Aurora Alerts
Get a free email when the Kp index reaches your chosen threshold. Solar Ruler monitors NOAA's real-time geomagnetic data around the clock and sends you a notification when aurora conditions match your location. One alert per day maximum — no spam, no marketing, just aurora notifications you can act on.
Solar flares and coronal mass ejections (CMEs) are what drive the strongest aurora events. An active sun today often means a Kp alert in your inbox 1-3 days later. CMEs travel at 300-3,000 km/s, so the delay depends on how fast the ejected plasma is moving. The fastest CMEs can reach Earth in under 24 hours; slower ones take 3-4 days.
Watch the Sun live →How Aurora Alerts Work
Solar Ruler's alert system monitors NOAA's Space Weather Prediction Center (SWPC) around the clock. NOAA operates a network of ground-based magnetometers and receives real-time solar wind data from satellites positioned at the L1 Lagrange point, about 1.5 million kilometers sunward of Earth. These instruments measure the geomagnetic disturbance level and distill it into a single number: the Kp index.
The Kp index is updated every three hours on a scale from 0 to 9. When the index reaches or exceeds the threshold you chose during signup, our system sends you an email alert. You'll receive at most one alert per 24-hour period, so even during a multi-day geomagnetic storm, you won't be flooded with messages. Each alert includes the current Kp value, a plain-language severity label, and a direct link to the Solar Ruler live aurora map so you can check real-time conditions before heading outside.
Because the Kp index is a global measurement — the same value applies everywhere on Earth at any given moment — the threshold you choose determines how often you'll hear from us. A Kp 3 threshold will trigger alerts several times per month during active solar periods, while a Kp 7 threshold may only trigger a few times per year. Choose the level that matches your latitude and tolerance for notifications using the guide above.
Understanding the Kp Index: A Complete Guide
The Kp index (short for “planetarische Kennziffer,” German for “planetary index”) is the gold standard for measuring geomagnetic activity. Developed in 1949 by Julius Bartels, it aggregates readings from 13 magnetic observatories between 44 and 60 degrees geomagnetic latitude, producing a single number that represents how disturbed Earth's magnetic field is at any given moment.
The scale runs from 0 to 9 and is quasi-logarithmic, meaning each step represents a significantly larger disturbance than the one before it. At Kp 0-1, Earth's magnetic field is essentially undisturbed and aurora is confined to a narrow ring around the geomagnetic poles, invisible to most people. At Kp 3, the aurora oval begins expanding equatorward, becoming visible from high-latitude locations like Fairbanks, Tromsoe, and Reykjavik on clear, dark nights.
At Kp 5, NOAA officially classifies the event as a G1 geomagnetic storm. The aurora boundary pushes down to roughly 55 degrees geomagnetic latitude, bringing displays within reach of southern Canada, northern-tier US states like Minnesota and Washington, Scotland, and southern Scandinavia. This is the sweet spot for many aurora chasers — frequent enough to catch a few times per year, strong enough to produce visible green curtains on the northern horizon.
At Kp 7 (G3 storm), the aurora can be seen from the central United States, central Europe, and comparable latitudes in the Southern Hemisphere. These events produce vivid, fast-moving curtains of green, purple, and red that can stretch overhead. At Kp 9 (G5 extreme storm), aurora has been reported as far south as Florida, Texas, Mexico, and even Colombia. These events are exceedingly rare — perhaps once or twice per solar cycle — but they produce unforgettable all-sky displays visible from almost anywhere on Earth.
What to Do When You Get an Alert
An aurora alert means conditions are favorable — but seeing the aurora still requires a few things to align. Here's your checklist for turning an alert into a sighting:
The Science Behind Aurora Alerts
Every aurora display begins on the surface of the Sun. When the Sun releases a burst of charged particles — either through a solar flare or a coronal mass ejection (CME) — that plasma cloud races through space as part of the solar wind. Most solar wind travels at 300-400 km/s, reaching Earth in 3-4 days. Fast CMEs can exceed 2,000 km/s and arrive in less than 24 hours.
When this plasma arrives at Earth, it collides with our planet's magnetosphere — the magnetic bubble that shields us from most solar radiation. If the incoming solar wind carries a strong southward-pointing magnetic field (negative Bz), it can partially merge with Earth's magnetic field lines in a process called magnetic reconnection. This opens a pathway for charged particles to funnel down along the field lines toward the polar regions.
