CME TRACKER · HELP

1What this is

CME Tracker is a live, interactive view of space weather between the Sun and Earth — it shows where coronal mass ejections are, where they're headed, and when (and whether) they'll hit us.

A coronal mass ejection (CME) is a billion-ton cloud of magnetized plasma blasted off the Sun. When an Earth-directed one arrives — typically 1–4 days later — it can compress Earth's magnetic field, light up auroras, and disrupt satellites, radio, and power grids. This tool catalogs every CME NASA has recorded over the last 90 days, draws each as an expanding cone on a top-down map of the inner solar system, and propagates it outward to estimate its arrival.

2Quick start

• Look at the center map. The Sun is in the middle, Earth is the blue dot on its orbit, and each colored wedge is a CME fanning outward. Color = speed.
• Pick a CME. Click a wedge, or a row in the CME Catalog on the left. The app jumps the clock to that storm and animates it toward Earth.
• Watch the dashboards on the right update — the Earth globe shows which face the storm would strike and how the magnetosphere reacts; the charts show the solar wind and geomagnetic activity.
• Press space to play time forward, or drag the timeline at the bottom. Press N (or LIVE) to snap back to real time.

3The heliocentric map

The central canvas is a top-down view of the inner solar system, looking down on Earth's orbital plane. The same scene can also be flown as a real three-dimensional one — see §4.

• The Sun sits at the center. Earth is the blue dot, moving along its orbit (the ring). Earth's position is computed for whatever moment the clock shows.
• CME cones expand outward from the Sun. Each cone's direction is the CME's measured launch direction, and it spans ± the measured half-angle on either side of that axis (so its full width is twice the half-angle). A cone aimed at Earth's dot will reach it; one pointing elsewhere sails past.
• Color encodes speed — cool (slow) to hot (fast):

• A CME whose direction NASA hasn't triangulated yet is drawn as a faint directionless shell (a full ring rather than a cone) — we don't pretend to know where it's going.
• When an Earth-directed CME reaches Earth's distance, the dot flashes to mark the impact.

