PURIM Unmasked

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By: Efraim Harari

The sun is a ball of gas, so it does not have a solid surface like the Earth. However, there are different layers of the sun, just as there are different layers of the Earth.The sun has six layers: the core, the radiative zone, the convective zone, the photosphere, the chromosphere, and the corona. The photosphereis the visible surface of the sun. It is the disk you see in the sky when you look at the sun through a telescope. (Never look at the sun directly, as it can cause blindness; always use a filtered telescope.)

In some ways, the photosphere of the sun is like the crust of the Earth. Both the photosphere and the crust are many miles thick. The top of the crust is the surface of the Earth. If we could stand on the moon and look at the Earth, we would see Earth’s surface, its crust. In the same way, if we look at the sun, we see the photosphere.

The following quote, from noted astronomer Professor N. Nidal, senior astronomer at the Greenwich Observatory in England, Professor of Astronomy at Australia’s National University, and visiting professor at the Harvard-Smithsonian Center for Astrophysics, can help explain the important role of the photosphere:

“The sun is a ball of gas, whose outermost temperature is 6000 degrees Centigrade. Gases at much higher temperature flow beneath the surface. According to our estimates, the temperature continues to rise as we approach the center of the sun, where it reaches 15,000,000 degrees Centigrade. Today we picture the center of the sun as a type of “nuclear reactor” that releases vast quantities of heat, which make their way slowly outward. As it moves out, the strength of this heat diminishes until it reaches the surface layer were it is ‘only’ 6000 degrees Centigrade. The extremely high temperatures within the sun cause gas storms of tremendous proportions, which even form waves that crash against the surface gases with unbelievable force. These outer layers themselves absorb the heat being radiated from within the sun, and restrain the shockwaves caused by these waves striking it. We call this outer layer the sheath.”

Of course our Sages from thousands of years ago were well aware of the protective role of the photosphere, even without the aid of telescopes or satellites (see Torah Talksection).

The Brightness of the Sun

The sun, which is a star, is a sphere of luminous gas, consisting primarily of hydrogen (about 75%) and helium (about 25%). What makes the sun so bright is its power source: through a process known as nuclear fusion, an abundance of energy is produced for the sun.

At the center of the sun, the force of gravity squeezes hydrogen atoms with huge amounts of pressure. Under ordinary conditions, the positive electric charges in hydrogen atoms make the atoms repel each other strongly, but the sun’s gravity is so great that the atoms fuse together instead, thereby forming deuterium and helium atoms and releasing vast quantities of energy. The energy released by fusion is about 10 million times greater than combustion (the reaction that causes coal and gasoline to burn).
This energy heats the sun’s interior to temperatures of 27 million degrees Fahrenheit.

The fusion reaction, along with the sun’s enormous size, allows the sun to continue to shine brightly on a daily basis.


The Sun’s Sheath

The midrash (Bereishit Rabbah6:6) states that “there is a sheath around the sun’s orb,” and explains this to be the meaning of the verse: He has set up a tent for the sun(Tehillim19:5).

The Sages refer to the sun’s sheath in several places (see Bava Metzia 86b, Malachi3:19, and Bereishit Rabbah26:6), always with the implication that were it not for its existence, life on Earth would suffer terribly and perhaps even perish. Today scientists realize that just as the Earth has a surrounding atmosphere, which both provides oxygen for life and protects us from the dangerous cosmic rays (high-energy particles that bombard the planet), so, too, the sun has a sheath that protects the inhabitants on Earth from the sun’s heat and dangerous rays. The Sages, however, knew of this sheath's existence, as well as the protective role it plays, from its source in the Torah.

Any Minute Now…

Light from the sun reaches Earth in around 8.3 minutes.