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

2. 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!

3. 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 light-years away)

5. Ellipses Ellipse – geometric shape of orbit
Circle = eccentricity
Line = 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

7. 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)

8. Occur because Earth rotates
Star trails
Occur because Earth rotates

9. Ecliptic: 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)

11. 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

12. 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?

13. 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”. 

15. 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.

16. 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)

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

19. 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

20. 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

21. 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

22. 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)

24. Moon’s Phases
GIBBOUS
CRESCENT

25. 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.

26. 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)

27. 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

28. 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).

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

30. 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).