Navigating

• Scroll / pinch to zoom, drag to pan. The ⤾ view button resets the framing.
• Hover a cone for a quick tooltip (speed, direction, geometry, ETA). Click it to select.
• The ▦ Layers menu (top-right of the map) opens with three one-tap presets — Monitoring (the daily-check view: slow CMEs hidden, spacecraft on, pinned to LIVE; key 1), Clean (just the map, both panels collapsed; key 2), and Sensory overload (everything on at once; key 3). A preset is a starting point, not a lock — every switch below stays individually tweakable after you apply one, and ?mode=monitoring in the URL applies one on load. Below the presets, the menu groups eight overlays, and at the bottom sits 🎬 Cinematic view — the app's default look (textured, slowly churning Sun, deep-space backdrop, glowing turbulent CME fronts, lit planets). Same physics, same data, same interactions — only the rendering changes. Prefer the original flat rendering? Untick it; your choice is remembered (?viz=classic applies it via URL). Parker spiral draws the curved shape the Sun's magnetic field is dragged into by the solar wind; Labels toggles on-map text; and Connectivity, Spacecraft and Solar flares are described next. Solar flares and Labels are on by default; the rest are off — including Sparkles (a drifting particle haze inside each CME wedge) and Side view, an edge-on inset showing each cone's solar latitude: the dimension a top-down map can't show. A CME can look Earth-aimed in longitude yet fire well above or below the ecliptic — the side view is where you catch it. Top view is a plan-view inset of the whole inner system: most useful in the 3D view, where it keeps true longitudes on screen while you fly the camera, but on the flat map it earns its place too — it stays zoomed out while you zoom in.
• Connectivity shows the single Parker-spiral field line that links the Sun to Earth, marked at its solar footpoint (~W55 in typical wind). The footpoint is computed from the wind speed measured at the displayed moment, so it moves as you scrub or replay: slow wind winds the spiral tighter (footpoint near W65), a fast stream relaxes it (near W35) — and when no measurement covers the displayed moment, the label says est. wind instead of pretending. A shaded green fan marks the well-connected zone — footpoint ±45° — because energetic particles travel along field lines: an eruption inside that fan reaches Earth in minutes, even when it's far off the Sun–Earth line. Select a CME and its source is flagged connected (amber, particles stream to Earth) or not connected (dashed), with the angle from the footpoint. And when the eruption demonstrably dosed Earth, measurement outranks geometry: the line turns hot (☢ SEP observed) and shows how long the protons actually took to arrive. This is why a west-limb flare that misses Earth can still dose it (see the radiation card).
• Spacecraft marks where the observatories this site pulls data from actually sit. Three of them cluster at Earth: the L1 trio (SOHO, ACE, DSCOVR) sits ~1.5 million km sunward of Earth — only about 1% of the way to the Sun, so it hugs Earth until you zoom in — while GOES and SDO orbit so close to Earth they're labelled on it rather than drawn separately. The interesting ones orbit the Sun independently: STEREO-A, well off the Sun–Earth line (a faint sightline shows its view toward the Sun) — the second viewing angle that lets NASA triangulate each CME's true direction and width; Parker Solar Probe, diving through the corona itself; and Solar Orbiter, whose Venus-resonant orbit tilts higher with every flyby to climb toward the Sun's poles — its label reads out its live latitude, the dimension the top-down map can't draw. Hover or tap any marker for a popup describing what that craft does — Solar Orbiter's popup also draws its orbit edge-on: the tilted ellipse against the flat ecliptic (Earth on the plane for contrast), its current height above or below it, and dashed guides at the planned 24° and 33° tilts of the coming Venus flybys. The layer is time-aware — a spacecraft only appears once the displayed time is past its launch, so a 2003 or 2012 replay shows only the craft flying then (no DSCOVR before 2015), and the 1859 Carrington replay shows an empty sky. Positions are approximate, plotted in the orbital plane.
• Solar flares draws each flare erupting at the Sun, timed to the playhead: a flare flashes when the timeline reaches its peak, then fades over about three days. It's drawn at the Sun's edge pointing in the flare's source direction — the same way the CME it launched points — and colored by GOES class (X red, M orange, C blue), with the strongest getting spikes. A dashed ring means that flare launched a CME; select that CME and its flare is highlighted. Play or scrub the timeline to watch flares fire in sequence.

4The 3D view

The ⬒ Top-down / ◱ 3D switch beside the Layers menu swaps the flat map for the same solar system rendered as an actual three-dimensional scene. Everything else is unchanged — same physics, same catalog, same timeline, same clicking and hovering, and both the cinematic and classic looks apply. Only the projection differs.

Why it exists: latitude. The flat map draws every CME from its measured longitude and half-angle, and has no way to show the third number NASA also measures — the cone's latitude. So a CME erupting 55° above the Sun's equator gets painted sweeping straight across Earth, and then the card calls it a miss. In 3D the cone is simply where it really is: sailing over Earth's head. That contradiction is the best single reason to switch views.

Moving the camera

• Drag to orbit the Sun; scroll or pinch to move closer or further out. ⤾ view resets the framing.
• The camera never rolls, and it stops just short of the poles, so the plane of the solar system always reads level however far you swing around. Look straight down and you are back to very nearly the flat map — which is what makes moving between the two views readable rather than disorienting.

Vantage points

The dropdown to the right of the view switch decides where the camera sits. (It greys out in top-down mode, which has no camera to place.)

• Free orbit — the default: you float outside the system looking in.
• From Earth — the camera stands on Earth and looks back at the Sun. This is the geometry a coronagraph sees, and it is worth understanding: a CME aimed at you does not look like a cone off to one side, it looks like a ring opening around the Sun. That is a halo CME — which is why halos are at once the dangerous ones (they are coming at us) and the hardest to measure, since a ring hides how fast it is really travelling and looks much the same whether it is heading toward you or directly away. Here you can watch a wedge become a halo just by changing seats. In this vantage, dragging looks around and scrolling changes the focal length rather than the distance.
• When a front finally sweeps over your vantage point, the frame washes in that CME's colour — the storm arriving, seen from inside it, at the transit time the model predicts.

