A solar flare observed in Dec. 2006 by NOAA’s GOES-13 satellite. Credit: NASA
The sun is at the bottom of the roller coaster with nowhere to go but up. NASA released a revised forecast this week on when the sun is expected to bounce back from its quiet spell. Solar activity like flares and sunspots wax and wane in an 11-year cycle. Among the more visible effects of high activity are increased sightings of the aurora borealis. We were supposed to bottom out on the cycle’s low end in March of 2008 with a new maximum in 2011 or 2012. The reality is we’re in the deepest valley of solar quietude in a century. Sunspot counts are extremely low and there’ve been no significant flares for more than two years.
Science is all about revision and modification based upon new information from the biggest source of all — Mother Nature. According to the latest solar forecast, the sun should remain generally calm over the next year and then start to rumble to life again. The new maximum of Solar Cycle 24 is predicted for May 2013 but with the fewest number of sunspots visible per day since 1928. Already there have been some uptick in activity with the appearance of a trickle of new spots and an increase the amount of energy the sun gives off in the radio end of the spectrum.
Yearly-averaged sunspot numbers from 1610 to 2008. Researchers believe upcoming Solar Cycle 24 will be similar to the cycle that peaked in 1928, marked by a red arrow. Credit: NASA/MSFC
Scientists make predictions based on current trends but don’t know for certain what route the sun might take. Will we experience a new Maunder Minimum – a 70-year-long period in the 17th century when the sun was spotless? Dean Pesnell of the Goddard Space Flight Center put it best: "Go ahead and mark your calendar for May 2013," says Pesnell. "But use a pencil."
This past week saw the 90th anniversary of the first empirical test of Einstein’s Theory of Relativity. That’s a fancy way of saying that scientists found proof in the real world of Einstein’s prediction that gravity bends light. According to the theory, objects like the sun are massive enough to literally curve local space and time – spacetime for short – around themselves, creating a kind of pocket or dimple in its fabric.
To help you visualize curved spacetime, imagine a child standing on a trampoline. The child’s weight changes the depth and curve of the dimple beneath their feet. A heavier child makes a deeper dimple. Substitute the sun for the child, and space for the trampoline surface and you begin to get the idea of how gravity affects space.
For an excellent, graphical illustration of spacetime, be sure to check out this short video:
Einstein predicted that light from a background star just touching the edge of the sun would be deflected upward and away from the edge by the sun’s enormous gravity. Credit: Jose Wudka
So how you prove the sun really warps space? Let’s say we look at a star in the same direction as the sun. Since the sun is too brilliant to see any stars near it, we’d have to wait for a total solar eclipse to do this. With the sun’s light blacked out by the moon during totality, we might get lucky enough to see a star close to the sun’s edge. Einstein said that the warping of space near the massive sun would cause the beam of starlight to appear to come from a slightly different direction compared to its real position in the sky.
Isaac Newton’s original Theory of Gravity predicted massive objects with lots of gravity would bend light too, but his prediction of how much was only half of Einstein’s. Relativity Theory predicted that a beam of starlight grazing the sun’s edge would be deflected by the incredibly tiny but measurable amount of 1.75 arc seconds. That’s the size of a dime seen from a distance of 1.3 miles. For comparison, the full moon is 1800 arc seconds across.
As soon as World War I ended, English astronomer Frank Dyson recruited Arthur Eddington, professor of astronomy at Cambridge, to sail to the island of Principe, off the coast of West Africa for the best view of the May 29, 1919 total solar eclipse. Eddington was charged to test Einstein’s theory by photographing stars near the sun to see if they were deflected by the amount predicted. Luckily, the eclipse happened against the background of a rich and bright star cluster, the Hyades in Taurus. Chances were excellent at least of few of them would be close enough to the sun’s edge to show a measurable deflection. (Einstein in 1921, left, and Arthur Eddington)
One of Eddington’s photos of the totally-eclipsed sun taken on May 29, 1919. Star used to prove Einstein’s prediction are shown between pairs of tick marks. Credit: Philosophical Transactions of the Royal Society of London
The total part of the eclipse lasted 400 seconds but only in the last 10 seconds did the sky clear. Eddington got an image and compared it to one taken of the same stars when the sun was not present. The result was a 1.61 arc second shift, in very close agreement with the prediction.
Media attention propelled Einstein to overnight celebrity. Since then, the Theory of Relativity has passed every test scientists have thrown at it. Despite its weird, counterintuitive predictions of warped space and time, Einstein’s brainchild accurately describes many aspects of the natural world.
(Credit on Einstein portrait: Oren Jack Turner; Eddington portrait: American Institute of Physics Niels Bohr Library)