Celestial Triangle

Good Evening, Shipmates!

I’d like to invite you all to step outside this Saturday and Sunday about an hour after sunset and look to the west; if you have clear or mostly-clear skies, a reasonably low horizon and not too many lights interfering with the view you’ll see three bright “stars” in a small, almost equilateral triangle formation, gleaming in the late twilight. All three will be of approximately the same brightness, but of wildly differing colors—one a steady golden hue, the second orange or yellow-brown, and the third a twinkling light blue. Unlike the annular solar eclipse in May or the Transit of Venus in June, you won’t need a telescope or special filters to enjoy this vista, but a pair of binoculars will show their colors plainly. Be sure to bring the kids out for this one, and have some fun with the facts and figures listed below.

So, what are we looking at? Most of you will already have guessed that one or more of our targets are planets, and you’re right; we are looking at a Conjunction (an apparently close approach of two or more celestial bodies as seen from our perspective) of the planets Saturn (Yellow or Golden), Mars (the Angry Yellow-Brown Planet) and Spica (alpha Virginis), the brightest star of the constellation Virgo and the 15th brightest star visible in our skies. As celestial events go this kind of apparition isn’t really very rare, but it is quite lovely, and given all the attention being paid to Mars these days quite an appropriate reason to brave the mosquitoes on a warm August evening.

As readers of my Blog will know, I have a soft spot for our ruddy, diminutive neighbor—the “fourth rock from the sun”. I’ve watched it through the telescope for much of my life through a succession of “oppositions” (see the Blog entry “Red Planet” for details of my obsession with the God of War) and kept careful track of our unmanned explorations over recent decades. A small constellation of orbiting probes have been scanning the planet for quite a few years, and rovers slowly crawling the Martian landscape have answered many of questions (and raised many more, which is as it should be) about the geology, weather and history of Mars. This weekend, in fact, is expected to mark a milestone in our Martian study; during Sunday night the largest interplanetary rover yet—NASA’s “Curiosity” is to enter our brother planet’s atmosphere and land to begin a new phase of the search for answers. “Curiosity” is a very ambitious program—and a risky one—but I await work of its safe arrival in Gale Crater with great anticipation.

On to Saturn. The sixth world out from the Sun, most famous for it’s spectacular and intricate system of rings, has also visited by man’s robotic emissaries. Even now the nuclear-powered Cassini probe orbits the “Lord of the Rings”, measuring and imaging the massive gas-giant planet’s storms, rings, and many moons. Run a search online for Cassini images of Saturn; prepare to be amazed!

Spica, as noted above, is one of the brighter stars gracing our skies, a Blue Giant binary (double star) over 10 times the mass of our Sun. Its companion star, which orbits the primary every four days, weighs in at over 7 times the mass of the Sun as well, making this a pretty impressive system. Spica is one of the closest Blue Giants to Earth.

Think about that for a moment. As you enjoy the quiet spectacle of the conjunction, and perhaps watch in weeks to come as the “Dance of the Planets” continues with Mars closing in on Saturn and both changing position relative to Spica, consider that Mars is the nearest of these three objects at an approximate distance of 240 million kilometers, Saturn next at about 1.5 billion km, with Spica a mind-pummeling 2.4 quadrillion kilometers*. Put another way, the Sun’s light reaching us now was reflected from Mars’ oxidized surface 14 minutes ago, Saturn’s icy rings and cloud tops nearly an hour and a half back in time, and shone out from Spica’s twin suns over 260 years in the past (in approximately 1752, the year that Ben Franklin demonstrated the principles of electricity using a kite, a key, and a thunderstorm!).

With all the distances involved, and the relative sizes of the participants in this celestial show, I think perhaps the most impressive fact is that the apparent brightness of each of our three neighbors is about the same; two planets, one tiny and the other the second largest in our solar system, and a double star incredibly far removed from our Solar System, all shine in the sky with nearly the same brightness, each in their distinct hues of red, gold and blue. Beautiful!

Space, as Douglas Adams once put it, is big. Really big. And this conjunction of two planets and a bright star is an opportunity to experience and share some appreciation of the scale of our Solar System and stellar neighborhood. It’d also be a good opportunity for a barbeque! So enjoy the burgers and steaks, and the show in the western sky; I’ll be watching as well from Joshua Humphreys’ bridge wing, out here on the Blue Stuff.


Tom Epps
Able Seaman
USNS Joshua Humphreys
Persian Gulf



* Please let me know if I flubbed the maths on that one!