What else changes in 3D

• Earth pulses on impact on exactly the same frame as it does on the flat map — it is the same arrival test, not a second animation that might disagree with it.
• Old fronts recede. On a busy day forty-odd cones are in flight at once, and the oldest are also the largest, so left alone they bury the Sun and planets entirely. Once a front has passed the body you are watching — whichever one the ◎ Directed at dropdown is set to — it fades back quickly, because from that moment it is history. Set the target to Mars and Mars-bound fronts stay bright the whole way out to Mars. Inbound CMEs are never dimmed.
• Spacecraft is worth turning on here. Parker Solar Probe and Solar Orbiter both fly tilted orbits, and this is the only view that can draw them where they actually are instead of reporting their height as a number in a label — Solar Orbiter swings up to roughly 0.18 AU clear of the plane, which is the entire point of the mission.
• Side view and Top view both work here, as picture-in-picture panels stacked at the bottom-left. The top view is the valuable one in 3D: perspective is what makes a three-dimensional scene worth having, and also what makes it worse at the question the flat map answers instantly — how far off the Sun–Earth line is this thing? Keeping the plan view in the corner gives you both answers at once.

Which view you get

The live map opens top-down: plan view reads distances and angular separations truly, and that is what makes it a good instrument. Historical replays open in 3D — a replay carries around twenty CMEs rather than several hundred, so the view stays clear, and those are exactly the storms where a cone's true latitude is the story. Either way, the moment you touch the switch yourself your choice sticks for the rest of the visit and nothing moves it again. ?view=3d and ?view=2d set it from a link, and &eye=earth picks the vantage — so “look at this storm from Earth” is something you can send someone.

5Time & playback

The tracker is a time machine: it can sit at the live moment, run forward to show forecasts, or rewind to replay what happened.

• The clock (top-left of the map) shows the displayed moment with a tag: LIVE (real time now), … AGO (the past), or +… FORECAST (the future).
• ▶ Play/pause animates time forward at the selected speed (also space).
• LIVE returns to live real time (also N or L).
• Speed buttons set how fast time runs: 1h/s, 3h/s, 6h/s, 12h/s, 1d/s (simulated hours-to-days per real second).
• The timeline at the bottom is a scrubber spanning the loaded window. Tick marks show when each CME launched and a dot marks its arrival; drag the orange playhead to any moment.
• Isolate — the ⧉ Isolate button (right of the speed buttons) drops two handles on the timeline. Drag them to bracket a stretch of time, and the map replays only the CMEs that launched inside it — handy for studying one burst of activity without the clutter of everything still in flight. Toggle it off to bring them all back.
• Timeline span — the 30d / 60d / 90d selector at the right of the transport sets how far back the scrubber reaches. Selecting an older CME from the catalog auto-widens the span so the playhead always stays on the bar.

6CME Catalog (left panel)

Every CME from NASA DONKI over the last 90 days. The count next to the title shows how many are visible vs. total.

Speed-class filter

The chips at the top filter both the list and the map by speed class. Slow S CMEs are hidden by default (they rarely cause storms); click a chip to show or hide that class.

Target planet — Earth, Mercury, Venus or Mars

The ◎ Directed at dropdown re-aims the whole app at another target. Pick Mercury, Venus, Mars — or the Solar Orbiter spacecraft — and the catalog verdicts, the directed-only filter, the arrival times, and the timeline all switch to it, and it gets ringed on the map. Because the inner planets move quickly, plenty of CMEs that miss Earth are aimed straight at one of them; Solar Orbiter's hit-test additionally accounts for its tilted orbit (it rides up to ±13° out of the ecliptic). Relatedly, selecting any CME shows a SolO view line in its impact card: the angle between the CME's axis and Solar Orbiter's vantage — ~90° means the spacecraft sees a clean side-on "limb" eruption (the geometry its imagers measure best), while head-on means it sees a hard-to-measure halo. (Arrival times off Earth are model estimates — our accuracy is validated at Earth only — and the storm, aurora & Kp readouts always describe Earth.)

