Constellation Arrowhead – connecting the dots

A fleeting vision in our night sky: the constellation Arrowhead. Graphic by Ger Erickson.

Beneath a night sky of diamonds scattered across the black velvet of space, our earliest ancestors looked up and saw patterns. They connected the dots: a group of stars became the diagram of a lion or bear, a queen or a hunter and his dogs. Those patterns were permanent. From millenium to millenium, the position of the stars never strayed, the diagram was never distorted.

But some heavenly objects did stray. The astronomers of ancient Greece named those objects planetai, wanderers. The planets. The star constellations are set in stone, but the planets wander into formations of their own that, like star patterns, remind us of familiar images. One of these temporary constellations is visible now. Let’s call it Arrowhead.

Step outside at 10 p.m. Pacific Time and look south. Across the horizon hangs the constellation known to the Babylonians as Mul Gir-tab, the creature with the burning sting. We call it Scorpius, the scorpion. Some civilizations have juggled two metaphors: the star pattern reminded the Indonesian Javanese people of both a swan (Banyakangrem) and a leaning coconut tree (Kalapa Doyong).

But in July of 2016, people of all cultures can savor the sight of a new, though fleeting, constellation. The planets Mars and Saturn plus the star Antares trace the pattern of an Arrowhead. The point of the arrow is Mars. The arrow’s lower barb is Antares; its upper barb, Saturn.

Scorpius and its current retinue of planets plus permanent retinue of star clusters. Graphic by Ger Erickson.

Arrowhead or no Arrowhead, the southern night sky of 2016 is rich in delights to the eye and imagination. Mars sweeps past Antares every two years but stargazers have linked the two reddish objects for millenia. “Mars” is the name the Romans gave the red planet, but the ancient Greek word for Mars is “Ares.” The Greeks considered the reddish star in Scorpius to be Ares’ rival: thus the name “Antares” – anti-Ares. The god of war, Ares, and the heart of the scorpion, Antares: a clash of formidable and forbidding powers in the heavens. 

Mars “sweeps past Antares” in only a visual sense. The light of Mars that strikes your retina takes 4½ minutes to make its current 50-million-mile journey to Earth. The light of Antares takes 550 years. How can a star so distant shine so brightly? It’s easy – when your radius is 883 times greater than the Sun’s and you shine 12,000 times brighter than the Sun. Were Antares to replace the Sun at the center of our solar system, it would engulf Earth and Mars.

Mars and Antares share a reddish hue, but the hue springs from a radically different source. Stars generate their own light; planets reflect the light of their parent star. Antares’ reddish light is the fire of an enormous thermonuclear furnace burning at a cool 6,500 F. The red of Mars is sunlight bounced off a few million square miles of iron-rich minerals – a big desert.

Got binoculars or a small telescope? Swivel over to Scorpius and you’ll be treated to the vision of some of the finest star clusters in our local cosmos – the M7 cluster and the Northern Jewel Box in particular.

The planet Saturn. Photo by 3quarks/iStock/Getty Images.

And let’s not space out on that golden planet way out in the solar suburbs, the farthest planet visible to the naked eye: Saturn, which completes one orbit of the Sun in 29 Earth years. Saturn is a prime example of the strangeness of the cosmos. The ringed planet is large enough, minus its rings, to fit nine Earths across its diameter like pearls on a string. Yet as a “gas giant,” Saturn is so light it would float on water. And as telescope owners are well aware, Saturn’s ring system is approaching its maximum tilt toward Earth. Late 2016-early 2017 is prime time to view one the wonders of our local universe: the golden rings of the golden globe we call Saturn.

Stargazing is more than an aesthetic pleasure. From the beginning of our species’ days on Earth, the ability to make the connection between patterns in the physical world and the world of the imagination has helped us survive and flourish. When we gaze into the night sky of A.D. 2016 and see a scorpion – or an arrowhead – we’re re-enacting an ancient and impactful feat. May you enjoy keeping that tradition alive this special summer by stepping out beneath the stars and connecting the dots.