The Helio House

Observing the Sun

Key Missions

From Data to Discovery

Data access

Timeline of discovery

Observing the Sun

Studying the Sun might sound straightforward, but almost everything important about solar activity happens in forms of light and particles that our eyes, and even ground-based telescopes, cannot detect. The Sun emits extreme ultraviolet light, X-rays, energetic particles, and steady streams of plasma that never reach Earth’s surface because our atmosphere blocks them. To understand what the Sun is doing, we rely on a network of spacecraft designed to observe it continuously and from multiple viewpoints.

Modern heliophysics is built on these observations. Without them, we would not be able to track solar flares, monitor space weather, or understand the structure of the solar wind.

Why We Observe the Sun From Space

Earth’s atmosphere protects us, but it also blocks most of the information that reveals how the Sun actually behaves. Ultraviolet and X-ray light, essential for identifying flares, hot plasma, and magnetic activity, cannot be seen from the ground. Even visible light observations are affected by weather and atmospheric turbulence.

Spacecraft solve these problems. Instruments above the atmosphere can capture all wavelengths and monitor the Sun around the clock. They also allow us to place cameras and sensors where they could never exist on Earth, at Lagrange points, in polar orbits, or even deep inside the solar wind itself.

Different Ways of Looking at the Sun

Multiple kinds of observations are needed because no single instrument can show the full picture.

  • Imaging instruments (like those on SDO and Solar Orbiter) show the Sun’s atmosphere in different wavelengths, revealing features such as sunspots, flares, and coronal loops.
  • Coronagraphs (like on SOHO) block the Sun’s bright disk to uncover CMEs and the outer corona.
  • In-situ instruments measure the solar wind and magnetic field directly by sampling the plasma around the spacecraft.

Each type of observation gives a different piece of information. Imaging tells us what the Sun is doing; in-situ measurements tell us how those changes affect the space environment around us.

Why We Need Multiple Viewpoints

The Sun is a 3D, constantly changing object. Observing it from only one line of sight leaves gaps in what we can see. Missions like STEREO, Solar Orbiter, and Parker Solar Probe provide alternative angles on eruptions, allowing us to determine the shape, direction, and speed of CMEs more accurately than with a single viewpoint.

Different distances also matter. Some spacecraft sit far from the Sun to watch its large-scale behaviour. Others, like Parker Solar Probe, fly extremely close to sample the solar wind before it has time to interact with anything else. Together, these vantage points let us connect events on the Sun with their effects throughout the heliosphere.

Why Continuous Observation Matters

Solar activity can change quickly. Flares and CMEs can erupt with little warning, and the solar wind varies from minute to minute. Continuous monitoring allows scientists, including space-weather forecasters, to detect changes in real time. Without this constant stream of data, predicting geomagnetic storms or protecting satellites would be far more difficult.

Key Missions

We understand the Sun the way we do today because a network of spacecraft observe it from different angles and distances. Each mission contributes a specific type of information: images, solar wind data, magnetic fields, or high-energy particles. Together they reveal how the Sun behaves and how its activity travels through the heliosphere.

This chapter introduces the major spacecraft used in heliophysics and space-weather monitoring. The focus is on what each mission does and why it matters.

SOHO – Solar and Heliospheric Observatory

Launched in 1995 by NASA and ESA, SOHO has become one of the most important solar missions ever flown. Its coronagraph instrument, LASCO (Large Angle and Spectrometric Coronagraph), blocks the bright solar disk so the faint outer corona becomes visible. This is where coronal mass ejections, large eruptions of plasma and magnetic field, expand into space.

SOHO provides the long, continuous CME record used for studying solar cycles and for forecasting space-weather events.

SDO – Solar Dynamics Observatory

NASA’s SDO produces high-resolution images of the Sun every few seconds, in multiple ultraviolet wavelengths. Its AIA (Atmospheric Imaging Assembly) instrument shows the solar atmosphere in fine detail, while HMI (Helioseismic and Magnetic Imager) maps magnetic fields on the surface.

SDO offers the main real-time view of the Sun used by both scientists and the public. Most “colourful” Sun images online come from this mission.

STEREO – Solar TErrestrial RElations Observatory

The two STEREO spacecraft were launched to observe the Sun from viewpoints away from Earth. By watching eruptions from the side, they make it possible to determine how wide CMEs are and which direction they are expanding.

Even with one spacecraft now active, STEREO continues to provide crucial off-angle observations that improve CME tracking and forecasting.

Solar Orbiter (ESA/NASA)

Solar Orbiter combines remote sensing (imaging) with in-situ measurements of the solar wind. It travels closer to the Sun than most missions and will gradually tilt its orbit to view the solar poles; a region that controls the solar cycle but is very hard to observe from Earth.