Directed-only filter

The ▲ <planet>-directed only toggle restricts the catalog — and the map & timeline — to CMEs headed at the selected planet (direct and glancing), hiding misses and undetermined ones. It combines with the speed filter, so you can zero in on, say, fast Earth-bound storms in one view.

Hide undetermined direction

The ⊘ Hide undetermined direction toggle removes CMEs whose direction NASA hasn't measured yet — the AWAITING TELEMETRY and DIRECTION UNDETERMINED rows — so the catalog and map show only events with a known geometry.

Reading a row

Each row shows the launch time (with the year for historical events), a speed-class badge, the speed in km/s, the source direction (e.g. N12W34 in solar coordinates), and the cone half-angle. The colored badge underneath is the geometry verdict:

Click a row to select it (the map jumps to it and animates). Use ↑/↓ to move through the list.

7Recent Flares (left panel)

Solar flares from GOES X-ray sensors over the last 7 days, strongest first. Class letters run A · B · C · M · X, each ~10× brighter than the last (X is the most intense).

• A flare tagged → CME launched a coronal mass ejection. Click it to jump to and select that CME — and the matching burst pulses on the Sun image.
• Flares without the tag produced radiation but no catalogued ejection.
• By default the list shows all flares. The toggle under the header flips to → launched a CME to show only the ones that produced a coronal mass ejection (the events relevant to tracking).

8Selected CME card (right panel)

When you select a CME, this card breaks it down:

• Speed & direction — the measured launch velocity and heading.
• Geometry — Earth-directed, glancing, miss, or awaiting telemetry, with the angular offset from the Sun–Earth line.
• Estimated arrival ± uncertainty — when the leading edge reaches Earth, with the model's error band (~±12 h).
• Transit time — how long the Sun-to-Earth journey takes.
• Source flare — the flare that launched it, if known (click-through).
• Storm potential — the predicted geomagnetic response as a range: the most-likely level and a plausible upside (e.g. "Kp ~4.8, up to 6.8"). The estimate is calibrated against a decade of observed storms, and the range isn't hedging — storm size mostly depends on the CME's magnetic-field orientation (Bz), which physically cannot be known until the cloud reaches the L1 monitor ~30–60 minutes before Earth.

9Inbound CME warning

When a CME is genuinely en route and worth watching, a pulsing banner appears over the map. It fires when a storm of G2 or stronger is plausible — the upside of the calibrated estimate range, not the midpoint, because that's the watch-worthy number. If several qualify, it shows the strongest, then soonest.

The banner carries a watch-style severity chip ("≤G2 MODERATE" — the plausible ceiling), the impact time, a countdown, and the estimated Kp range (e.g. "Kp 4.8–6.8"); its color and pulse rate scale with that ceiling. Dismiss it with × — it stays hidden until a different CME becomes the top threat.

10Earth — sun-facing side (right panel)

A globe rendered from the Sun's point of view, so you see which face a storm would strike on arrival. It updates to whatever moment the clock shows. In cinematic view it renders real NASA Blue Marble imagery (re-projected to the sub-solar hemisphere) with aurora curtain rays; classic view keeps the original drawn globe.

• Day/night terminator & sub-solar point — the lit hemisphere and the spot where the Sun is directly overhead. This is how the tool knows which side of Earth is sun-facing when a CME arrives.
• The magnetosphere — the blue field bubble. It compresses when solar-wind dynamic pressure rises, and energy couples in when the field turns southward (negative Bz).
• Aurora ovals — drawn around both poles and sized by the Kp index; high Kp pushes them toward the equator.

The small tag by the title states what you're seeing: live now, at map time, ⚡ CME impact, ✓ Earth clear (a near-miss), replay, or at CME arrival. The caption beneath spells out the sub-solar point, the aurora Kp, and the wind/Bz coupling.

Who drives the globe: selecting a CME with an Earth arrival pins the globe to that arrival moment while playback is paused (the at CME arrival preview — which face gets hit). The moment you move the timeline yourself — drag or arrow keys — the globe follows your playhead instead, and stays with you until you select a CME again, which re-arms the preview.

