What you need to know to pass the test! ASTRONOMY What you need to know to pass the test!

Light year: the distance light travels in one year The Milky Way (spiral galaxy) Light year: the distance light travels in one year Light 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!

The Orion Nebula, 1,500 light years from Earth. Image credit: NASA/JPL-Caltech The closest star to Earth, other than the Sun, is Alpha Centauri (approx. 4.4 light-years away)

Ellipses Ellipse – geometric shape of orbit Circle = 0.000 eccentricity Line = 1.000 eccentricity Ellipse – geometric shape of orbit Eccentricity (ESRT equation) – size of orbit, out-of-roundness The more eccentric an orbit is, the more oval-like shape it is The less eccentric an orbit is, the more circular-like (round) it is

Spectral lines Spectral lines shifted toward longer wavelengths (red-shift) indicate a star moving farther away from the observer Spectral lines shifted toward shorter wavelengths (blue-shift) indicate stars moving toward the observer Hubble’s Law: the universe is expanding (red shift)

Occur because Earth rotates Star trails Occur because Earth rotates

Ecliptic: apparent path of the Sun against the background stars (constellations)

(Polaris) Draw a line through the two “pointer stars”, which points to the North Star (Polaris)

Heliocentric (correct) Sun centered universe Geocentric (not correct) Earth centered universe Rotation The turning of a planetary object on its own axis Earth: 23 h 56 d 4 s Revolution The movement of one planetary body around another Earth: 365 d 26 h

Sun’s Altitude The 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 21 June 21 The intensity of insolation is greatest when?

Daily path of Sun sunset noon time sun daylight sunrise For 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”. 

Horizon: imaginary lines around the edge of the Earth (latitude) Azimuth: distance in degrees, measured clockwise from the due North position Zenith: position directly overhead Celestial Meridian: imaginary line overhead from the South point, through the Zenith, connecting to the North point.

Seasons As 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 the Sun, the tilt of its axis (23.5o) causes the Sun to move between 23.5oN (June 21) to 23.5oS (December 21)

What is the reason for the seasons? TILT! Winter Summer Summer

Solstice 2 times of the year when the noon sun shines overhead at an angular distance of 23.5o from the Equator Equinox 2 times of year when the noon sun is directly overhead at the Equator Perihelion The point in a planet’s elliptical orbit when it is closest to the Sun Apehelion The point in a planet’s elliptical orbit when it is farthest from the Sun Apehelion Perihelion

Shadow Length Why does your shadow length change throughout the day?... The Sun rises in the and sets in the As the Sun changes its position in the sky overhead, our shadow lengthens or shortens shorter when the Sun is more directly overhead – summer longer when the Sun is less directly overhead – winter As the Sun’s altitude increases, shadow length East West decreases

On which date is Earth tilted most toward the Sun? June 21 Summer Solstice Winter Solstice June 21 Longest day of year—14 hrs. Sun is highest in the sky December 21 Shortest day of year—8 hrs. Sun is lowest in the sky On which date is Earth tilted most toward the Sun? June 21 On which date is Earth tilted most away from the Sun? December 21

Kepler’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 the masses of the objects and inversely proportional to the distance between their centers squared. (a planet moves faster in its orbit when it is located closer to the Sun at perihelion)

Moon’s Phases GIBBOUS CRESCENT

The 1st phase is always the New Moon. The lit side of the Moon is the side facing the Sun. ---- The 1st phase is always the New Moon.

Waxing: 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 waxing Waning: The decreasing of the moon’s visible illuminated surface (from Full to New)

Synodic 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 Earth Perigee: The Moon in its closest position to the Earth Apogee: The Moon in its farthest position from the Earth

Eclipses When 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).

Tides Earth Tides result from the combined action of the Moon's gravitational pull on the Earth

There 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).