The eclipse seen from above: what satellites reveal about the Sun

Observation of a solar eclipse by the HINODE satellite — Solar eclipse: an image captured from space, revealing the outer layers of the Sun, invisible from the Earth's surface. The solar eclipse of May 20, 2012, observed by the Hinode satellite, a solar observatory developed by the Japanese space agency (JAXA).
Image source: Hinode/Jaxa/Nasa (new window).

Scientific summary

The Astronoo article presents the observation of solar eclipses from space by the HINODE and PROBA-2 satellites. Thanks to their instruments sensitive to X-rays and extreme ultraviolet, these observatories study the solar corona, magnetic loops and coronal mass ejections without the disturbances of the Earth's atmosphere. Lunar occultations seen in orbit offer valuable diagnostics on the temperature, density and dynamics of the coronal plasma. These data improve our understanding of solar activity and feed models of space weather.

Why does observing a solar eclipse from space change our understanding of the Sun?

This article explores what satellites reveal about the hidden Sun during solar eclipses. From orbit, spacecraft such as HINODE and PROBA-2 escape the limitations of the Earth's atmosphere: turbulence, absorption of X-rays and extreme ultraviolet, and the short duration of totality. They can therefore observe the solar corona continuously, track multiple passages of the lunar limb and map hot magnetic structures. These observations reveal coronal loops, thermal gradients, waves and instabilities linked to solar flares. They help to understand why the corona is hotter than the photosphere and how solar activity influences Earth's space environment. The answer to the question posed is therefore twofold: satellites offer both a stereoscopic vision and a spectral analysis impossible from the ground, while providing continuous data for space weather. This article details the instruments, the phenomena captured and the contribution of space missions to the study of eclipses.

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Solar eclipse seen by the HINODE satellite

A satellite dedicated to the solar corona

The Japanese satellite HINODE, launched in 2006 by JAXA in collaboration with NASA and ESA, specializes in observing the solar corona with extreme precision. During a solar eclipse, HINODE is not just a passive spectator: it becomes an advanced diagnostic tool for the coronal plasma.

Diagnosis of the coronal plasma during the eclipse

Thanks to its optical telescope (SOT) and its X-ray spectrometer (XRT), HINODE records variations in intensity, temperature and magnetic structuring in the solar corona, where the solar atmosphere extends over hundreds of thousands of kilometers beyond the visible disk. During an eclipse observed on July 22, 2009, HINODE revealed with finesse dynamic coronal arches and coronal mass ejections (CMEs) in progress, thanks to the natural occultation offered by the Moon.

This space perspective makes it possible to eliminate terrestrial atmospheric disturbances, thus offering spectral and thermal profiles of rare precision.

The observations of the Hinode satellite

A partial eclipse filmed from orbit

Partial solar eclipse of November 25, 2011, seen from Antarctica, Tasmania, southern South Africa and most of New Zealand.
Image source: Hinode/XRT (new window).

This sequence shows a partial eclipse observed in Antarctica and part of the southern hemisphere. The data from Hinode/XRT make it possible to follow the occultation of the solar disk and to analyze active regions in soft X-rays.

Use of HINODE instruments and phenomena captured

The HINODE satellite, placed in a heliosynchronous orbit at an altitude of about 600 km, continuously observes the surface and the corona of the Sun. During the partial eclipse of January 4, 2011, the satellite's trajectory allowed several passages of the lunar limb in front of the solar disk during its orbital revolution, what are called multiple occultations.

Instruments

XRT (X-Ray Telescope): observed regions of the solar corona in soft X-rays, sensitive to plasmas at several million kelvins.
SOT (Solar Optical Telescope): analyzed the photosphere and the lower chromosphere.
EIS (EUV Imaging Spectrometer): made it possible to obtain detailed spectra of the solar atmosphere.

Phenomena

Variation of the X intensity in the corona as the Moon hid certain active regions.
Observation of fine coronal structures, such as magnetic loops, highlighted by the progressive occultation.
Detection of thermal gradients in the corona, thanks to the before/after occultation comparison.
Measurement of rapid intensity fluctuations, linked to magnetic instabilities or Alfvén-type waves.

Solar eclipse seen by the PROBA satellite

PROBA-2: an extreme-ultraviolet eye on the solar corona

The series of PROBA satellites (PRoject for OnBoard Autonomy), developed by ESA, has also played a remarkable role in the observation of eclipses, in particular with PROBA-2, launched in 2009. This satellite is equipped with the SWAP instrument (Sun Watcher using Active Pixel System detector and Image Processing), an EUV (Extreme Ultraviolet) camera that films the solar corona in wavelengths around 17.4 nm.

Eclipses filmed from space: lunar passages seen by PROBA-2

During eclipses, such as that of March 20, 2015 or August 21, 2017, PROBA-2 captured astonishing sequences in which the Moon, by partially or totally occulting the solar disk, makes it possible to observe in detail the activity of the corona. Unlike terrestrial observations, limited by the atmosphere and the brief duration of totality, PROBA-2 records several passages of the lunar limb over the Sun during its heliosynchronous polar orbit.

What the EUV reveals: magnetic topology and coronal dynamics

The physical interest of these data lies in the dynamic mapping of the solar magnetic field lines and in the study of rapid fluctuations of the EUV emission. These measurements, impossible to carry out from Earth, help feed models of space weather, essential for forecasting geomagnetic storms.

References

FAQ: Everything you need to know about solar eclipses seen by satellites

Why observe a solar eclipse from space?

From space, satellites avoid the disturbances of the Earth's atmosphere. They can observe the X-rays and extreme ultraviolet emitted by the solar corona, invisible from the ground. They also benefit from a longer observation duration and multiple passages of the lunar limb.

Which satellites have observed solar eclipses?

The HINODE (JAXA/NASA/ESA) and PROBA-2 (ESA) missions have provided remarkable images. Other space solar observatories, such as SOHO or SDO, also participate in the study of the corona and solar activity.

What is the solar corona?

The corona is the outer envelope of the Sun's atmosphere. It extends over millions of kilometers and reaches temperatures of several million degrees. It is the seat of magnetic loops, coronal mass ejections and the solar wind.

Why is the corona hotter than the Sun's surface?

This question remains a great mystery of astrophysics. Space observations suggest that magnetic fields and Alfvén-type waves transport and dissipate energy in the corona, heating it to extreme temperatures.

What do eclipses seen from space contribute to space weather?

They make it possible to test models of the propagation of solar flares and geomagnetic storms. Continuous measurements help predict disturbances that can affect satellites, communications and power grids.

Can you see a solar eclipse from a satellite with the naked eye?

No. Direct observation of the Sun, even during a partial eclipse, is dangerous without an appropriate filter. Satellites use specialized instruments, such as X-ray or extreme ultraviolet telescopes, to observe the Sun safely.