July’s journey through space and time

SKYWATCHER’S GUIDE

The globular cluster Messier object 92 (M92) in Constellation Hercules is populated with many red giants, hot luminous horizontal branch stars, low mass main sequence stars and blue stragglers. The approximately 400,000 stars are thought to be around 13.8 billion years old, nearly the same age as the universe. A globular cluster is so named due to its roughly spherical shape. NASA, ESA, GILLES CHAPDELAINE — COURTESY PHOTO

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The night sky in July a phenomenon that reminds skywatchers how remarkable it is just to be alive and to experience such wonders.

As impressive as winter’s constellations are, they don’t hold a candle to the staggering grandeur of the summer’s immense Milky Way galaxy stretching from horizon to horizon, arcing high overhead.

During the winter months, Earth’s night skies face out toward the great beyond, but in the summer they face inward toward the Milky Way’s galactic core. Observers can see three of the Milky Way’s overlapping arms, or bars, populated by hundreds of millions of suns, wrapped around the center’s supermassive, albeit invisible, black hole.

Some of the nights’ features can be seen with the naked eye, but the darker the sky and the more powerful your light-gathering equipment, the more your spirit is buoyed. Consider visiting an international dark sky park in Colorado like Dinosaur.

After twilight, look due south and about 23 degrees above the horizon to locate magnitude 1.05 Antares, the heart star of Constellation Scorpius, which reaches its highest position for the year — culminates — at 9 p.m. July 20.

Antares, the so-called “rival of Mars/Ares” due to their similarities of color, is a monstrously huge red supergiant that varies in size about 19 percent. If imagined at the center of the solar system, the variable pulsating star’s surface would extend past Mars’s orbit, ending up somewhere in the middle of the asteroid belt. At a distance of 550 light-years, the light that you see this month was emitted from the star the same year that Michelangelo was born in Caprese, Italy.

S-shaped Scorpius can easily be envisioned as a scorpion with a long tail with stinger tail stars, sometimes called the “cat’s eyes.” When combined with Constellation Libra, as was done by the ancient Greeks, the image of the arachnid’s colossal claws, or chelae, reaching toward zenith is even more vivid. In fact, Libra’s alpha and beta stars are still called Zubenelgenubi and Zubeneschamali, the southern and northern claw, respectively. Libra was seen as a separate entity by later Greeks, formally becoming its own constellation in Greco-Roman Claudius Ptolemy’s 2nd century astronomical treatise “Almagest.”

Due to its location upon the Milky Way, Scorpius holds many deep sky objects including open clusters and nebulae. Under moderately dark skies, look near the stinger to find Messier object 7, the Ptolemy Cluster, an open cluster of 30 naked-eye and 80 telescopic blue stars. More than 120 blue stars in the Butterfly Cluster (M6) glitter prettily low in the south some 1,560 light years distant. The light you see this week left M6 during the last days of the collapsing Western Roman Empire.

Directly above Scorpius is Constellation Ophiuchus, the serpent bearer, which culminates at 9 p.m. July 25. Two beautiful globular clusters, M10 with approximately 100,000 stars and M12 with 200,000, lie at the heart of the constellation.

It’s perhaps surprising that the famous Constellation Hercules, also culminating at 9 p.m. July 25 directly above Ophiuchus, has no more than two stars brighter than magnitude 3 out of a total of 22 defining main stars. Point the telescope directly overhead to observe M92, a globular cluster of between 330,000 and 400,000 stars.

This spectacular cluster is about 13.8 billion years old — the oldest known cluster and about the same age as the universe. At 26,700 light years distant, the photons that are absorbed by your retina cells tonight left the cluster when vast ice sheets covered North America, humans were painting on caves in Lascaux and Chauvet, France, and megafauna roamed far and wide.

Find nearby M13, the Great Hercules Cluster, a haze in binoculars that can be mistaken for a nebula.

The Delta Aquariid meteor shower rambles from July 12 to Aug. 21. Although it doesn’t have a defined peak, look for 15-20 meteors per hour on moonless nights around July 30. About 5-10 percent of Aquariids leave persistent trains, trails of glowing ionized gas that last a few seconds after the meteors have passed through the atmosphere.

The moon is full 2:36 p.m. July 10 and is called the Full Buck Moon.