Timothy Ferris on galaxies, the universe, and time

Abell 2744, Pandora’s Galaxy Cluster, from the Hubble Frontier Fields. Click through and get lost for a while.

This passage has been lodged in my head since I first read it years ago, and it is still the best short explanation I’ve read for the scale of galaxies and the universe. From Seeing in the Dark, pages 253-254:

Were the Sun a grain of sand, Earth’s orbit would be an inch in radius, the solar system the size of a beach ball, and the nearest star another grain of sand four miles away. Yet even on that absurdly compressed scaled, the Milky Way galaxy would be a hundred thousand miles wide. Galaxies are so big that once you get up to their scale, the universe starts to take on an almost country-cottage intimacy. The larger galaxies in clusters like the Local Group, to which Andromeda and the Milky Way belong, typically lie only a couple of dozen galactic diameters apart from one another – comparable to dinner plates at the ends of a twenty-foot-long dining table. Add in the galaxies’ halos of stars, globular clusters, associated hydrogen clouds, and dark outer disks, and they almost impinge on each other. On the same scale, the Virgo supercluster, of which the Local Group is an outlying member, comprises ten thousand plates scattered across an area not much larger than a football stadium, and the entire observable universe has a radius of only about twenty miles. From a galaxy’s point of view, the universe isn’t all that large.

The Andromeda Galaxy in ultraviolet light, from NASA’s Galaxy Evolution Explorer. You want to click through for the full image – trust me.

The trouble is that it’s difficult – probably impossible – for a human to make the mental leap to galactic scale. The very concept of space is inadequate for dealing with galaxies; one must invoke time as well. The Andromeda galaxy is steeply inclined to our line of sight, only fifteen degrees from edge-on. Since the visible part of its disk is roughly one hundred thousand light years in diameter, the starlight reaching our eyes from its more distant side is about one hundred thousand years older than the light we simultaneously see coming from the near side. When the starlight from the far side of Andromeda started its journey, Homo habilis, the first true humans, did not yet exist. By the time the near-side light started out, they did. So within that single field of view lies a swath of time that brackets our ancestors’ origins – and that, like the incomplete dates in a biographical sketch of a living person (1944-?), inevitably raises the question of our destiny as a species. When the light leaving Andromeda tonight reaches Earth, 2.25 million years from now, who will be here to observe it? We think of Einstein’s spacetime as an abstraction, but to observe a galaxy is to sense its physical reality.

Andromeda as photographed by Isaac Roberts in 1899 (borrowed from Wikipedia)

…As objects of study, galaxies are bottomless. If we spent eons observing the Andromeda galaxy with ever better equipment, we would, presumably, learn a great deal – indeed, one hopes that this will happen – but there would always be more to learn, if only because so many things keep changing there. To pick a literally glaring example, it is estimated that more than fifty thousand stars have exploded in Andromeda in the past two million years: The light from all those supernovae is already hurtling through space toward our telescopes, part of Andromeda’s past and our future. A galaxy is not so much a thing as it is a grand, glorious exemplification of the scope of cosmic space and time.

Astronomy Quote #2

M33, the Triangulum galaxy, with pink star-forming regions and bluish clusters of newly-formed stars.

Once the sky was fully dark I had a look at the Triangulum galaxy, which at a distance of less than three million light years from Earth is a local object by intergalactic standards. Its rangy spiral arms, tangled with glowing clouds of gas, spilled out beyond the field of view. As often happens, I was struck by the fact that all of these things, unimaginably big or small or hot or cold as they may be, really are out there. Like giant squid or loaves of French bread–and unlike, say, postmodernism or public opinion polls–they confront us with the regality of the materially real.

– Timothy Ferris, Seeing in the Dark, p 64

 

Photo from APOD.

Astronomy Quote #1

M1, the Crab Nebula, the remnant of a star that exploded almost 1000 years ago. The heavy elements in the universe--including the ones in our bodies--were created and dispersed by exploding stars.

I know that the molecules in my body are traceable to phenomena in the cosmos. That makes me want to grab people in the street and say, “Have you heard this!?”
– Neil DeGrasse Tyson

 

Photo from APOD.

Here’s something weird

Apparently Sirius, hands down the brightest star in the sky, was blood red in antiquity but blazes blue-white today, just 1500 years later. The evidence is compelling. The problem is, no known astrophysical process can account for the change. Read all about it here, and go here for more discussion.

By the way, I love it when stuff like this comes along. It doesn’t mean that science is wrong or that science doesn’t work. It means that there is plenty of stuff that we haven’t figured out, and some of it is, like, huge. As someone who loves figuring stuff out, I take a lot of comfort from that. I want some of that pie for myself. But in this area, at least, I can also get some satisfaction just from looking at other people’s plates.

How wonderful that we have met with a paradox.  Now we have some hope of making progress.  ~Niels Bohr