The Sun How big is the sun? This image illustrates how large the sun is compared to the earth and our solar system. Tools Maximize Toolbar Wiwi Title Minimize Toolbar 94 OnlineShare Powered by Close window Click Here to Share Read more about The Sun - How Big is the sun by nineplanets.orgThe Sun - How Big is the sunnineplanets.org

History of Our Sun  Worshipped as a deity (god) by many cultures throughout history  Called Helios by the Greeks  Called Ra by the Egyptians Ra, the god of the Sun Helios, Greek god carrying the Sun to its position in the sky

Why is the Sun important?  Supports most life on earth by providing warmth required for survival (exception: underwater hydrothermal vent ecosystems)  Allows plants to grow via photosynthesis which in turn absorb carbon dioxide and create oxygen

How does the Sun produce light and heat?  Deep in the sun's core, nuclear fusion reactions convert hydrogen to helium, which generates energy.  During fusion, hydrogen atoms are fused together to create a helium and release a tremendous amount of energy

 Particles of light called photons carry the fusion energy through the sun's spherical shell, called the radiative zone, to the top layer of the solar interior, the convection zone. There, boiling motions of gases (like in a lava lamp) transfer the energy to the surface. This journey takes about 100,000 years.journey How does the Sun produce light and heat?

Layers of the Sun  Bottom layer of outer sun: photosphere  Followed by the chromosphere  Ending with the corona, “crown” of light from the Sun

 Prominences are arcs of gas that are anchored in the photosphere layer of the Sun  Prominences extend through the corona layer of the Sun Features of the Sun – Prominence

 Sunspots are small, dark spots seen on the surface of the Sun  Sunspots are caused by strong magnetic fields on the Sun’s surface  One sunspot has North magnetic polarity and one sunspot has South magnetic polarity.  Caused by the Sun’s rotationSun’s rotation Features of the Sun – Sunspots

 Sunspots form over periods lasting from days to weeks, and can last for weeks or even months. The average number of spots that can be seen on the face of the Sun is not always the same, but goes up and down in a cycle. Historical records of sunspots show that this sunspot cycle has an average period of about eleven years.  Every solar cycle, the number of sunspots, flares, and solar storms increases to a peak, which is known as the solar maximum. Then, after a few years of high activity, the Sun will ramp down to a few years of low activity, known as the solar minimum. This pattern is called the "sunspot cycle” or the "activity cycle". Features of the Sun – Sunspots

Features of the Sun – Solar WindSolar Wind  Sun releases solar wind. The solar wind is a stream of energized, charged particles, primarily electrons and protons, flowing outward from the Sun, through the solar system at speeds as high as 900 km/s and at a temperature of 1 million degrees (Celsius)! It is made of plasma. Our magnetic field protects the Earth from the solar wind, and as the solar wind’s charged particles interact with our magnetic field, auroras are created.

 A solar flare is defined as a sudden, rapid, and intense variation in brightness. A solar flare occurs when magnetic energy that has built up in the solar atmosphere is suddenly released.solar flare  Radiation from past solar flares has been responsible for disrupting satellites, stretching the visibility of the Aurora Borealis down to the tropics, causing electronics and cellular devices to fail, and even causing telegraph wires to burst into flames.  Scientists predict the sun’s solar flares will reach their peak in 2012 Features of the Sun – Solar FlaresSolar Flares

Daily Motions of The Sun – Earth System  Sun, Moon, planets, and stars rise in the East and set in Westrise in the East and set in West  These daily motions occur as a result of Earth’s rotation  Sun, Moon, planets, and stars do not orbit around Earth everyday; just looks that way because the Earth rotates

How we know the Earth rotates  Flowing air and water diverted from north- south direction to east- west direction  The length of a day as we observe it is a little longer than the time it takes for the Earth to rotate once on its axis  Time from one sunrise/sunset to the next is called a solar day

Daily Motions of the Earth  Precession is a gravity- induced, slow and continuous change in the orientation of a Earth’s rotational axis Precession  The Earth's rotation axis is not fixed in space. Like a rotating toy top, the direction of the rotation axis executes a slow precession with a period of 26,000 years

 We see weather changes, day length changes, temperature changes as result of Earth’s motion around the Sun  The plane in which Earth orbits the Sun is called the ecliptic Annual Motions

 Earth’s axis tilted to the ecliptic at 23.5 degrees  As a result of the tilt of Earth’s axis and Earth’s motion around the Sun, the Sun changes its altitude in the sky  The Earth’s tilt is most directly responsible for the seasons that we see every yearseasons Effects of Earth’s Tilt

Solstices  As Earth moves around Sun, the altitude of the Sun decreases in the northern hemisphere  Summer solstice-Sun is at highest altitude in the sky (June 21); number of daylight hours at maximum  Summer solstice-Sun is directly overhead at Tropic of Cancer (23.5N latitude)  Winter solstice-Sun is at lowest altitude in the sky (Dec 21);number of daylight hours at minimum; Sun is directly overhead at Tropic of Capricorn (23.5S latitude)

Equinoxes  Two positions Earth is not pointed at Sun; as result both hemispheres receive same amount of sunlight and Sun is directly overhead at the equator  Called autumnal and vernal equinox (equinox means “equal nights”)