Tag Archives: planets

February Skywatch


It’s been an exciting month for skywatchers! Last month I talked about some of the easy sights for backyard telescopes in the constellation Orion, which is looming large in our evening skies. The first couple weeks of February though, offer an even more impressive naked-eye sight in our morning sky: the possibility of glimpsing all five visible planets arranged in a straight line across much of the sky. The arrangement is best right now and will continue throughout the first week of February.

Standing outside before dawn, look to the east. Venus is bright above the eastern horizon, and if you have a clear view you may catch elusive Mercury even lower toward the Sun’s glow. Saturn is above Venus to the south, with Mars riding high in the southern sky. Jupiter is the bright object beyond Mars, toward the southwest. Altogether, the planets make a lovely arrangement that spreads across nearly the entire southern skies. The best time to look for them is just before sunrise, around 5:30 to 6:30, at which time the Sun’s glare begins to wash them out.

The mornings of this first week also bring an additional sight to the arrangement: a lovely slender crescent moon which passes by Mars on February 1st, is near Saturn by the morning of the 3rd, and moves down toward Venus on the 5th. An arrangement like this, with all the planets neatly in a row along the ecliptic, is fairly rare, so make an effort to rise early and take a look at this vista of the closest worlds of our solar system.

I mentioned last month I’d spend this column talking about telescope basics, but planetary happenings are enough to push that back a bit. Besides the arrangement of visible planets, astronomers grew quite excited this week with news of new evidence that might indicate the existence of an undiscovered ninth planet in our solar system.

When you look up at the pre-dawn sky this week, you can see all the visible planets in our solar system, which are all the planets that were known throughout most of history. It was only in the late 1700s that we began to realize there were other planets in our own backyard, and this most recent announcement may herald that our family of planets is about to expand again, for the first time in over a century.

All of this obviously makes astronomers pretty excited but also cautious, as there have been lots of false claims for Planet X in the past.

Until William Herschel stumbled upon Uranus in his telescope sights in 1781 and subsequent calculations showed that it wasn’t something like a comet, Saturn was considered the outer boundary of our planetary system. As astronomers observed the new planet though, they eventually realized that something was causing it to speed up and slow down in its orbit. The French astronomer Le Verrier correctly deduced that this was caused by an additional planet in our solar system and predicted its location, and Neptune was thus discovered in 1846.

Since then, astronomers on and off have believed they’ve seen evidence in the motions of the outer planets to hint at other planets lurking out there in the darkness. It was while searching for such a world that Illinois native Clyde Tombaugh found Pluto in 1930. However, it was later realized that Pluto was far too small to be causing any gravitational perturbations and in fact the perturbations themselves didn’t actually exist.

But this is where things get interesting, because it turned out that Pluto was actually simply the first in an entire class of tiny, distant solar system bodies called Kuiper Belt objects. Indeed, it was the discovery of more and more of these objects—some farther away and more distant than Pluto—that eventually caused Pluto to be reclassified as a dwarf planet.

Now, two astronomers from Caltech have published a paper arguing that the orbits of a handful of Kuiper Belt objects show evidence for an even larger body, about the size of Neptune, in the far reaches of the solar system. The reasoning is similar to that which led to the discovery of Neptune: it appears as though a large, massive object is affecting the orbits of these objects. Mathematical modeling indicates these observations could be explained by a ninth planet.

Of course this doesn’t mean that it’s there for sure. That’s how science works: observations provide evidence, and scientists offer a theory or hypothesis to explain it. A good hypothesis is one that can be tested. And that’s exactly what’s happening now: telescopes are being trained toward the outer reaches of the solar system to see if this posited body does indeed exist. If it does, it should be large enough to spot in very large telescopes, despite its enormous distance.

And if it is spotted, the total number of planets in the solar system will go back up to the number we learned in grade school.

This column originally appeared in the Kankakee Daily Journal.

Planets & Stars

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.