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Posted By: GeoJerry, 01-15-2019, 02:03 PM

I was fascinated by this photo from Colorado CJ and wanted to get an idea of the scale of the image. The blue line is the diameter of the galaxy and according to Wikipedia is 110,000 light years in length. How long would it take an Apollo astronaut to travel across the dust ring in the central part of the galaxy, i.e. travel the red line from start to finish?

If the blue line is 110,000 light years, then with my engineer's scale the red line measures out to about 2,040 light years. Since light travels 186,000 miles in one second, and there are 31,536,000 seconds in a year, the red line measures 1.197 x 10^16 miles in length. Our intrepid astronaut, if he could travel the straight line at 25,000 miles an hour, would need about 55 million years to cross the dust ring. This also means that a pixel from the galaxy image would be on the order of tens of light years across. I hope I got my math right.

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01-15-2019, 02:12 PM - 1 Like   #2
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It gets really weird when you consider even higher speeds; because not only are you considering the amount of time it'd take to get to your destination but also the amount of time you'd actually experience.

Sagan’s Andromeda Crossing

Thus, for a round-trip with a several-year stopover to the nearest stars, the elapsed time on Earth would be a few decades; to Deneb, a few centuries; to the Vela cloud complex, a few millennia; to the Galactic center, a few tens of thousands of years; to M31, the great galaxy in Andromeda, a few million years; to the Virgo cluster of galaxies, a few tens of millions of years; and to the immensely distant Coma cluster of galaxies, a few hundreds of millions of years. Nevertheless, each of these enormous journeys could be performed within the lifetimes of a human crew, because of time dilation on board the spacecraft.
01-15-2019, 02:59 PM   #3
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I am the second nerd to view this thread. I suspect there will be many (and I will be in good company!). Thank you for the information. It is of no practical use to me but because I am human I just have to know.
01-15-2019, 06:18 PM - 1 Like   #4
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That would be a lot of "Are we there yet?"if you bring the kids along!!!!

01-15-2019, 07:25 PM   #5
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And it gets even more challenging if one thinks about the gravity field of Andromeda (which seems to be of similar mass to the Milky Way). Our Sun (and the Earth and all the Solar System) for example are whizzing around the Milky Way at some 500,000 miles per hour just to stay in orbit. So that intrepid astronaut may need a lot more velocity than 25,000 mph to avoid being dragged back into the black hole at the center of Andromeda.
01-15-2019, 09:20 PM - 1 Like   #6
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The Andromeda galaxy and our Milky Way are on a collision course and are expected to impact one another in almost 4 billion years. Mind you, the stars are sufficiently spread out that the chance of actual solar collisions is thought to be minimal. As well, it is not known for sure if it will be a direct hit or a near miss. More info here:

Andromeda?Milky Way collision - Wikipedia
01-16-2019, 03:09 PM   #7
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And just think - this is just one galaxy in a universe with billions of galaxies.


01-16-2019, 07:53 PM   #8
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The astronaut would also be long dead. To do it in someone's lifetime you'd need to get closer to the speed of light so relativity helps out, but the energy required would be phenomenal. The fastest interstellar probe so far is Voyager 1 at about 62,000 kmh. According to my calculations, it would take 35,520,480 years to travel 2,040 light years at 62,000 kmh. The fastest spacecraft we've built is now the Parker Solar Probe, but even so its speed is still an insignificant fraction of light speed.
01-17-2019, 07:58 PM - 1 Like   #9
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Adding a soundtrack ��

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