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The Solar System Objectives: 6.01 Analyze the theories of the formation of the universe and solar system. 6.02 Analyze planetary motion and the physical laws that explain that motion:
§ Rotation. § Revolution. § Apparent diurnal motions of the stars, sun and moon. § Effects of the tilt of the earth's axis.
Why Astronomy? Astronomy the scientific study of the universe
► By observing we have discovered § New planets § Stars § Black holes § Nebulas
► By studying these objects we have learned § more about the
origin of Earth § processes involved in
the formation of our solar system.
Organization of the Universe
► The solar system includes: the sun, planets,
and many smaller objects (asteroids and comets)
► The solar system is part of a galaxy: The Milky Way
How do we Measure Distances in the Universe?
Astronomical unit - the average distance between the Earth and the sun; approximately 150 million kilometers (symbol, AU)
► Astronomers also use the speed of light to measure distance.
Telescopes
Are instruments that collect electromagnetic radiation from the sky and concentrate it for better observation.
► Telescopes that collect only
visible light are called optical telescopes.
Electromagnetic Radiation ► Radiation made up of waves with electric
and magnetic properties (hence electromagnetic radiation)
Longest wavelength, least penetrating
Shortest wavelength, most penetrating
Telescopes ► Two types of optical
telescopes: § refracting telescope - uses a
set of lenses to gather and focus light from distant objects
§ reflecting telescopes - uses a curved mirror to gather and focus light from distant objects
How did the solar system form? ► Origin long debated. ► In the 1600s and
1700s, many scientists thought that the sun formed first and threw off the materials that later formed the planets. ► This was incorrect.
Solar System formation – pt2
► In 1796, French mathematician
Pierre Simon, § nebular hypothesis – more on this tomorrow
► solar nebular - rotating cloud of gas and dust § (also any nebular from which stars and
planets may form)
► The sun is composed of about 99% of all of the matter that was contained in the solar nebula.
Earth’s Movement
Rotation - the spin of a body on its axis ► Earth’s rotation takes about one day.
► Earth rotates from west to east.
► The hemisphere of Earth facing the sun experiences daylight, while that facing away from the sun experiences nighttime.
Earth’s Movement- pt2 Revolution - motion of a body that travels
around another body in space; one complete trip along an orbit
► Each complete
revolution of Earth around the sun takes 365 1/4 days, or about one year.
► Earth’s orbit around the sun is an ellipse, so Earth is not always the same distance from the sun.
Earth’s Movement – pt 3
Perihelion - the point in the orbit where the planet is closet to the sun
Aphelion - the point in
the orbit of a where the planet is farthest from the sun
Why do we have seasons? ► Earth’s axis is tilted at 23.5 degrees...
§ Changes the angle at which the sun’s rays strike Earth’s surface
► North Pole tilts away from the sun § Rays are not as direct § Northern Hemisphere has:
► Fewer daylight hours ► Less energy ► Lower temperatures
► Meanwhile, it is opposite for Southern Hemisphere § Rays more direct: longer daylight, warmer temps,
more energy
Equinox = Equal amounts of light and dark
Equinox - the sun’s rays strike Earth at a 90° angle along the equator. The hours of daylight and darkness are approximately equal everywhere on Earth on that day.
► Autumnal equinox § September 22 or 23 § Marks the beginning of fall in the Northern
Hemisphere.
► Vernal equinox § March 21 or 22 § Marks the beginning of spring in the Northern
Hemisphere.
Solstice = Sun far from equator Solstice - the point at which the sun is as
far north or as far south of the equator as possible
► Summer solstice § June 21 or 22 § Marks the beginning of summer in the
Northern Hemisphere. ► Winter solstice
§ December 21 or 22 § Marks the beginning of winter in the
Northern Hemisphere.
Earth-Moon System ► Earth and the moon revolve around each other.
Together they form a single system that orbits the sun.
► The balance point of the Earth-moon system is located within the Earth’s interior, because Earth’s mass is greater than the moon’s mass.
► The orbit of the moon around Earth forms an
ellipse
§ When the moon is farthest from Earth, the moon is at apogee.
§ When the moon is closest to Earth, the moon is
at perigee.
Moon’s Rotation and Revolution
► The moon rises and sets 50 minutes later each night because of both Earth’s rotation and the moon’s revolution.
► The moon revolves around Earth in
27.3 days.
► The moon’s revolution around Earth and its rotation on its axis take the same amount of time. Therefore, observers on Earth always see the same side of the moon
Moon Phases ► As the moon revolves around Earth, different amounts
of the moon are lighted. § The apparent shape of the visible part of the moon varies. § Varying shapes are called phases. § The period from one new moon to the next one is 29.5
days. ► Size of the lighted part is increasing, the moon
is said to be waxing. ► At full moon=the entire near side is illuminated
by the light of the sun.
► Size of lighted part is decreasing, the moon is waning.
Eclipses ► An eclipse occurs when one
body passes through the shadow of another.
► Total solar eclipse, § Moon passes between Earth
and the sun. § Sun’s light is completely
blocked by moon. § The shadow of the moon
falls on Earth. ► Lunar eclipse
§ Earth is positioned between the moon and the sun
§ Earth’s shadow crosses the lighted half of the moon.
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