The sunspot is more than five times the size of Earth. It is in the sights of NASA’s orbiting Solar Dynamics Observatory, which monitors the sun 24/7 for energetic activity.
Just after AR-1339 — the catalog number assigned to this active region on the sun — rotated into view, other satellites in Earth orbit detected a large solar X-ray flare.
All this activity is a sign that the sun continues to become more and more active as it climbs out of the deep solar minimum that has persisted over the past couple of years. And when the sun becomes more active, things light up here on Earth. The bright display of the northern lights that was observed in our area early last week was caused by a coronal mass ejection (CME) from the sun.
The sun’s visible surface is called its photosphere. The photosphere isn’t really a surface at all; at least not in the way most of us commonly think.
Even if you had asbestos shoes, you couldn’t walk on the sun’s photosphere because it is just a layer of gas. It is a layer of gas that is about 6,000 degrees Celsius, and that marks the greatest depth into the sun that we can see.
The photosphere is the “last scattering surface” for rays of light making their way out of the sun into the darkness of space.
Sunspots appear dark because they are a 1,000 degrees Celsius or so cooler than the photosphere. Since they are cooler, they appear darker.
The sun glows brightly only because it is hot.
It came as a surprise when it was discovered that the photosphere isn’t the hottest part of the outer layers of the sun.
There is a thin layer called the chromosphere lying above the photosphere that is hotter. And extending far out from the sun above the chromosphere, there is a tenuous region called the corona.
The sun’s corona can be observed briefly during a total solar eclipse.
The temperature of the gas in the sun’s corona rises to a scorching 3 million degrees Celsius.
It is from this outermost region of the sun that sometimes matter and energy is cast out into space in the form of a CME. If a CME is aimed at Earth, the northern (and southern) lights light up.
Over the next few days — as AR-1339 moves into plain view on the sun, crackling with X-ray energy — CME’s and the northern lights are possible, so keep your eyes to the sky.
For more information about the possibility of northern lights, and a look through a telescope at the moon and Jupiter and other things, make your way to GVSU’s Meijer Campus in Holland tonight for a program called “Autumn Sky Spectacular.” The program begins at 7 p.m. indoors, rain or shine, followed by an outdoor observing session (weather permitting) from 8-10 p.m.
GVSU’s Meijer Campus is at 515 S. Waverly Ave. in Holland.
— By Doug Furton, a member of the physics faculty at GVSU. Send questions and suggestions to firstname.lastname@example.org.