The Sun 1 of 200 billion stars in the Milky Way. Our primary source of energy.

The sun is the largest object in the solar system, in both size and mass. It would take 109 earths lined up edge to edge to fit across the sun, or almost 10 Jupiters. The sun is about 330,000 times more massive than earth and 1,048 times more massive than Jupiter. In fact the sun contains more than 99% of all the mass in the solar system. But gaseous, so only ¼ the density of earth (barely more than water).

Therefore it controls the motions of the planets and other objects in the solar system. Though we move the sun, too.

Inside the Sun

The sun consists of hydrogen, about 73 The sun consists of hydrogen, about 73.4% by mass, and helium, 25%, as well as a small amount of other elements. This composition is very similar to that of gas giant planets, which suggests that the sun and the gas giants represent the composition of the interstellar cloud from which the solar system formed.

Within the Sun’s core Fusion occurs Within the Sun’s core Fusion occurs. Hydrogen atoms are fused together to form helium atoms. The byproduct is an extreme amount of energy in the form of heat and light.

The core (1) of the sun is around 27 million degrees F The core (1) of the sun is around 27 million degrees F. The core also has a pressure 200 billion times that of earth. The sun is about 4.6 byo. At the sun’s rate of hydrogen fusing, it is about halfway through its lifetime, with another 5 billion years or so left. 1

Above the core is the radiation zone (2) Above the core is the radiation zone (2). In this area gamma rays from the core are changed into x-rays, ultraviolet, and visible light. 2

Next comes the convection zone (3) this is the zone that carries the energy the rest of the way to the sun’s surface. It takes about 170,000 years to transfer energy to the surface of the sun through these zones. 3

The Sun’s atmosphere

The lowest layer of the sun’s atmosphere or the surface of the sun is called the photosphere. This is what we see. The photosphere is about 11,000 degrees F, the same as the core of the earth. Photo = light

Here, we see granules (the size of texas) Here, we see granules (the size of texas). Almost like bubbles rising in hot water (convection).

Absorption spectra tell us what elements are in the sun

Above the photosphere is the chromosphere Above the photosphere is the chromosphere. Normally, this layer is only visible during solar eclipses. It is tens of thousands degrees, but not hot/bright enough to see everyday. Can only see during an eclipse because it’s much less bright than the photosphere.

The top layer is called the corona and extends several million kilometers from the top of the chromosphere and has temperature range in the millions. Scientists still don’t understand why it is hotter than the lower layers… Only visible in an eclipse. Solar winds extend from the corona

Sun’s Forces

The gas from the corona flows outward at high speeds and forms the solar wind. As this wind of charged particles, or ions, flows outward through the entire solar system, it hits each planet in a flood of particles.

At 1 AU, 93,000,000 miles, the distance earth is from the sun, solar winds can be measured at about 400 km/s. The charged particles are deflected by the earth’s magnetic field and are trapped in two huge rings in earth’s magnetic field. This is what causes the auroras.

Sunspots Sunspots vary in an 11-year cycle.

The sun’s magnetic field disturbs the solar atmosphere periodically and causes new features to appear. The obvious features are sunspots, which are dark spots on the surface of the photosphere. Galileo predicted the suns rotation period by studying sunspots.

The grainy appearance on the surface of the sun you saw in the previous slide is called granulation. The granules are convection cells that can be as large as Texas.

Sunspots are actually very bright, but they appear darker than the surrounding area on the sun because they are cooler, around 7,400 degrees F. These are located in regions where the Sun’s intense magnetic fields poke through the photosphere.

These magnetic fields prevent hot gases inside the sun from rising to the surface and heating the spots, making them cooler. They typically last around two months.

Astronomers have observed that the number of sunspots changes regularly and on average, reaches a maximum number every 11.2 years, then steadily declines. It is believed by some that this 11.2 year cycle causes subtle climate variations here on earth. Also, there were severe weather changes on earth during the latter half of the 1600’s when the solar activity cycle stopped and there were no sunspots for nearly 60 years. This time period was known as the “Little Ice Age” because the weather was very cold in North America and Europe.

Highly active solar flares are also associated with sunspots Highly active solar flares are also associated with sunspots. These are violent eruptions of particles and radiation from the surface of the sun.

Often, the released particles escape the surface of the sun in the solar wind and earth gets bombarded with the particles a few days later. These particles can interfere with communications and damage satellites.

Create aurora borealis (northern lights)

Prominence

Prominence is an arc of gas that is ejected from the chromosphere, or gas that condenses in the inner corona and rains back to the surface. These can last from a few hours to a few months. Like flares, prominences also are associated with sunspots, and hence, occurrences of both vary with the solar activity cycle.