ASTR-101 Lessons

Until recently, most of the advances in the non-magical area of astronomy were made by Muggles, and we witches and wizards learned about their findings second-hand.  This lesson will be primarily devoted to the non-magical tools that have aided in these great discoveries, many of which are also used, or have been adapted to be used, by magical folk as well.

Telescopes

A telescope is an optical instrument that magnifies a distant object and makes it appear brighter.  They are astronomy’s most important tool and were used to discover Uranus, Neptune, and Pluto. With their aid, Muggle astronomers have discovered, and continue to discover, new asteroids, comets, stars and galaxies (collections of stars), moons, and even planets orbiting other stars.  By examining the colour of light from distant galaxies with the 100-inch-wide Hooker telescope, then the biggest one in existence, an American astronomer Edwin Hubble was able to conclude that the universe is expanding, initiating the branch of astronomy called cosmology, which studies the origin and evolution of the universe.  More information about Hubble can be found here.  As you can see, the telescope is truly an invaluable tool.

The earliest telescopes had two lenses at opposite ends of a tube.  At the far end of the tube is the light-gathering lens, called the objective lens.  This lens is convex – that is, thicker in the middle than at the edges – like a magnifying glass and is called a positive lens.  Distant objects seen through a magnifying glass on its own appear blurry. To make them appear sharp, you need another lens at the near end of the tube, called the eyepiece.  In the earliest telescopes, the eyepiece was concave – that is, thinner in the middle than at the edges – and was called a negative lens. This was the design of the first Muggle telescope, invented by Hans Lippershey, a Dutch eyeglass maker, in 1608.  It made distant objects look three times as big as with the naked eye. If you want to build a telescope of this kind, instructions can be found here. 

Diagram of a telescope.
Source: here

Two years later, Galileo Galilei, a famous astronomer, improved on that design.  He found that by making the objective lens less curved, he could improve the magnifying power from three to 20, making it a more useful astronomical tool.   He used it to discover the four largest moons of Jupiter, which are therefore called the Galilean moons. He also discovered that Venus has phases like the Moon, confirming Copernicus’s belief that the Earth revolves around the sun rather than the other way around (more on this later in the course).  As a result, any telescope whose eyepiece is a negative lens is now called a Galilean telescope.

Galileo’s telescope.
Source: here

One problem with the Galilean telescope is that it has a very narrow field of view, so you can only see a very small part of the sky with it.  Johannes Kepler (more on him later in this lesson) found that if the eyepiece is also a positive lens, you can see much more of the sky. Everything you look at appears upside down, but astronomers don’t care much about that because they can easily adjust to it; therefore, this type of telescope is called an astronomical telescope.  People who want to look at things on Earth, like navigators on ships, don’t want either of those disadvantages, so they use what is called a terrestrial telescope. In that sort of telescope, the eyepiece has two positive lenses; the one nearest your eye turns what you see right side up again.

Since their invention, all three types of telescopes have been altered and improved in order to enable the user to adjust the focus.  In the newer models there are two tubes instead of one, a wider tube containing the objective lens, and a narrower tube, which can be slid in or out, containing the eyepiece.  In the terrestrial telescope, the magnifying power can be adjusted too - the farther apart the two lenses of the eyepiece are, the greater the magnifying power. With the astronomical type, you have to change the eyepiece in order to change the power, but astronomers are prepared to do that rather than have an extra lens, which absorbs a bit of the precious light they need for their observations.

Telescopes that use only lenses are called refracting telescopes, as lenses refract light (more on that in later years).  However, refracting telescopes of any design have a problem: the objects seen at the edge of the field of view appear to have colour fringes because of the way light bends differently along the edges of the glass.  Modern refracting telescopes use several lenses in the eyepiece to solve that problem, but in 1688, Isaac Newton solved it by using mirrors instead of lenses – he invented the reflecting telescope, so called because mirrors reflect light – so telescopes that use his design are called Newtonian telescopes.  Many improvements have since been made on Newton’s design, and these days professional astronomers use reflecting telescopes almost exclusively.

