astronomy
Observable phenomena related to the moon:
- phases of the moon: depending on the Moon�s position relative to the Sun, we see different parts of the illuminated Moon.
- the month:� Moon changes through a complete cycle of phases in about 29.5 days
- eclipses
To understand these phenomena, we have to change our perspective and think about the Moon�s orbit.
Some properties of the Moon:
Radius 356,000 km 407,000 km 15% change from max to min Period of revolution around the Earth 27.322 days
w.r.t. background stars (that�s why it is not 29.5 days) Period of rotation around its internal axis 27.322 days The lunar �day�
Phases of the Moon
?? Where�s the Sun in this picture?
At any time, half of the Moon is illuminated by the Sun.
At any time, half of the Moon is visible to us.
Phase Terminology:
Waxing Growing larger (looks like curve of �D�) Waning Growing smaller (looks like �C�)
Grows or shrinks from the right (thanks to Michael Myers for the movie).
Quarter Moon We see half of the illuminated half of the Moon Full Moon We see all of the illuminated half of the Moon New Moon We see none of the illuminated half of the Moon
Crescent Less than Quarter Moon Gibbous More than Quarter Moon
The elongation is the angle between the Sun and the Moon.� For example, at new moon, the elongation of the Moon is 0 degrees.
The Galileo picture and the exercise make another important point:� the phase of the Moon that you see does not depend on your latitude; it only depends on the Moon�s position relative to the Sun.
Rotation of the Moon
Another important feature of the Moon�s motion is that its rotation period is the same as its orbital period.� This is called synchronous rotation.
As a result, we only see one side of the Moon.
- phases of the moon: depending on the Moon�s position relative to the Sun, we see different parts of the illuminated Moon.
- the month:� Moon changes through a complete cycle of phases in about 29.5 days
- eclipses
To understand these phenomena, we have to change our perspective and think about the Moon�s orbit.
Some properties of the Moon:
Radius 356,000 km 407,000 km 15% change from max to min Period of revolution around the Earth 27.322 days
w.r.t. background stars (that�s why it is not 29.5 days) Period of rotation around its internal axis 27.322 days The lunar �day�
Phases of the Moon
?? Where�s the Sun in this picture?
At any time, half of the Moon is illuminated by the Sun.
At any time, half of the Moon is visible to us.
Phase Terminology:
Waxing Growing larger (looks like curve of �D�) Waning Growing smaller (looks like �C�)
Grows or shrinks from the right (thanks to Michael Myers for the movie).
Quarter Moon We see half of the illuminated half of the Moon Full Moon We see all of the illuminated half of the Moon New Moon We see none of the illuminated half of the Moon
Crescent Less than Quarter Moon Gibbous More than Quarter Moon
The elongation is the angle between the Sun and the Moon.� For example, at new moon, the elongation of the Moon is 0 degrees.
The Galileo picture and the exercise make another important point:� the phase of the Moon that you see does not depend on your latitude; it only depends on the Moon�s position relative to the Sun.
Rotation of the Moon
Another important feature of the Moon�s motion is that its rotation period is the same as its orbital period.� This is called synchronous rotation.
As a result, we only see one side of the Moon.