phases of the moon - university of texas at austincmcasey/ast307_fa16/lec04.pdfhow we see the moon...

Phases of the Moon

Day side of the Earth

Night side of the Earth

Phases of the Moon

Day side of the Earth

Night side of the Earth

Phases of the Moon

Day side of the Earth

Night side of the Earth sunrise

sunset

Phases of the MoonHow we see the moon from Earth

Phases of the moon alter as the moon revolves around Earth.

“New Moon” — we only see the night-side of the

moon during our daytime.

Phases of the MoonHow we see the moon from Earth

“Waxing Crescent” — we see only a sliver of the moon’s

day-side around our sunset

Phases of the MoonHow we see the moon from Earth

“Waxing Crescent” — we see only a sliver of the moon’s

day-side around our sunset

Phases of the MoonHow we see the moon from Earth

“Waxing Crescent” — we see only a sliver of the moon’s

day-side around our sunset

Phases of the MoonHow we see the moon from Earth

“Waxing Crescent” — we see only a sliver of the moon’s

day-side around our sunset

Phases of the MoonHow we see the moon from Earth

“Waxing Crescent” — we see only a sliver of the moon’s

day-side around our sunset

Phases of the MoonHow we see the moon from Earth

First Quarter Moon — the moon has completed 1/4 of its orbit around Earth from “New Moon” phase, 90o/perpendicular to

sun in sky

Phases of the MoonHow we see the moon from Earth

First Quarter Moon — the moon has completed 1/4 of its orbit around Earth from “New Moon” phase, 90o/perpendicular to

sun in sky

Phases of the MoonHow we see the moon from Earth

“Waxing Gibbous” — more than 50% of the moon’s

surface (from Earth’s vantage point) appears illuminated

Phases of the MoonHow we see the moon from Earth

“Waxing Gibbous” — more than 50% of the moon’s

surface (from Earth’s vantage point) appears illuminated

Phases of the MoonHow we see the moon from Earth

“Waxing Gibbous” — more than 50% of the moon’s

surface (from Earth’s vantage point) appears illuminated

Phases of the MoonHow we see the moon from Earth

“Full Moon” — we see the entire day side of the moon

during our night. Moon is 180o opposite the sun in the sky (highest

in sky at midnight)

Phases of the MoonHow we see the moon from Earth

“Waning Gibbous” — we see most of the day-side of the

moon during our night (peaks after midnight)

Phases of the MoonHow we see the moon from Earth

“Waning Gibbous” — we see most of the day-side of the

moon during our night (peaks after midnight)

Phases of the MoonHow we see the moon from Earth

Third Quarter Moon — moon has completed 3/4 of its orbit around Earth. Peaks in sky at

sunrise

Phases of the MoonHow we see the moon from Earth

“Waning Crescent” — we see only a sliver of the moon’s

day-side around our sunrise

Phases of the MoonHow we see the moon from Earth

“Waning Crescent” — we see only a sliver of the moon’s

day-side around our sunrise

Phases of the MoonHow we see the moon from Earth

“Waning Crescent” — we see only a sliver of the moon’s

day-side around our sunrise

Phases of the MoonHow we see the moon from Earth

“Waning Crescent” — we see only a sliver of the moon’s

day-side around our sunrise

Phases of the MoonHow we see the moon from Earth

“Waning Crescent” — we see only a sliver of the moon’s

day-side around our sunrise

What time of day or night will the 1st quarter moon set?

A. Around Sunset B. Around Midnight C. Around Sunrise D. Around Noon

EarthshineIn some instances, light is reflected off the Earth to the moon

and back. So the “dark side” of the moon can be seen.

This usually occurs around the crescent phase at sunset.

Image credit: M. Taha Ghouchkanlu

Does the moon rotate about its axis? Do we see all of its surface?

Discuss…

Does the moon rotate about its axis? Do we see all of its surface?

Discuss…

The moon rotates one full revolution per orbit so we always see the same face.

This is called tidal locking.

Most moons in the solar system and many planets around other stars share

this behavior.

Other examples of tidally-locked bodies exist in the Solar System. Pluto and its moon Charon are both tidally locked to

each other.

Planetary Alignment… is this a miracle or pretty usual?

Discuss.

Planetary Alignment… is this a miracle or pretty usual?

Discuss.

The planets are ALWAYS in alignment, whether or not we can see them, because they sit in the

disk of the solar system.

B O D I E S I N T H E S O L A R S Y S T E M O C C U P Y O N LY A C E R TA I N PA R T O F T H E S K Y…

The ECLIPTIC =

The plane of the Solar System’s

‘Disk’ as viewed from Earth

Where is the sun in this diagram?

Ecliptic

Where is the sun in this diagram?

Ecliptic

Where is the sun in this diagram?

Ecliptic

Why can’t it be over here?

Ecliptic

Why can’t it be over here?

Mercury & Venus close to the sun in the sky as seen from Earth: they

always appear near sunrise or sunset

Mercury & Venus close to the sun in the sky as seen from Earth: they

always appear near sunrise or sunset

You can calculate the maximum angle of Mercury (a = 0.387 AU) and Venus (a = 0.723 AU)

in the sky. This angle is called elongation.

Outter planets (Mars - Neptune) could appear any time of day or night based on their relative position in their orbits

w.r.t. Earth

Which photograph of Venus and the Moon is real, which is fake, and why?

Photograph A Photograph B

THE ZODIAC — What is it?

The stars of the constellations that fall on the ECLIPTIC.

If it is January, time of “Capricorn” then we know the

sun is currently in the constellation of Capricorn (which we can’t see because it’s

daytime)

THE ZODIAC — What is it?

The stars of the constellations that fall on the ECLIPTIC.

If it is January, time of “Capricorn” then we know the

sun is currently in the constellation of Capricorn (which we can’t see because it’s

daytime)

Next time: SEASONS & Eclipses.

What we have learned

Structure of the Celestial Sphere & how to map the sky: Altitude / Azimuth, and Right Ascension / Declination

Causes of the phases of the moon.

Planetary Alignment in the Sky: the Ecliptic and the zodiac.