[Reading Science] Total Solar Eclipse, the Key to Unlocking the Secrets of the Sun

Total Solar Eclipse Occurs in North America on the 8th (Local Time)
Opportunity to Illuminate the Sun's Mysterious 'Corona' for 4 Minutes 30 Seconds
NASA and KASI Fully Prepared for Research

A continuous shot of the solar eclipse that occurred in the North American region in 2017. [Image source=Reuters Yonhap News]

What is the most important star in the solar system? Undoubtedly, it is the Sun. The Sun not only provides light and heat to the solar system but also emits solar wind that interferes with communications on Earth and affects the climate. Studying the Sun is not easy because it is too bright to observe. However, there is an optimal time to study the Sun from Earth: during a total eclipse.

This year, on the 8th (local time), a total eclipse will occur from the south to the northeast along the right side of the North American continent. The total eclipse will pass through Mexico, the United States, and Canada. The previous total eclipse also occurred in the United States in 2017.

Principles of Solar Eclipses. Photo by Korea Astronomy and Space Science Institute

Watching a total eclipse is not easy. It does not happen frequently and can only be seen in specific regions. The duration is only a few minutes. If clouds cover the sky, it cannot be seen. When an eclipse is predicted, scholars and astronomy enthusiasts from around the world rush to the eclipse site. Astronomy enthusiast Mr. Jeong said he could not miss this rare opportunity and headed to the United States. He said, "I took a vacation because it is the best condition to see the aurora and the total eclipse."

An eclipse is an astronomical phenomenon where the Moon's shadow covers the Sun. Among eclipses, a total eclipse occurs when the Moon's shadow completely covers the Sun. Total eclipses have attracted human attention since ancient times. The concern that a total eclipse is a sign of disaster has now disappeared. Instead, it is the best opportunity for solar research.

Total solar eclipse and corona photographed in the United States by the 2017 KASI total eclipse observation team. Photo by Korea Astronomy and Space Science Institute

Yeonhan Kim, a senior researcher at the Korea Astronomy and Space Science Institute, said this total eclipse is quite significant. Kim explained, "A total eclipse provides optimal conditions for observing the Sun, but it occurs only once every few years, and sometimes the location is remote or inaccessible. A total eclipse can only be seen within about 100 km along the path the Sun takes," adding, "Beyond this distance, only a partial eclipse can be seen. Since the Moon's umbra must cover the Sun, a total eclipse is an even rarer phenomenon." Kim also shared his experience of traveling to mountainous remote areas for total eclipse research.

The next total eclipse will occur on August 12, 2026, in Iceland and Spain. On September 2, 2035, it is expected to occur in Pyongyang and Goseong, but since the total eclipse will only be visible in North Korean territory, it will be difficult for our researchers to access.

Moreover, this total eclipse will last up to 4 minutes and 30 seconds. Total eclipses allow only very short durations, sometimes as short as about 2 minutes. This eclipse is an optimal observation opportunity in terms of accessibility and duration.

For astronomers, total eclipses are important research subjects because they provide the only chance to study the Sun’s outermost atmosphere, the corona, from the ground. The corona is usually impossible to observe due to the Sun’s brightness. During a total eclipse, when the Moon covers the Sun, the corona emitted outside the Sun can be seen.

The corona has an average temperature of millions of degrees and is the site of powerful solar surface explosions such as solar flares and coronal mass ejections, equivalent to millions of hydrogen bombs detonating. These phenomena spread into space as solar wind. Solar wind causes weather changes and significant damage to Earth's environment.

According to the Astronomy and Space Science Institute, the most representative challenges in solar research are the heating mechanism of the corona and the acceleration mechanism of the solar wind. While the Sun’s temperature decreases from the center outward, the corona, the outer atmosphere, is heated to millions of degrees. The solar wind accelerates from tens of kilometers per second at the Sun’s surface to hundreds of kilometers per second near Earth.

NASA has already made thorough preparations to study this total eclipse. NASA plans to send research teams divided among three aircraft flying at 50,000 feet (about 16.6 km) altitude to observe the eclipse from the sky. Flying above the clouds allows observation of the eclipse regardless of weather. Weather is the decisive factor for eclipse observation. Increasing altitude extends the observation time by 25% compared to the ground, up to 6 minutes and 22 seconds.

(Right) CODEX installed in a large chamber for testing in a thermal vacuum environment simulating outer space. (Left) CODEX installation location on the International Space Station. Photo by Korea Astronomy and Space Science Institute

Two NASA teams will photograph the corona, and the third team will measure the Earth's ionosphere. NASA explains that this observation will help understand the structure and temperature of the corona and the Sun’s impact on Earth's atmosphere. Furthermore, it is expected to assist in finding asteroids that can orbit near the Sun.

Our research team will not miss the opportunity to study the corona. During this eclipse, the Korea Astronomy and Space Science Institute will dispatch two observation teams to Lampasas and Ricks in Texas. One team will study the corona, and the other will conduct the final ground observation for the core research of the CODEX coronagraph for the International Space Station, developed jointly with NASA. The coronagraph is a special telescope device that artificially blocks the solar disk to observe the Sun as during a total eclipse.

The two observation teams will attempt to observe the low corona region, ranging from 1 to 4 solar radii, using the polarization camera and new spectropolarimetric equipment, which are core technologies of CODEX scheduled for launch in September. To reduce the risk of observation failure due to bad weather, observations will be conducted at two locations about 200 km apart.

The results will serve as complementary research data to the mid-corona observations (3 to 8 solar radii) that CODEX will conduct on the International Space Station after its launch in September.

CODEX was jointly developed by the Korea Astronomy and Space Science Institute and NASA. It is the world’s first instrument capable of simultaneously observing the temperature and velocity of the solar corona in space and producing two-dimensional images. CODEX is currently in the final assembly stage and is scheduled to be launched in September this year, operating on the International Space Station for up to two years.

Dr. Yeonhan Kim, the Korean lead developer of CODEX at the Astronomy and Space Science Institute, said, "CODEX, developed jointly with NASA, will greatly contribute to solving the mysteries of corona heating and solar wind acceleration, which are major challenges in solar research," adding, "Testing new observation techniques and instruments during a total eclipse is an essential process before deploying instruments in space."