The magnificent constellation Orion may be seen at various times, during most of the year. For example, we may glimpse the celestial giant low in the eastern sky a half hour before sunrise on August 1, its rise may be noted at midnight October 1, and we may enjoy its splendor low in the west in the evenings of early spring. However, for most sky viewers the colossal celestial hunter is most associated with sparkling winter nights. Along with its innate stellar gems, Orion serves well as an indicator to neighboring jewels of the sky.
Starting around Thanksgiving, bright stars in and around Orion begin to dominate our views of the southern evening sky. Renewing acquaintances with these luminaries is a pleasure savored by many, and we especially enjoy such sights during wintery walks after dinner.
For those unfamiliar with this magnificent stellar display, I recommend a quick sky tour on the next clear evening. Mark your starting line at the unique array of three stars marking Orion’s Belt. The symmetry of this trio, with nearly equal stellar separation and brightness, is eye-catching even though the group doesn’t comprise the most vivid members of Orion’s realm. Nevertheless, the Belt stars’ location halfway between bright yellow-orange star Betelgeuse and brilliant white Rigel provides an unmistakable centerpiece for our winter evening stargazing.
Arrayed from east to west the Belt stars’ names are: Alnitak, Alnilam, and Mintaka. Each appears white with brightness rankings of the second magnitude; however, they have disparate distances from the solar system of approximately 800, 2,000, and 900 light years. Therefore, the Belt’s striking relationship is a lovely coincidence—not an actual physical association. Orion’s boxy figure is completed with two additional second magnitude stars, Bellatrix and Saiph, complementing brighter Betelgeuse and Rigel. Both appear white, with Bellatrix to the northwest of the Belt and Saiph to the southeast.
Once spotted, Orion’s identity usually stays with us for a lifetime, and it provides fine service as a guide to beautiful and interesting adjacent sky objects. Visualizing Orion’s Belt as the shaft of an arrow, it can be seen as pointing toward the northwest aiming our sight to Aldebaran, the star which marks the “eye” of Taurus the Bull.
An exciting sky event occurring the night of January 19 will be quite visible (if it’s not cloudy) with the help of binoculars or telescopes. The bright gibbous Moon occults first magnitude Aldebaran for viewers in most of the continental United States and Canada. The unilluminated eastern edge of the Moon moving from west to east will get between us and Aldebaran, hiding the star to begin the occultation. For viewers in New York City the event is predicted to begin at 9:31:53 p.m. the evening of the 19th. Aldebaran will emerge at the bright western side of the lunar disk as the star reappears at 10:43:29 p.m.
For viewers outside the tri-state area, you can go to The International Occultation Timing Association site, scroll down to “Upcoming Bright Star Occultation Events” and click the (Aldebaran) “20 Jan - Occultation of alpha Tau” event. Note there is a large initial list of disappearance times for 1003 locations, next you have to scroll way down to reach the separate list of reappearance times.
Continuing our tour of the winter evening sky, follow the line of Orion’s Belt toward the lower left (southeast) to reach Sirius, brightest star in the entire night sky.
Striking another sight line from Rigel up past Bellatrix will take up to one of the most vivid stars in the sky—Capella in the constellation Auriga the Charioteer. Comprising two nearly identical giant stars, with each presenting a color blend that appears as a single white object, the pair is 43 light years from our eyes. Separation of components of Capella is about equal to the span between the Sun and Venus. Capella is nearly overhead during evening hours of winter, a fitting place for a star with such a name.
Whereas Capella, with a brightness magnitude of zero (a click more vivid than first magnitude Betelgeuse and Aldebaran), quickly catches our attention, two second magnitude stars – the “twins,” Castor and Pollux, should not be overlooked during an overview of winter highlights. Again starting at brilliant Rigel at the lower right of Orion’s figure, scan past Betelgeuse then continue about 1-1/2 times further to catch the twin stars of Gemini. The northerly star of this pair is Castor, a complex system of six mutually orbiting stars, located 52 light years from the Solar System.
The other twin star of Gemini is Pollux, at a distance from us of 34 light years and with a notable feature of its own. Pollux presents a yellow blend of light and it’s orbited by a planet of mass about 2.9 times that of Jupiter, the solar system’s biggest world. Pollux’s planet is at about the same distance from that star as Mars is from the Sun. The “super Jupiter” orbits Pollux once every 590 Earth days.
Before concluding our brief winter tour, take another look at Orion’s Belt. Next, drop your gaze a bit to the center of the space bounded by that trio and Saiph and Rigel. There on exceptionally clear nights we can see a third magnitude “object” that’s actually a triple star system named Iota Orionis. The Iota system’s distance from us is about 2,300 light years, making it one of the most distant stars seen with unaided eyes. It’s a member of a vast star assembly known as the Orion OB1 stellar Association, and Iota helps mark what is known from classical mythology as the Sword of Orion. The Iota Orionis star system is on the edge of Orion’s spectacular Great Nebula, one of the most marvelous celestial sights. On clear frosty nights that nebula has the appearance of a “fuzzy star”—a highlighted portion of a vast region of star birth activity.
In my next post, I’ll explore in more detail several of the remarkable sites in this wonderful region of the sky.