Astronomers are to thank for discovery of helium


By Tom Burns - Stargazing



Scientists and balloon enthusiasts are beginning to worry about a possible shortage of helium. That concern is strangely ironic.

The two simplest elements, hydrogen and helium, make up about 98% of the cosmos. However, giant gas clouds and stars contain virtually all of those elements. On Earth, helium is difficult to obtain.

Helium’s discovery resulted from the work of many scientists over hundreds of years.

The first clue came in 1665. Sir Isaac Newton took a triangular piece of glass called a prism and split the sun’s light into colored bands. He discovered that the way we see light is an illusion. It is actually composed of different bands, or wavelengths, of color.

In 1802, British chemist William Wollaston used a complex set of lenses and prisms called a spectroscope to look at the spectrum of sunlight. He noticed that these color bands are not continuous. Dark gaps existed between some of the colors.

That observation was perhaps the most important of all time for astronomical research, but Wollaston did not realize its significance.

In 1812, using a better spectroscope than Wollaston’s, German physicist Joseph von Fraunhofer discovered that the spectrum of light is composed of hundreds of discrete bands. He also rediscovered the mysterious dark bands, which eventually were named after him — the Fraunhofer lines.

In 1857, German chemist Robert Bunsen invented a gas burner that produced a nearly colorless flame. Perhaps you used a Bunsen burner in high school. It is not just a torture device used to flunk students in beginning chemistry.

The advantage of Bunsen’s burner was that when a scientist burned a chemical with the device, the light produced could not be confused with the light from the chemical. Scientists could now see what colors chemicals produce when they are heated.

Gustav Kirchhoff, a co-worker of Bunsen’s, studied the colored bands produced by such burning chemicals and found that their spectra are not continuous — in spades. Each pure substance produced only a few colored bands. Each chemical now had a color fingerprint, and scientists could analyze those colors to find out what anything was composed of.

But Kirchhoff went further in his study. He set up containers of various pure substances and shone light through them. He discovered that the substances absorb precisely the same color bands as they would have emitted if they had been burned.

These absorbed colors show up as black lines in the spectrum. Kirchhoff had finally explained Wollaston’s and Fraunhofer’s mysterious dark bands.

In particular, Kirchhoff noticed that two lines in the yellow portion of the sun’s spectrum matched up with two of Fraunhofer’s dark lines. In the lab, he determined that they were the fingerprint lines for sodium. Sodium must be present in the sun.

It didn’t take long for astronomers to exploit this technique. Swedish physicist Anders Angstrom noticed that the dark spectral lines produced by the sun exactly matched those of light that shines through a container of hydrogen.

Thus, explosions beneath the sun’s surface probably create its light. As the light shines through the non-burning outer part of the sun, hydrogen absorbs some of the color bands. Hydrogen must be present in the sun.

In August 1868, French astronomer Pierre Jules Cesar Janssen made the arduous journey to India to study a solar eclipse. He intended to study the sun’s atmosphere, which is a difficult task because of the brightness of the sun’s disk.

However, during an eclipse, the sun’s disk is briefly blocked. As anyone who has seen a total solar eclipse will tell you, the view of the sun’s outer atmosphere, called the corona, is a glorious sight.

Janssen’s wanted to study the sun’s chromosphere, the layer of atmosphere just inside the corona. The chromosphere is exceedingly narrow. At only 1,200 wide, it is thinner than the skin of an onion compared to the 900,000-mile-wide sun. During an eclipse, it is visible for only an instant.

Using the recent discoveries pioneered by Kirchhoff, Janssen detected a bright, yellow line in the sun’s spectrum. He assumed that the line was an indication of sodium in the sun’s atmosphere.

Sodium tends to produce such a yellow line when it is heated Bunsen-style. No other known element created the bright yellow line. Presumably, the presence of sodium was a cause of the sun’s slightly yellow color.

Just two months later, English astronomer Joseph Lockyer used a self-built spectroscope with the capability of observing the chromosphere without the benefit of a solar eclipse. He also saw the yellow line. Like Janssen, he assumed that sodium was the cause.

He was disabused of that notion when he consulted chemist Edward Franklin. The yellow line, Janssen decided, was from a newly discovered element.

