The Moon Flashcards
How old is the Moon?
4.5 billion years old (within 50 million years of Earth’s formation)
How far away is the Moon from the Earth?
384,000 km
How large is the Moon relative to Earth?
Moon diameter: 3,474 km
Earth diameter: 12,742 km
Earth is 3.67 times larger
How long does it take the Moon to revolve around the Earth?
27.32 days
How long does it take the Moon to revolve around its axis?
27.32 days
Why does the Moon rise 50 minutes later each night?
- Because of Earth’s rotation and the Moon’s revolution
- Earth rotates CC, Moon orbits CC, Moon appear to move east to west- Moon moves slower in sky
- Takes an extra 1/29 of Earth’s rotation (50 min) for the horizon to catch up to the moon
Why does the Moon have phases?
- The Moon shines by reflected light
- The changing relative positions of the sun, Earth, and Moon
- The sun’s light always illuminates half of the moon
- As the Moon revolves around Earth, different amounts of the near side of the Moon, which faces Earth, are lighted
- The apparent shape of the visible part of the moon varies
What are various phases of the Moon?
New moon Waxing crescent First quarter Waxing gibbous Full moon Waning gibbous Third quarter Waning crescent
What is the time period from one full moon to the next full moon?
29.5306 days
Why is the time from one full moon to the next different from one revolution around Earth?
- The difference of 2.2 days is due to the orbiting of the Earth-Moon system around the sun
- In 27.3 days (Moon orbits Earth) the two bodies move slightly farther along their orbit around the sun
- The Moon must go a little farther to be directly between Earth and the Sun (2.2 days)
What is the relationship between time of day, phase of Moon, and where the Moon is in the sky?
- A new moon rises when the sun rises
- A full moon rises when the sun sets
- A first quarter moon rises at noon
How do you determine the phase of the Earth as seen from the Moon?
Opposite of the phase of the Moon as seen from Earth new moon - full moon waxing crescent - waning gibbous first quarter - third quarter waxing gibbous - waning crescent
How do you calculate the phase of the Moon for any date in the past?
1) Calculate the number of days between the two dates:
- number of days divided by 4, leap years times 366, non leap years times of 365
- number of days in each month up to the date
2) Days divided by 29.5306
3) Decimal point on the clock
What are the differences between a solar eclipse and a lunar eclipse? (geometry of the Earth-Sun-Moon system, phase of the Moon, etc)
Solar: new moon, Earth-Moon-Sun
Lunar: full moon, Moon-Earth-Sun
Why don’t we have eclipses every month?
- The orbit of the Moon is not on the same plane as the orbit of Earth around the sun
- The Moon crosses Earth’s plane twice a month but there will only be an eclipse if the phase is full or new
Why is someone more likely to have seen a total lunar eclipse than a total solar eclipse?
- Lunar eclipses are visible everywhere on the dark side of Earth
- A total solar eclipse can only be seen by observers in the small path of the Moon’s shadow as it moves across Earth’s lighted surface
What are maria and how did they form?
- Large, dark, round, flat areas of basalt on the moon formed when:
a) planetesimals crashed into the Moon when it was very young (4-4.5 billion years ago)
b) the huge depressions (from asteroid impacts) filled with lava which cooled to form a dark volcanic rock (basalt) 3.2-3.9 billion years ago (lava gushed up from the Moon’s melted interior)
What are craters and how did they form?
- A bowl-shaped depression that forms on the surface of the moon when from the impact of asteroids and comets
- Formed 4 billion years ago when debris left over from the formation of the solar system struck the Moon
- 240 km to microscopic
- Most obvious craters- less than 1 billion years old
What are simple craters and how did they form?
- Bowl-shape
- 15 km to microscopic
- Raised rim
- Floor filled with debris
- Most common
What are complex craters and how did they form?
- Larger than simple craters
- Terraced walls
- Central peak- formed by larger object crashing into moon or a higher speed (rebound effect- liquid solidifies)
What are multi-ringed basins and how did they form?
- Huge object
- Flat center (molten rock)
- Mountain ranges around impact
- Bulls-eye pattern
Apogee
The point when the Moon is farthest from Earth in its orbit
Corona
- Outermost layer of the sun’s atmosphere
- Magnetic field
- Very dim- only visible during solar eclipse/total darkness
Earthshine
- Sunlight that is reflected off Earth
- Reason that you can still see the darker part of the Moon
- Sun - Earth - Moon - Earth
Eclipse
-One celestial body passes through the shadow of another another
Gibbous
The side of the Moon that is facing the Earth is mostly illuminated (more than half)
Lunar highlands
- Formed when the Moon did
- Densely cratered regions on the Moon
- Relatively light colored
- Represent the first crust of the Moon
Lunation
A lunar month, from one new moon to the next (29.53 days)
Penumbra
The outer part of the Earth and Moon’s shadow, sunlight is only partially blocked
Perigee
The point when the Moon is closest to Earth in its orbit
Sidereal month
- The time it takes for the Moon to make 1 orbit
- 27.32 Earth days
Synodic month
- One full moon to the next
- 29.5306
Syzygy
When the Earth, Moon, and Sun are alligned
Umbra
The inner, cone-shaped part of the shadow cast by the Earth and the Moon
Solar eclipse
-Moon is directly between the sun and part of Earth, the umbra of the Moon falls on Earth
-New moon
-1-2 times per year
-Shadow 100 km or less on Earth
-Sun completely blocked for 7 minutes
-
Lunar eclipse
-The passing of the Moon through Earth’s shadow at full moon
-1-2 times per year
-Seen by everyone of dark half of Earth
-Totality lasts for over an hour- Earth’s umbra 2 1/2 times larger than the Noon
-
How did the Moon form?
1) Earth hit by a planet-size object 4.5 billion years ago
2) Impact was a glancing blow (no scar because Earth’s surface was liquid)
3) Impacting planet was obliterated (its core merged with core of Earth)
4) Much of the mantle + crust of Earth blown out into orbit around Earth (vaporized and then solidified)
5) Created Saturn-like ring around Earth
6) Over time, ring particles collided to form the Moon
As the sun shines of any spherical object in the solar system, how much of the object is illuminated?
- Half
- The half that is not facing the sun is in darkness
Waxing
When more and more of the side of the Moon that is facing the Earth is lit from from day to day
Waning
When less and less of the side of the Moon that is facing the Earth is lit from from day to day
Why was the Moon hot 4.5 billion years ago after it formed?
1) Impacts from asteroids- transferred to heat energy
2) Earth was radioactive
What is an annular eclipse?
- Earth at perihelion
- Moon at apogee
- The Moon’s umbra does not reach Earth
- Sun is never completely blocked out
- Thin ring of sunlight visible around outer edges of the Moon
- No corona visible
Where do people see a partial solar eclipse?
Outside the umbra but within the penumbra
What is a penumbral eclipse?
- When the entire moon passes through Earth’s penumbra
- Eclipse is barely visible
What is a partial lunar eclipse?
When only part of the moon passes into Earth’s umbra
Why do totally eclipsed moons appear red?
- Sunlight is bent around Earth through our atmosphere
- Mainly red light reaches the moon
What is the diamond-ring effect?
- The last bits of normal sunlight before darkness during a solar eclipse
- Often glistens like a diamond on a ring