The amount by which a telescope magnifies distant objects is called the telescope’s power.  Basically, the weaker the objective lens or mirror is and the stronger the eyepiece is, the more powerful the telescope will be.  Aside from magnifying things, astronomers want to see things that are too dim to be seen with the naked eye, and the bigger the objective lens or mirror is, the more light it will gather.

Suppose you replace the objective lens or mirror with one whose diameter (that is, its width) is twice as big.  Will it gather twice as much light?  Nope!  The amount of light it gathers is proportional to its area, not its diameter.  The new lens is twice as wide and twice as long, so its area is 2 times 2 = 4 times as great, so it will gather four times as much light.

Two by two square grid
Source: here

That would be easier to visualise if the lenses were shaped like squares instead of circles, so let’s consider the image above, showing four equal squares fitting neatly into a bigger one. The sides of the larger square are twice as long as those of the little ones, and you can see that the area of the big one is four times that of each of the little ones.  A proof for circles will be given in Year Seven.

If instead the new lens is three times as big in diameter as the old one, its area, and therefore its light gathering power, is 3 times 3 = 9 times as great.  How many times as much light will the new lens gather if it is four times as big in diameter as the old one?

At this point you’ll have to bear with me while I interrupt the discussion of telescopes by introducing a bit of mathematics, which will be needed later on this year.  If you take any number and multiply it by itself, you get the square of that number, so called because, as we have shown in the case of the number 2, the area of a square is proportional to the square of the length of its sides.  The square of 1 is 1, the square of 2 is 4, the square of 3 is 9, and so on.  The square of a number is represented by a superscript 2. For example, 2² = 4.

And now, back to the telescopes.  Another advantage of making the objective lens or mirror bigger is that it improves the resolution of the telescope – that is, how close together two points of light can appear to be and still be seen as two distinct points instead of one.  The reason for this will be discussed in Year Six. Of course, by close together I don’t mean the distance between them in miles or kilometers. If one of the two points of light is between you and the other one, they can be trillions of miles apart and still appear to be close together, whereas if you are between them, they could be close to you and still appear far apart.  The observed closeness of two points of light is measured as an angle, not a straight-line distance. 

Source: here

The ancient Greeks divided the circle into 360 degrees.  If one star is on the eastern horizon and another one is on the western horizon, they are half a circle – 180 degrees – apart. You would have to turn your head halfway around to look from one to the other.  If they are 1/180th of that distance apart, then they are one degree apart, and you would only have to move your eyes a little bit to move from the first to the second.  Now, someone with average vision can, at best, distinguish two points of light about 1/20th of a degree apart with the naked eye. However, astronomers have a need to see objects that appear much closer together than that. Rather than writing many tiny fractions of a degree to describe the observed closeness between two stars, they use even smaller units known as arcminutes and arcseconds.  A degree is divided into 60 arcminutes and an arcminute is divided into 60 arcseconds.

If you double the diameter of the objective lens or mirror, you double the resolution – that is, you can resolve two stars that appear twice as close together.  If the diameter of a lens or a mirror is about 12 centimeters, the resolution is about one arcsecond. Telescopes are getting bigger and bigger; the biggest one so far is the Keck telescope, 10 meters in diameter.  Can it resolve two stars that are 0.012 arcseconds apart? Not without a very expensive trick. The problem is that movement of the air makes the stars appear to move around (and twinkle too), making it hard to achieve a resolution much better than one arcsecond no matter how big the telescope is.  Large modern telescopes solve this problem by using what is called adaptive optics, in which the mirror deforms hundreds of times per second to compensate for the apparent movement of the stars. But there is another solution to this problem: putting your telescope above the atmosphere by launching it into orbit around the Earth, which brings us to our next tool used by Muggle astronomers.

