Rotating Question Curious About Astronomy? Ask an Astronomer

Do the Sun's or Earth's magnetic field reverse?

I heard that the polarity tested in the sun shows that a change of polarity is taking place and the same thing is happening on earth. Do you have any information about that and if so any idea about consequences?

The sun goes through an 11-year sunspot cycle, where every 11 years, the number of sunspots on the sun decreases to a minimum, rises to a maximum, then reaches a minimum again. In reality, though, the cycle is really 22 years long, because at each minimum, the polarity of the sunspots reverses. You see, sunspots usually come in pairs, with one spot having north magnetic polarity, and the other having south polarity. In any single cycle, for the north or south hemisphere of the sun, the north-polarity spot is either on the west or the east of the south-polarity spot. In the next cycle, those polarities reverse. With the same method that is used to determine sunspot polarity, scientists can also determine the global polarity of the Sun itself by looking at the part of the heliosphere above the magnetic poles. This has demonstrated that the entire solar magnetic field is reversing along with the polarity of the sunspots.

We also know that the global magnetic field of the Earth has reversed polarity many times in the past. We know this because when undersea volcanoes erupt, the iron minerals in the lava crystallize along the Earth's magnetic field lines. As the sea floor spreads out away from the rift zones, we get an excellent history of the Earth's magnetic field. The sea floor closest to the rift is youngest, and that farthest from the rift is oldest. If you look at the crystal alignments, you see bands of crystals, parallel with the rift all pointing north, then suddenly all pointing south, then north again, etc. This is clear evidence that the Earth's magnetic field reverses regularly.

Consequences of all this, I'm not sure. No one really understands why the Earth's field does this. We do know that the field is generated deep in the core of the Earth, so deep in fact, that even for major upheavals down there, we would be unlikely to tell the difference, except by careful measurement of earthquakes and, of course, the magnetic field reversal.

January 2004, Kristine Spekkens (more by Kristine Spekkens) (Like this Answer), Dave Kornreich (more by Dave Kornreich) (Like this Answer)

Still Curious?

Get More 'Curious?' with Our New PODCAST:

Related questions:

More questions about The Sun: Previous | Next

More questions about The Earth: Previous | Next

How to ask a question:

If you have a follow-up question concerning the above subject, submit it here. If you have a question about another area of astronomy, find the topic you're interested in from the archive on our site menu, or go here for help.

Table 'curious.Referrers' doesn't existTable 'curious.Referrers' doesn't exist

URL: http://curious.astro.cornell.edu/question.php?number=202
This page has been accessed 35640 times since September 11, 2002.
Last modified: January 29, 2004 5:16:43 PM

Legal questions? See our copyright, disclaimer and privacy policy.
Ask an Astronomer is hosted by the Astronomy Department at Cornell University and is produced with PHP and MySQL.

Warning: Your browser is misbehaving! This page might look ugly. (Details)