What you need to know
to pass the test!
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
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)
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)
Geocentric (not correct)
Sun centered universe
Earth centered universe
Rotation
Revolution
The turning of a planetary
object on its own axis
The movement of one
planetary body around
another
Earth: 23 h 56 d 4 s
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
The intensity of insolation is greatest when?
June 21
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
Equinox
2 times of the year when the
noon sun shines overhead at
an angular distance of 23.5o
from the Equator
2 times of year when the noon
sun is directly overhead at
the Equator
Perihelion
Apehelion
The point in a planet’s
elliptical orbit when it is
closest to the Sun
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
East
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,
decreases
shadow length
and sets in the
West
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 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 (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
Waning: The decreasing
of the moon’s visible
moon is waxing
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).