11The Sun (SDO)

Imagery from NASA's Solar Dynamics Observatory — live when the playhead is at "now" (refreshed every few minutes), and time-synced to the playhead otherwise: scrub or play into the past and the panel shows the closest archived full-disk frame (hourly, via Helioviewer), with a timestamp chip marking the moment. Frames are cached as you go, so replaying a storm gets smoother the more you watch. Before SDO's first light (May 2010) a placeholder appears instead. Three views:

• Corona 193Å — the million-degree corona; coronal holes and active regions.
• Chromo 304Å — the cooler chromosphere; prominences and filaments.
• Sunspots — the visible-light photosphere with sunspot groups.

Recent flares pulse at their location on the disk — timed to the playhead, so they match the frame you're looking at — and numbered active regions (sunspot groups) are marked when the image is current. The caption summarizes the current regions and flare tally.

12Solar wind & geomagnetic charts

Measured conditions at the L1 point (about 1.5 million km sunward of Earth — our ~30–60 min early-warning post) and at the ground:

• L1 nowcast: the highest-confidence short-range read. Because L1 sits ~1.5 million km sunward, whatever it measures reaches Earth ~30–60 min later (sooner when the wind is fast) — a measurement with a travel time, not a model. When quiet it shows the current wind, Bz, and that travel time; when a shock crosses L1 it flags an incoming sudden commencement with a live countdown to Earth; sustained strongly southward Bz warns that energy is about to couple into the magnetosphere. A nowcast, not a forecast — it reports only what's been measured.
• Solar wind — 7 days: wind speed and the interplanetary magnetic field Bz. Bz turning southward (negative) is the key storm trigger — it lets solar-wind energy pour into the magnetosphere.
• Geomagnetic activity (Kp): the planetary K-index in 3-hour steps. Kp ≥ 5 is a geomagnetic storm; the bars are colored by severity.
• Radiation storm (S-scale): solar-proton flux on NOAA's S1–S5 scale (set by the ≥10 MeV flux crossing 10 pfu) — the one space-weather hazard with a direct radiation dose to people (astronauts, polar-route aircrew), so the card names who's affected at each level. The top shows current conditions live, or that storm's peak in a replay. Select a CME and a line appears for the radiation storm that eruption produced: protons arrive within minutes–hours of launch (not days later with the CME), so a flare can dose Earth long before its CME arrives — and even a CME that misses Earth can dose it via magnetic connectivity.

The header strip mirrors the latest live values — wind speed, proton density, Bz, Kp — plus a Data indicator showing whether the feed is live/cached and how fresh it is. All four readouts are buttons: click one (or focus it and press Enter) and it opens a visual popup that makes the number mean something. Each is described below; popups close on Esc or a click anywhere else, and only one opens at a time.

The Solar wind popup — the freight already in flight

Solar-wind speed matters for one reason: it sets the warning time. So the popup draws the Sun→Earth corridor with the wind currently en route, as a clearly-labeled time-lapse (at true speed the crossing takes days): a bright parcel departs the Sun and crosses to Earth, its label counting the trip as it goes ("in flight 1.0 d · Earth in 2.2 d") — a 3–4 day journey at typical speeds, which is exactly the lead time this site's forecasts live on. Calendar ticks under the corridor turn it into a forecast timeline: each tick marks where the wind arriving on that day is right now — Monday's weather is already two-thirds of the way here, Wednesday's is just leaving the Sun.

The header readout during a moderate 535 km/s stream — click it to see what's in flight.

The corridor as a calendar: the parcel is a day into its 3.2-day trip, and the ticks show Monday's wind nearing Earth while Wednesday's is still leaving the Sun.

The lapse factor is stated on-canvas where it applies, and the note flags the working assumption honestly: the conveyor holds today's speed for the whole trip, and real streams genuinely vary — which is exactly why the arrival days shift when the wind speeds up or slows down.

The Density popup — the measurement, drawn to count

Density is defined as protons per cubic centimeter, so this popup isn't a metaphor: it draws a 1 cm cube of space holding exactly the current reading's worth of protons, drifting through with the wind. The count follows the live number — when a CME's compressed sheath arrives and density jams from ~5 to 20–50+, you watch the cube crowd up, one of the first visible signs of impact.

