And so a new year begins. By this statement we mean, of course, that Betelgeuse has finally emerged in the pre-dawn sky following a seemingly interminable two-month hiatus within the obscuring twilight veil. One might recall that Betelgeuse vanished into the evening twilight on May 21st. Its July 21st return heralds the beginnning of another Orion Cycle.
If you had been watching the eastern pre-dawn sky this morning you might well have caught a glimpse of Orion’s eastern shoulder star for a fleeting moment before the intensifying dawn twlight absorbed it. Had you been watching the eastern pre-dawn sky yesterday, the sky would have been just slightly too bright to allow you to observe Betelgeuse. If you watch the same sky tomorrow morning, you’ll see it for a full four minutes longer than you were able to watch it today. Astronomers say that around latitude 43 degrees, Betelgeuse’s heliacal rising is July 21st: the first morning the star becomes visible. In the same vein, astronomers will say that Betelgeuse’s heliacal setting is May 21st: the last time the star remains visible before it exits stage west.
Unless you’re living north of the 82nd north parallel, where it is circumpolar and always visible, or you live south of the 82nd south parallel, where it is never visible, Betelgeuse, like the other stars, will regularly rise and set. In all the regions between 82 degrees north and 82 degrees south, Betelgeuse will not remain visible all year, but, instead, will spend some time too close to the Sun to be seen. The duration of its absence, as well as the dates of its heliacal rising and setting, varies with latitude. Because Betelgeuse is positioned about eight degrees north of the celestial equator, its helical rising date will be earlier the farther north you venture. Betelgeuse emerged a few days ago well north of us. Of course, those farther south will have to wait a bit longer before Orion’s fire opal star ascends out of the morning twilight.
We all know that stars (Polaris apart) do not remain in the same place throughout the year. They rise four minutes earlier each day as a consequence of Earth’s orbital motion around the Sun. This increase accounts for nearly half an hour a week, or two hours every month. By the end of August, Betelgeuse will be visible for nearly two and a half hours before it fades into the twilight. Six months from now, Betelgeuse will return to prominence in our winter evening sky, just as it’s done for centuries.
This is not a constant, however. At least not in the long term. The nearly 26,000-year precessional wobbling of Earth’s axis will gradually shift Betelgeuse and the other stars so that eventually they’re heliacal risings and settings dates will change. The earliest generation of Stonehenge builders would have seen Betelgeuse vanish into the evening twilight by mid-March and return by mid-May: the very time when we now bid it farewell.
However, this long-term shift accounts for only one degree every 73 years. For the rest of our lives, we can expect Betelgeuse to disappear around May 21st and return on July 21st.
So, through today’s heliacal rising of Betelgeuse we are connected, albeit remotely, to next May, a time that seems now to be decades in the future, but which will, most assuredly, arrive with startling haste. A new Orion cycle begins.
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