eye in dark skies, these have to be “felt out” in brighter city skies. Once spotted though, they’re still an impressive sight. They are best viewed at lowest magnification in the telescope (or even with a pair of binoculars) and are examples of open or galactic clusters, composed of hundreds of young (six to twelve million years old) stars seven thousand to eight thousand light years away. In the telescope eyepiece they fill the view with dozens of bright, crowded stars.

Now, leaving the best for last (and omitting the fabulous Andromeda Galaxy which is nearby but washed out in city skies), we move to Almach, also known as γ (gamma) Andromedae, to the southeast of Cassiopeia, marking one of the feet of the constellation Andromeda. Almach is one of the most impressive double stars in the sky. Its component stars are a bit closer together than those of η Cassiopeiae but they have a brilliant, sharp color contrast between the yellow/gold primary and the dimmer blue companion star. Like ι Cassiopeiae though, one of the components of Almach (the dimmer blue star) is itself a close double as well, though I have not been able to separate these components in my backyard telescope. It doesn’t stop there though: one of those stars is in addition an even closer binary star with a period of only three days, making the whole system actually a quadruple star system.

I occasionally hear that the early evenings of autumn make people feel winter is finally here and sometimes even lead to seasonal doldrums. I maintain though that darker, earlier evenings are a fantastic opportunity to get out and learn about the dynamic, tangled lives of those bright stars above us. Hopefully these objects give you a place to start!

This column appeared first in the Kankakee Daily Journal.

Planets & Stars

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Planets: Ours and Others: From Earth to ExoplanetsPlanets: Ours and Others: From Earth to Exoplanets by Therese Encrenaz
My rating: 4 of 5 stars

The art of an insightful, timely, and scientifically rigorous overview is a difficult one. This is compounded when the subjects are as broad as planets and stars, respectively. Fortunately for the educated non-specialists, there two slender volumes succeed where many astronomy texts fail: they provide a comprehensive, up-to-date survey of two fields with enough breadth to be useful and accessible to the astronomy educator while retaining enough technical grit for those desiring more depth.

The first volume (Planets), by an atmospheric planetologist at the Paris Observatory, frames the current state of exoplanetary research and the search for life in the context of comparative planetology, starting with Earth and moving through our planetary system.

Beginning with a brief introduction to observing and exploring planets (including exoplanetary detection), Encrenaz moves into a description of theories of planetary formation and then on to the bulk of the book, treating the physical properties of planets. Using Earth as test case and exploring things like geological activity and the water cycle, she provides in-depth comparison of the atmospheres, compositions, and internal structures of the planets of our solar system, touching briefly on some outer-system moons as well.

All of this sets the stage for the final third of the book, a look at exoplanetary systems– their discovery, their properties, and a quick overview of the status of the search for life in the cosmos. The chapters here remind that this is not a book on exoplanets exclusively: rather, it’s a survey of what we know about planets, which any more must include a detailed exposition of the ways other planetary systems are informing this knowledge.

In some respects, this is more helpful than a book on exoplanets alone, allowing an understanding of our own planetary context in light of these new discoveries.

Birth, Evolution and Death of StarsBirth, Evolution and Death of Stars by James Lequeux
My rating: 4 of 5 stars

The second volume is a survey of the physical processes (including a fascinating and detailed analysis of the interstellar medium) governing the life of stars. Lequeux, also of the Paris Observatory, takes a slightly more technical approach. Indeed, it was at times difficult to follow his account of the complex processes taking place within a star at various points in its life cycle.

However, the technical aspects provide a conceptual rigor often glossed over in more popular texts. Topics covered include the birth, physics, evolution, and death of single stars as well as a chapter on the “zoo” of double stars. It concludes with a glimpse of the larger questions of galactic evolution that stellar life and death play into.

Perhaps most importantly, this account discusses the many open questions in stellar evolution, especially star death, and the importance of modeling stellar interiors.

Both books are slender, less than 200 pages each, and filled with diagrams, images, and (especially in Lequeux’s) equations. Both are translations of works originally published in French, and the awkward language at times bears witness to this though never actively detracting from the text.

Neither volume is a textbook (there are no problem sets, for instance), nor are they purely popularizations, maintaining a balance between general survey and in-depth technical treatment. Often I read a survey text and learn nothing new; in contrast, these works are introductions written by active experts in their respective fields, lifting the veil on the physics behind the concepts but keeping a wide and fairly accessible scope, filled with a wealth of new information.

This review first appeared in the September 2015 issue of The Planetarian.

Double and Multiple Stars and How to Observe Them

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Double and Multiple Stars: And How to Observe ThemDouble 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)