Measuring the sun through solar eclipse

David Dunham, an astronomer and founder of the International Occultation Timing Association, discusses with the media the solar eclipse that occurred on March 9 in Gosowong Mining area, Kau, North Maluku, Indonesia.


In 1780, in the middle of the American Revolutionary War, a war of independence for 13 American colonies that eventually overthrew the authority of Great Britain in the succeeding years and, eventually, founded the United States of America, a cease-fire was granted on October 27 in Penobscot Bay in Maine to make a safe passage for Harvard Prof. Samuel Williams’s total solar-eclipse expedition.

According to Harvard College Observatory: The First Four Dictatorships by Bessie Zaban Jones and Lyle Gifford Boyd, the total solar eclipse laid between enemy lines. Since both parties in the war declared that they were interested in science above political differences, Williams performed his observations on the limits of the total solar eclipse and took note of the observations of what is called as the “Baily’s beads.” This was named after Francis Baily, an English observer, when he extensively observed and described the beads on May 15, 1836, in Roxburghshire in England, 56 years after Williams did.

Today these beads, which Williams called “small drops” or “stars,” seen when the sun’s limb becomes so small and the light from the edge of the sun shines between the mountains of the moon, are of importance to many observers with the right tools for solar eclipse. These include astronomers David and Joan Dunham, both founders of the International Occultation Timing Association and have been working in the astronomy academe and aerospace industry for over 40 years and have also been observing eclipses for already 46 years.

Measuring the sun

“We’re trying to measure the diameter of the sun from the timing of the Baily’s beads disappearances and reappearances, which depends upon the diameter of the sun and the detailed profile of the moon obtained from Kaguya by the Japan Aerospace Exploration Agency and Nasa [National Aeronautics and Space Administration] Lunar Reconnaissance Orbiter,” David Dunham said in an interview with the BusinessMirror during the solar-eclipse observation in Indonesia.

According to the Dunhams, the importance of the observations stems from a claim in 1979 by John Eddy, a scientist from the Harvard-Smithsonian Center for Astrophysics, and Aram Boornazian, a mathematician, that the sun’s radius has changed by a very large amount.

“We didn’t believe the report that the sun’s diameter was decreasing so fast by an arcsecond a century. That just didn’t seem right,” Joan Dunham said.

She added, “We thought on how we could check that through the data we already have or the techniques that we already had and an eclipse was coming that time.”

She thought that through observing the diameter of the sun at the time of the eclipse and compare it with Eddy and Boornazian’s estimate to see if it has changed or not.

David Dunham said that if there was a change in the sun’s diameter, it would have affected the temperature of the Earth.

“If the sun’s diameter has changed that large, the temperature of the Earth should change to more than a degree or 2-degrees Celsius [increase] and should be noticeable.”

When asked if it has contributed to climate change, David was hesitant to reply. “The industrial revolution has added tons of carbon dioxide in the atmosphere and it’s been measured very accurately that greenhouse gases have greatly increased.” Though it surely affects the weather, it would only for the time the total solar eclipse has lapsed. The temperature drops during an eclipse compared to what is normal during the day, because the moon is covering the heat away but for only a short time.


Growing interest in solar-eclipse expeditions

From their experiments, it only took a single eclipse to disprove the claim, yet, the two astronomers are still on the move to document more eclipses.

“Since about late 1980s, we’ve had measurements from space and, mostly, it has been only measurements of the brightness of the sun. But there hasn’t been really good observations of the diameter of the sun from space,” David Dunham said regarding the interest on solar eclipses and its implications on current and future research.

Scientists often question the data obtained by space satellites because of the curiosity generated by the thermal cycles of the day and night that satellites experienced. These includes heating of the parts of the satellite which greatly affect the data. There are also limitations imposed, such as the Solar and Heliospheric Observatory spacecraft that constantly measures the corona of the sun but can only see as far as three-tenths of the solar radius.  “Well, the solar physicists are still very interested in solar eclipses, especially in making detailed measurements of the corona.”

David Dunham also explained that any variations of the diameter of the sun is very interesting, since it would indicate the stability of the sun and its processes, such as nuclear fusion, a high-energy reaction of two lighter nuclei to form a single heavy nucleus.

“The sun is still holding on for a long time,” David said. “The scientists before the discovery of nuclear fusion thought the sun was being heated by gravitational collapse of the materials of the sun, but they realized that that could only keep the sun for about 100,000 years, but we know the sun is already shining for about 4.6 billion years.” As soon as scientists discovered that it was nuclear fusion that was driving the sun, it was just a matter of analyzing the hydrogen and the helium. Eventually, the hydrogen can run out, it can be burned through these processes of the sun, but that’s going to take another 4 billion years.

“When hydrogen starts getting depleted, then the sun starts collapsing, because the sun is an equilibrium between the energy being generated from the hydrogen burning of the nuclear fusion and the gravitational pull of all its materials,” David said.

2016 total solar eclipse

The total solar eclipse on March 9 had a path that covered North Maluku, Sulawesi, Sumatra, Borneo to Palembang in the Indonesian archipelago and had a duration of more than four minutes at around 00:51 UTC to 00:55 UTC.

According to Avivah Yamani, an Indonesian astronomer and communicator of Indonesian astronomy news web site Langitselatan, the total solar eclipse triggered the government to act on science for Indonesia.

“Celestial events can boost tourism and gives opportunity for public outreach and education, especially in the remote areas of Indonesia,” Yamani said in an interview with the  BusinessMirror. She said students had the chance to see the total and partial solar eclipse in Indonesia.

The Philippines witnessed a partial solar eclipse, as many observers and enthusiasts observed the eclipse through the use of solar glasses and solar filter-covered telescopes at around 7:51 in the morning for the first contact.

According to Yamani, the next solar eclipse in the Asian region that would cover Philippines and Indonesia and some other countries would be on 2019. It would be an annular eclipse, where a “ring of fire” would appear, since the moon will not cover the sun’s discs completely.

“Another eclipse would be on 2023, which would be a hybrid solar eclipse where there would be totality and annular in one eclipse path,” she further added. As for the Philippines, the country would wait for 2042 to experience a total solar eclipse.


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