Oh, When Darkness Comes Trivia Quiz

Answer: Moon

While Mercury and Venus can, and do, pass between the Earth and the Sun, their distance is such that we see it as a dark spot moving across the Sun, which is called a transit. The Moon is close enough to the Earth for its apparent size in the sky to be almost exactly the same as that of the Sun - the Sun is much larger, but also much farther away. So when the Moon is between the Earth and the Sun, a significant shadow is formed on the surface of the Earth.

This blocking of the Sun's light is called an eclipse.

Answer: Predicted

To use more technical language, a total eclipse is an occultation - the Moon completely covers the face of the Sun. The other two types of eclipse are transits- the Moon covers most, but not all, of the Sun. In a partial eclipse, this is because because they are not perfectly lined up. An annular eclipse occurs when they are lined up, but the Moon is slightly further away from the Earth than average, so its apparent size is less than that of the Sun.

The different types of eclipse are explained by the fact that the Earth and the Moon both travel in elliptical paths, not circles, and the orbit of the Moon is inclined at a slight angle (about 5 degrees) to the plane in which the Earth travels around the Sun (the ecliptic). If the Moon moves between the Earth and the Sun when it is slightly above or below the ecliptic, the eclipse will be partial. If it is on the ecliptic, the eclipse is called a central eclipse, but may not be total. Since both the Earth and the Moon have regularly changing distances from the Sun and from each other as they orbit, there will be times when the Moon appears at least as large as the Sun, and covers it completely, giving a total eclipse. But there will also be times when it appears slightly smaller, so even when the alignments are perfect there will be a circular rim of the sun, called an annulus, showing around the outside, producing an annular eclipse.

Answer: New Moon

New Moon is the stage of the Moon's apparent changes of shape when seen in the sky when it is essentially lined up with the Sun, and is not seen in the night sky (unless as a very dim object). This is the time when it will pass between the Earth and the Sun during the day.

The Full Moon stage, when the Earth is between the Moon and the Sun, leads to lunar eclipses during eclipse season. Each eclipse season lasts for a bit over a month.

Answer: True

Eclipse seasons last for about 35 days, and the Moon's phase cycle is 29.5 days, so there will be either one or two solar eclipses in each season. The seasons are separated by about six months, so there will be two full seasons in a year, giving a minimum of two solar eclipses in the year. And, since they do not exactly coincide with a calendar year, a solar eclipse at the very end of a season that is the start of a calendar year could mean that year still has time for two more eclipse seasons. That gives a maximum of five solar eclipses in a calendar year.

Answer: 18 months

If the Moon and the Earth travelled in circular orbits, and they moved in the same plane, then there would be a total solar eclipse every month, whenever there is a New Moon. (This is assuming that this hypothetical situation has the Moon at the right distance for totality.) However, their orbits are elliptical and inclined to each other, leading to the eclipse seasons that occur roughly each six months, with one or two eclipses in each season. However, many of these will be partial or annular eclipses. On average, there will be a total solar eclipse once every 18 months.

However, these eclipses are not all seen at the same spot. If you had to guess how long you need to wait to see another eclipse at the same spot where you just saw one, the answer would be somewhere between 350 and 420 years, depending on where you are.

The number 75 was thrown in as the familiar (to astronomy students) time for the return of Haley's Comet.

Answer: First contact

Technically, the Sun and the Moon are tangential at the moment when their rims first touch, but that word would also apply to the moment when the Moon is moving on after the eclipse, which astronomers call fourth contact. The intervening numbers apply to the stages of the eclipse: second contact is when most of the sun has been covered at the start, and third contact is when light starts to appear again at the end. Totality is between second and third contacts.

Answer: Baily's beads

This effect is caused by the fact that the moon's surface is not smooth, so just before it completely obscures the Sun there is a time when sunlight can be seen through the lower parts of the surface, while the mountains obscure the light in places, producing what looks like a string of lights alternating with dark spaces. They are named after the astronomer who first provided the accepted explanation for their occurrence in 1836 (although Edmond Halley was the one who had first recorded observation of the phenomenon, in 1715).

When only one light can be seen, it is called the diamond ring effect, appearing as a bright light just before totality. The end of totality is marked by another diamond ring effect, a second batch of Baily's beads, and the gradual uncovering of the Sun.

Answer: Corona

The photosphere is the layer of the Sun from which light is primarily emitted. It is extremely dangerous to look directly at the photosphere, even when most of it is covered; this makes eclipse watching a potentially dangerous activity if one tries to view it directly.

Outside the photosphere is the chromosphere, which has a reddish colour that can be clearly seen during an eclipse (but not at totality, when it is covered). Then comes the corona, a cooler and thinner layer that sends out plasma, called the solar wind. It is usually not visible because the photosphere produces so much more light, so astronomers take advantage of its visibility during an eclipse ot study it in more detail.

Finally is the heliosphere, the least dense portion, which carries the solar wind out from the sun. It is considered to start at about a tenth of the distance between the Earth and the Sun, and continues until the heliopause, where the solar wind is stopped by other interstellar winds. This is about 120 AU from the sun, where AU stands for Astronomical Unit, the average distance between Earth and Sun.

Answer: 7 minutes

The exact time depends on a number of factors. If the Earth is at aphelion, the point of its orbit farthest from the Sun, the apparent size of the Sun is at its smallest. If the Moon is at perigee, the point of its orbit closest to the Earth, its apparent size will be at its largest. These two factors are the most important ones involved in producing a longer eclipse. Since the orbits of the Earth and the Moon are slowly changing over time, so too does the maximum possible time of totality vary. At the moment, the maximum time for totality is 7 minutes 32 seconds.

While totality only lasts for around seven minutes, the entire process from first contact through fourth will take significantly longer - up to four hours or so for a total eclipse, less for a partial eclipse.

Answer: Einstein

Specifically, Einstein had stated that the Sun's gravity should change the direction of light passing near it by an amount that differed from what was predicted by the then-accepted theory of gravitation developed by Sir Isaac Newton in 1687.

Sir Frank Watson Dyson, the Royal Astronomer and the chair of Joint Permanent Eclipse Committee of the Royal Society (general science) and the Royal Astronomical Society, decided in 1916 to organise an expedition to test Einstein's theory. He chose the 1919 total eclipse, with measurements being made in the Brazilian town of Sobral (by a group headed by astronomers from the Greenwich Observatory) and on the island of Principe, off the western coast of Africa (by a group from the Cambridge Observatory that included Arthur Stanley Eddington, whose name is now associated with the experiment). The eclipse was chosen because it was going to take place when a bright group of stars called the Hyades would be nearby, and could be photographed when they were visible during totality. The plan was to measure their apparent location in the night sky earlier, at a time when the sun was not close. Comparing those photographs with the ones taken during the eclipse showed that their position had apparently shifted exactly as Einstein's theory predicted, and almost twice what was predicted by Newton's theory of gravity.