Sunspots and Prominences

Monday, Apr 15, 2024 1:07 PM

Greetings, stargazers.

The total eclipse happened. I was lucky enough to be able to get to it and avoid the clouds, but stupid enough to spend much of the time during totality snapping photos instead of just gawking in amazement like a reasonable person.

Like most of you who looked at the sun last week, I used the standard solar glasses. I also used some of the same specialized solar film to cover binocular lenses, a small telescope, and the front of my camera. These filters block enough light that the surface of the sun, called the photosphere, could be safely viewed. With only slight magnification several sunspots were also easily visible.

The sun goes through an eleven-year cycle of sunspot activity, and we are now at a year of peak solar activity. Sunspots are dark, cool areas on the sun, but dark and cool are only relative to the surrounding surface. If a sunspot is viewed without the surrounding photosphere, it would be much brighter and hotter than the filament in an incandescent light bulb.

As the radiant energy from the core of the sun is transported to the surface, the outermost layer of transport is called the convection layer. Heat from the interior is bubbling up to the surface, like a pot of boiling chili on the stove being heated from the bottom. With enough magnification, and through a special hydrogen alpha filter, the granulation from this convection can be seen.

If something disrupts this convection, there will be an area that is cooler than its surroundings. In the case of the sun, the thing that disrupts the convection is its magnetic field. Magnetic fields are created whenever there are moving electrical charges, and the ionized gasses in the sun certainly count as electrically charged particles.

Because the sun isn’t a solid object, the different latitudes of the sun move relative to one another, which results in a twisting up of the magnetic field lines. Imagine wringing a wet towel to dry it out. With enough twisting, the towel will kink and make a loop sticking out from the main twist. The kinks in the sun’s magnetic field that stick out through the surface are what disrupts the convection and makes a relatively cool place that we see as a sunspot.

Another interesting thing that can be seen along a magnetic field line that sticks out of the sun is called a solar prominence. These are filaments of hydrogen gas that appear magenta to our naked eye. They are always there, but because they are so much dimmer than the photosphere, they are not normally visible. However, during a total eclipse, these magenta filaments of hydrogen gas can be seen above the surface. Because this is a particularly active time during the solar cycle, more of these prominences could be seen.

It should be noted that these glowing pink things should be called prominences and not flairs. Flairs are eruptions of high-energy electromagnetic radiation, rather than hot hydrogen gas like a prominence. For scale, the ones we could see on the edge of the sun were much bigger than the Earth.

This month:

This is your last chance of the year to see the winter constellations around Orion. The winter hexagon asterism surrounding Orion has many of the brightest stars in the sky, including Betelgeuse and Rigel in Orion, Aldebaran in Taurus, Capella in Auriga, Caster and Pollux in Gemini, Procyon in Canis Minor, and the brightest of them all, Sirius in Canis Major. But they are all setting soon after sunset.

Jupiter is setting very soon after sunset as well.

Comet 12P/Pons-Brooks is near Jupiter, but moving fast, so use an online chart for its detailed location. If it wasn’t so low in the sky near sunset it might be visible to the naked eye.

Galaxy season is in full swing, with Leo and Virgo both high in the Easter sky after dusk. Browse those regions of the sky with a telescope to see lots of faint fuzzy smudges through the eyepiece.