Expert Explains the Spectrum of Light and the Expanding Universe to Optimists

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The Palisades Optimist Club meeting on August 16 featured Dr. Jeff Rich, outreach coordinator for the Carnegie Institution for Science Observatories.

He reminded Circling the News of the opening of the Woody Allen film “Annie Hall.”

Alvy Singer (Allen’s alter ego) is speaking to a psychiatrist.

“Why are you depressed, Alvy?” Dr. Flicker asks.

“The universe is expanding,” Alvy says. “The universe is everything, and if it’s expanding, some day it will break apart and that will be the end of everything.”

“Why is that your business?” interrupts Alvy’s mother. Turning to the psychiatrist, she announces, “He’s stopped doing his homework!”

“What’s the point?” Alvy says.

“What has the universe got to do with it!” his mother shouts. “You’re here in Brooklyn! Brooklyn is not expanding!”

But Alvy was right: There’s indeed proof that the universe is expanding, according to Dr. Jeff Rich.

In his Zoom talk, “Spectra: Splitting Light to Study the Universe,” the scientist explained how the Milky Way (the galaxy where earth and sun are located) and the Andromeda Galaxy (the galaxy that is closest to the Milky Way) are expanding toward each other. “They will probably merge and in six billion years, this would be an even bigger galaxy,” Rich said.

One worried Optimist asked, “How are we benefit from this knowledge? Are we safer or better?”

Rich assured the man that a merger could result in new star formation but given that the beginning of the merger is at least one billion years away, “it won’t affect us.”

How do scientists know the universe is expanding? It goes back to rainbows – prisms – light.

“Color, brightness and shape all tell us something about what is happening [in space],” Rich said.

When light passes through an element it has a unique fingerprint. The color of the light would be different in all of the 118 known  elements in the periodic table – e.g., hydrogen, carbon, lithium and beryllium would all show a different color.

This observation means that scientists can measure what elements are in space by observing the color of the light.

This is actually how helium was discovered. In 1868, Jules Janssen observed an unexplained line in the sun’s chromosphere (a layer in the Sun between 250 miles and 1,300 miles above the solar surface) during a solar eclipse.

Norman Lockyer found the same line two months later and concluded that it was an element in the sun unknown on earth. He named it D3.

In 1882, Luigi Palmieri discovered a spectral line in the lava of Mt. Vesuvius. Thirteen years later, William Ramsay isolated the gaseous element, helium, on earth.

Annie Jump Cannon used glass-plate photographs on which starlight had been spread out by a prism at the telescope focal point. She could identify the similarities and differences in the physical properties of stars. Cannon published her first catalog of stars in the Annals of the Astronomical Observatory of Harvard College Observatory, in 1901.

By observing measuring the emissions, which show as a color, astronomers can also tell a star’s age. “The color of a star tells us its temperatures,” Rich said. “Movement changes the color of a spectrum. If a star is moving towards us, there is a blue shift (hotter) and if it is moving away, then there is more of a red shift.”

Which is proof, according to scientists, that the universe is expanding. An Optimist asked, “How do you separate one galaxy from another? What is the line that delineates?”

Boundaries are constantly changing, Rich said, because “independent galaxies and stars are gravitationally bound to one another because of matter and mass.” He said that galaxy mergers and acquisitions are ongoing.

“Two satellites of the Milky Way galaxy are slowly being torn apart and being absorbed by the MW,” he said.

Visit: Obs.carnegiescience.edu.

 

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