What's the difference between a solar flare and a coronal mass ejection?
One reaches Earth at the speed of light in about 8 minutes; the other is a cloud of matter that needs days.
A solar flare is a flash of radiation; a , or CME, is a cloud of matter. A solar flare is a relatively intense, localized emission of in the Sun's atmosphere, while a CME is a significant ejection of plasma from the Sun's corona into space. Flares often come with CMEs, but not always.
The difference shows up in the clock. Light from a flare travels at the speed of light, so its effect on Earth begins about 8 minutes after the eruption. Flare X-rays and extreme ultraviolet light are absorbed by the upper atmosphere and can briefly interfere with short-wave radio. A CME is slower: measured speeds run from 20 to 3,200 kilometres per second, averaging 489, so a CME typically reaches Earth one to five days after leaving the Sun.
Solar flare
- A burst of light and X-rays
- Travels at the speed of light, about 8 minutes to Earth
- Can briefly disturb short-wave radio
- Ranked A, B, C, M, X
Coronal mass ejection
- A cloud of plasma thrown into space
- Average speed 489 km/s
- Typically 1 to 5 days to reach Earth
- Can cause geomagnetic storms and auroras
A CME is the one that can reach Earth's magnetic field and cause geomagnetic storms, auroras and, in rare cases, damage to power grids. Both come from , near the sunspots, and both follow the Sun's cycle: around solar maximum the Sun produces about three CMEs a day, near minimum about one every five days.
The first flare ever recorded was seen on 1 September 1859 by two English astronomers, Richard Carrington and Richard Hodgson, who each spotted it independently through a telescope.
Try it
How long does a CME take to arrive?
y = 1x + 0
Challenge · The average CME speed, 489 km/s, is about 1.8 million km/h. Set it and read off when the line reaches Earth's distance, about 150 million km: roughly 83 hours, three and a half days.
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Recap
A flare is light, arriving in minutes; a CME is a cloud, arriving in days.
💡 A trick to remember it · Flash then cloud: the flash is a camera bulb, the cloud is a slow-moving storm front.
Surprising fact · A flare's light reaches us in about 8 minutes, while a typical CME takes one to five days.
Sources (4)
No source, no claim. Every fact in this lesson (16 claims) cites at least one of these.