117 Studying the Sun
You might have heard that you should never look at an eclipse. First of all, all lunar eclipse phases are safe to view. The partial phase of a solar eclipse, or an annular solar eclipse requires a proper solar filer. It is NOT the eclipse that causes eye damage, it is the sun. During solar eclipse totality, no filter whatsoever is required.
In 1814, optician and physicist Joseph Frauenhofer (1787-1826) invented the first spectroscope. Frauenhofer was comparing the spectra of fire to that of the Sun when he noted dark lines in the sun’s continuous spectrum. Named the Frauenhofer lines , these absorption lines are a function of the sun’s photosphere.
Such a spectrum is created when light passes through a gas or a liquid, or strikes a solid surface. You see the spectrum of the absorption; the wavelengths of light absorbed by the material are absent in the spectrum, leaving blank spaces behind
Perhaps the most-impressive is Hydrogen-Alpha, H-a . H-a filters center on a wavelength of 6562.8 Å and allow through only a tiny part of the red light the sun produces, blocking all other colors. Solar flares and prominences are best seen through an H-a filter.
Studies of the element calcium, Ca, on the sun are done at Calcium H (3969Å) and Calcium K-lines (3933.7Å). This is instrumental in determining the solar atmosphere’s depth.
Other specific features are visible at narrow bandwidths. High granulation and supergranulation detail, and impulsive-phase flare eruption kernels are visible at the Sodium Na-D line (5895.9Å). Flare and magnetic lines research is conducted at the Helium D3 line (5875.61Å); this is one of the most impressive visually.
Light emitted by highly charged iron (Fe) ions at high temperatures is best studied in the Ultraviolet, UV. And X-Rays are released from the sun’s upper atmosphere and corona.
Our Sun is important – critical – to life on Earth, yet is it not the calm star, which we all might presume…
Watch on YouTube these NASA solar videos:
“Fiery Looping Rain on the Sun,” Video Link Note the Earth to scale from 1:06 to 1:22.
“Eruptive events on the sun can be wildly different. Some come just with a solar flare, some with an additional ejection of solar material called a Coronal Mass Ejection (CME), and some with complex moving structures in association with changes in magnetic field lines that loop up into the sun’s atmosphere, the corona” (NASA, retrieved, March 29, 2015).
On July 19, 2012, an eruption occurred on the sun that produced all three events:
- A moderately powerful solar flare exploded on the sun’s lower right hand limb, sending out light and radiation
- Next came a CME, which shot off to the right out into space.
- And then, the sun treated viewers to one of its dazzling magnetic displays — a phenomenon known as coronal rain
The Solar Dynamics Observatory’s AIA Instrument collected the footage in this video. SDO collected one frame every 12 seconds, and the movie plays at 30 frames per second, so each second in this video corresponds to 6 minutes of real time. The video covers 12:30 a.m. EDT to 10:00 p.m. EDT on July 19, 2012.
“Magnificent Eruption,” Video Link
“On August 31, 2012 a long filament of solar material that had been hovering in the sun’s atmosphere, the corona, erupted out into space at 4:36 p.m. EDT. The coronal mass ejection, or CME, traveled away from the sun at over 900 miles per second. This movie shows the ejection from a variety of viewpoints as captured by NASA’s Solar Dynamics Observatory (SDO), NASA’s Solar Terrestrial Relations Observatory (STEREO), and the joint ESA/NASA Solar Heliospheric Observatory (SOHO)” (Courtesy NASA, September 5, 2012).
Consider the following questions based on the YouTube videos:
- What was your first reaction to seeing/hearing these videos?
- How would you describe the Earth when compared to the Sun in size in the first video, “Fiery Looping Rain on the Sun?”
- As we ‘look’ at our Sun in the sky, it seems fairly quiet. Yet what do these videos show us?
- Why would we want to monitor the Sun’s activity? What can this teach us about other stars?
- Your speculation: if one of these Coronal Mass Ejection outbursts were to strike Earth directly, could it cause any problems?