As these particles — mostly electrons and protons — spiral down into the upper atmosphere at altitudes of 100-300 km, they collide with oxygen and nitrogen molecules. These collisions excite the atmospheric molecules, causing them to release photons of light. Oxygen produces the familiar green glow (at 557.7 nm wavelength) and the rarer deep red (at 630 nm, seen during strong storms at higher altitudes). Nitrogen contributes blue and purple hues. The result is the shimmering curtains of light we see as the aurora borealis (north) and aurora australis (south).
The stronger the solar wind disturbance, the higher the Kp index climbs, and the further from the poles the aurora oval expands. This is why your Kp threshold directly determines how often you'll see alerts — and how spectacular the display might be when you do. A Kp 3 event produces a narrow band of green near the poles, while a Kp 7+ storm can paint the entire sky in rippling curtains of green, pink, and purple visible from mid-latitudes.
Frequently Asked Questions
How often will I receive alerts?
It depends on your threshold and the current solar cycle. During solar maximum (which we are currently in), Kp 5+ events happen several times per month. Kp 7+ events are less common — perhaps a few times per year. Kp 9 events are rare, averaging once every few years. Regardless of activity, you'll never receive more than one alert per 24-hour period.
Can I change my Kp threshold after subscribing?
Yes. Unsubscribe using the form at the bottom of this page (or the link in any alert email), then re-subscribe with your preferred threshold. The process takes less than a minute.
Why did I get an alert but couldn't see the aurora?
Several factors affect visibility beyond the Kp index: cloud cover can block the view entirely, light pollution from nearby cities can wash out faint aurora, the Moon can brighten the sky enough to obscure low-intensity displays, and the aurora may peak while your location is still in daylight. The Kp index tells you that geomagnetic conditions are strong enough for aurora at your latitude — it doesn't guarantee clear skies or darkness.
What time of night is best for aurora viewing?
Aurora can appear any time it's dark, but statistically the most active period is between 10 PM and 2 AM local magnetic time. For most locations, this aligns roughly with 10 PM - 2 AM clock time. Substorms — sudden bursts of auroral activity — are most common during this window. However, during strong Kp 7+ storms, aurora can persist from dusk to dawn.
Do I need to be in a rural area to see aurora?
For Kp 3-5 events, yes — you'll need reasonably dark skies away from city lights. For Kp 7+ events, aurora can often be seen from suburban areas and even city outskirts if you have a clear view toward the pole. The brightest Kp 9 events have been photographed from city centers. As a general rule: the darker your sky, the more you'll see.
Will my email be shared or sold?
Never. Your email address is stored solely for the purpose of sending aurora alerts. It is never shared with third parties, never used for marketing, and never sold. You can delete your subscription permanently at any time using the unsubscribe form below.
What is solar maximum and why does it matter?
The Sun follows an approximately 11-year cycle of magnetic activity. During solar maximum, sunspots, solar flares, and CMEs are far more frequent, leading to more geomagnetic storms and more aurora. The current Solar Cycle 25 is expected to remain near peak activity through 2025-2026, making this an excellent time to subscribe to aurora alerts — storms that would be rare during solar minimum are happening regularly right now.
I subscribed but never received a confirmation email.
Check your spam or promotions folder — automated emails are sometimes filtered there. If you're using Gmail, look in the Promotions tab. You can mark the email as "Not Spam" to ensure future alerts arrive in your primary inbox. If you still don't see it, try unsubscribing and re-subscribing with the same email address to trigger a new confirmation.
Explore More on Solar Ruler
Aurora alerts are just one part of your toolkit. Combine alerts with these other Solar Ruler features to maximize your chances of catching a display:
Privacy and Data
Solar Ruler takes your privacy seriously. When you subscribe to aurora alerts, we store only your email address, your chosen Kp threshold, and the date you subscribed. This data is stored securely in Firebase and is used exclusively for sending aurora alerts. We never share, sell, or use your email for any other purpose. You can unsubscribe at any time using the link in every alert email or the form below, which immediately deactivates your subscription.
Unsubscribe
Enter your email address to remove it from aurora alerts immediately.