Monday, August 27, 2012

macro, micro, sunspots, islands

When I showed some sunspots to Malcolm on Saturday, I gave him some hints as to what to look for, including the umbra and penumbra. I went on: "They are usually in groups. A big one. Then a peppering of little ones nearby." He was very impressed by the view in the Celestron 8-inch with the baader planetarium solar film.

He asked how long they lasted and if they were catalogued. I explained that they were temporary. They'd come and go, expanding and contracting. But, in general, they'd persist for days. One could follow them as the sun rotated. Which takes many days. And as spots appear, they're be numbered. I alluded to the Spaceweather web site, which uses the "Boulder Sunspot Number" scheme.

Strong magnetic phenomena on the photosphere of the Sun reduces convection and therefore reduces the surface temperature. This in turn produces a region that appears darker in visible light, in contrast to the brighter surrounding region. Spots can be 80 000 kilometres in diameter; the Earth is under 13 000.

It is believed the sunspots form as a result of stressed magnetic flux tubes which break through surface. Under the sunspots are powerful rotating downdrafts. Not unlike hurricanes.

When I said that sometimes the sunspot groups reminded me of archipelagos, he chuckled. I could tell Malcolm thought it apt.

The macro and the micro:

An archipelago is a group of islands, perhaps arranged in a chain, or just clustered close together.

Archipelagos are often formed through volcanism in subduction zones or hotspots. Or they may be formed as continental fragments, breaking away from the main continental mass through tectonic activity. Volcano calderas will sometimes fill with water.

The main Cocos (Keeling) Islands, to the right of the image, form a ring approximately 20 kilometres in diameter.

Coral atolls form around the islands and then remain as the islands sink creating complete or partial rings around the islands. The ocean water near the islands and atolls is shallow. The central lagoon of the Cocos in contrast is very deep.

Reef-building corals thrive in warm tropical and subtropical waters. Heated by the star is the centre of our solar system.

  • sunspot group captured by the NASA SDO probe in May 2012
  • the Cocos (Keeling) Islands in the Indian Ocean from the NASA Earth Observatory

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