Key Takeaways
- A total solar eclipse occurs when the Moon precisely covers the Sun’s disk as seen from a narrow path on Earth
- Solar storms can disrupt satellite navigation, power grids, aviation communications, and HF radio networks
- The Sun is currently near the peak of Solar Cycle 25, which has proven more active than forecasters initially predicted
The Geometry Behind 4 Minutes of Darkness
On April 8, 2024, a total solar eclipse swept a 185-kilometre-wide path from Mexico through the United States to eastern Canada, including parts of southern Ontario. For observers along that centerline, the Moon fully blocked the Sun for up to 4 minutes and 28 seconds, revealing the solar corona — the Sun’s outer atmosphere — as a glowing, gossamer halo visible to the naked eye only in those moments.
That precise visual coincidence — the Moon appearing to exactly cover the Sun’s disk — is a remarkable accident of geometry. The Sun is approximately 400 times larger in diameter than the Moon, but the Sun is also approximately 400 times farther away. The two objects appear almost exactly the same angular size in Earth’s sky, roughly 0.5 degrees across. This match is not physically required by any law of physics. It is the result of the Moon’s current distance from Earth during this period of its orbital evolution, and it will not last indefinitely. The Moon is slowly receding from Earth at a rate of approximately 3.8 centimetres per year, meaning that in the deep future the Moon will appear too small to fully cover the Sun, and total solar eclipses as currently experienced will become impossible.
The next total solar eclipse visible from North America after April 2024 will occur on August 23, 2044, crossing parts of western Canada.
What Is a Solar Eclipse?
A solar eclipse occurs when the Moon passes directly between Earth and the Sun, casting a shadow on Earth’s surface. The outer, lighter part of the shadow is the penumbra, where the Sun is only partially blocked — this produces a partial eclipse. The innermost, darkest part is the umbra, where the Sun is completely blocked, producing a total eclipse. If the Moon is at or near its farthest point from Earth in its slightly elliptical orbit (called apogee), it appears slightly smaller than the Sun and cannot fully cover it, producing an annular eclipse — a “ring of fire” effect.
The Moon completes one orbit around Earth approximately every 29.5 days. Why doesn’t a solar eclipse happen every month? Because the Moon’s orbital plane is tilted about 5 degrees relative to Earth’s orbital plane around the Sun. Most of the time, the Moon passes above or below the Sun from Earth’s perspective at new moon. Eclipses only happen when the Moon crosses the orbital plane (at points called nodes) at the same time as a new moon.
The path of a total eclipse across Earth’s surface is narrow because the Moon’s umbra is small — typically less than 270 kilometres in diameter — and it sweeps across Earth quickly, producing totality for only a few minutes at any given location.
The Solar Corona: Visible Only in Totality
During the brief minutes of a total eclipse, the blinding light of the photosphere — the Sun’s visible surface — is blocked, and the far dimmer corona becomes visible. The corona extends millions of kilometres into space and is, paradoxically, far hotter than the surface it emanates from. The photosphere burns at approximately 5,500 degrees Celsius. The corona reaches temperatures of 1 to 3 million degrees Celsius. Why the corona is so much hotter than the surface it surrounds is one of the significant unsolved problems in solar physics, actively studied by missions including NASA’s Parker Solar Probe, which made its closest-ever solar approach in December 2024 at about 6.1 million kilometres from the Sun’s surface.
Historical eclipses have produced important scientific discoveries. The 1868 eclipse led to the identification of helium in the solar spectrum before it was discovered on Earth. The 1919 eclipse expeditions led by Arthur Eddington confirmed Einstein’s general relativity by measuring the bending of starlight passing near the Sun — one of the most celebrated experimental verifications in the history of physics.
Space Weather: The Sun as a Source of Disruption
The Sun produces more than light and heat. It continuously emits a stream of charged particles — the solar wind — that flows through the solar system at speeds of approximately 400 to 800 kilometres per second. It also produces far more energetic events: solar flares and coronal mass ejections (CMEs), which can hurl billions of tons of magnetized plasma toward Earth in a matter of hours.
When a CME directed at Earth reaches our planet, it interacts with the magnetosphere — the protective magnetic field generated by Earth’s interior. The magnetosphere deflects much of the solar wind continuously, but a powerful CME can compress the magnetosphere substantially and trigger a geomagnetic storm. The intensity of these storms is classified on a scale from G1 (minor) to G5 (extreme).
In May 2024, Earth experienced the strongest geomagnetic storm since 2003 — a G5 event caused by a series of solar flares and CMEs from an active sunspot region. The storm produced auroras visible at unusually low latitudes, including across much of the continental United States and central Europe. It also caused temporary disruptions to some GPS signals and high-frequency radio communications. Agricultural GPS systems in parts of the US Midwest reported positional errors significant enough to affect precision planting operations.
How Space Weather Affects Satellites and GPS
The Global Positioning System (GPS), operated by the United States Space Force, relies on precise timing signals transmitted from a constellation of satellites at medium Earth orbit. Solar energetic particles can disturb the ionosphere — the upper layer of Earth’s atmosphere — causing the GPS signals passing through it to be delayed, refracted, or scattered. The result is degraded positioning accuracy that can last for hours.
For aviation, space weather creates additional challenges. Airlines routing flights over polar regions use high-frequency(HF) radio as a backup communication system because satellite coverage is limited over the poles. Solar radiation storms can absorb HF radio waves in the polar ionosphere, creating communication blackouts that force aircraft to divert to lower-latitude routes and burn additional fuel. The Federal Aviation Administration (FAA) monitors space weather alerts from NOAA’s Space Weather Prediction Center (SWPC) to manage these situations.