By showing the Sun up close while also sampling the plasma around it, Solar Orbiter connects surface activity with solar-wind behaviour.

ACE – Advanced Composition Explorer

DSCOVR – Deep Space Climate Observatory

ACE and DSCOVR sit near the L1 Lagrange point between the Earth and Sun, where they measure the solar-wind speed, density, temperature, and magnetic field before it reaches Earth.

These measurements provide the main near-real-time input for space-weather prediction. They give forecasters a short warning, often 30 to 60 minutes, before solar-wind disturbances arrive at Earth.

WIND (NASA)

The WIND spacecraft, launched in 1994, samples solar-wind plasma and energetic particles. Although older than many other missions, WIND remains scientifically valuable because its long dataset helps scientists compare conditions across multiple solar cycles.

It provides continuous measurements of particles and magnetic fields that support SEP (solar energetic particle) studies and long-term solar-wind research.

GOES – Geostationary Operational Environmental Satellite

Operated by NOAA, the GOES satellites carry X-ray sensors that continuously monitor the Sun’s brightness. These measurements form the official flare classification system: A, B, C, M, and X classes. GOES provides one of the fastest and simplest ways to detect the start of a solar flare, making it essential for real-time alerts.

Parker Solar Probe (NASA)

Parker Solar Probe flies closer to the Sun than any spacecraft in history. Its orbit gradually shrinks with each Venus flyby, allowing it to enter the outer corona and directly sample the solar wind at its source. Parker has revealed new structures such as “switchbacks,” helped map the origins of the fast and slow solar wind, and provided the first in-corona measurements of plasma and magnetic fields. Its data fills the gap between what we see from imaging missions and what solar-wind monitors measure farther from the Sun.

Voyager 1 & 2 (NASA)

Voyager 1 and Voyager 2 were launched in 1977 to explore the outer planets. After completing those missions, they continued outward and eventually became the first spacecraft to cross the heliopause – the boundary where the solar wind ends and interstellar space begins.

As they passed into this region, they recorded changes in plasma density, magnetic fields, and cosmic-ray levels. Voyager’s measurements show how far the Sun’s influence extends and how the heliosphere interacts with the surrounding galaxy.

From Data to Discovery

Spacecraft produce enormous amounts of information about the Sun, but the raw data they collect usually isn’t something you can look at and understand immediately. A detector might record counts of photons, particle impacts, or magnetic field readings that need careful processing before they become the images and plots you see online.

This chapter explains, in simple terms, what happens between a spacecraft taking a measurement and a scientist making a discovery.

From Raw Signals to Usable Information

When a spacecraft observes the Sun, its instruments don’t send back photographs or finished graphs. They send back measurements: voltage levels, pixel intensities, particle counts, timing information, and sensor readouts. These need to be calibrated and corrected so they accurately reflect what was happening at the Sun.

For imaging missions like the Solar Dynamics Observatory, this means adjusting for detector sensitivity, removing noise, correcting for spacecraft motion, and converting pixel values into physical units. For in-situ missions like ACE or DSCOVR, the process involves turning electrical signals from particle detectors into solar-wind speed, density, temperature, and magnetic-field direction.

Only after this processing do we get the clear images and plots used for research and forecasting.

Connecting Images and Measurements

Different spacecraft tell different parts of the story, and combining them is essential.

Images show where activity begins: a sunspot developing, a flare erupting, or a coronal mass ejection expanding outward. In-situ data reveals what that activity does when it reaches a spacecraft, whether that’s a change in solar-wind conditions or a burst of energetic particles.

A CME seen leaving the Sun in a coronagraph is later detected as a shock in the solar wind at L1. A flare seen in ultraviolet is linked to a rise in X-ray brightness recorded by GOES. SEP events detected by WIND or Parker Solar Probe can be traced back to the flare or CME that accelerated them.

By matching “what we see” with “what we feel,” scientists build a complete picture of solar activity and its effects.

Timing Is Key

To link events across different missions, scientists rely heavily on timing. Spacecraft clocks are precise, allowing researchers to determine when an eruption began, when it left the corona, and when its effects reached different locations in space.

This timing helps answer questions such as:

  • Did the CME actually hit Earth or pass by?
  • Did the particle storm come from the flare or from the CME shock?
  • How fast was the solar wind blowing when it arrived?

Many major discoveries, including how particle storms travel and how flares evolve, come from comparing timing across several instruments.

Seeing Hidden Features Through Multiple Wavelengths

The Sun looks different depending on the wavelength of light being used. Ultraviolet reveals hot plasma in the corona. X-rays show the most energetic regions in flares. Coronagraphs show the faint outer atmosphere. Visible-light magnetograms show surface magnetic fields.

