Saturday, October 24, 2015

Tonight's Sky for October 24: The Awesome Great Andromeda Galaxy at Zenith at Midnight

Tonight, the Great Galaxy (there are many) in Andromeda will be at zenith (straight up) at midnight. This is an interesting sight for three cool facts that many people do not even know about..

First up: being a lover of trivia, the Great Galaxy is the most distant (2.7 million light years) object capable of being seen under all but the darkest skies (eagle-eyed observers may be able to see more distant galaxies under the darkest of skies, of which none exist East of the Mississippi). To put that in perspective, when the photons of light that you see radiating from Andromeda tonight left the galaxy, there were no humans, although our distant ancestors were starting their long journey from ape to human. Not only do astronomers see across space, they see through time. Another big thought: if the galaxy were to fall into the monster of all black holes (no black hole is that big) tonight, we wouldn't know about it for another 2.7 million years. 

The night sky in a couple billion years.

Second: we are looking at a crash of cosmic proportions in progress. Our own Milky Way Galaxy and Andromeda are gravitationally bound together, being by far the largest members in our galactic neighborhood, known as the Local Group of galaxies. Unfortunately, these two titans are on a collision course. In about 4 billion years, the Milky Way and Andromeda will 'crash' into each other at a combined speed of around 250,000 mph (or about 70 miles per second). Why the quotes? While the galaxies will run into each other, the chance of two stars actually hitting each other are virtually non-existent thanks to the immense distances that separate the stars. What will happen according to current models is this: the collective gravitational interaction of the two galaxies moving through each other will fling stars in all directions and the stars not flung out into space will eventually slow down and form a combined galaxy.

Third: as another fun point of trivia, the Great Andromeda Galaxy was the subject of one of the first deep-sky astrophotos. Photography as we know it was invented in 1827 and shortly thereafter astronomers started pointing camera-equipped telescopes at the Moon, with impressive results. Below is the first known photograph of the Moon, taken by JW Draper in March, 1840 with a daguerreotype camera. 

The 1st known picture of the Moon.

However, while quick lunar snaps were easy to master, long exposures required to gather enough photons to produce an image of a dim deep sky object required both advances in camera (more sensitive media) and observatory (more precise tracking) technology. Result: the first photos of a deep sky object (M42 and the Pleiades) was not taken until 1886 by Issac Roberts, who would go on to photograph Andromeda in the following year. That photo is below.

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