7.6 protons per cubic centimeter — click to see all eight of them.

7.6 p/cm³ — eight protons in a sugar-cube of space. The same cube of the air you're breathing holds ~25 quintillion molecules.

The fine print keeps it honest: the dots are magnified ~10¹²× (a real proton at this scale would be invisible), the reading is an average so any actual cube fluctuates moment to moment, and every proton travels with an undrawn electron that keeps the wind electrically neutral.

The Bz popup — the magnetic gate

Bz gets the most consequential visualization because it is the most consequential number: it decides whether the wind's energy gets in at all. The popup animates dayside magnetic reconnection from the live field. Earth's dayside field lines always point north — the fixed door frame. The incoming field dashes are tilted to the measured Bz/|B|: pointing north, they can't reconnect, and you watch them slide around the magnetopause and past Earth — gate closed, same wind, no storm. Pointing south, they splice with Earth's field at the nose (the flashes), and the opened lines peel poleward, funneling energy into the polar cusps and brightening the aurora caps.

The readout turns red when Bz swings south enough to drive storming — click for the gate.

A strongly southward spell (Bz −12.4 nT): the gate meter pegged at "wide open — G3+ if sustained," aurora caps glowing.

The CLOSED→WIDE-OPEN meter is driven by the physical coupling term v·Bs — the same quantity the tracker's alert system watches at L1 — mapped to the calibrated storm tiers. Its honesty notes ride along in the popup itself: a 2-D cartoon of real physics with compressed scales, reconnection is continuous (the snaps pace it, they don't count anything), and the reading is measured at L1, so the scene you're watching reaches Earth ~30–60 minutes later.

The Kp meter & forecast popup

The header's Kp readout includes a mini-meter: nine segments spanning the full 0–9 scale, lit to the current value and colored along the quiet-green → storm-red ramp — so you can see at a glance where the current number sits in the range (storms begin at segment 5, where the ambers start).

The meter during a G3 storm — seven segments lit, deep into the amber zone.

Click the meter (or press Enter on it) and a panel opens charting the past week of measured 3-hour Kp alongside NOAA's official 3-day forecast. Solid bars are measurements, dimmed bars are NOAA's preliminary estimates, and hollow outlined bars are the forecast — model output never masquerades as measurement. Dashed amber markers show where this site's drag model expects inbound CMEs to arrive, with their estimated Kp, so you can see whether NOAA's forecast bump lines up with a CME we're tracking.

A real storm in progress: the week's history peaking past G3 at "now", NOAA's forecast settling, and two inbound-CME arrival markers from the tracker's model.

13Historical event replay

Opening any storm from Famous CMEs loads it and turns the whole app into a scrubbable replay of it — great for seeing extremes and sanity-checking the model against known events. A banner shows you're in replay; ↩ Live returns to real time. Replays open in the 3D view, where a storm's true latitude is visible — switch back to ⬒ Top-down at any time and it will stay there. For the full story behind each one — history, impacts, and the science — see Famous CMEs.

Provenance is labeled honestly: measured archive data vs. reconstruction (estimated). For the 2012 near-miss, a special card shows what STEREO-A measured — the storm Earth was spared — while the globe correctly stays calm.

Shareable links. Each replay has its own web address (for example cmetracker.ai/live?event=gannon-2024), so you can bookmark a storm or send someone a link that opens straight into that replay. Your browser's back and forward buttons step between events too.

14How accurate is it?

This isn't marketing — it's a real back-test. Every arrival the model would predict is compared against NASA's catalog of observed shock arrivals (hundreds of real CME→shock pairs); the full scoreboard and error histogram live on the science page.

• Typical (median) error ≈ 12 h; mean ≈ 15 h, with a 95% confidence interval shown on the card.
• Essentially unbiased — it doesn't systematically run early or late.
• Like-for-like on the same event set, NASA's full MHD model (WSA-Enlil) does somewhat better on the mean — ~11 h vs. our ~15 h — with the medians closer together (ours ≈12 h). Expected, since Enlil resolves the structured solar wind a two-parameter drag model only approximates; staying within a few hours of it is a strong showing for the simpler model.
• The histogram shows the spread; big misses are usually slow or poorly-observed CMEs.

