Observing the Moon and Eclipses

Astronomy 311Professor Lee

CarknerLecture 4

What were the most important contributions to planetary science of Tycho, Kepler, and Galileo respectively?

a) Observing with a telescope, Determining the laws of planetary motion, Measuring the motions of the planets

b) Determining the laws of planetary motion, Observing with a telescope, Measuring the motions of the planets,

c) Observing with a telescope, Measuring the motions of the planets, Determining the laws of planetary motion

d) Measuring the motions of the planets, Determining the laws of planetary motion, Observing with a telescope

e) Measuring the motions of the planets, Observing with a telescope, Determining the laws of planetary motion

What period in history saw the greatest increase in our understanding of the physical properties of the solar system?

a) 200 BC – 200 ADb) 1550 AD -1650 ADc) 1650 AD – 1800 ADd) 1900 AD – 1950 ADe) 1950 AD – 2000 AD

Moon Basics

Shows 1 complete set of phases in one month

Phase is determined by how much of

the lit side we can see

New --

Quarter -- see 1/2 illuminated side

Full --

Crescent --

Gibbous -- more than 1/2 of illuminated side

Waxing --

Waning -- decreasing brightness

Sidereal and Synodic

Sidereal period -- time for moon to return to initial position with respect to the stars (27.3 days)

Synodic period -- time for moon to return to initial position with respect to the sun (29.5 days)

Why is a Synodic Month Longer than a Sidereal

Month?

Where is the Moon?

Since the moon makes one orbit in about 30 days, it moves 1/30 of a complete circle in the sky in one day

Moon is ~12 degrees further east

each night

Eclipses

Solar Eclipse

Happens during New moon Lunar Eclipse

Happens during Full moon

When do Eclipses Happen?

Moon’s orbit is tilted by about 5 degrees with respect to the ecliptic (plane of the Sun and Earth)

Only have eclipses when Sun falls on line of nodes (line where the orbital plane of the Earth and Moon intersect)

Line of Nodes

Shadows on the Moon

Umbra -- Darkest part of the shadow

Penumbra -- Less dark part of shadow, region is still getting some sunlight

Penumbral eclipses can be hard to notice

Geometry of a Lunar Eclipse

Types of Lunar Eclipses Total Eclipse -- Moon is completely covered

Partial -- Moon is partially covered

Penumbral --

You can still faintly see the Moon even during a total lunar eclipse because of scattered light (circular sunset)

Lunar Eclipse

Types of Solar Eclipses

Total Eclipse -- Sun is completely covered

Partial -- Sun is partially covered

Annular Eclipse Moon is about 400 times smaller than

the Sun, but is also about 400 times closer

When the Moon is the furthest from the Earth it does not completely cover the Sun

Annular Eclipse --

Annular Eclipse

Solar Eclipse from Space

Next Eclipses Eclipses visible from central U.S.

Lunar – Total solar eclipse – August 21, 2017

For any given location, you see many more lunar than solar eclipses

Next Time

Read chapter 2.5-2.8 for next time

Summary Orbit

one complete orbit in one sidereal month

same side always faces the Earth Phases

complete set in one synodic month where the Moon is in sky at a

particular time depends on the phase

Eclipses caused by Earth or Moon blocking out

the Sun only occur when line of nodes points

at Sun are darkest when in the umbra occur in cycles