Presentation on theme: "What you need to know to pass the test!"— Presentation transcript:
1What you need to know to pass the test! ASTRONOMYWhat you need to know to pass the test!
2Light year: the distance light travels in one year The Milky Way(spiral galaxy)Light year: the distance light travels in one yearLight is the fastest-moving stuff in the universe. It travels at an incredible 300,000 kilometers (186,000 miles) per second. So, in a year, light travels far!
3The Orion Nebula,1,500 light years fromEarth.Image credit:NASA/JPL-CaltechThe closest star to Earth, other than the Sun, is Alpha Centauri (approx light-years away)
5Ellipses Ellipse – geometric shape of orbit Circle = eccentricityLine = eccentricityEllipse – geometric shape of orbitEccentricity (ESRT equation) – size of orbit, out-of-roundnessThe more eccentric an orbit is, the more oval-like shape it isThe less eccentric an orbit is, the more circular-like (round) it is
7Spectral linesSpectral lines shifted toward longer wavelengths (red-shift) indicate a star moving farther away from the observerSpectral lines shifted toward shorter wavelengths (blue-shift) indicate stars moving toward the observerHubble’s Law: the universe is expanding (red shift)
8Occur because Earth rotates Star trailsOccur because Earth rotates
9Ecliptic: apparent path of the Sun against the background stars (constellations)
10(Polaris) Draw a line through the two “pointer stars”, which points to the North Star (Polaris)
11Heliocentric (correct) Sun centered universeGeocentric (not correct)Earth centered universeRotationThe turning of a planetary object on its own axisEarth: 23 h 56 d 4 sRevolutionThe movement of one planetary body around anotherEarth: 365 d 26 h
12Sun’s AltitudeThe higher the arc of the Sun, the more direct its’ rays are and the greater duration of insolation (length of daylight). The changing altitude of the Sun influences seasonal temperature change.VERNAL EQUINOX (1st day of Spring – March 21)SUMMER SOLSTICE (1st day of Summer – June 21)AUTUMNAL EQUINOX (1st day of Fall – Sept. 23)WINTER SOLSTICE (1st day of Winter – Dec. 21)The maximum altitude of the Sun occurs when?June 21June 21The intensity of insolation is greatest when?
13Daily path of Sunsunsetnoon time sundaylightsunriseFor every 15o arc in the Sun’s path overhead, there is one hour of daylight. The amount of time required for the Earth to rotate from one noon time to the next is known as “solar noon time”.
15Horizon: imaginary lines around the edge of the Earth (latitude) Azimuth: distance in degrees, measured clockwise from the due North positionZenith: position directly overheadCelestial Meridian: imaginary line overhead from the South point, through the Zenith, connecting to the North point.
16SeasonsAs Earth revolves around the Sun, different portions of its surface are tilted 23.5o toward the Sun at different times of the year.SUMMER: tilted toward the Sun (most direct rays)WINTER: tilted away from the Sun (indirect rays)As Earth revolves around theSun, the tilt of its axis (23.5o)causes the Sun to movebetween 23.5oN (June 21) to23.5oS (December 21)
17What is the reason for the seasons? TILT!WinterSummerSummer
19Solstice2 times of the year when the noon sun shines overhead at an angular distance of 23.5o from the EquatorEquinox2 times of year when the noon sun is directly overhead at the EquatorPerihelionThe point in a planet’s elliptical orbit when it is closest to the SunApehelionThe point in a planet’s elliptical orbit when it is farthest from the SunApehelionPerihelion
20Shadow LengthWhy does your shadow length change throughout the day?...The Sun rises in the and sets in theAs the Sun changes its positionin the sky overhead, our shadowlengthens or shortensshorter when the Sun is moredirectly overhead – summerlonger when the Sun is lessdirectly overhead – winterAs the Sun’s altitude increases,shadow lengthEastWestdecreases
21On which date is Earth tilted most toward the Sun? June 21 Summer SolsticeWinter SolsticeJune 21Longest day of year—14 hrs.Sun is highest in the skyDecember 21Shortest day of year—8 hrs.Sun is lowest in the skyOn which date is Earth tilted most toward the Sun? June 21On which date is Earth tilted most away from the Sun? December 21
22Kepler’s Laws of Planetary Motion First Law: All planets move in ellipses with the Sun at one focus.Second Law: The line joining the Sun and a planet sweeps out in equal areas in equal time.Third Law: The gravitational force of a planet is directly proportional to the product of themasses of the objectsand inverselyproportional to thedistance between theircenters squared.(a planet moves fasterin its orbit when it islocated closer to the Sunat perihelion)
25The 1st phase is always the New Moon. The lit sideof the Moonis the side facingthe Sun. ----The 1st phase is always the New Moon.
26Waxing: The increasing of the moon’s. visible illuminated surface Waxing: The increasing of the moon’s visible illuminated surface (from New to Full)You can tell if the moon is waxing or waning by looking at the right side ---if it’s shaded, the moon is waning & if it’s lit, then the moon is waxingWaning: The decreasing of the moon’s visible illuminated surface (from Full to New)
27Synodic Month: 29-1/2 days for the Moon to complete a cycle of phases Sidereal Month: 27-1/3 days for the Moon to go in its revolution around EarthPerigee: The Moon in its closest position to the EarthApogee: The Moon in its farthest position from the Earth
28EclipsesWhen the Moon in its orbit around the Earth shadows the Sun's light as viewed from the Earth (solar eclipse), or when the Moon passes through the shadow cast by the Earth (lunar eclipse).
29TidesEarthTides result from the combined action of the Moon's gravitational pull on the Earth
30There are 2 high and 2 low tides every day, which alternate and are 6 hours apart. The Sun also produces a tidal force on the Earth, but this force is weaker than the tidal force by the Moon because the Moon is closer. (The tidal force by the Sun is weaker than the tidal force by the Moon even though the gravitational pull by the Sun is stronger than the gravitational pull by the Moon.)When the Sun and the Moon are aligned at right angles, the high tides are very high (Spring tides) and the low tides are very low (Neap tides).