Lesson 3) Three in a Row

Professor Turing enters the classroom. In his hand, there are copies of old newspapers about eclipses and other astronomical phenomena. As he enters the classroom, he reveals a few images, each of which features two astronomical bodies.

Syzygy Types

 Good evening, students, and welcome back to Astronomy. Last week, we discussed the concept of syzygy. What do you recall about a syzygy? Yes, a syzygy is an event that occurs when three astronomical bodies line up with each other. In the case of spring tides, we are talking about the Sun, the Earth, and the Moon. But a syzygy can also be two planets and a moon, two moons and a planet, or any combination of astronomical bodies.

Syzygy is quite rare in Astronomy. As I mentioned in the previous lesson, spring tides occur during syzygy or near syzygy. We do not often get true syzygys during most Full Moons and New Moons. Because of the angles of orbits, as well as the timing involved, it is hard to obtain a full syzygy, as it would require the three astronomical bodies to be fully aligned with each other. When we do achieve a full syzygy, though, we will know because we will experience a rather unique event - an eclipse.

When you are standing on the Earth (or any astronomical body - but for simplicity, I will use the Earth as a reference point), there are a few ways to know that the Earth and two other bodies are in syzygy. Three of these situations are transits, occultations, and eclipses. Please note that in the definitions below, the words “smaller” and “larger” refer to observed size from one’s point of view.

Transit: Io Transits Jupiter
Image Source: NASA

When a smaller astronomical body moves in front of a larger astronomical body, this event is called a transit. The above picture shows Io transiting Jupiter. When referring to transits, please use the form {smaller body} transits {larger body}.  During a transit, you should be able to see the larger body behind the smaller body. Please note that while the picture above happens to be taken from a Muggle spacecraft, and since the spacecraft is not an astronomical body, it is not an example of syzygy. However, if the picture had been taken from Earth, such a transit would show a syzygy between the Earth, Io, and Jupiter.

Occultation: Just Before Jupiter is Occulted by the Moon
Image Source: Wikipedia

When a larger astronomical body moves in front of a smaller astronomical body, the event is called an occultation. During an occultation, you may only be able to see the larger body, as the smaller body may be hidden behind it, but just before the occultation, you will be able to see both the larger and smaller body. The image above was taken a few moments before Jupiter is occulted by the Moon. When referring to occultations, please use the form {smaller body} is occulted by {larger body}.  As stated previously, the words “smaller” and “larger” refer to observed size, not actual size. Jupiter is the smaller object in the upper right corner, while the Moon is the larger object in the image. Since this image was taken from the Earth, the occultation of Jupiter by the Moon also resulted in a syzygy between the Earth, the Moon, and Jupiter.

When the interaction between two astronomical bodies results in one being momentarily hidden from view, the event is a special kind of occultation called an eclipse. Eclipses can occur either when an astronomical body directly blocks another from view, such as a solar eclipse, or when a shadow of an astronomical body blocks another from view, such as a lunar eclipse.

Solar and Lunar Eclipses from Earth

Daily Prophet Article on an Eclipse
Image Source: Harry Potter Wiki

When we talk about eclipses seen from the Earth, we are usually talking about solar eclipses and lunar eclipses. I will talk a little about both in this lesson, as it is important to know the difference between them. However, while this year will have more of a focus on lunar eclipses, I will explain more about solar eclipses next year. You will also learn about eclipses and their effects in other classes.


Total Solar Eclipse
Image Source: Wikipedia

Solar eclipses are an example of an occultation. In a solar eclipse, the Moon moves in between the Earth and the Sun. When seeing a total solar eclipse from the Earth, we would see the Moon covering all but the corona, or outer edge, of the Sun. Based on the definition, we can also see that a solar eclipse happens during New Moons and that a solar eclipse is also an occultation in which the Sun is occulted by the Moon. The image of the eclipse above depicts a solar eclipse. In particular, the image above shows a total solar eclipse. Partial and annular solar eclipses are also possible. In these cases, the Moon does not completely block out the Sun. Solar eclipses are a syzygy of the Sun, Moon, and Earth.

Total Lunar Eclipse
Image Source: Wikipedia

In lunar eclipses, the Earth’s shadow covers the view of a Full Moon. In other words, a lunar eclipse is a syzygy between the Sun, the Earth, and the Moon. A total lunar eclipse is distinguished by its distinctive red color, as seen in the picture above. In this situation, the shadow of the Earth completely falls over the Moon. Partial lunar eclipses are also possible when the Sun, the Earth, and the Moon are not completely aligned.

If you want to watch an eclipse, please refer to NASA’s page on eclipses. On this page, you can see when and where to view future solar and lunar eclipses. When you do view a solar eclipse, please only do so through indirect means, as looking at a solar eclipse with your magical telescope or with your naked eye could cause irreversible damage. Lunar eclipses are Full Moons and thus cannot be viewed through your magical telescope. However, they are safe to view with your naked eye, and if you get some friends to watch the eclipse with you, they make great social events.

Thank you for your time. Class is dismissed, and see you next Wednesday evening.

The Moon, The Lifebringer

NOTE - This course will soon be undergoing rewrites. Stay tuned!