Eclipses: Crash Course Astronomy #5

Summary

This script explores the fascinating phenomenon of eclipses, highlighting the rare alignment of the Sun and Moon's apparent sizes due to their relative distances. It explains the mechanics of solar and lunar eclipses, the Moon's tilted orbit, and the different types of shadows cast, including the dramatic total solar eclipse and its beautiful corona. The script also discusses safety during eclipse viewing, the global visibility of lunar eclipses, and the historical use of eclipses to determine the Earth and Moon's sizes, ending with a note on the Moon's gradual drift away from Earth.

Takeaways

• 🌞 The Sun and the Moon appear to be about the same size in the sky due to the Sun being approximately 400 times wider than the Moon and also about 400 times farther away.
• 🌕 An eclipse occurs when the Moon passes directly between the Earth and the Sun, resulting in a solar eclipse, or when the Earth blocks the Sun's light from reaching the Moon, resulting in a lunar eclipse.
• 🛰️ The Moon's orbit is tilted about 5° with respect to Earth's, which is why solar and lunar eclipses do not occur every new and full Moon respectively.
• 🌑 During a solar eclipse, the Moon casts an umbra, a dark shadow, and a penumbra, a lighter shadow, on Earth, with the umbra allowing for a total solar eclipse where the Sun is completely blocked.
• 🌓 The experience of a total solar eclipse includes the visibility of the Sun's corona, an outer atmosphere, and phenomena like Baily's Beads as the Moon's edge covers the Sun.
• 💫 The 'Diamond Ring' effect is observed during a solar eclipse when a small portion of the Sun is visible as a bright spot just as the Moon moves off the Sun's face.
• 👀 Viewing a solar eclipse requires extreme caution and proper eye protection to prevent damage to the retinas from intense sunlight, especially at the end of totality.
• 🌌 A lunar eclipse is visible to anyone on Earth facing the Moon, as it involves the Moon moving into Earth's shadow, which can give the Moon a deep orange or red hue due to the scattering of light by the Earth's atmosphere.
• 🌍 The Earth's shadow on the Moon during a lunar eclipse can be used to estimate the relative sizes of the Earth and Moon, a method used by ancient Greeks to understand the cosmos.
• 🌑 The Moon is slowly moving away from the Earth at a rate of about 4 centimeters per year, which will eventually prevent total solar eclipses from occurring in about a billion years.
• 🌐 The script is sponsored by Squarespace and is part of the Crash Course Astronomy series, highlighting the educational and entertaining nature of the content.

Q & A

Why do solar and lunar eclipses occur?

Solar and lunar eclipses occur due to the alignment of the Earth, Moon, and Sun. A solar eclipse happens when the Moon passes between the Earth and the Sun, casting a shadow on the Earth. A lunar eclipse occurs when the Earth is between the Moon and the Sun, casting a shadow on the Moon.

What is the significance of the Sun and Moon appearing to be the same size in the sky?

The Sun and Moon appearing to be the same size in the sky is significant because it allows for total solar eclipses. The Sun is about 400 times wider than the Moon and also about 400 times farther away, which makes their apparent sizes equal, enabling the Moon to completely cover the Sun during an eclipse.

Why don't we have solar and lunar eclipses every new and full moon respectively?

We don't have eclipses every new and full moon because the Moon's orbit is tilted about 5° relative to Earth's orbit. This tilt means the Moon can pass above or below the Sun in the sky, missing alignment and thus not casting a shadow on the Earth or Moon.

What are the two types of shadows cast by the Moon during an eclipse?

The two types of shadows cast by the Moon are the umbra and the penumbra. The umbra is a narrow, dark shadow cone where the Moon completely blocks the Sun, while the penumbra is a wider, lighter shadow cone where the Sun is only partially blocked.

What is the phenomenon known as 'totality' during a solar eclipse?

Totality is the brief period during a solar eclipse when the Moon completely covers the Sun, allowing the Sun's faint corona to become visible. This is considered the most spectacular part of a total solar eclipse.

What are Baily's Beads, and how do they occur during a solar eclipse?

Baily's Beads are bright patches of sunlight that appear around the eclipsed Sun just before and after totality. They occur due to the Moon's uneven edge, particularly its craters, which allow sunlight to stream past and create these bright spots.

What is the Diamond Ring effect, and when does it occur during a solar eclipse?

The Diamond Ring effect occurs just as totality ends during a solar eclipse. It is when a single point of the Sun is unblocked, creating a bright spot on one side of the Moon, which, together with the surrounding light, resembles a diamond ring.

Why is it dangerous to look at the Sun without proper eye protection during an eclipse?

Looking at the Sun without proper eye protection can be dangerous because the intense solar radiation can damage the retinas. This is especially risky during an eclipse because after totality, when the Moon moves off, the sudden flash of sunlight can catch viewers by surprise and cause harm.

How can the Earth's shadow during a lunar eclipse be used to determine the relative sizes of the Earth and Moon?

During a lunar eclipse, the size and shape of the Earth's shadow on the Moon can be used to determine the relative sizes of the Earth and Moon through geometric calculations. Ancient Greeks used this method to estimate the sizes of these celestial bodies.

Why do the Moon and Sun appear red when they are on the horizon?

The Moon and Sun appear red when they are on the horizon because of the scattering of light by the Earth's atmosphere. Blue and green light are scattered away, leaving only the red light to reach the observer, which gives the celestial bodies a reddish hue.

What is the long-term effect of the Moon moving away from the Earth on total solar eclipses?

As the Moon slowly moves away from the Earth, it will eventually be too far away to completely cover the Sun, meaning that there will come a time, estimated to be about a billion years from now, when total solar eclipses will no longer occur.