Storm magnitude has its own back-test. The Kp estimate is calibrated against 221 observed CME→storm events (2014–2024): the most-likely level is right or within one G-level about 84% of the time, and no launch-time model can do much better — at a fixed prediction, real outcomes still span roughly ±2 Kp, because the deciding variable (the CME's field orientation) is unknowable until L1. That's why everything here shows a range rather than a single confident number; a single-level call only becomes honest ~30–60 minutes out, when the field is actually measured.

The model is the analytic Drag-Based Model (Vršnak et al. 2013): each CME starts at 21.5 solar radii with its measured speed and coasts toward the ambient solar-wind speed under aerodynamic drag. Most of the remaining error comes not from the propagation but from the input — the coronagraph-derived speed and direction, especially for halo CMEs.

Want the full derivation? The science & math behind CME Tracker walks through every equation — the drag model, the cone geometry, the ephemerides, the storm heuristic, and the validation methodology — with the limitations stated plainly.

15Controls reference

Keyboard

Mouse

Other tools

• UT toggles between UTC and your local time zone everywhere (display only — no change to the physics).
• Collapsible panels — the chevron tabs (‹ / ›) at the left and right edges of the map hide the catalog or the dashboards, expanding the map to fill the space. Your choice is remembered between visits.
• The ▦ Layers menu groups the map overlays — Parker spiral, Connectivity, Spacecraft, Solar flares, Side view, Top view, Sparkles and Labels (see §3).
• The ⬒ Top-down / ◱ 3D switch changes the projection, and the dropdown beside it places the 3D camera — Free orbit or From Earth (see §4).
• The ◎ Directed at dropdown re-aims the geometry & arrivals at Mercury, Venus, Mars, or Solar Orbiter (see §6); ⧉ Isolate replays just a chosen stretch of the timeline (see §5).
• Historical replays have shareable links (e.g. ?event=gannon-2024); your browser's back/forward steps between them (see §13). ?view=3d&eye=earth shares a camera, and ?cme= a specific CME.
• Live feeds refresh automatically every few minutes; the Data indicator shows freshness.

16Glossary

CME

Coronal mass ejection — a large eruption of magnetized plasma from the Sun.

Solar flare

A sudden burst of radiation from the Sun, classed A/B/C/M/X by X-ray brightness. Often (not always) accompanies a CME.

Solar wind

The continuous stream of charged particles flowing out from the Sun (~300–800 km/s).

IMF / Bz

The interplanetary magnetic field carried by the solar wind. Its north-south component, Bz, is decisive: strong southward (negative) Bz drives geomagnetic storms.

Kp index

A 0–9 scale of global geomagnetic disturbance, in 3-hour steps. Kp ≥ 5 = storm.

NOAA G-scale

Storm severity from the peak Kp:

Half-angle

Half the angular width of the CME cone, as fitted from coronagraph imagery. The map draws each cone spanning ± the half-angle around its axis.

Halo CME

A CME aimed nearly along the Sun–Earth line, so it appears as a halo around the Sun in coronagraphs — usually Earth-directed.

R☉ / AU

Solar radius (~696,000 km) and astronomical unit (~150 million km, the Sun–Earth distance). CMEs are tracked from 21.5 R☉ outward.

DBM

Drag-Based Model — the analytic propagation model used here (see §14).

L1

The Sun–Earth Lagrange point ~1.5M km sunward, where DSCOVR/ACE measure the wind ~30–60 min before it reaches Earth.

Magnetosphere

The protective magnetic bubble around Earth; the magnetopause is its sunward boundary, which compresses under a storm.

Sub-solar point

The point on Earth where the Sun is directly overhead.

17Frequently asked questions

What is a coronal mass ejection (CME)?

A coronal mass ejection is a large eruption of magnetized plasma — often a billion tons of it — blasted off the Sun's corona. When an Earth-directed CME arrives, typically 1–4 days after it launches, it can compress Earth's magnetic field and trigger a geomagnetic storm, auroras, and disruptions to satellites, radio, and power grids.