Naming it after the Greek sun-god Helios, the charioteer who carried the sun across the sky in a golden chariot, he called it helium.

Over the years, astronomers have refined their equipment and given us a pretty clear notion of what the sun is made of. About three-fourth of it is hydrogen, and most of the rest is helium. It also has trace amounts of oxygen, carbon, neon, nitrogen, magnesium, iron and silicon. Most of the rest of the elements that make up the universe are also present in very tiny amounts.

For decades, astronomers assumed that helium only existed in the sun. But in 1895, Scottish chemist William Ramsey was able to isolate a tiny amount of helium from a chunk of radioactive uranium.

And there’s the rub. The sun produces enormous quantities of helium as a byproduct of the sun’s thermonuclear fusion. Four hydrogen atoms fuse to make two helium atoms and a whole lot of energy.

On Earth, hydrogen exists in abundance because it likes to chemically bond with everything. Take a tank of liquid hydrogen and place it next to a tank of liquid oxygen, and all you have to do is combine them in a controlled way. The result is a rocket capable of taking you to the moon or Mars.

The byproduct of the controlled explosion is good, old dihydrogen oxide, commonly called water. Yes, that’s steam coming out of the back of most rockets when they launch.

The opposite is also true. It’s an easy enough matter to take some water, separate the hydrogen from the oxygen, and you’ll have hydrogen aplenty.

Helium likes to bond with nothing, and hydrogen fusion in the form of a hydrogen bomb is, thank goodness, a rare occurrence.

Helium is so inert that it also plays a role in rocket launches. Rocket scientists need an inert chemical to force the hydrogen and oxygen out of their respective tanks, and helium fills the bill quite nicely.

As Swedish chemists Per Teodor Cleve and Nils Abraham Langlet discovered in 1895, our only source of helium on Earth is the slow decay of radioactive elements like uranium. The process takes millions of years.

Over great lengths of time, small caches of helium mixed with natural gas build up in caves and voids beneath the Earth’s surface. Primarily, helium exists in natural gas in trace amounts. Refiners don’t even think about extracting the helium unless it makes up a massive .3 percent of the harvested gas.

The largest of those caches are in the western United States, which means that the U.S. government controlled virtually all the world’s helium.

Even the underground helium is not secure. Because helium is lighter than air, it often moves from underground into the upper atmosphere and trickles into space.

The Bureau of Land Management administered the US helium reserve. By 1996, the BLM had built up a sizable stockpile of helium. However, during that year, Congress decided to privatize the production of helium.

The BLM was required to sell off all its helium reserves at rock-bottom prices. As a result, the cost of helium was and remains artificially low.

At current production rates, the world will run out of helium in 25 – 30 years. That’s no joke. An ample supply of gaseous and liquid helium is crucial to our economy and our individual well-being.

Because helium is lighter than air, people use it in birthday balloons, weather balloons, and blimps. Hydrogen is even more lightweight, of course. But hydrogen is also explosively volatile. Those folks who require further evidence should Google “Hindenburg disaster.”

Besides the apparent advantage that helium is light and doesn’t blow up, it also has an extremely low boiling point. Consequently, helium is exceptionally frigid when cooled to a liquid.

As a result, liquid helium is essential in any scientific research involving super-conductivity, where magnets must be kept at just a few degrees above absolute zero. Only liquid helium can get that cold. In that regard, you can thank helium for the superconducting magnets that power MRI scanners.

As you stare at your smartphone or computer, consider that ultra-cold liquid helium is necessary for the production of silicon semiconductor chips.

A helium-neon laser powers the bar-code reader at your local grocery. Helium is used in welding to shield welds from water vapor. As we have seen, it pressurizes rocket tanks.

Helium is thus a rare and precious commodity.

Its discovery was a watershed for astronomy and the world. And it all came about because of a single, bright yellow line in a rainbow band of colors.

https://www.delgazette.com/wp-content/uploads/sites/40/2021/07/web1_Burns-1.jpg

By Tom Burns

Stargazing

Tom Burns is the former director of the Perkins Observatory in Delaware.

Tom Burns is the former director of the Perkins Observatory in Delaware.