Satellites

A satellite of a planet is an object that is in orbit around the planet.  Moons are natural satellites, whereas an artificial satellite is a human-made object launched into orbit by means of a rocket.  Artificial satellites have many purposes. Muggles have what is called a GPS (Global Positioning System) that uses satellites to locate the position of a receiver, like the ones in Muggles’ cars.  Satellites are also used for communication, like telephone, television, and internet transmission, to look at and photograph the Earth, to examine clouds, temperature, and rainfall to make more accurate weather forecasts,  and, of course, to put telescopes above the atmosphere, which is one contribution that they make to astronomy. The Hubble telescope, named after Edwin Hubble, is one such telescope orbiting Earth. It is about 2.5 meters wide, so it should be able to resolve two stars that are 0.05 arcseconds apart.  But when it was launched in 1990, its resolution was more than one arcsecond! A flaw in the primary mirror was found to be responsible for the blurred images. A team of astronauts was sent up in 1993 to correct the problem, after which the resolution improved to the expected 0.05 arcseconds. Since then it has sent sharp and beautiful pictures back to Earth and made many important discoveries, including finding distant galaxies and black holes, improving the accuracy of the rate at which the universe is expanding, showing that the rate of expansion is accelerating, and estimating more precisely the age of the universe. If you would like to see some of these pictures and learn more about what astronomers have learned from the Hubble telescope, there is further reading here, which in turn provides further sources for more in-depth reading.

Satellites have other uses besides carrying telescopes: they house other tools like cameras, radars, and remote sensors, tools to collect and analyze space particles, and more that give us other important information.  Some of them also carry people, which serves to arouse public interest in space travel and increase the prestige of the country that launches them.  The space race between the United States and the Soviet Union during the Cold War between those two nations is a prime example.

Sputnik.  
Source: here

The first satellite, called Sputnik - a Russian word meaning “fellow traveler” - was launched in 1957 by the Soviet Union.  By the time the United States had successfully launched its first satellite four months later – Explorer 1 – after some embarrassing failures, the Soviet Union had already launched their second satellite, which carried a dog named Laika. Shortly thereafter, they launched their third satellite, which carried the first man into outer space – Yuri Gagarin, grandfather of Professor Gagarina, a former professor of this course.  This was a wake up call for the United States, because satellites can also be used to spy. The Americans responded in 1958 by creating the National Aeronautics and Space Administration (NASA) to catch up with the Soviet Union in the space race, and they also greatly increased funding for universities to create a pool of future rocket scientists. If you would like to learn more about NASA, go to its web site by opening this link.  The United States finally won the space race in 1969 when they landed two men, Neil Armstrong and Buzz Aldrin, on the Moon and brought them safely back to Earth.  Further information can be found here.  While they were on the Moon, the command module, piloted by Michael Collins, orbited the Moon, so it too was an artificial satellite.  After six more voyages to the Moon, one of which failed to land there (Apollo 13), the country lost interest, and since then astronauts and cosmonauts (Russian astronauts) have only been sent into low Earth orbit.

But the Soviet Union was still ahead in one area – launching a woman into space.  In 1963 Valentina Tereshkova, a textile worker who later became an engineer, spent almost three days in space.  Several female American pilots, believed to be better trained than Tereshkova, were not sent into space because of prejudice in the United States where it was thought that women were unfit for space travel.  Twenty years were to pass before the Americans first launched a woman into space – Sally Ride. Since then, NASA no longer takes gender into consideration in evaluating candidates for space travel. 

 Valentina Tereshkova.  
Source: here

Spacecraft have orbited other celestial bodies besides Earth and our moon; in fact they have orbited all the planets, some of their moons (like Saturn’s biggest moon Titan), and some asteroids and comets, and have given astronomers much information about them.

Space Agencies in Other Countries 

The United States and Russia are not the only countries that have space programs.  Several European countries contribute to the European Space Agency, and there are space agencies in numerous other countries including Canada, India, Japan, and China.   Sometimes they go it alone - for example, the China National Space Administration first landed a rocket on the far side of the Moon on January 3, 2019 - and sometimes they cooperate with each other in their space programs.  For example, the Americans, Russians, Europeans, Canadians, and Japanese cooperated to build the International Space Station, which is also a satellite, and which often houses people from more than one country at the same time.  Some wizards have actually worked under cover with those other space agencies, but not in NASA, because in 1790 MACUSA, the American equivalent of the British Ministry of Magic, passed Rappaport’s Law, an edict enforcing total segregation between magical people and No-Majs (the American name for Muggles).  As a Canadian, I can’t resist mentioning that Canada invented the Canadarm, a robot that is attached to an artificial satellite and used to deploy, maneuver, and capture payloads. Of course, people and supplies have to be transported to and from the International Space Station, which brings us to our next tool used by Muggle astronomers.