The most extreme historical example of space weather affecting terrestrial infrastructure is the Carrington Event of September 1859, when a massive CME produced geomagnetic storms so intense that telegraph systems across North America and Europe failed, with some systems sparking fires. The relatively limited technological infrastructure of 1859 meant the damage was containable. A Carrington-scale event today, striking a world dependent on satellites, power grids, internet routing, and precision navigation, would be catastrophic by comparison.
The Current Solar Cycle and Its Implications
The Sun operates on an approximately 11-year cycle of magnetic activity, swinging between solar minimum — when sunspots and eruptions are rare — and solar maximum, when they are frequent. Solar Cycle 25 began in December 2019. The initial forecasts from NOAA’s Solar Cycle 25 Prediction Panel were relatively conservative, expecting a cycle of similar intensity to the weak Solar Cycle 24 that preceded it.
The Sun has significantly exceeded those forecasts. Solar Cycle 25 has produced substantially more sunspot activity and solar flares than predicted, and solar maximum — typically a period of roughly a year around peak activity — was reached in approximately late 2024 and early 2025. As of April 2026, the Sun is in the declining phase from solar maximum but remains more active than average.
This elevated activity has direct consequences for the growing constellation of satellites in low Earth orbit. Increased solar activity heats and expands the upper atmosphere, increasing atmospheric drag on satellites in orbits below approximately 600 kilometres. SpaceX’s Starlink constellation, which operates primarily in the 540 to 570 kilometre range, experienced satellite losses in February 2022 when a geomagnetic storm increased atmospheric drag just after a batch of 49 satellites reached orbit, preventing them from raising their altitude before they deorbited. The company reported that up to 40 of those satellites were lost.
Protecting Against Space Weather
Awareness of space weather threats has grown substantially in both the private sector and among government agencies. NOAA’s SWPC provides 24-hour forecasting and real-time alerts through its spaceweather.gov portal. The agency issues watches, warnings, and alerts at five severity levels for geomagnetic storms, solar radiation storms, and radio blackouts.
The European Space Agency operates its Space Weather Service Network to support European infrastructure operators. In the United States, a 2015 executive order and a subsequent 2019 National Space Weather Strategy and Action Planformalized the federal government’s responsibilities for space weather preparedness.
The ESA’s Vigil spacecraft, planned for launch in 2031, will be placed at the L5 Lagrange point — a position trailing Earth in its orbit around the Sun — to provide early warning of solar activity that would otherwise be invisible from Earth or the L1 point until it rotates into view.
Summary
Solar eclipses and space weather represent two distinct but related aspects of humanity’s relationship with the Sun. Eclipses are predictable geometric events with fixed recurrence patterns that have enabled scientific discoveries for centuries. Space weather is an ongoing physical phenomenon driven by the Sun’s magnetic activity cycle, producing effects on Earth’s technological infrastructure that range from minor GPS degradation to the potential for continent-scale power failures in extreme cases. Solar Cycle 25 has been more active than initially forecast, adding urgency to space weather preparedness efforts at the same time as the global satellite constellation has expanded to record sizes.
Appendix: Top 10 Questions Answered in This Article
What causes a total solar eclipse? A total solar eclipse occurs when the Moon passes directly between Earth and the Sun, with the Moon’s small umbral shadow falling on Earth’s surface. It is visible only from a narrow path, typically less than 270 kilometres wide, because the Moon’s shadow is small.
Why don’t solar eclipses happen every month? The Moon’s orbital plane is tilted approximately 5 degrees relative to Earth’s orbital plane around the Sun. Most months, the Moon passes above or below the Sun at new moon. Eclipses occur only when the Moon crosses the orbital plane at the same time as a new moon.
When is the next total solar eclipse visible from North America? The next total solar eclipse visible from North America after the April 8, 2024 eclipse will occur on August 23, 2044, crossing parts of western Canada.
What is space weather? Space weather refers to conditions in the space environment affected by solar activity, including the solar wind, solar flares, and coronal mass ejections. These phenomena can affect satellites, GPS accuracy, power grids, radio communications, and aviation operations.
What was the Carrington Event? The Carrington Event was an extreme geomagnetic storm caused by a massive coronal mass ejection in September 1859. It disrupted telegraph systems across North America and Europe, causing fires in some telegraph offices. A similar event today would pose severe risks to modern infrastructure.
How does solar activity affect GPS accuracy? Solar energetic particles and geomagnetic storms disturb the ionosphere, causing GPS signals to be delayed, refracted, or scattered as they pass through it. During strong storms, positional errors can degrade significantly for hours.
What is Solar Cycle 25 and how active is it? Solar Cycle 25 began in December 2019. Despite initial conservative forecasts, it has been significantly more active than predicted, with solar maximum reached in approximately late 2024 to early 2025. As of April 2026, the Sun is declining from peak activity but remains above average.
How did space weather affect Starlink satellites in 2022? In February 2022, a geomagnetic storm increased atmospheric drag on 49 newly launched Starlink satellites before they could raise their orbits. SpaceX reported losing up to 40 of those satellites as they deorbited back into the atmosphere.
What is the solar corona and why is it unusual? The solar corona is the Sun’s outer atmosphere, visible during total solar eclipses as a glowing halo. It reaches temperatures of 1 to 3 million degrees Celsius — far hotter than the Sun’s visible surface at approximately 5,500 degrees Celsius — a paradox that remains an active area of solar physics research.
What is NOAA’s Space Weather Prediction Center? NOAA’s Space Weather Prediction Center, or SWPC, is the official US government source for space weather forecasts, watches, warnings, and alerts. It monitors solar activity continuously and provides real-time information to satellite operators, utilities, airlines, and the public through its spaceweather.gov portal.
