Hello, friends, and welcome to another episode of Sciency Words.  Each week, we take a closer look at some science or science-related term so we can expand our scientific vocabularies together!  Today on Sciency Words, we’re talking about:

THE SOLAR WIND

The stars twinkle in our sky because Earth’s atmosphere scatters starlight.  The Sun has an atmosphere too, so it shouldn’t surprise you to learn that when astronomers observe stars that happen to be near the Sun (as viewed from Earth), they can see that the Sun’s atmosphere also scatters starlight.

What might surprise you—and what did surprise astronomers in the 1950’s—is that this scattering effect can extend very, very far into the space around the Sun.  The Sun’s atmosphere must be huge!  As reported in this 1959 article from Scientific American, the Sun’s atmosphere might be so big that it encompasses Earth!

Pursuing this and other lines of evidence (such as the apparent correlation between flare activity on the Sun and aurorae here on Earth, as well as apparent 11 year fluctuations in cosmic radiation levels), American astrophysicist Eugene Parker wrote this paper in 1958, introducing a concept now known as the solar wind.

As you might imagine, the Sun’s atmosphere is hot.  Absurdly hot.  Remember that temperature is really just a measure of the average velocity of atoms, and you’ll soon realize (as Parker did) that atoms in the Sun’s atmosphere must have enough velocity to escape the Sun’s gravity.  And since those atoms would also be ionized, these streams of ionized particles coming from the Sun would serve as extensions of the Sun’s magnetic field.

The term solar wind doesn’t appear in that 1958 paper.  Parker first introduces that term in this 1959 paper, in which he defends his idea and responds to critiques from other astrophysicists.  As Parker explains:

In view of the simple hydrodynamic origin of the expansion, it seems appropriate to term the stream a solar wind.

Also in 1959, the Soviet Union’s Luna 1 space probe gathered the first empirical evidence that the solar wind really does exist, leading to confirmation that Eugene Parker’s solar wind hypothesis was correct.

And today, a NASA spacecraft named in Parker’s honor is spiraling closer and closer to the Sun, gathering more data about the solar wind and other mysterious phenomena associated with the Sun.

Next time on Planet Pailly, now that we’ve talked about the solar wind in our own Solar System, we’ll check out the space weather forecast for the solar system next door.

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