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Artist’s impression of the Milky Way, showing the location of our Sun and the spiral arms in our galaxy. Image credit: ESO.

The above image spans about 90 degrees from north on the left to east on the right, and 90 degrees top to bottom. It’s assembled from 16 frames, each a 60-second exposure with a 50mm lens. The green glow along the horizon is air glow, perhaps with a bit of aurora thrown in, and the bright yellow glow at right is light pollution from Radium, 45km away in the Columbia River valley.

Along the left edge of the image, the Milky Way glitters with a million stars and is mottled by dark patches of interstellar dust and gas that block the light of the stars behind them. The Sun is located about 2/3 of the way from the center of our galaxy, and when looking towards Perseus and Auriga we are looking outwards through the disk of our galaxy, away from the center, towards the edge of the disk.

This part of the Milky Way contains dozens of open star clusters, with the brightest and clearest ones annotated in the image. Star clusters are groups of young stars, roughly the same age and formed in the same interstellar gas cloud. They are still loosely boundy together by gravity, and usually contain many large, bright, short-lived stars. The largest and brightest stars have a mass 100x our Sun, and are 1000s of times brighter. They lead short lives because their mass causes them to consume their hydrogen quickly, and will end up exploding as a supernova after only a few million years. Our beloved Sun, brilliant as it is, is a low-mass star, which burn for billions of years.

Between Cassiopeia is the Perseus Double star cluster, a beautiful sight in binoculars, that is just visible to the naked eye under these dark skies. The famous Pleiades cluster, the Seven Sisters, is just rising above the peaks in the center of the image.

M31 Andromeda Galaxy, image credit: KarelTeuwen.be

M33 Triangulum galaxy, image credit: VLT Telescope, ESO

M74 galaxy, Hubble image

Our home galaxy is part of the Local Group of galaxies, and our two largest and nearest neighbors are clearly visible in this image. The largest and closest is the M31 Andromeda and the 2nd closest is the M33 Triangulum galaxy. “Near” is relative in the universe, and Andromeda is 2.5 million light-years and Triangulum is 2.7 million light-years away. M31 is just barely visible to the naked eye, appearing as a faint fuzzy patch under very dark skies. M31 was the subject of a great scientific debate in 1920s over the nature of these “spiral nebula” and was the key to opening up the true vastness of the universe when Edwin Hubble was able to measure the distance to this galaxy, definitively placing it far outside our own galaxy.

On the right side of image, in the constellation Pisces, is the M74 galaxy, a spectacular spiral galaxy that is face on from our perspective, and at 32 million light-years away it’s far outside of our local group.

The brilliant red “star” at lower right is Mars, very bright right now because it’s nearly at it’s closest approach to Earth, which happens roughly every two years, this year on Oct 13.

Pleiades is part of the constellation Taurus, and the fact that it’s rising already is a reminder that winter will soon be upon us, so we better enjoy these warm nights while we can!

– Darren Foltinek