On August 14, 2014, visitors at the Public Observatory viewed the Sun using the calcium-K telescope, which shows the Sun in purple light. This particular wavelength reveals sunspots, seen as dark blobs, and the bright areas around them, called plages. Darker areas indicate cooler temperatures, while brighter regions are hotter.
On this day, there were two large sunspot groups visible on the Sun. Solar activity had been fluctuating recently; just one week before this image was taken, there were four large sunspot groups. Such changes are normal for this period in the 11-year sunspot cycle, which is currently in the midst of "solar maximum," the time with the most intense activity.
It just so happens that exactly one year earlier we had also observed the Sun with the calcium-K telescope. At that time the Sun was getting close to solar maximum. On that day, there were three large sunspot groups and a handful of smaller ones scattered across the Sun.
The difference in sunspot activity between the two images, separated by one year, is fairly subtle. Each date provides only a snapshot of the overall solar activity level during that week. But paying attention to these changes on the Sun is how early astronomers first figured out that there was a solar cycle at all. At the Public Observatory, we get to observe this daily evidence of the constant changes and dynamic processes that drive our Sun.
Image Number: WEB14380-2014
Credit: Image by Shauna Edson, Phoebe Waterman Haas Public Observatory
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