Nicolaus Copernicus (19 February 1473 – 24 May 1543) was one of the most important figures in astronomy history. In order to find a better model to predict planet motions, Copernicus developed the heliocentric theory based on Aristarchus’s work. He calculated both the orbital period and distance to the Sun, providing geometric relationships and therefore strengthening the sun-centered idea. His book, De Revolutionibus Orbium Coelestium(“On the Revolution of the Heavenly Spheres”), triggers a shift from the Ptolemaic model to the sun-centered system, which greatly improves the understanding of the universe.
In 1517, Martin Luther argued for spiritual repentance and opposed Roman Catholic Church’s practice of selling plenary indulgences in the Ninety-five Thesis, which starts the Reformation in Europe.
Contemporary Historical Figure
Leonardo di ser Piero da Vinci (15 April 1452 – 2 May 1519) was one of the most famous figures during the Renaissance. Known for his paintings Mona Lisa and The Last Supper, Leonardo da Vinci is also a great sculptor, architect, and scientist.
Reflection
It is so interesting to put concurrent historical events in loosely related fields together. While someone was looking at the night sky and trying to prove that the Earth is not the center of the Earth, another person was crossing the ocean under sail, leading people to the discovery of a new continent. I start to realize that people never rest on their journey of exploration. In the 15thand 16thcenturies, pioneers challenged the widely-help “truths” or made new discoveries, which eventually brought huge changes in every aspect of the society. Histories in every field are indeed similar: in order to explore the unknown, people experience numerous failures and never stop in quest of truth in their mind, which continuously pushing the wheel of the history forward.
In class, we discussed the implications and mechanics of light travel time. A major takeaway was the concept that because of the incredibly fast yet undeniably limited speed of light we are able to see VERY distant objects as they were VERY long ago.
If you are like me, you might try to see what this looks like at the extremes. So, I found myself asking a question. If we consider angles, would the diameter of an object not have an impact on the image if the center would get to us before the edges? Yes! the size of an object will have an effect on what we see, but the impact is much smaller than one might think. Let’s look at some scenarios:
You are one light year away from 100,000 light year wide, face-on galaxy. Wow! This implies that the center of the galaxy is only one year behind us while the edges are 50,000 years in the past. That means that not only are these edge stars ancient, but they have also moved 50,000 years of traveling from where we see they are. The practical representation of this is our own galaxy, The Milky Way.
You are 70,000 light years away from a 10,000 light year wide, face-on galaxy. So, if you draw the triangles and use some basic trigonometry, you would find that the light-travel time-difference between Earth and the center and Earth and the edges is about 170 years which is about how long it took mankind to determine the universe has accelerate expansion after figuring out how to use stellar parallax which is rather profound. This describes our nearest galaxy, the Sagittarius Dwarf Galaxy.
Now consider a galaxy that is 2,500,000 light years away and 100,000 light years in diameter. In this scenario, the light-travel time-difference is approximately 500 light years between the edges and the center. Which is about the time it took mankind to discover water on Mars after Copernicus proved the Earth orbited the Sun.
First, I will address 2 and 3. In these scenarios I have described hundreds of years of difference in the position of the center and edges of galaxies. Could this describe why galaxies look spirally? In short, no. The spiraling effect this would have would be minimal and constant unlike the drastic and ever changing winding that takes place in spiral galaxies. This is understood when you consider the scale and speed of these galaxies. If our solar system and galaxy are typical then the average star orbits a galaxy at 0.0000004% of a rotation per year which means that for case 2 the position of the edge stars are only a mere 0.00007% percent of the full circle from where they should be, and for case 3, the number only rises to 0.0002%.
Okay, so lets do the same thing for case 1. The number only changes such that the furthest star in our own galaxy is 0.02% of it’s orbit behind where we expect it to be.
If anything this is a testament to how immense the universe is. That the time difference between two images can be so large and the macrostructure of galaxies appear unaffected is amazing.
If you want to see how dark matter affects the winding of galaxies, here is a video.
Kinda related both of those things, today I’m going to be asking: “Where did the idea that the Moon was made of cheese come from?”
To start, I did a simple google search which lead me to Wikipedia. It turns out that people never believed the Moon was made of cheese. ~suprise~ But, it did potentially start as a folklore with that as the plot. Supposedly, a conniving Fox tricked a Wolf into descending into a well with the lure that the Moon’s reflection was cheese inside the well.
So then I thought, “When was cheese even invented? Like, could relatively modern astronomy be more recent than cheese?” Turns out that is a fat no. Another quick google search showed that cheese is has been around since circa 5500 BC well before the first telescope was even considered.
I mean it’s not totally unreasonable to believe that ancient people much like modern people are susceptible to horrific theories. Look at the Flat Earth Society. So, a sect of counter culture ancient people could have very realistically made up this theory when they were bored of farming.
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“Stellarium is a free open source planetarium for your computer. It shows a realistic sky in 3D, just like what you see with the naked eye, binoculars or a telescope.”
– Stellarium webpage
Stellarium is an amazing bit of software to use for help with astronomical observing. It is free and you can download it here. It has many different functions, but the most useful allows you to enter your actual location, and the time that you will be, were, or currently are observing the sky above you. (In fact, you can see the night sky from any location in the world, from any time in the history of Earth – past, present, or future.)
Then the software will show you which stars in the sky will be visible to you! Whats more, the program’s many different functions will show the different names of the stars, map out constellations, and even give you an idea of the atmospheric conditions (most importantly, the sunlight) during your time observation. In short, Stellarium is a super-useful tool if you are planning an observation night!
