| How many great circles are on a sphere? Solution: An infinite number. Any circle whose center is at the center of the sphere is a great circle, and you can place that circle in any orientation you want. The distance between me and the North Pole is equal to the distance between me and the South Pole. Where am I? Solution: On the equator. The coordinates of Brock University are 43.1176° N, 79.2477° W. What do these coordinates mean? Solution: The first number is latitude: the university is located 43.1176 degrees to the north of the equator. The second number of longitude: the university is located 79.2477 degrees west of the Prime Meridian (passing through Greenwich, England). Is declination analogous to latitude or longitude? Is right ascension analogous to latitude or longitude? Solution: Declination is the angle to the north or south of the celestial equator, so that's analogous to latitude. Right ascension is the angle to the east of the March equinox, so it's analogous to longitude. What did Foucault prove with his pendulum? Solution: From the fact that the pendulum's direction of oscillation was slowly rotating over time, it follows that the Earth is rotating around its axis. This is a great example of a simple experiment that literally anyone can do, and yet can prove something that people have denied for thousands of years! "The seasons are due to the distance between the Earth and the Sun changing throughout the year." True or false? Solution: False. This is actually a common misconception. The real reason for the seasons is the Earth's axial tilt. If the distance to the Sun was the cause for the season, then we would have two summers and two winters during each year! Which two effects are responsible for the seasons, and how? Solution: 1. The Sun's rays hit the ground at different angles throughout the year, due to the Earth's axial tilt. When the Sun hits the ground at a small angle, the rays spread out and each point on the ground gets less heat, resulting in a winter. When the Sun hits the ground at a large angle, the rays hit the ground more directly and each point on the ground gets more heat, resulting in a summer. When it's summer in the northern hemisphere it's winter in the southern hemisphere, and vice versa, since when one hemisphere "leans into" the Sun, the other "leans out". 2. In addition to rays hitting the ground more directly, in the summer the Sun spends more time in the sky, so it has more time to heat the ground before night falls. Which solstice happens in June? What does it mean in each hemisphere? Solution: The June solstice happens every year around June 21. In the northern hemisphere, it's the summer solstice: the day where the Sun is highest in the sky and the day is the longest. In the southern hemisphere, it's the winter solstice: the day where the Sun is lowest in the sky and the day is the shortest. What are the two tropics, and what do they mean? Solution: The Northern Tropic (Tropic of Cancer) is the northmost latitude where the Sun can be directly overhead (at the zenith). The Southern Tropic (Tropic of Capricorn) is the southmost latitude where the Sun can be directly overhead (at the zenith). It's the December solstice, and the Sun does not rise all day. Where on Earth am I? Solution: On the arctic circle, or north of it. At this time, it is the winter solstice in the northern hemisphere, and the arctic circle is the southernmost point where the Sun will not rise on this day. What's the difference between a solar day and a sidereal day? Solution: A solar day is the rotation period of the Earth with respect to the Sun, while a sidereal day is the rotation period of the Earth with respect to the fixed stars. A solar day is approximately 24 hours long, while a sidereal day is approximately 23:56 hours long. What are the three periodic astronomical events used to create calendars? Solution: Years are measured by the orbital period of the Earth around the Sun. Months are measured by the orbital period of the Moon around the Earth, at least in early calendars and also in some contemporary calendars (e.g. Jewish and Islamic). Days are measured by the rotational period of the Earth around itself. Why do we need leap years? Solution: The periods of rotation of the Earth around its axis and around the Sun don't divide each other exactly. Therefore, a year is NOT 365 days, it's approximately 365.2422 days. This small difference becomes significant as the years accumulate, so we have to cancel it out by adding one extra day on some years. If the Moon is full and high in the sky, where is the Sun located in space? Can we see it in the sky? Solution: The Sun will be located on the opposite side of the Moon. We won't be able to see it in the sky, since if we can see the Moon, that means the Sun is "below" us. People on the other side of the planet will see the Sun, but not the Moon. Which part of the Moon is visible 1 week after a new moon? Solution: The Moon will be at the first quarter phase, so the right half will be visible. "The back side of the Moon is in perpetual darkness, and thus it can be called the dark side of the moon." True or false? Solution: False. The Moon exhibits synchronous rotation, so the same side of the Moon always points towards the Earth. But the back side is not always dark. When a new Moon appears, the back side of the Moon is fully lit. It is only completely dark during a full Moon, and it is not any more dark on average than the front side. "The tides are due to water on the Earth being gravitationally attracted towards the Moon." True or false? Solution: False. If that was true, then there would be a tide on just one side of the Earth, the side closer to the Moon. However, in reality, the water level is higher also on the opposite side. The Moon's gravity does influence the tide, but not by directly attracting the water. Rather, the Earth is slightly distorted due to the Moon's gravity attracting different parts of it with different strengths, and this change in the shape of the Earth causes water to flow and produce the tides. You stand near Lake Ontario and watch it for 24 hours. How many high tides will you see? Solution: Two, one when the Moon is directly above you, and another when the Moon is on the other side of the Earth. "Both the Sun and the Moon cause tides." True or false? Solution: True. Both bodies exert gravitational forces on the Earth, but the Moon produces a larger tidal effect. By how much will be the average distance to the Moon increase 10 years from now? Solution: The Moon moves away from the Earth by 3.8 cm per year, so that's 38 cm in 10 years. How is a solar eclipse created? What about a lunar eclipse? Solution: A solar eclipse happens when the Moon casts a shadow on the Earth, or in other words, the Moon fully or partially blocks light from the Sun from reaching the Earth. A lunar eclipse is the opposite: it happens when the Earth casts a shadow on the Moon, or in other words, the Earth fully or partially blocks light from the Sun from reaching Moon. Does every planet with a moon experience total solar eclipses? Solution: No. The apparent size (i.e. the size in the sky, not the actual size) of both the Sun and the Moon needs to be approximately the same for that to happen. What are the umbra and penumbra? Solution: The umbra is the central cone where the shadow from a spherical body (e.g. the Moon or the Earth) is darkest. A person within the umbra will see the light from the Sun completely blocked, and will experience a total eclipse. The penumbra is the outer part of the cone, where the shadow is lighter. A person within the penumbra will see the light from the Sun partially blocked and will experience a partial eclipse. Is a solar eclipse visible from everywhere in the same hemisphere? Solution: No, only if you are in the small area that's inside the umbra of the Moon's shadow. Is a lunar eclipse visible from everywhere in the same hemisphere? Solution: Yes, because the shadow is not on you, it's on the Moon, so everyone sees the same thing as long as they can see the Moon. "During a solar eclipse, it is safe to look directly at the Sun." True or false? Solution: False, except during totality - the short time when the Sun is totally eclipsed by the Moon, which lasts a few minutes at the most. At that time, and ONLY at that time, it is safe to look directly at the Sun. However, it might be hard to tell exactly when the Sun is 100% eclipsed, so it is highly recommended not to look directly at the Sun if you are on your own, even during totality. Instead, you should attend an official eclipse event led by qualified people, such as professional astronomers or physicists. An example of such an event is the one planned for the total solar eclipse of April 8, 2024 at Brock University, where qualified experts, including the professor of this course, will be on site to ensure everyone is viewing the eclipse safely by distributing eclipse glasses and letting you know exactly when it is safe to look directly at the Sun without the glasses. |