Astronomy 04 Astronomy 04 The Solar System Chapter 15: "The Sun - A Garden Variety Star”

The Sun is huge .. It contains over 98% the mass of the solar system. It is over one million times Earth’s volume.

The Sun is 110 times Earth’s diameter.

The Sun’s volume is significantly greater than that of all of the planets combined.

The Sun and Planets

Red Giant & Supergiant Stars

The Sun is composed primarily of hydrogen (73%) and helium (25%).   Cecilia Payne-Gaposchkin - discovered the chemical composition of the Sun but assumed the discovery was wrong.

The sun is composed of four regions .. core radiative zone convective zone photosphere

The solar core is where the Sun produces its energy. We’ll talk more about this later.

The radiation & convection zones are regions where the energy produced in the core is transported to the Sun’s visible surface.

The photosphere is the visible surface of the Sun where the gases become opaque and marks the boundary beyond which we cannot see.

The photosphere is a layer about 250 miles thick. The gas here is hot - about 11,000F - but very tenuous with a density of 1/10,000th Earth's atmosphere at sea level.

Features of the Photosphere: Granules Sunspots Prominences Flares

  The photosphere has a mottled appearance because it is covered by granules. Granules are rising hot gas bubbles about 400-600 miles in diameter, which last only 5-10 minutes.

Granulation

Sunspots are darker, relatively cooler regions on in the photosphere. Their lifetimes vary from a few hours to a few months. The largest have reached diameters of 30,000 miles.

Heinrich Schwabe, an amateur astronomer, kept daily records of sunspots and discovered the ten-year sunspot cycle.

The Period of the Sunspot Cycle may vary from 8-12 years. Spot number may vary from 100+ spots at maximum to zero at minimum.

Prominences are "flames" of hot gas that also occur near sunspots that rise from the photosphere and reach high into the corona.  

  There are quiescent prominences that appear to hang motionless.   There are eruptive prominences that eject matter upward into the corona at speeds of over 400 miles per second. There are surge prominences that resemble eruptive prominences but eject matter into the corona at speeds of up to 800 miles a second.

Chapter 8: “The Sun – Our Star”  

Solar flares are explosions on the surface of the Sun that last for 5-10 minutes and release the energy of a million hydrogen bombs. The energy released in a single flare emits enough energy to power the U.S.A. for 100,000 years.  

Although the Sun is gaseous, we speak of the Sun's atmosphere, which consists of the chromosphere corona.

The chromosphere is a layer of the sun immediately above the photosphere. The chromosphere is visible only during a total solar eclipse and is about 1500 miles thick.

Temperatures rise as we move from the photosphere through the chromosphere and corona.

The transition region is a thin region in the Sun's atmosphere above the chromosphere where temperatures rise to a million degrees.

The outermost part of the Sun's atmosphere is called the corona, which extends millions of miles into space. Here we see the corona photographed during a total solar eclipse.

The corona is hotter than either the photoshere or chromosphere because of the effect of the Sun's strong magnetic field on the electrically charged gas in this region.

Coronal Mass Ejections are associated with solar flares and blast immense quantities of coronal material (protons and electrons) into space.  

  The solar wind is a stream electrically charged particles, mostly protons and electrons that flow out from the Sun at speeds of 900,000 mph. The Sun loses about 10 million tons of material a year via the solar wind. We are protected from this radiation by the Earth's magnetic field, which directs particles into the atmosphere around the poles causing auroras.

Aurora

Aurora

Possible sources of Sun’s energy: Thermal (combustion) but even if the Sun was composed of combustible material the Sun could not produce energy at the rate it does for more than a few thousand years. Gravitational – Heat generated as the Sun collapses about 40 meters per year. This could keep the Sun shining for 100 million years but geologists have determined that Earth (hence the Sun) must be older.

Albert Einstein   E = mc2 Energy can be generated by breaking up heavy atomic nuclei into lighter atomic nuclei. This process is called nuclear fission. Energy can also be generated when lighter atomic nuclei come together to form a heavier atomic nucleus. This process is called nuclear fusion.

The proton-proton cycle is a multi-stage nuclear reaction that can be summed up as follows: H + H + H + H = He + Energy (light and Heat) + atomic particles (solar wind)

A balance exits in the Sun between the forces of gravity and internal gas pressure. Gravity acts to collapse the Sun but the internal gas pressure resists the force creating a balance known as Hydrostatic Equilibrium.

Hydrostatic Equilibrium