Because each wavelength highlights a different layer or temperature, combining them reveals processes that would otherwise be invisible. A flare may brighten in X-rays first, then appear in ultraviolet, then launch a CME visible only in a coronagraph. Understanding all three together gives insight into how solar eruptions unfold.

This is why missions like SDO and Solar Orbiter observe in many wavelengths at once.

Linking Near-Sun Observations With Solar Wind Data

Once plasma leaves the Sun, it becomes the solar wind. Missions like Parker Solar Probe, Solar Orbiter, ACE, WIND, and DSCOVR sample this plasma directly. By comparing these measurements with images of the source region on the Sun, scientists can determine where certain types of wind originate, how fast CMEs travel, and how magnetic structures evolve as they move outward.

How This Becomes Space-Weather Forecasting

The same data used for science is also used for practical forecasting.

  • GOES detects the start of flares.
  • SOHO and STEREO show whether a CME is Earth-directed.
  • ACE and DSCOVR measure solar wind changes before they reach Earth.
  • Models combine these inputs to estimate CME arrival times and geomagnetic storm strength.

Space-weather centres rely on this continuous flow of observations to protect satellites, astronauts, and power systems. All of this begins with spacecraft measurements that are processed, interpreted, and compared across missions.

Why Different Missions Matter Together

No single mission can show the full picture. The Sun is too complex, too dynamic, and too extended in space.

Coronagraphs show the outer corona.
Ultraviolet telescopes show the middle corona.
Magnetographs show the surface.
Solar-wind monitors record what reaches Earth.
Parker Solar Probe and Voyager sample regions we can’t see at all.

Accessing the Data

You don’t need to be a scientist to explore real solar data. Many of the images, plots, and measurements used in heliophysics are public, updated in real time, and completely free to access. This chapter is a simple guide to where those datasets live, what they show, and how to use them at a basic level.

Live Views of the Sun

SDO – Solar Dynamics Observatory (NASA)

High-resolution images updated every few seconds. You can view the Sun in many ultraviolet wavelengths.

SOHO – Solar and Heliospheric Observatory (NASA/ESA)

The best place to see the corona and CMEs through LASCO coronagraph images.

STEREO – Off-angle Sun images

Useful for seeing eruptions from the side.

Solar Wind and Space-Weather Data

NOAA SWPC – Space Weather Prediction Center

The most user-friendly place to see current solar wind, X-ray flux, geomagnetic activity, and alerts.

Direct products:

NOAA Dashboard (very clean + beginner friendly)

Plots solar wind speed, density, IMF, proton flux, X-ray flux, aurora probabilities, etc.
https://www.swpc.noaa.gov/phenomena/space-weather-dashboard

Exploring Solar Eruptions

HEK – Heliophysics Event Knowledgebase

Catalog of flares, CMEs, active regions, filament eruptions, etc.
https://www.lmsal.com/hek/

Helioviewer

A simple, visual tool that lets you layer images from SDO, SOHO, Solar Orbiter, and more.
https://helioviewer.org/

Perfect for beginners who want to “scroll around the Sun.”

Particle Data and SEP Events

GOES Proton Flux

Real-time radiation storm monitoring.
https://www.swpc.noaa.gov/products/goes-proton-flux

NASA/ACE & WIND Data (via CDAWeb)

Energetic particles, solar wind, and magnetic field measurements.
https://cdaweb.gsfc.nasa.gov/

Fermi GBM Solar Flare Data

Great for high-energy flares and gamma-ray observations.
https://fermi.gsfc.nasa.gov/

Solar Orbiter and Parker Solar Probe

Solar Orbiter Data (ESA)

All imaging + in-situ data accessible once public.
https://soar.esac.esa.int/soar/

Parker Solar Probe Data (NASA)

Released in batches; includes near-Sun plasma, magnetic fields, and particles.
https://sppgway.jhuapl.edu/

Long-Term Solar Wind & Planetary Data

OMNI Data (NASA)

Combined, long-term dataset of solar wind, IMF, and geomagnetic indices dating back to the 1960s.
https://omniweb.gsfc.nasa.gov/

Ulysses Archive

The only mission to explore the high-latitude solar wind.
https://spdf.gsfc.nasa.gov/pub/data/ulysses/

Voyager Project (NASA)

Data from the heliopause crossings and outer heliosphere.
https://voyager.jpl.nasa.gov/science/

Beginner Tools

These pages are ideal for website visitors who want to explore without touching raw data files.