How accurate are CME arrival-time predictions?

CME Tracker's arrival estimates have a typical (median) error of about 12 hours, validated by back-testing the model against 282 real shock arrivals in NASA's catalog (2014–2024). That is competitive with NASA's full magnetohydrodynamic model, WSA-Enlil (~11 h). Most of the remaining error comes from the coronagraph-measured launch speed and direction, not the propagation math. Treat arrivals as indicative, not operational forecasts.

How does the model predict when a CME will hit Earth?

It uses the analytic Drag-Based Model (Vršnak et al. 2013). Each CME starts at 21.5 solar radii with the speed NASA's coronagraphs measured, then decelerates (or accelerates) toward the ambient solar-wind speed under aerodynamic drag — so fast CMEs lose much of their speed before arrival. A 3,000 km/s CME can arrive at under half that speed.

How much warning is there before a solar storm hits Earth?

It depends on the source. A CME's arrival is forecast 1–4 days ahead (±~12 h). The highest-confidence warning, though, comes ~30–60 minutes out: spacecraft at the L1 point (~1.5 million km sunward) measure the solar wind and magnetic field before it reaches Earth, so when a shock crosses L1 the tracker's L1 nowcast counts down its arrival with near-certainty. Solar-flare radiation, by contrast, arrives in about 8 minutes.

Will a CME hit Earth, or miss it?

Each CME is drawn as a cone in its measured launch direction; Earth is hit only when it falls inside that cone. The catalog labels every CME Earth-directed, glancing, misses Earth, or awaiting telemetry (direction not yet determined). The 2012 near-miss replay shows a Carrington-class CME that crossed Earth's orbit and missed because Earth was elsewhere.

What is the difference between a solar flare and a CME?

A solar flare is a sudden burst of radiation (graded A/B/C/M/X by X-ray brightness) that reaches Earth in about 8 minutes. A CME is a slower, physical cloud of plasma that takes days to arrive. They often erupt together, but either can occur without the other.

What are the Kp index and the NOAA G-scale?

Kp is a 0–9 measure of global geomagnetic disturbance. The NOAA G-scale maps the peak Kp to storm severity: G1 (Kp 5, minor) through G5 (Kp 9, extreme). A higher Kp pushes auroras toward the equator — CME Tracker sizes its aurora ovals by Kp. The header's Kp meter shows where the current value sits on the 0–9 scale; click it for a week of history and NOAA's 3-day forecast.

Is CME Tracker real-time, and where does the data come from?

Yes. CMEs and flares come from NASA DONKI, live solar wind and Kp from NOAA SWPC, and solar imagery from NASA SDO; historical replays use CDAWeb OMNI/STEREO and GFZ Potsdam. It is free to use, with no account required.

For official space-weather forecasts, see NOAA SWPC.

18Data sources & credits

• CMEs & flares: NASA DONKI + shock catalog.
• Solar imagery: NASA SDO; archived time-of-event frames via Helioviewer.
• Solar wind, Kp, flares, radiation (live): NOAA SWPC — including the high-cadence L1 (DSCOVR/ACE) feed that powers the nowcast.
• Historical wind / Kp: CDAWeb OMNI & STEREO; GFZ Potsdam.

Curious what this site knows about you? Very little, on purpose — see the privacy statement.

Put it on your own site: there's a free embeddable live widget (an iframe, no scripts) and an open JSON API with the current headline numbers — pick a theme and copy the snippet at Embed CME Tracker.

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19Feedback

This is a one-person project and I'd genuinely like to hear from you — what's useful, what's confusing, a bug, or a feature you'd want. If you teach with it, please say so — I want to make it work better in the classroom.

Stay in the loop

Want to know when a storm is coming? Subscribers get a two-stage warning: a heads-up days ahead when a significant Earth-directed CME is detected (stated honestly as a range — "G1 likely, could reach G3"), and a confirmation ~30–60 minutes out when the L1 monitor actually measures storm conditions inbound — the "if you want to see the aurora, go now" email. Plus the occasional feature note. No spam, unsubscribe in one click. (Privacy: we store your address and nothing else.)

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