The Butterfly-Shaped Hole in the Sun

In September 2025, a striking feature appeared on the surface of the Sun that captured both scientific and public attention, a vast, butterfly-shaped coronal hole. While the poetic nickname reflects its unusual appearance, the phenomenon itself is a significant event in solar physics and space weather forecasting. Understanding what this means requires a closer look at the nature of coronal holes, the solar wind they generate, and their potential influence on Earth.

Coronal Holes and Their Characteristics

Coronal holes are regions in the Sun’s outer atmosphere, or corona, where the Sun’s magnetic field is not closed but extends outward into interplanetary space. This open configuration allows charged particles and plasma to escape more freely, creating fast streams of solar wind. These areas appear darker in extreme ultraviolet and X-ray imagery because they are cooler and less dense compared to the surrounding corona.

Although coronal holes are a common feature of the solar cycle, their position, size, and timing determine their impact on Earth. When a coronal hole is located near the Sun’s equator and faces Earth directly, the solar wind it produces is more likely to interact with Earth’s magnetosphere. The strength of that interaction depends largely on the speed and density of the solar wind, as well as the orientation of its embedded magnetic field.

The “Butterfly” Coronal Hole

On 11 September 2025, NASA’s Solar Dynamics Observatory recorded images of a coronal hole spanning nearly 500,000 kilometers across large enough to accommodate approximately 40 Earths side by side. Its central position on the solar disk ensures that the solar wind released from this region is Earth-directed. The hole’s distinctive wing-like outline led observers to describe it as a “butterfly-shaped hole,” though its scientific significance lies in its scale and position rather than its shape.

The Journey of Solar Wind to Earth

Once released, high-speed solar wind streams take between two and five days to travel the 150 million kilometers from the Sun to Earth. Scientists expect the solar wind from this particular hole to reach Earth between 13 and 14 September 2025.

The impact of this arrival depends on two critical factors. First, the velocity and density of the solar wind will determine how much energy is carried. Second, the magnetic orientation, known as the interplanetary magnetic field (IMF Bz), plays a decisive role. If the solar wind’s magnetic field points southward, it couples efficiently with Earth’s northward magnetic field, allowing energy to enter Earth’s magnetosphere and drive geomagnetic storms. If, however, it points northward, the interaction is much weaker. Because this orientation can only be measured once the solar wind approaches Earth, forecasts often carry a degree of uncertainty.

Scientific and Practical Implications

1. Auroras: Enhanced auroras in regions where they are rarely visible.

2. Satellites: Minor navigation errors and communication signal fluctuations.

3. Aviation: Potential rerouting of high-latitude flights due to radio blackouts.

4. Power Grids: Slight voltage fluctuations, especially in northern countries with large grid infrastructures.

Forecasts and Expected Impacts

Agencies around the world have issued predictions for this event. The NOAA Space Weather Prediction Center expects mostly G1 (minor) geomagnetic storm conditions, while the U.K. Met Office has indicated the possibility of G2 (moderate) activity. Independent monitors, including SpaceWeatherLive, have emphasized the hole’s unusually large size and central location, suggesting that G1 conditions are likely and G2 storms cannot be ruled out.

[Geomagnetic Storm Scale (G1–G5)

The Geomagnetic Storm Scale (G1–G5) is a classification system developed by the NOAA Space Weather Prediction Center (SWPC) to describe the intensity of geomagnetic storms caused by solar activity (such as coronal mass ejections or coronal holes). These storms disturb the Earth’s magnetic field and can affect satellites, power grids, navigation systems, and even produce auroras.

• G1 – Minor Storm

  • Occurs about 1700 times per solar cycle (11 years).

  • Small impact on power systems (minor voltage fluctuations possible).

  • Very weak impact on satellites.

  • Aurora may be visible at high latitudes (northern US states, northern Europe).

• G2 – Moderate Storm

  • Occurs about 600 times per solar cycle.

  • Some power grid issues possible, especially at high latitudes.

  • Small effects on spacecraft operations (orbit corrections, signal issues).

  • Aurora can be seen at mid-latitudes (e.g., northern US states like New York, parts of central Europe).

• G3 – Strong Storm

  • More serious power system voltage control problems.

  • Spacecraft systems may need resetting.

  • Aurora visible much farther south (e.g., across most of the USA, northern India, southern Europe).

• G4 – Severe Storm

  • Widespread power grid disturbances possible.

  • Satellite operations degraded.

  • Auroras can be visible in low-latitude regions, as far south as Texas or Spain

• G5 – Extreme Storm

  • Complete voltage collapse and grid blackouts possible.

  • Severe damage to satellites, long-duration GPS/communication failures.

  • Aurora visible in tropical regions.

For the butterfly hole, scientists predicted G1–G2 level storms, meaning mostly minor to moderate disturbances, but with beautiful aurora displays extending beyond the polar regions.]

This timing is also noteworthy because it coincides with the approach of the autumnal equinox. Around the equinoxes, Earth’s axial tilt makes the planet’s magnetic field more receptive to solar wind energy, a phenomenon known as the Russell–McPherron effect. This means that even moderate solar wind streams can result in stronger geomagnetic activity than they might at other times of the year.

Geomagnetic Storm Consequences

If forecasts are accurate, Earth may experience geomagnetic disturbances in the range of G1 to G2 on the NOAA storm classification scale. At these levels, the consequences are relatively modest but still scientifically and socially significant.

High-latitude regions are likely to witness intense auroras, while G2 conditions could allow auroral activity to extend into mid-latitudes, potentially visible across northern Europe, North America, and parts of Asia. Satellite operations may be affected by increased drag in low-Earth orbit and minor disturbances in electronic systems. High-frequency radio communications, often used in aviation and maritime operations, could experience temporary disruptions, especially in polar regions. Global navigation systems such as GPS may show brief reductions in accuracy. Power grids, although generally resilient at these levels, remain under careful monitoring because of the possibility of geomagnetically induced currents.

Historical Context

Events like the butterfly-shaped coronal hole remind us that even in the absence of massive solar flares or coronal mass ejections, the Sun’s quieter features can have measurable effects on Earth. In March 2015, a coronal hole contributed to a G4 geomagnetic storm, with auroras seen unusually far south. More recently, in April 2023, another large coronal hole generated one of the strongest storms of that solar cycle. These examples demonstrate that coronal holes are not merely routine features but can at times produce significant space weather events.

            The butterfly-shaped hole on the Sun in September 2025 is both a visually striking and scientifically important event. Though forecasts suggest only minor to moderate geomagnetic activity, the combination of its size, location, and timing near the equinox underscores the complexity of solar-terrestrial interactions. For most people on Earth, the event will pass unnoticed, except perhaps for those fortunate enough to witness vivid auroras. For scientists, however, it offers another opportunity to refine forecasting models and deepen our understanding of the Sun’s influence on Earth.