Space Shuttles

In the early 1980s, NASA began a program called the Space Transportation System, using artificial satellites, called space shuttles, that are partially or totally reusable.   They were used to launch numerous other satellites, interplanetary probes, and the Hubble Space Telescope to conduct science experiments in orbit and to participate in the construction and servicing of the International Space Station.  There were two accidents on space shuttles, which killed a total of 14 astronauts.  The program was terminated in 2011, and since then the United States has been relying on the Russian spacecraft Soyuz to transport astronauts and supplies to and from the International Space Station.  The United States is working on a couple of new programs, which are on schedule for first flights in 2019 and 2020.  Update: The first unmanned flight was docked with the International Space Station on March 3, 2019 and brought supplies to the three astronauts on board.   Further information about space shuttles can be found here.

Radar

Long-range radar antenna, used to track space objects and ballistic missiles.
Source: here

Many of you who grew up in Muggle households probably think of radar as a device used by the military to detect enemy planes and missiles.  Well, that was the purpose for which it was invented, but it has many other uses as well. Radar is a detection system that uses radio waves or microwaves to determine the range, angle, or velocity of objects.  You can imagine it like throwing many small bouncy balls against a wall to see where they bounce back to. A radar bounces waves off an object and studies those that are reflected by the object.  It has many uses besides military: air and ground traffic control, locating landmarks and ships at sea, ocean surveillance, monitoring the weather, geological observations, and (our subject of interest) radar astronomy.  Many astronomical objects have been studied by radar: the Moon, Venus, Mars, Mercury, the four biggest moons of Jupiter, Saturn’s rings and its largest moon, Titan, and a few nearby asteroids and comets. With radar, astronomers get information about the surface of these objects, which we wizards then find useful in our study of how they affect our magic (Lessons Four, Five, and Six will discuss this matter further).  Further information about radar and radar astronomy can be found here and here, respectively.

Rovers

A rover is a vehicle designed to move across the surface of a planet or a moon.  Some have been designed to transport people, whereas others are robots that are either driven from the Earth or are self-driving.  Rovers are used to study the planet or moon they land on by taking pictures, readings of the atmosphere, or samples of dust and rock.  So far, rovers have only been landed on the Moon and Mars, and all of them but one - Yutu, a Chinese lunar rover - were launched either by the United States or Russia. One of those rovers, called Curiosity, launched by the United States, is currently searching for evidence of past or present life on Mars and generally trying to determine whether the planet could ever have supported life.  Further information about rovers can be found here.

Side-by-side images depict NASA's Curiosity rover (illustration at left) and a moon buggy driven during the Apollo 16 mission. 
Source: here

 If a rover can be driven from the Earth, the driver can decide at any moment what is the most interesting place for it to visit.  But to do so, he has to see quickly how the rover is responding to his commands. A signal does not arrive at its destination the instant it is sent; it travels at the speed of light, which is very fast, but if the distance between the source and the destination is too great, the delay makes driving a rover from the Earth impractical.  A rover on the Moon can be driven from the Earth because it takes only one and a quarter seconds for a signal to travel from the Earth to the Moon or from the Moon to the Earth. But a rover on Mars has to be self-driving because it takes at least four minutes, and sometimes as long as 24 minutes, for a signal to travel between the Earth and Mars.

And that brings us to the end of our study of some of the important astronomical tools that have been invented by Muggles.  In our next lesson we will study some of the magical astronomical tools utilized by wizarding astronomers. Meanwhile, you will have two assignments to do, both retakeable.  The essay, which is not mandatory, will require you to summarize some information from an outside source that will be provided.

I see that some of you are already looking at the time.  Well, now that you’re finally free to go … hey, easy now!  You can’t all fit through the door at the same time.