Throw open the door and welcome back Orion at dawn. The Hunter's return brings relief from the heat and gives us a fresh shot at exploring winter deep-sky objects in comfort.
We might rise at dawn to see an eclipse, a bright new comet, or a meteor shower. But few of us would deliberately lose sleep to see a constellation. Unless that constellation was Orion. Every August, I attend a star party where seeing Orion rise in morning twilight is something of a badge of honor. If you're serious about making the most of the night, you'll stay up until Betelgeuse flits between the oak leaves.
After weeks of summer heat and humidity, we seek the cool breath of winter, finding it just before dawn in the guise of Orion. I love seeing him tilt upward above the trees in late summer while listening to the soft clatter of leaves in the breeze.
Exploring the Orion Nebula while wearing a short-sleeved shirt is a rare privilege, and there's no better time to grab a pencil and make a sketch. Or take a guided photo of the Belt or one of the constellation's many nebulae. Sure beats numb fingers and the agony of wind chill.
Mid-southern latitude skywatchers must associate their Orion with the coming of summer, a concept difficult to imagine for northerners but no less valid. So it is with associations we make between the stars and the seasons. Frost and the rich aroma of leaf decay are forever paired with the Pegasus Square as icy stillness is with Orion.
Earth's tour around the Sun recycles the constellations once a year. Every August at dawn, we stand with our backs to the galactic center, looking outward through the Orion Arm (or Spur) and into the Perseus Arm of the Milky Way galaxy. Nearby stars within the Spur align to form the striking belt and rectangular outline of the Hunter. Every day that passes, he's up four minutes earlier than the one before, "pushed" westward by Earth's revolution to the tune of 1.6 million miles (2.6 million km) a day. Come October, Orion rises at midnight; in late December, he appears at nightfall.
Each year's reacquaintance with the constellation provides another opportunity to dig out that deep-sky object or double star that weather or commitments prevented you from seeing the previous season. We all know the benefits of recycling; when it comes to skywatching, it means the opportunity for a fresh look with every yearly orbit.
You may do things differently, but I return at least 10 times a season to gaze at the Orion Nebula, which offers so much on so many levels.
A short list of things to look for inside this beautific bubble:
* Trace the extent of the nebula's outer "arms." Can you follow them all the way out until they touch to form a loop?
* Dig out the half dozen or so faint stars buried within the "curdled milk" of the nebula's bright central region near the Trapezium.
* Check the brightness and behavior of young variable stars such as T Orionis, which show continuous and erratic changes in brightness easily followed in small telescopes.
* Resolve the fifth and sixth members of the Trapezium multiple star on nights of good seeing.
* Examine how the appearance of the nebula changes when viewed through a variety of narrowband filters. You'll be surprised how different the it looks in OIII vs. H-beta filters.
* Visualize the nebula in three dimensions by deliberately viewing the dark patches of nebulosity in both M42 and neighboring M43 as in the foreground silhouetted against the bright material behind it.
And that's just one object in a constellations replete with every kind of deep-sky bonbon but a globular cluster. (For that you'll have to hop down to nearby Lepus to M79.) Sometimes a new telescope inspires taking a fresh look at a returning constellation. This season, I'm looking forward to wending my way along the brighter (northern) half of Barnard's Loop with a 10-inch short focus instrument and O III filter. Such a large object could mean several nights of adventuring. Maybe I'll put on a sweater and begin my pilgrimage in September.
Would that we could live lives more in line with the great cosmic cycles, say on the order of 100,000 years. That's about the time remaining for the Orion Nebula to process itself into a Pleiades-like star cluster, a dazzling heap of stellar gems with a few remaining wisps of lingering nebulosity. Would we still find more to see in Orion on that distant date as Earth traces yet another orbital loop? Of course!