The Sun is a highly dynamic star undergoing constant, powerful changes. Understanding the processes within our star is crucial because its activity directly influences Earth and the entire solar system. Solar flares, coronal mass ejections, and the continuous outflow of particles known as the solar wind constitute “space weather,” which can disrupt satellite communications, power grids, and navigation systems. By studying the Sun, scientists aim to predict these events, understand stellar physics, and learn how the star’s energy is generated and released.
Observing the Sun from Ground Based Observatories
Observing the Sun from Earth’s surface provides the advantage of using larger, more complex instruments that are easier to maintain and upgrade. Specialized solar telescopes capture light primarily in the visible and radio wavelengths, which can penetrate the atmosphere. The world’s largest dedicated solar telescope is the Daniel K. Inouye Solar Telescope (DKIST), located on Haleakalā, Hawaiʻi.
A major challenge for ground-based observation is the blurring caused by atmospheric turbulence. To counteract this effect, telescopes like DKIST utilize adaptive optics. This system employs a deformable mirror with numerous actuators that adjust its shape thousands of times per second to correct for distortions in real-time. This dynamic correction allows DKIST to resolve features on the solar surface as small as 20 kilometers across.
Despite these advanced technologies, ground-based observatories face limitations. The Earth’s atmosphere absorbs much of the Sun’s light, especially in the high-energy ultraviolet (UV) and X-ray portions of the electromagnetic spectrum. Observations are also limited to the daytime, which prevents scientists from continuously monitoring the evolution of solar events like active regions and sunspots over a full 24-hour cycle. These constraints necessitate the use of space-based assets to obtain a complete picture of solar activity.
Space Missions for Direct and Remote Sensing
Space missions overcome the limitations of ground observation by placing instruments above the atmosphere. This orbital perspective allows for continuous monitoring of the Sun across the entire electromagnetic spectrum, including the high-energy UV and X-ray wavelengths that reveal the superheated plasma of the corona. The Solar Dynamics Observatory (SDO) provides nearly continuous, high-resolution, full-disk images of the Sun in multiple wavelengths.
SDO captures approximately 1.5 terabytes of data back to Earth every day. Its Atmospheric Imaging Assembly (AIA) instrument takes images of the corona and transition region every 12 seconds, allowing scientists to track the rapid dynamics of solar flares and coronal mass ejections (CMEs). These remote sensing instruments are complemented by spacecraft designed for in situ measurements.
The Parker Solar Probe (PSP) and Solar Orbiter are two current missions working in tandem. Parker Solar Probe flies closer than any previous spacecraft, venturing within 6.2 million kilometers of the solar surface. PSP focuses on in situ measurements, directly sampling the solar wind plasma, magnetic fields, and energetic particles as they stream from the corona.
Solar Orbiter primarily uses remote sensing instruments to take images and spectra of the Sun’s atmosphere from a distance. Its unique orbit is designed to eventually provide the first high-resolution images of the Sun’s polar regions, which are inaccessible from Earth’s orbital plane. By coordinating their data, the two spacecraft provide a comprehensive view: Solar Orbiter offers the large-scale context of the Sun’s atmosphere, while Parker Solar Probe delivers the detailed, local conditions within the solar wind.
Peering Into the Solar Interior with Indirect Methods
Direct imaging and remote sensing are useful for studying the Sun’s surface and atmosphere, but they cannot penetrate the interior, where the star’s energy is produced. To map the core and the layers beneath the surface, scientists rely on a technique called helioseismology. This method is analogous to how geologists use seismic waves from earthquakes to study Earth’s internal structure.
Helioseismology works by analyzing sound waves that are constantly generated near the Sun’s surface and travel through its interior. These pressure waves cause the solar surface to oscillate up and down with a characteristic period of about five minutes. By precisely measuring the frequency and travel time of these waves as they emerge at the surface, scientists can infer the temperature, composition, and internal rotation rates of the Sun’s hidden layers.
This technique has revealed the existence of the tachocline, a transition layer between the Sun’s radiative interior and its convection zone, where the rotation rate shifts. Helioseismology provides a detailed map of the Sun’s internal flows, showing that the outer third of the Sun rotates differentially, with the equator spinning faster than the poles. Computational modeling is used to interpret these subtle wave patterns, translating the complex seismic data into simulations of the Sun’s magnetic field generation and its long-term activity cycle.