what you need to know to pass the test!. light year: the distance light travels in one year light is...
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What you need to know to pass the test!
ASTRONOMY
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!
The Milky Way
(spiral galaxy)
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
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
Circle = 0.000 eccentricityLine = 1.000 eccentricity
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)
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 pointsto 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 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 21
The intensity of insolation is greatest when?
June 21
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”.
Daily path of Sun
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.
SeasonsAs 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)
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 LengthWhy 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 shadowlengthens 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
Summer Solstice Winter SolsticeJune 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 skyOn 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 MotionFirst 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 inversely proportional to thedistance between theircenters squared.(a planet moves fasterin its orbit when it islocated closer to the Sunat perihelion)
Moon’s Phases
GIBBOUS
CRESCENT
The lit side
of the Moonis the side
facingthe Sun.
----The 1st
phase is always
the New Moon.
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)
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
EclipsesWhen 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).