YOUR NIGHT SKY IN THE RMI: THE GALACTIC CLUSTER

JULY 22, 2017 / JORDAN VINSON

It is summer time in the Marshalls, and that means great views of the Milky Way’s galactic core. To check it out, look south-southeast after sundown and fix on Scorpius, a large, popular constellation that looks like a scorpion— or, if you will, a giant fishhook. Look leftward a few degrees and fix on Sagittarius, the eight brightest stars of which resemble a sort of teapot. (Following ancient Greek beliefs, Sagittarius is really a centaur.) The true rotational center of the galaxy lies behind the star forming Sagittarius’ “spout” on its right side and the stars forming the tip of Scorpius’ venomous tail (or the pointy end of the fishhook). The bulge of the core encompasses this area and reaches northward a few degrees well into Ophiuchus, the serpent bearer.

Toward the northernmost portion of the bulge, you’ll notice a nice bright “star” that doesn’t flicker like nearby Antares, the red supergiant in Scorpius. That’s Saturn. Moving through orbit at an average speed of 515,000 mph, Saturn, Earth, the sun and the rest of the solar system take 230 million years to do a complete revolution around the galactic bulge. The last time we were in this position in orbit around the center of the Milky Way (in terms of our position relative to neighboring galaxies in the Local Group) it was the Triassic period on Earth, a time when the first dinosaurs and mam mals were evolving into distinct life forms.

Located nearly 30,000 light years from the core, the Earth’s vantage point of the entirety of the galaxy is somewhat limited. The NASA depiction above illustrates our position relative to the rest of our spiral-armed Milky Way. While we have brilliant views of the core and the galactic arms reaching outward on our “side” of the galaxy, we cannot see past the galactic bulge and enjoy the sights of the star clusters, nebulae and more lying “on the other side.”

There’s another thing astrophysicists cannot see but know is there. It’s the supermassive black hole lying at the dead center of the core. Named Sagittarius A, it is a massive emitter of radio waves and is believed to be spatially large enough to fill the orbit of Mercury and contain the mass of 40,000 suns.

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