As the weather finally warms (we hope) and spring progresses, many stargazers look up with mixed feelings. The glories of the winter Milky Way are setting in the west, and the summer Milky Way, even more spectacular than its winter sibling, just peeps above the horizon before morning twilight.
However, with our own galaxy out of the way, we begin to see with greater clarity the larger universe. That’s what drives normally sane people to keep their 10-year-old clunker of a car to purchase instead hundreds – nay, thousands – of dollars of telescopic equipment to see the Realm of the Galaxies.
Rising in the east just after dark is a great void where our own galaxy does not block the view of the cosmos. Go out around 10 p.m. and look east. The Y-shaped constellation Virgo, the Virgin, looks a bit like a champagne glass tilted slightly as if some cosmic giant has lifted it to take a sip.
You can’t see it with just your eyes, but overflowing from Virgo’s rim is a froth of hundreds of faint patches of light that we have come to call galaxies. The whole area is littered with them. They overflow Virgo’s cup into Coma Berenices and Leo above and Corvus and Crater below.
Just 100 years ago, astronomers looked at those faint ovals and spirals of light and debated furiously about what in heaven’s name they were. Many concluded that they were stars like our sun in the process of formation.
Others argued that they were distant “island universes” like our Milky Way, but the mind and heart simply reject such a notion. How could there be so many galaxies with so many stars? How could the cosmos be so vast? Was not the Milky Way itself huge beyond human imagination?
We know better now. The universe is vast beyond measure and is made up of perhaps a trillion galaxies. Those “island universes” are, for the most part, expanding away from each other at mind-bending velocities.
The beginning of that revolutionary change of perspective can be traced to a single moment when an Indiana farm boy made good.
Vesto Slipher had grown up under the dark skies of Mulberry, Indiana. His fascination with the sky paid off when he left the farm for Indiana University in 1896 to study astronomy.
He had to wait a bit before finishing his doctorate, however. A publicity-hungry amateur astronomer named Percival Lowell had built himself a honking huge telescope in the Arizona desert. Lowell needed a real astronomer to do something with it. In 1901, the inexperienced Slipher took a “temporary” position at Lowell’s observatory to do so. He ended up spending the rest of his life there.
And thus it was that young Slipher faced the august and aged body of professional astronomers at the American Astronomical Society meeting of 1914. What he was about to say would forever change the way we look at our universe.
When it came to understanding the cosmos, Slipher had the same problem that faces all astronomers. If you want to know what a star or galaxy is made out of, you can’t reach out and grab a sample of it. Astronomers must work with the only information they have – the light from those galaxies gathered by the giant eyes of telescopes. They have to use a considerable amount of ingenuity to squeeze from the light all the information hidden there.
One of the main things that astronomers do with light is to split it into its component parts, or spectral lines.
Most school children have done so. They have held a prism in a beam of sunlight and looked at the lines of color that are produced – red on the low end, yellow in the middle, and violet on the high end. They are looking at a simple spectrum of the light.
Astronomers use very sophisticated prisms to split the light from various astronomical objects into many bands of color. From the presence or absence of certain of the colored bands and their placement or order, they can tell quite a lot about the composition, distance and even the velocity of the object. They can even tell whether it is moving toward or away from our earthly vantage point.