NASA Scientific Visualization Studio (SVS)

Animations, data-driven visualizations, and clips showing flares, CMEs, and missions.
https://svs.gsfc.nasa.gov/

SOHO Movie Maker

Quick way to generate small clips of eruptions.
https://soho.nascom.nasa.gov/data/movies/

Timeline of Discovery

Our understanding of the Sun has grown through centuries of observation, each new technique revealing something the previous one couldn’t. This timeline is not a complete history, but a clear path showing how solar astronomy evolved into modern heliophysics and how spacecraft made today’s discoveries possible.

Early Observations (1600s-1800s)

The first detailed studies of the Sun came from simple telescopes. Astronomers such as Galileo sketched sunspots and noticed that they moved, showing that the Sun rotates. Over time, observers realised that sunspot numbers rise and fall in a roughly 11-year cycle, an early hint that the Sun is not constant.

Photography in the 1800s allowed the corona to be captured during solar eclipses. These images showed streamers, loops, and structure in the outer atmosphere long before we understood what caused them.

The Birth of Space Science (1900s–1950s)

Early 20th-century scientists linked solar activity to changes on Earth. Radio bursts were discovered in the 1940s, showing that flares release more than just light. Balloon experiments and early rockets detected ultraviolet and X-ray emissions that never reach the ground.

During the International Geophysical Year in 1957–58, the first satellites began providing continuous measurements above the atmosphere. This marked the shift from classical astronomy to the start of space-based solar physics.

The First Space Missions (1960s–1980s)

Missions such as OSO (Orbiting Solar Observatory), Skylab’s solar telescopes, and SOLRAD (Solar Radiation) began offering extended ultraviolet and X-ray observations. They confirmed that the corona is far hotter than the surface and that flares release sudden bursts of high-energy radiation.

Ulysses was launched to study the high-latitude solar wind, becoming the first mission to travel over the Sun’s poles.

A New Era: SOHO and Yohkoh (1990s)

The 1990s transformed heliophysics. The Japanese mission Yohkoh observed the Sun’s X-ray corona in unprecedented detail, revealing flare structures and coronal heating processes.

SOHO arrived soon after. Its coronagraph observations became the foundation for CME research. With SOHO, scientists could finally watch the outer corona continuously and track eruptions from the earliest stages.

These missions established the modern approach: observe the Sun in many wavelengths and monitor its atmosphere without interruption.

High-Resolution Sun: SDO (2010s onward)

NASA’s Solar Dynamics Observatory began returning rapid, high-resolution images in several ultraviolet wavelengths. Its images capture magnetic loops rising, twisting, and erupting over timescales of seconds.

SDO provided the sharpest view of the Sun’s corona ever achieved, helping explain flares, filaments, and the structure of active regions. Its continuous coverage also became a key tool for space-weather operations.

A New Perspective: STEREO

The two Solar TErrestrial RElations Observatory spacecraft changed how we view eruptions by providing angles away from Earth. This allowed 3D reconstruction of CMEs and improved forecasting accuracy. With STEREO, scientists could finally confirm how wide eruptions are and whether they are directed toward Earth or not.

Touching the Sun: Parker Solar Probe (2018–present)

Parker Solar Probe became the first spacecraft to fly through the Sun’s outer corona. Its measurements are directly sampling the region where the solar wind is heated and accelerated, something no previous mission could do.

Observations from Parker Solar Probe are helping solve long-standing questions about the origins of the solar wind, the nature of magnetic “switchbacks,” and the structure of the corona close to the Sun.

The Polar View: Solar Orbiter (2020–present)

Solar Orbiter, a joint ESA/NASA mission, combines imaging and in-situ measurements. Its orbit will gradually rise out of the Sun’s equatorial plane, giving the clearest views yet of the solar poles (although not a perfect view!). These areas control the solar cycle but have always been challenging to observe.

Solar Orbiter’s close-up images and unique perspective are expected to fill major gaps in our understanding of magnetic-cycle evolution.

Crossing the Boundary: Voyager (2012–present)

Voyager 1 crossed the heliopause in 2012, followed by Voyager 2 in 2018. These crossings provided the first direct measurements of the transition from the solar wind to interstellar space, something theorised for decades but never observed.

The Voyagers continue to send back data from the outer heliosphere, helping scientists understand how far the Sun’s influence reaches and what lies beyond.

Looking Ahead: IMAP (2025+)

The Interstellar Mapping and Acceleration Probe (IMAP) will investigate the boundary of the heliosphere by measuring particles that originate at its edges. IMAP will help clarify how cosmic rays enter the heliosphere and how the solar wind interacts with the interstellar medium, building on results from IBEX and Voyager.

A Growing Story

Every mission built on those before it. Early sketches became photographs, photographs became space-based images, and today’s images are supported by in-situ measurements and near-Sun sampling. Our understanding of the Sun is still evolving, and upcoming missions will continue to push closer, see sharper, and measure the heliosphere more completely.