When you watch a solar eclipse, you often think of the moon passing between the Earth and the sun, then temporarily blocking sunlight from reaching Earth. This alignment is known as syzygy (sounds like siz-uh-jee).

However, last week the European Space Agency (ESA) launched two spacecraft aimed at mimicking the behavior of the moon by creating an artificial solar eclipse for the first time ever. The idea? To demonstrate the utility of a technology called Precise Formation Flying (PFF) and study the Sun’s atmosphere, known as the corona. The mission is called Proba-3 (Project for On-Board Autonomy).

“At the moment, this (the corona) is a region of the Sun that has been little explored, and scientists today do not really understand some of the phenomena that occur there,” Ester Bastida, Proba-3 systems engineer, said in a recent ESA report -Video. One of the key questions about the corona that scientists want to understand is why it is significantly hotter than the sun itself.

While the sun’s surface is about 5,500 degrees Celsius (9,932 degrees Fahrenheit), the corona – the sun’s thin outer atmosphere – can reach temperatures of 1 to 3 million degrees Celsius (1.8 to 5.4 million degrees Fahrenheit).

Although the Sun’s circumference is about 4,373,000 kilometers (2,717,000 miles), corona solar flares can reach Earth, nearly 150 million kilometers (93 million miles) away.

How does the Proba-3 produce a solar eclipse?

The Proba-3 launched on December 5 from the Satish Dhawan Space Center in India, one of the world’s busiest space launch facilities.

The two spacecraft satellites will be launched into space about 60,000 km (37,280 miles) above Earth on the PSLV-C59 rocket built by the Indian Space Research Organization (ISRO). The Coronagraph spacecraft (CSC) is responsible for guiding the Occulter (OSC), the second spacecraft with a 140 cm (55 in) diameter disk that casts a controlled shadow on the Coronagraph spacecraft.

According to ESA, the two spacecraft will use precision formation flight (PFF) technology to position themselves exactly 150 meters (492 feet) apart and align with the Sun, “so that one spacecraft obscures the radiant disk of the Sun from the other “.

To be successful, the eclipse maneuver must be accurate to the millimeter and, if necessary, produce a solar eclipse lasting up to six hours so researchers can study the solar corona.

What do the researchers hope to achieve with this mission?

One of the goals is to demonstrate PFF technology, which uses GPS and radio links between satellites for initial positioning while maintaining a precise distance between the Coronagraph spacecraft and the Occulter spacecraft.

Initially, the two satellite spacecraft remain connected. But once separated, they can maintain their formation – they are then 25-250 m (82-820 feet) apart.

The second goal is to use the built-in corona observation equipment to understand why the corona is hotter than the Sun. One of the instruments on board is a coronagraph – a telescopic device that helps block out the light of a star or other very bright object so that other things can be seen. The Proba-3 coronagraph has a long-winded name: Association of Spacecraft for Polarimetric and Imaging Investigation of the Corona of the Sun (ASPICCS).

This technology simulates the viewing conditions of a total solar eclipse with remarkable accuracy while eliminating the disturbances typically caused by Earth’s atmosphere.

Why is this such a big deal?

Due to its extremely low brightness, the corona normally remains invisible and appears millions of times brighter than the sun’s bright surface. It is only visible to the naked eye during solar eclipses, when the moon blocks the sun’s intense light.

“By studying the solar corona, we can better predict space weather and extreme geomagnetic storms, which can cause significant disruption to satellites and systems on Earth,” ESA said in a recent video about the mission.

Total solar eclipses are very rare – each location on Earth typically only experiences one once every 375 years, and they only last a few minutes.

If Proba-3, which has an orbit of 19 hours and 36 minutes, If their mission is successful, the scientists won’t have to wait. They can study the corona for six hours in each orbital cycle of the mission.