The Sun has weather
Start with the one idea everything else hangs on: the Sun doesn't just shine, it erupts — throwing billion-ton clouds of magnetized plasma called coronal mass ejections into space at hundreds to thousands of kilometers per second. A CME is matter, not light: it takes one to three days to reach Earth, and that travel time is why storms can be forecast at all. Its cousin the solar flare is a flash of light — here in 8 minutes, no outrunning it.
Read the ten-minute explainer, then look at today's real Sun:
📖 What is a CME? (the explainer) ☀ What did the Sun launch in the last 48 hours?
Check yourself. On the today page, find the newest CME and answer: how fast is it, and is it aimed at Earth? If it says "not Earth-directed," you now know more than most news headlines about why that CME makes no storm here.
Check yourself — Module 1
1. A big solar flare and a CME erupt together. Which reaches Earth first?
The flare is radiation traveling at light speed; the CME is matter that takes one to three days. That gap is the whole basis of storm forecasting.
2. Why can geomagnetic storms be forecast days ahead at all?
Coronagraphs see the eruption on day one; the plasma needs 1–3 days to arrive. The travel time IS the warning time.
3. A fast CME launches from the Sun's far side, pointed away from us. What happens at Earth?
Most CMEs miss us entirely. That's why the catalog marks each one Earth-directed or not — speed only matters if the aim is right.
Check yourself above, then continue — answers aren't stored anywhere.