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 NOW) 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 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 its width is the measured angular half-width. 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) groups three overlays. 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 is described next.
• Connectivity shows the single Parker-spiral field line that links the Sun to Earth, marked at its solar footpoint (~W55, computed from the live wind speed). Energetic particles travel along these field lines, so a flare near the footpoint 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. This is why a west-limb flare that misses Earth can still dose it (see the radiation card).

4Time & 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).
• NOW snaps back to live real time (also N).
• 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.

5CME 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 planet. Pick Mercury, Venus, or Mars and the catalog verdicts, the directed-only filter, the arrival times, and the timeline all switch to that planet, which gets ringed on the map. Because the inner planets move quickly, plenty of CMEs that miss Earth are aimed straight at one of them. (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.

6Recent 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).

7Selected 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 strength on the NOAA G-scale.

8Inbound CME warning

When a CME is genuinely en route and expected to cause a storm, a pulsing banner appears over the map. It only fires for meaningful threats — class C or faster and a predicted Kp ≥ 5 (G1+). If several qualify, it shows the strongest, then soonest.

The banner carries a severity chip (G1–G5), the impact time, a countdown, and the estimated Kp; its color and pulse rate scale with severity. Dismiss it with × — it stays hidden until a different CME becomes the top threat.

9Earth — 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.

• 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.

10The Sun now (SDO)

Live imagery from NASA's Solar Dynamics Observatory, refreshed every few minutes. 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, and numbered active regions (sunspot groups) are marked. The caption summarizes the current regions and flare tally.

11Solar 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.

12Historical event replay

The ▷ Historical CMEs menu (top-right of the map) loads a famous storm 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.

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/?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.

13How accurate is it?

The Model skill card 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).

• 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.
• NASA's full MHD model (WSA-Enlil) does somewhat better (~11 h) — expected, since it 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.

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.

14Controls 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, and Labels (see §3).
• The ◎ Directed at dropdown re-aims the geometry & arrivals at Mercury, Venus, or Mars (see §5); ⧉ Isolate replays just a chosen stretch of the timeline (see §4).
• Historical replays have shareable links (e.g. ?event=gannon-2024); your browser's back/forward steps between them (see §12).
• Live feeds refresh automatically every few minutes; the Data indicator shows freshness.

15Glossary

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:

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 §13).

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.

16Frequently 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.

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.

17Data sources & credits

• CMEs & flares: NASA DONKI + shock catalog.
• Solar imagery: NASA SDO.
• 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.

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18Feedback

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.

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