Astr: Earth/moon System, Ch 4

Front 1

Synchronous rotation

Back 1

The moon's sidereal rotation period equals its sidereal revolution period. The moon shows only the near side.

Front 2

Lunar liberations

Back 2

More than 50% of the Earth's surface is visible over a sidereal month - the surface "wobbles" and "nods" despite being locked into synchronous rotation. 59% is actually visible over the moon's orbital period.

Hint 2

Wobble

Front 3

Diurnal liberation

Back 3

Due to diurnal parallax.

An observer can see 1° father west in lunar longitude at moonset than at moonrise.

Front 4

Liberation in latitude

Back 4

East-West visibility due to moon's elliptical orbit.

Because the moon's rotational speed is faster at perigee, a few more degrees of the right-hand face are visible just after perigee. The reverse is true just after apogee. About 6°

Front 5

Liberation in longitude

Back 5

Due to moon's 6.5° of axial tilt.

More of the southernmost part of the moon's face is visible when the moon is North of the ecliptic, and vice versa.

Front 6

Oblate spheroid

Back 6

Sphere with a slight spare tire at the equator. Due to rapid rotation.

Front 7

Cause of precession

Back 7

Net torque on equatorial bulge due to tides attempts to align equatorial and ecliptic planes, instead causing the Earth's axial poles to change direction in a circle around the ecliptic pole

Front 8

Tide

Back 8

Distortion of equipotential surface. Most evident in Earth's oceans bulging towards the moon, but present even in solid bodies.

Front 9

Lunar vs solar tide

Back 9

Lunar tides are twice as strong as solar tides

Front 10

Spring tide

Back 10

Lunar and solar tides coincide to produce higher-amplitude tides

Front 11

Neap tide

Back 11

Lunar and solar tides sum destructively, causing lower amplitudes in tides. Sun and moon are at right angles.

Front 12

Cause of late tidal bulge

Back 12

A tidal bulge does not point directly at the moon because it encounters friction as it traverses the Earth.

Front 13

Tidal braking

Back 13

The moon pulls more strongly on the near tidal bulge causing bet torque which decreases Earth's angular momentum.

.0016 sec/century

Front 14

How quickly is the moon receding?

Back 14

4 cm/year

Front 15

Roche limit

Back 15

The minimum radius at which a body can orbit another without being ripped apart by tidal forces

Front 16

Hill radius

Back 16

Maximum orbit size before satellite will escape planetary orbit

Front 17

Moon phases

Back 17

Front 18

Waxing

Back 18

Visible portion turns towards observer, appears to grow. After new moon and before full. Lit on the right side. "White on the right grows night to night."

Front 19

Waning

Back 19

Visible portion of moon turns away from observer, appears to shrink. After full moon and before new. Lit on the left side.

Front 20

Moon's tilt relative to ecliptic plane

Back 20

5.1°

Front 21

Sidereal month

Back 21

Sidereal (measured against background stars) orbit of moon

27.322 days

Front 22

Synodic month

Back 22

Synodic (measured against Earth) period of moon; time elapsed between repeated phases

Front 23

Lunar eclipse

Back 23

Earth casts shadow on moon; Sun and Moon are at opposite nodes

Front 24

Solar eclipse

Back 24

Moon casts shadow on Earth; Sun and Moon are at same node

Front 25

Node

Back 25

Point at which the ecliptic plane intersects the Moon's path

Front 26

Line of nodes

Back 26

Line at which ecliptic plane intersects Moon's orbital plane

Front 27

Umbra

Back 27

Portion of shadow in which light source is completely blocked

Front 28

Penumbra

Back 28

Portion of shadow in which light source is partially blocked

Front 29

Annular eclipse

Back 29

Because the Moon is at apogee, the Sun is not completely blocked even in a total solar eclipse. A ring (annulus) of the Sun is visible around the Moon.