Astronomy Unit

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

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 2 hydrogen atoms to 1 helium atom, which produces an extreme amount of energy. This energy is transferred to the Earth via radiation.

Forms of Energy Released by Sun All forms of electromagnetic energy, excluding gamma rays are produced by the Sun. (X rays,ultraviolet, visible light, microwaves, radio waves, infrared) Higher frequency forms of energy, such as X Rays and UV rays, are filtered out by our atmosphere.

Forms of Energy Released by Sun Solar flare(cosmic ray)-a sudden, rapid release of charged particles from the Sun, often associated with intense brightness. Solar flare Solar wind-a constant stream of energized, charged particles, primarily electrons and protons, flowing outward from the Sun. Our magnetic field protects the Earth from the solar wind/flares, causing particles to be deflected around the Earth. Some of these particles interact with our magnetic field near the poles, causing auroras to be created.

Solar Wind (has commercial) Solar Flares

Rotation of Earth Rotation-turning around one’s own central axis. Responsible for us having day and night. The Sun rises in the east and sets in the west, as do the Moon, planets, and stars as a result of Earth’s rotation. One Earth rotation equals a day, but actually only takes 23 hr 56 min.

Precession  Precession is a gravity- induced, slow and continuous change in the orientation of Earth’s rotational axis that takes years to come to completion. Precession  Changes the view of the stars from the poles, but doesn’t affect the seasons.

Nutation In addition to causing tides, the moon’s orbit around Earth also causes the Earth to nod, or bob throughout its rotational period, called nutationnutation Occurs over an 18 year period, changes the direction of Earth’s tilt by less than a ½ degreee. This only very slightly increases or decreases the amount of seasonal effects.

How is equatorial circumference of Earth different from pole to pole? Earth’s constant rotation causes the matter along its central point of rotation (the equator) to bulge outwards, making the equatorial circumference greater than the pole to pole.

Revolution of Earth Revolution-time it takes for an object to complete its orbit around another object. Takes the Earth approximately 365 days to revolve around the sun. In combination with tilt of Earth’s axis, revolution is responsible for annual changes in length of days and temperature variations

Tilt of Earth’s Axis, Reason For Seasons Earth’s axis tilted to the ecliptic (plane in which Earth revolves around Sun) at 23.5 degrees The Earth’s tilt is most directly responsible for the seasons that we see every yearseasons More direct sunlight leads to warmer temperatures, which is why summer is experience in our hemisphere when Earth is tilted towards the Sun. During winter, our hemisphere is tilted away from the sun, allowing there to be less direct sunlight and therefore colder temperatures.

Solstices Summer solstice-Sun is at highest altitude in the sky (June 21); number of daylight hours at maximum, Winter solstice-Sun is at lowest altitude in the sky (Dec 21);number of daylight hours at minimum

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. Reason for milder temperatures in spring and fall is because neither hemisphere is pointed towards the Sun.  Called autumnal and vernal equinox (equinox means “equal nights”)

Moon’s Relation to Ocean Tides – The Moon revolves around the Earth just as the Earth revolves around the Sun. – The Moon’s gravity pulls on Earth along an imaginary line connecting Earth and the Moon, creating bulges of ocean water. – When the Sun and Moon are aligned, the result is higher-than- normal tides, called spring tides. – When the Moon is at a right angle to the Sun-Earth line, the result is lower-than-normal tides, called neap tides.

The moon does not emit light, it only reflects sunlight Half the moon’s surface is always reflecting light; however, we may not always see all of the lit surface. The amount seen we see is referred to as a moon phasephase Moon Phases

Solar Eclipses A solar eclipse occurs when the Moon passes directly between the Sun and Earth and blocks our view of the Sun.

Lunar Eclipses A lunar eclipse occurs when the full Moon passes through Earth’s shadow. A lunar eclipse can happen only at the time of a full moon, when the Moon is in the opposite direction from the Sun.

Hierarchy of the Universe-Listed top to bottom, largest to smallest Universe-all existing matter Consists of Galaxies-made of many stars Some stars in the galaxy might have Planetary systems-planets and other objects orbiting a star Such as our solar system in which our Planet, Earth, revolves around the Sun

Kepler’s Law, Planetary Orbit A scientist, Johannes Kepler, made observations of the motion of planets around the Sun and made some determinations. Kepler’s first law states that Earth, as well as other planets, revolve around the Sun in an elliptical, or oval shaped, that is centered upon two points, or foci. The Sun is always one of the foci, or central points.

Relationship of Barycenter to Planetary Orbit Isaac Newton also determined each planet orbits a point between it and the Sun called the barycenterbarycenter The barycenter is the balance point between two orbiting bodies (where all the mass of an object is concentrated) If one of two bodies orbiting each other is more massive than the other, the center of mass is closer to the more massive body If two bodies are similar in mass, their center of mass is near the middle position between them For any planet and the Sun, the center of mass is just above the surface of the Sun (or within the Sun) because the Sun is more massive than any planet

Barycenter and Sun’s Motion Our Sun stays relatively in the same position in relation to the planets of our solar system, but the Sun is not stationary. It moves as the planets tugs on it, causing it to orbit the solar system’s barycenter. The Sun never strays too far from the solar system barycenter, considering most of the solar system’s mass is in the Sun. Flash

Constant Motion in the Universe Just as Earth revolves around the Sun, our solar system revolves around the central point of our Milky Way galaxy. All solar systems in a galaxy are rotating around the galaxy’s central point.

Current State of the Universe The observation has been made using redshifts that galaxies are moving away from Earth in every direction; as they get further away, the rate at which they move away from us increases. The universe is expanding!

A spectrum is visible light arranged according to wavelengths. We can determine the composition of a star by identifying certain spectrum indicators.

Example, emission spectrum of hydrogen gas is seen above. Because stars emit this pattern of emission, or reflected, wavelengths of light, we can prove they contain hydrogen.

Spectra of Stars Wavelength Shift – Spectral lines are shifted in wavelength by motion between the source of light and the observer due to the Doppler effect. If a star is moving toward the observer, the spectral lines are shifted toward shorter wavelengths, or blueshifted. If the star is moving away, the wavelengths become longer, or redshifted. flash If a star is moving toward the observer, the spectral lines are shifted toward shorter wavelengths, or blueshifted. If the star is moving away, the wavelengths become longer, or redshifted. flash

Why is it proposed the universe is expanding? According to the big bang theory, the universe began as one extremely dense point of matter and rapidly expanded outward. This matter eventually combined to create all the planets, stars, and other objects in the universe. Universe is still expanding as it was at the time of the proposed “big bang”, just at a slower rate.

Why does the Earth rotate? Upon Earth’s initial formation, remnants of matter floating in the vacuum of space began to collide with one another, creating a spinning motion. As more and more gas and debris came together around this one central spinning area, the gravitational pull of this object increased. This increase in gravitational pull continued to attract more and more matter, becoming larger. When it got big enough, the gravity was strong enough to attract gaseous materials and form an atmosphere. This is essentially how planets were formed.

Why does the Earth revolve around the Sun? Earth would continue moving in a straight line if not for its proximity to the Sun. The Sun’s gravitational pull, which is extremely greater than ours due to the Sun’s mass, keeps our planet and all the other planets in our solar system in orbit.