Lecture 4

Motion of the - phases of the Moon - Solar and Lunar David Haworth -

Time & Calendar sunlight Properties of the and Moon

Koupelis - chapters 1 & 6

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Phases are caused by the illumination by the Sun

Third quarter Simple observations of the Moon

David Haworth

• displays phases with a period of 29.5 days waning • always opposite to the Sun

• half Moon at 90 degrees from the Sun Full Moon • always displays the same hemisphere to the Earth • path along the sky deviates from the ecliptic waxing • Lunar eclipses always at full Moon, but not every ! • Solar eclipses at new Moon are less frequent First quarter

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Sidereal en Synodic periodes orbital period and rotation period are synchronised

Sidereal month: Moon reaches the same position wrt the stars (27.3 days) Synodic month: Moon reaches the same position wrt the Sun (29.5 days) A second Full Moon in the same month: ‘’

3 6 A Lunar does not occur every month! Lunar eclipses The Moon traverses the shadow cone of the Earth

Umbra : area of the shadow cone from which the Sun is totally invisible. The around the Earth is inclined by 5 degrees with respect to the orbit of the Earth around the Sun (ecliptic). Penumbra : area of the shadow cone from which the Sun is partially visible. What is the maximum declination the Moon can reach?

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The eclipsed Moon (composite) A does not occur every month!

Visible from anywhere on Earth where the Sun is below the horizon.

3 kinds of Lunar eclipses

A : eclipse in the Penumbra

B : total eclipse of the Moon The orbit of the Moon around the Earth is inclined by 5 degrees C : partial eclipse of the Moon with respect to the orbit of the Earth around the Sun (ecliptic). What is the maximum declination the Moon can reach?

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The Earth atmosphere bends (refracts) the sunlight like a lens, and filters out the blue light. Solar eclipses

The shadow of the Moon moves across the Earth

The Moon displays a dark red/copper glow during a total Lunar eclipse: ‘Blood Moon’ A total is only visible from a narrow strip on Earth.

9 12 By the way, the orbit of the Moon is also elliptical.

Libration

‘Super Moon’ analemma of the Moon

31 January 2018: a Super Blue Blood Moon

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Total Solar eclipse: The Corona of the Sun the umbra of the Moon’s shadow ‘touches’ the Earth becomes visible for a few minutes.

Annular Solar eclipse: the umbra of the Moon’s shadow does not ‘touch’ the Earth

The shadow of the Moon seen from space.

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тoтAL solАFl ЕCLIPSЕS: 1997_2o20

60'N

з0"N Ф .= 00 з0.s Total solar eclipse sequence

60"s Predicted paths of total and annular Solar eclipses.

0' 60.Е 120.Е \ 1 Тhese dark b trаоkof the Ul тoтAL solАFl ЕCLIPSЕS: 1997_2o20 ANNULAR soLAR ЕCL|PSЕS: 1997-202o

60'N 60'N

з0"N з0.N Ф Ф э .= 00 0" --(б

з0.s з0.S

60"s 60"s

0' 60.Е 120.Е \ 1180.W 120'W 60"W 0" 60"Е 12o.Е 180" Е Longitude Тhese dark b Longitude trаоkof the Ul ANNULAR soLAR ЕCL|PSЕS: 1997-202o

60'N 15 18

з0.N Ф э 0" --(б

з0.S

60"s

180.W 120'W 60"W 0" 60"Е 12o.Е 180" Е Longitude Total solar eclipse sequence Tides ‘Diamond ring’ Baily’s Beads Totality caused by differential gravity

Because the Earth rotates faster than a Lunar period, the ocean’s waters are dragged forward by the Earth.

Due to friction, the Earth rotation slows down while the Moon moves further away from the Earth.

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Compared to the Moon, the Sun’s gravity ‘pulls’ 180x harder on the Earth, but the Sun is also 390x more distant.

The differential gravity from the Moon is 2.2x stronger than that from the Sun.

spring neap tide

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Eclipse

Time

&

Calendar

Eclipses only happen when line-of-nodes points toward the Sun. Eclipse pattern repeats every 11 , not every 12 months. This is a consequence of the precession of the Moon’s orbit with a period of 18.6 years: The line-of-nodes rotates over 19.4 degrees every year.

21 24 Seasons & constellations Note that the Earth is further from the Sun in July than in January. Therefore, a Solar day in January lasts longer than a Solar day in July. concept of a year ⇒ ➙ equation of time! Planets Analemma ⇒ concept of a The result of: Sun - obliquity of the Earth axis of rotation ⇒ concept of a day - elliptical orbit of the Earth

B.t.w. Leap year Sunday The Julian kalender was Monday replaced in 1582 by the Mardi Gregorian calender. Mercredi This fixed the error due to Jeudi the definition of a Julian Vendredi More about time/calendar later on year as 365.25 days. Saturday

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Sidereal time vs Solar time Distinguish sidereal time from (mean) Solar time. Months A sidereal day is shorter than The Moon revolves around the Earth in 29,5 days (synodic month). a Solar day! Consequently, 12 MONths almost make up a year, but not quite: 12 x 29.5 = 354 dagen

Some 11 extra days are required to fit 12 months in 1 year. → distribute these extra days over the months.

Note: the number of days in a month follows MAMJJASONDJF, with some interesting consequences…

The mean Solar time in Greenwich (GMT) is the reference time (Universal Time: UT), which defines the time zones.

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The Earth

Mass and volume yield an average density <ρ> <ρ> = 5.52 gr/cm3

This is significantly more dense than the surface material (water and silicates):

the Earth contains a core of iron and nickel

27 30 Almost unique to the Earth : a magnetic field Seismological research has revealed:

There is a liquid outer core below the mantle; the inner core is solid.

The crust ‘floats’ on the (convective) mantle.

De magnetic poles do not coincide with the geographic poles. The Earth magnetic field directs charged particles from the Solar wind Furthermore, the Earth retains an atmosphere! to the magnetic poles.

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Aurora Borealis - Northern Lights Unique to the Earth: plate tectonics

Andreas Coсos; 53uц P|ate.:

Paсifiс ')''^ Plate -'',i''t'"'^.,{i )," oouno",,( AntarсtiсP|a|e l

www.youtube.com/watch?v=uLahVJNnoZ4

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Almost unique to the Earth : a magnetic field

The Earth magnetic field directs charged particles from the Solar wind to the magnetic poles.

33 36 The Moon The dual face of the Moon ‣ diameter is 27% of Earth ‣ phases due to illumination by the Sun ‣ impact craters and maria, dust seas (lava) ‣ from Earth, we always see the same side: synchronous rotation ‣ <ρ> = 3.34 gr/cm3: the core is small or absent ‣ no atmosphere

‣ no magnetic field Origin: likely composed from crust material from the Earth ‣ often Lunar eclipses (impact theory) but not every month!

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The Lunar surface

The gravity on the Moon is much less than on Earth (17%)

There are many more craters and far less maria on the far-side of the Moon: an uneven distribution of mass inside the Moon.

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The dual face of the Moon Internal structure of the Moon

t,tron-riсh сore?

140 I кm, l 1740km

Partially molten? Mantlе

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