Basics of Astronomy

Astronomy Tackles some fundamental questions What is our place in the universe? How did we get here? Are we alone?

Astronomy vs. Astrology ad_cfht.jpg

_________- the pseudo-science that studies how the motion of the stars and planets affect peoples lives. Available daily in your horoscope.

_________– The science of probing the universe to derive the properties of celestial objects and the laws under which the universe operates.

Astrology contributed to Astronomy since the position of the Sun, Moon, and stars was needed to determine a person’s sign. Planets, Sun, and Moon move in a band around the sky known as the______. Babylonians divided the zodiac into 12 sections. (the “signs”) Different cultures may have different divisions.

Constellations  Configuration of stars named in honor of mythological characters or great heroes  Today 88 constellations are recognized  Constellations divide the sky into units, like state boundaries in the United States  The brightest stars in a constellation are identified in order of their brightness by the letters of the Greek alphabet – alpha, beta, and so on

Location of celestial objects Although incorrect, the ______________________ is a useful way of looking at the sky. Equatorial system of location A coordinate system that divides the celestial sphere Similar to the latitude-longitude system that is used on Earth's surface

Terms ________________– an imaginary plane extending from Earth’s equator out to the celestial sphere. ___________– the angular distance north or south of the celestial equator. Similar to latitude on Earth.

Terms _______________– the angular distance measured eastward along the celestial equator from the position of the vernal equinox. Similar to Earth’s longitude. ______________– point in the sky where the Sun crosses the celestial equator at the onset of spring.

Planetary Motions ________– Turning of a body on its axis. (Earth 24 hours) __________– motion of a body around some point in space. (Earth 1 year) ___________

Earth’s Rotation ______________– Time interval from zenith to zenith of the Sun at a location. ____________ – Time interval for Earth to make one complete rotation (360°) with respect to another star, not the Sun.

Earth’s Revolution Average speed (66,000 mph) Average Distance from Sun ( __ million miles = 1 AU) Distance at perihelion (91.5 million miles) Distance at aphelion (94.5 million miles) Tilt on axis and revolution are reasons for seasons. asons_seasons.swf asons_seasons.swf

Earth’s Revolution _________– The apparent annual path of the Sun against the backdrop of the celestial sphere. _____________________ – the imaginary plane that connects Earth’s orbit with the celestial sphere.

Plane of Ecliptic vs. Celestial Equator

Milankovitch Theory Milutin Milankovitch Formulated a mathematical model to explain changes in Earth’s climate during the Pleistocene. Model is based on variations in Earth’s orbit and the amount of incoming solar radiation available at various times.

Elements of Milankovitch Model __________ – Variations in the elliptical nature of Earth’s orbit. _______ – Changes in the angle of tilt of Earth with its orbit. _________ – Wobbling of the Earth on its axis.

Eccentricity (~100,000 y)

Obliquity (~41,000 y)

Precession (~26,000 y)

Precession Very slow Earth movement Direction in which Earth's axis points continually changes. Currently points toward Polaris. In 13,000 years, winter in the Northern Hemisphere will occur when Earth is farthest from the Sun (aphelion), will have summer when Earth is closest to the Sun (perihelion). Exact opposite of today.

Fig. 2.16, p. 52

What does that mean? Northern Hemisphere summers will be warmer. Montreal in summer then will feel like Washington D.C. now. Northern Hemisphere winters will be colder than present. Southern Hemisphere is opposite, cooler summers, warmer winters.

Additional Motions Sun and solar system is moving toward the star Vega. Solar system revolves around the galaxy. Milky Way is moving, approaching the Great Galaxy in Andromeda.

Earth-Sun relations  Earth motions _________ on its axis _________ around the Sun  Seasons Result of Changing Sun angle Changing length of daylight

Fig. 2.17, p. 53

Daily paths of the Sun at 40º N latitude

Relationship of sun angle and solar radiation received on Earth

Earth-Sun relations  Seasons Caused by Earth's changing orientation to the Sun Axis is inclined 23½º Axis is always pointed in the same direction Special days (Northern Hemisphere) _______ solstice June Sun's vertical rays are located at the Tropic of Cancer (23½º N latitude)

Relationship of sun angle to the path of solar radiation

Earth-Sun relations  Seasons Special days (Northern Hemisphere) _______ solstice December Sun's vertical rays are located at the Tropic of Capricorn (23½º S latitude) ___________ equinox September Sun's vertical rays are located at the Equator (0º latitude)

Earth-Sun relations  Seasons Special days (Northern Hemisphere) ________________ equinox March Sun's vertical rays are located at the Equator (0º latitude)

Earth-Sun relationships

Characteristics of the solstices and equinoxes

Earth—Moon Interactions Average distance from Earth to the Moon is 238,329 miles. Moon orbit is elliptical. Interactions of Earth, Moon and Sun cause familiar phenomena…eclipses, phases of the Moon.

Moon Phases  Phases of the Moon When viewed from above the North Pole, the Moon orbits Earth in a counterclockwise (eastward) direction The relative positions of the Sun, Earth, and Moon constantly change ____________ are a consequence of the motion of the Moon and the sunlight that is reflected from its surface

Phases of the Moon

Earth – Moon Movements Earth-Moon _________ month Cycle of the phases Takes 29 1/2 days ___________ month True period of the Moon's revolution around Earth Takes 27 1/3 days

Motions of the Earth-Moon system Earth-Moon The difference of two days between the synodic and sidereal cycles is due to the Earth-Moon system also moving in an orbit around the Sun Moon's period of rotation about its axis and its revolution around Earth are the same, 27 1/3 days Causes the same lunar hemisphere to always face Earth (tidally locked)

Eclipse Simply shadow effects that were first understood by the early Greeks ________– Central completely dark part of a shadow produced during an eclipse. _________– portion of a shadow from which only part of the light source is blocked.

Eclipses Two types of eclipses Solar eclipse (eye of god) Moon moves in a line directly between Earth and the Sun Can only occur during the __________ phase

Solar Eclipse

Solar Eclipse Mythology Thought a dragon or demon was devouring the sun. Would bang pots, drums, shoot guns to frighten spirit away. In Tahiti, thought of as a divine cosmic “love-making”. Said to have stopped the battle and led to peace between the Medians and the Lydians in 585 BC.

Lunar Eclipse Moon moves within the shadow of Earth Only occurs during the _________ phase For any eclipse to take place, the Moon must be in the plane of the ecliptic at the time of new- or full-Moon Because the Moon's orbit is inclined about 5 degrees to the plane of the ecliptic, during most of the times of new- and full-Moon the Moon is above or below the plane, and no eclipse can occur The usual number of eclipses is _____ per year

Lunar Eclipse