Ch01 Lecture part3 video

Summary

This lecture delves into the celestial mechanics of the Moon, explaining its phases and movement across the sky due to Earth's rotation and the Moon's orbit. It explores the waxing and waning cycles, the Moon's different phases, and the rare occurrences of solar and lunar eclipses. The presentation also touches on the Earth's atmospheric effects during eclipses, causing the red hue of a lunar eclipse and the visibility of the Sun's corona during a solar eclipse. The lecture concludes with insights into predicting eclipse seasons based on the orbits of the Earth and Moon.

Takeaways

• 🌓 The Moon has different phases due to the relative positions of the Earth, Moon, and Sun, which affect how much of the Moon is illuminated and visible from Earth.
• 🌅 The Moon rises in the east and sets in the west, following the Earth's rotation and its own orbit around the Earth.
• 🌑 A new moon is when the Moon is not visible from Earth because the side facing us is not illuminated by the Sun.
• 🌒 Waxing phases include the crescent and gibbous phases, where the visible portion of the illuminated Moon increases from new to full moon.
• 🌕 A full moon occurs when the entire face of the Moon is lit up and visible, which happens when the Moon is on the opposite side of the Earth from the Sun.
• 🌗 Waning phases are when the illuminated portion of the Moon decreases from full to new moon, including the waning gibbous and crescent phases.
• 🕒 The Moon's orbit around the Earth takes about 27.3 days, but a full lunar cycle (from new moon to new moon) takes about 29.5 days due to the Earth's movement around the Sun.
• 🌞 Solar eclipses occur when the Moon's orbit aligns with the Earth's orbit around the Sun, casting a shadow on the Earth.
• 🌜 Lunar eclipses happen when the Earth's shadow falls on the Moon, which can give the Moon a reddish hue due to the scattering of light by the Earth's atmosphere.
• 🔭 The Earth's atmosphere bends red light towards the Moon during a lunar eclipse, causing it to appear red, which is a result of all the sunrises and sunsets on Earth being projected onto the Moon.
• ☀️ The visibility of the Moon and the occurrence of eclipses can be predicted based on the understanding of the Earth's and Moon's orbits, with eclipse seasons where solar and lunar eclipses are likely to happen.

Q & A

Why does the Moon appear to rise in the east and set in the west?

The Moon appears to rise in the east and set in the west due to the Earth's rotation on its axis. This is similar to how the Sun and stars move across the sky from east to west.

What causes the different phases of the Moon?

The different phases of the Moon are caused by the changing angles between the Earth, the Moon, and the Sun. As the Moon orbits the Earth, different portions of the Moon's surface are illuminated by the Sun, resulting in various visible phases.

What is the term used for the phase when the Moon is not visible from Earth?

The phase when the Moon is not visible from Earth is called the 'new moon.'

How is the waxing crescent phase of the Moon different from the waning crescent phase?

The waxing crescent phase occurs between the new moon and the first quarter, where the visible portion of the Moon is increasing. The waning crescent phase occurs between the third quarter and the new moon, where the visible portion is decreasing.

What is the term for the phase when half of the Moon is illuminated as seen from Earth?

When half of the Moon is illuminated as seen from Earth, it is called the 'first quarter' or 'last quarter' phase.

Why does the Moon's rise time change each day?

The Moon's rise time changes each day because the Moon orbits the Earth approximately 50 minutes later each day due to the Earth's rotation and the Moon's orbit around the Earth.

What is the difference between a sidereal month and a synodic month?

A sidereal month is the time it takes for the Moon to orbit the Earth once, which is about 27.3 days. A synodic month is the time it takes for the Moon to go through one full cycle of phases, from new moon back to new moon, which is about 29.5 days.

What causes a solar eclipse?

A solar eclipse occurs when the Moon is positioned directly between the Earth and the Sun, casting its shadow on the Earth and blocking the Sun's light.

What causes a lunar eclipse?

A lunar eclipse occurs when the Earth is positioned directly between the Sun and the Moon, casting the Earth's shadow on the Moon.

Why does the Moon appear red during a lunar eclipse?

During a lunar eclipse, the Moon appears red because the Earth's atmosphere scatters shorter wavelength light (blue light), while longer wavelength light (red light) bends around the Earth and reaches the Moon, giving it a reddish hue.

How can the occurrence of solar and lunar eclipses be predicted?

The occurrence of solar and lunar eclipses can be predicted by understanding the orbits of the Earth around the Sun and the Moon around the Earth. The alignment of these orbits at certain periods allows for the prediction of eclipse seasons.