Stargazers: Pre-dawn sky a preview of coming attractions
Despite living in the Anza-Borrego Desert of Southern California — one of the hottest places on Earth — I long for summertime, not only for its warm (OK, hot!) weather and abundant growth, but because its nighttime sky is amazingly rich. So, it’s usually around March when I begin wandering outdoors before dawn to sneak a peek at what awaits us in the evening sky half a year down the road.
There’s no great mystery about why the early-morning sky appears different from that of the evening; our planet rotates on its axis once every day, and as we spin with it, we face outward in different directions at different times.
Tonight, we face the stars associated with the Northern Hemisphere winter, toward constellations such as Orion and Taurus shining brightly in the southwestern sky after dark. They are followed closely behind by those of early spring: Cancer, Leo and even the Big Dipper. By dawn, however, the Earth will have turned us far enough around that those star groupings will be replaced by others — those that make up what we know as the summertime sky.
The true splendor of this part of the heavens can be truly enjoyed only by viewing it from dark rural areas with no light pollution. That’s because its most beautiful feature is the wispy band of the Milky Way, which you’ll see arching low across the sky from northeast to southeast.
Beginning in the northeastern sky, you’ll find the faintest part of the Milky Way passing through the “W” shape of the constellation Cassiopeia, the queen. As you follow it toward the right, you’ll soon encounter three bright stars — Vega, Deneb and Altair — that outline the shape of what Northern Hemisphere stargazers know as the summer triangle. This geometric shape offers a convenient milepost, because the Milky Way passes directly through its center.
Further to the south you’ll see the Milky Way flowing past the celestial arachnid known as Scorpius, aka the Scorpion. Scorpius is one of the few constellations that actually resemble their namesakes, with its claws at the top, its bright reddish-orange star Antares representing its heart, and its long curving tail and stinger, which now, unfortunately, lie just below the horizon.
The first thing you’ll notice about the Milky Way is that it’s not uniform in brightness. It is instead mottled with dark rifts along its entire length. These are known to astronomers as giant molecular clouds, or GMCs, massive globs of interstellar material that stand in stark silhouette against the Milky Way’s brighter stellar band. It is within these GMCs that massive star- and planet-forming birthing areas exist, hidden from eyes not privileged enough to be peering with infrared telescopes.
Now, if you just can’t tear yourself from a warm bed to check out this early-morning celestial tapestry, I certainly understand. Simply mark your calendar, because in only a few months, all this will appear at a less ungodly hour!
Visit Dennis Mammana at www.dennismammana.com.