Cool Sun Facts · Space weather
What the Sun is doing, and what reaches Earth
NOAA's measurements, event list, K index and messages, each with its own time. A flare, a cloud thrown out towards Earth, a forecast and an aurora are four different things, and this page keeps them apart.
From the Sun to your sky, now
Soft X-rays from GOES
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The flare classes are levels of peak flux in the 0.1–0.8 nm band: A from 10⁻⁸ W/m², each letter ten times the last, up to X at 10⁻⁴ (NOAA). Flare light reaches Earth as it is seen, so there is no countdown after a flare (NASA).
Flares NOAA recorded in the last seven days
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Earth's magnetic field: the K index
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NOAA's estimated planetary K index: 0 to 9 over three-hour spans, from observatories at middle latitudes; 5 or more is a geomagnetic storm.
The solar wind, before it reaches Earth
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NOAA's real-time solar wind, measured by the spacecraft NOAA has marked as its active source, at L1, about 1.5 million km upstream of Earth. Typical values there are near 375 km/s and 5 protons per cm³; Bz is the north-south part of the magnetic field the wind carries, in nanotesla (nT). These are measurements; NOAA's forecasts and watches are in the messages below.
NOAA's latest messages
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Headings of NOAA's alerts, watches and warnings, with their issue times.
One storm, step by step: May 2024
A historical example, so the whole chain can be followed even on a quiet day. Every step is from NASA or NOAA, linked.
1 What the Sun did
From 3 to 9 May 2024 NASA's Solar Dynamics Observatory saw 82 notable flares, mostly from two active regions, 13663 and 13664. Between 7 and 11 May eight were X-class, the strongest X5.8.
2 Was anything thrown towards Earth?
On 9 May NOAA reported at least five Earth-directed coronal mass ejections, and that several strong flares were associated with region 3664, a sunspot group 16 times Earth's diameter. That association is NOAA's, stated in its report.
3 What NOAA forecast
The same day NOAA issued a Severe (G4) Geomagnetic Storm Watch, its first since 2005, with the clouds expected from midday on 10 May.
4 What reached Earth
The first cloud arrived at 12:37 pm EDT on 10 May (16:37 UTC), and G4 conditions followed at 1:39 pm EDT. The storm went on to reach G5, the top of the scale, for the first time since 2003; NASA's ICESat-2 went into safe mode.
5 What people saw
Aurora at unusually low latitudes, including the southern United States and northern India.