Moonth of Phases

http://radiojove.gsfc.nasa.gov

Important Words

• Crescent: less than half of the moon visible to Earth is lit

• Gibbous: more than half of the moon visible to Earth is lit

More Important Words

• Waxing: illuminated portion of the moon facing Earth is increasing

• Waxing is from the Old English weaxan meaning “to grow.”

• Wax on light (from new moon to full)

• Waning: illuminated portion of the moon facing Earth is decreasing

• Waning is from the Old English wanian meaning “to lesson”

• Wane off light (from full moon to new)

Still another important word

• Quarter Moon: Half of the moon facing the Earth is illuminated

But wait… if we see half the moon lit, was isn’t it called a half moon?

• This is because the moon is a quarter (or three quarters) through its cycle of phases (or we see a quarter of the entire moon lit…)

Your moon model data table should look like this!

Be SureTo Look At The #s

http://www.nmm.ac.uk/upload/img/phases.gif

In your model what represented the Earth, the Sun and the Moon?

• Earth: You

• Sun: the lamp

• Moon: the Styrofoam ball on the stick

How much of the lighted part of the ball did you see when facing the

lamp?

• NONE!

Explain what happened to the illuminated portion of the moon

after each turn.

• The portion of the moon illuminated (lit) increased with each turn until the entire moon facing the Earth was illuminated. After this the portion of the moon illuminated decreased with each turn.

Whether you could see it or not, how much of the ball’s surface was

always lit by the lamp?• HALF OF THE

MOON IS ALWAYS ILLUMINATED BY THE SUN!

• We just do not always see all (or any) of this half here on Earth!

http://www.opencourse.info/astronomy

Why do we see different phases of the moon?

• The moon revolves around the Earth, so the relative positions of the Earth, moon and sun cause the phases

• The changing amount of the lit portion of the moon visible on Earth = Phases

http://www.lpi.usra.edu/

Why we have phases:

http://home.hiwaay.net/~krcool/Astro/moon/moonphase/

What would happen if the model was not above head?

• Moon would be dark at full moon location – in your shadow

• Would be a lunar eclipse!

http://www.dkimages.com/

Moon Info

• It takes the same amount of time for the moon to rotate on its axis as it does to revolve around the Earth (27.3 days)

• This is why the Earth only sees one side of the moon – in order to see the other side you need to get on a space ship and go around the moon!

• There are 29.5 days from a new moon to the next new moon

Moon Info

• The lit part of the moon always points towards the sun.

• When waxing: light is on the right

• When waning: shadow is on the right

http://www.astro.virginia.edu

The moon rise, moon set• The time of the moon rise and set depends on its

phase• Rises in the East and sets in the West – due to

Earth’s rotation• Remember: moon rises about 50 min later each day

of the moon phase cycle (~ 25 to 75 mins)

• http://aa.usno.navy.mil/cgi-bin/aa_rstablew.pl

•

Phase Rise Time Midpoint in sky Set Time

New Sunrise Noon Sunset

1st quarter Noon Sunset Midnight

Full Sunset Midnight Sunrise

3rd quarter Midnight Sunrise Noon

Can you identify the phase?

Waxing Gibbous

Full

Waning Crescent

Waning Gibbous

New

Last (3rd) Quarter

First Quarter

Waxing Crescent