Our Tempestuous Sun – Amateur Astronomers Association

How Did Our Sun Form and What Is It Made Of? Earth’s Sun had a violent birth. It formed from a solar nebula – a cloud of gas and dust of an earlier star (or stars?) that exploded then collapsed under the weight of its rotational gravity, See Figure 1. This cataclysm occurred approximately 4.6 billion years ago[1]. Roughly 4.5 billion years old, our sun is considered a yellow dwarf[2] that is held together by its own gravity. Its structure is not solid. It is a big ball of dense and extremely hot gaseous material called plasma, the fourth state of matter after liquid, solid and gas. Solar scientists have identified the sun’s chemical constituent mass percentages as mainly hydrogen -73.46% and helium -24.85%, with trace elements of oxygen – 0.77%, carbon -0.29%, iron -0.16%, neon -0.12, nitrogen -0.09%, silicon -0.07%, magnesium -0.05%, sulfur -0.04%, and other -0.10[3]. [1] https://www.lpi.usra.edu/education/timeline/gallery/images/Solar-System/ [2] https://solarsystem.nasa.gov/solar-system/sun/in-depth/. This also means that our Sun took 100,000,000 (one hundred million) years to form from the explosion and collapse of the earlier star(s) under the weight of its rotational gravity. [3] https://www.swpc.noaa.gov/sites/default/files/images/u2/Solar%20Physics%20And%20Terrestrial%20Physics.pdf

The convection zone, the sun’s third inner layer, see Figure 3 is where thermal convection (stirring) occurs due to temperature differences within the fluid. This zone is cooler than and captures the energy from the radiative zone, preventing it from escaping. Producing a stirring of the matter, the warmer material rises through the cooler layers carrying heat to the surface where it is visible “as granules and supergranules”[1], see Fg3, ib [1] “The Solar Interior” Author Dr. David H. Hathaway, https://solarscience.msfc.nasa.gov/interior.shtml; See, also, https://solarscience.msfc.nasa.gov/feature1.shtml

The photosphere is our sun’s first atmospheric (outer) layer, see Figure 4, and the fourth inner layer from the core[1]. It is a thin layer that surrounds the sun, radiating the light we see with our eyes and/or feel on our skin. It is considered the surface of our sun and is totally transparent – invisible – to our eyes. The word “photosphere” derives from the Greek roots “photos” meaning light, and “sphaira” meaning sphere, something round[2]. The photosphere layer is 250 miles/155 kms thick and close to 10,000°F/5537°C and is the center of solar activity where we “see sunspots, solar flares, granules and convection cells”[3] (with the appropriate solar telescope, solar viewer or solar glasses). See, https://www.nasa.gov/sun. Though majestic and beautiful, the photosphere is not a place where you
want to have lunch – ouch!. [1]https://nso.edu/for-public/sun-science/photosphere/ [2] https://www.vedantu.com/physics/photosphere ^{^[3]} https://nso.edu/for-public/sun-science/photosphere/

The chromosphere is the second atmospheric layer of our sun and the fifth layer from the sun’s core. It is 250m/402km to 1300m/2100km above the surface of our sun and is extremely hot with temperatures varying between 14,000°F/800k at the top and 6700°F/400k at the bottom[1] However, the chromosphere layer is weird. The temperature there increases further away from the sun in contrast to the lower layers where the temperature increases closer to the sun’s center. “(I)n this layer (and higher layers) it actually gets hotter if you go further away from the Sun, unlike in the lower layers, where it gets hotter if you go closer to the center of the Sun.” Ib. Go figure .

The corona is the third atmospheric layer of our sun[2], and the sixth layer from the sun’s core. The sun’s corona has a white aura or halo. It is also where solar prominences arise. The corona is totally transparent (invisible) to the naked eye unless utilizing a telescope lens filter or solar observing glasses. Never look directly into the sun without eye protection! The corona’s temperature is 1.8mm °F/1mm °C, hotter than the photosphere below it and has no upper limit[3]. [1] https://www.nasa.gov/mission_pages/iris/multimedia/layerzoo.html [2] https://www.nasa.gov/mission_pages/iris/multimedia/layerzoo.html, https://solarscience.msfc.nasa.gov/interior.shtml [3] https://www.nasa.gov/mission_pages/iris/multimedia/layerzoo.html What Color is Our Sun? Well, the answer to this question is not simple. The sun emits wavelengths of light in the visible spectrum in equal amounts [1]. Earth’s atmosphere scatters these wavelengths as it filters the light through our environment. This filtering makes the sun appear yellow or white to our human eye. See, https://www.space.com/what-color-is-the-sun. For example, Fg5 is a photo of the sun. It looks totally white. [1] The sun emits light across the electromagnetic spectrum including all the colors of visible light. NASA’s Imagine the Universe. [1] “The Solar Interior” Author Dr. David H. Hathaway,https://solarscience.msfc.nasa.gov/interior.shtml; See, also, https://solarscience.msfc.nasa.gov/feature1.shtml [1] https://nso.edu/for-public/sun-science/photosphere/ [1] https://www.vedantu.com/physics/photosphe ^[1] https://nso.edu/for-public/sun-science/photosphere/ [1] https://www.nasa.gov/mission_pages/iris/multimedia/layerzoo.html [1] https://www.nasa.gov/mission_pages/iris/multimedia/layerzoo.html, https://solarscience.msfc.nasa.gov/interior.shtml [1] https://www.nasa.gov/mission_pages/iris/multimedia/layerzoo.html [1] The sun emits light across the electromagnetic spectrum including all the colors of visible light. NASA imagines the Universe. The clouds obscure the corona and our eyes see all the colors the sun is emitting in the visible wavelength as white. However, in Fg8, the sun’s corona is visible as a yellow halo as no clouds obscure its full view. Astronauts on the Space Station however, see the sun as white with no corona because “from the space station, much of the atmosphere isn’t in the way to scatter light from the sun, so the full visible spectrum comes through as a bright white.”[1]

Why Are Sunrises and Sunsets Red or Reddish Orange? Sunrises and sunsets appear red or reddish orange to an observer because the beam of sunlight arriving at earth during those times takes a longer path through earth’s atmosphere, scattering more violet and blue light (photons). “[S]cattering events [make] the light that reaches an observer early or late in the day [ ] noticeably reddened. Thus, it could be said that sunsets are red because the daytime sky is blue.”

Now we know a bit of our sun’s history. In the next issue we’ll examine its temperamental solar weather. See you then.