A page from a children’s book I wrote as a first-year. From left to right, Tycho Brahe, Johannes Kepler, Galileo, and Copernicus.
I thought to start out the semester, I would look back and provide a little context for myself and everyone else as to how we as humans used to do astronomy. I learned some of the basics of the history of astronomy in a class called the Scientific Revolution. We discussed some of the big astronomical names during the Middle Ages, including Brahe, Kepler, Galileo, and Copernicus, and the contributions they made to the field.
The most recent, and probably most popular, is Galileo Galilei. Obviously, Galileo was very conspicuous in his views, popularizing the heliocentric model. But he also improved upon the traditional refracting telescope, and through that, discovered Jupiter’s largest 4 moons, now named after him as a group. He also spent lots of time observing the moon. Being able to see craters, he made the claim that heavenly bodies were not themselves perfect, which in large part made him so controversial.
Also a pioneer in observational astronomy, Tycho Brahe was a character. I would like to talk about his massive amount of wealth allowed him to build the most complicated and accurate observatory of its time, but I really just want to mention the weird life this Dane lived. He was consistently portrayed as having a silver or bronze nose because, when he was younger, he got a duel over a mathematical proof. In the duel, his nose was cut off, as you may have suspected by now. In case that isn’t ridiculous enough, he once lent his pet moose to a fellow noble as party entertainment. The moose proceeded to get drunk and fall down some stairs to its death. Gizmodo has a fun article that goes a bit more in depth on the guy.
Brahe’s successor, Johannes Kepler, was unfortunately not as inherently wild. However, he did come up with what are called Kepler’s Laws. His first states that the planets move in ellipses, which came as the miracle to solving Mars’ motion at the time.
Finally, we have the man that started the whole shebang. Nicolaus Copernicus was one of the first “modern” astronomers to propose the heliocentric model. The reason that he did so without much notoriety at the time was that he published his work with a foreword mitigating the implications of a model outside of the field, and did so keeping most of his work hidden until right before he died. The Copernican Tables contain about 40 years-worth of meticulous observations that sparked the Copernican Revolution, only to contribute to the larger Scientific Revolution.
If there’s one straightforward lesson from astronomy, it’s that we’re tiny. We’re small compared to the Earth’s vast size, which is small compared to the sun, which is tiny compared to the space that contains our solar system, which is a tiny dot in one arm of the Milky Way galaxy, which is one of roughly two trillion galaxies in the observable universe.
It’s almost impossible to try to grasp the universe’s size directly. Because it’s far beyond the size of anything we interact with daily, it’s hard to comprehend. It’s easier if we scale it to the size of the United States, and see how big it makes things we’re more familiar with (e.g. the size of the universe). We can go step by step through some of the steps between the size of the Earth and the size of the Milky Way.
To begin, we need the size of the United States. We can use the distance from Portland, Maine to Los Angeles (about 2,600 miles) as an estimate of its size. This lets us start to scale. The Earth’s diameter is about 12,700 km, but the distance to the Moon is 384,000 km. So, if we scaled down the Earth and the Moon to put the Earth in Los Angeles and the Moon in Maine, the Earth’s radius would be about 86 miles. If one “corner” of the Earth were in Los Angeles, the opposite side would only reach about halfway to Nevada.
The Sun is much further away. The Sun is about 150 million km from the Earth, almost 400x further than the Moon. If we scaled down the universe to fit the Sun in Maine while keeping the Earth in LA, the Earth would only be .22 miles wide. Viewed from above, a circle containing the Earth would .6 square miles – .1% of Los Angeles’s actual 487 square miles.
This shows how little space the Earth truly takes up, relative to its distance from the Sun. But what if we go a step further? What if we put one edge of the Milky Way in Los Angeles, and the other side in Maine? The short answer: things stop making sense. The Milky Way is 1,000,000,000,000,000,000 km across, or 621 million billion miles. To scale that down the to the size of the US (2,600 miles), the Earth would become 53 nanometers. A fingernail is somewhere around .4mm thick. So if we scaled down the Milky Way to the size of the US, you could fit 7,500 Earths side-to-side and it would only be as wide as your fingernail is thick.
About 1/50th a hair’s width. That’s the size of the error which seriously set back the Hubble telescope. Perkin-Elmer diagnostics was tasked with grinding down the primary mirror, a 7.8 foot wide *almost* flat surface. The mirror’s curvature was determined by a reflective mirror array which bends a laser to precisely trace the surface’s desired arc. A lens in the reflective corrector was misaligned by a millimeter [1], which projected a barely askew curvature and was not corrected until NASA investigated why Hubble’s images were coming back blurry. In order to rectify the aberration a new set of lenses (known as COSTAR, since replaced in 2009) were manually installed by astronauts in 1993, three years after the Hubble’s launch [2]. Here, look at this before and after of M100, both taken by Hubble. It’s clear that COSTAR was a necessary replacement so that Hubble can clearly see the distant objects it was designed to focus on- the telescope can track targets as small as 0.05 arc-sec, the size of a dime 86 miles away [3].
M100 in 1993, before and after the corrective servicing. Credit: NASA
While searching for a website that is useful for observing the solar system, I found the NASA Solar System Exploration website. The landing page rotates through all of the planets in our solar system and provides quick facts about each planet. Currently, listed below this display are facts telling the time until a total lunar eclipse, number of planets in our solar system, and number of planets beyond our solar system. Another number listed describes the one-way light time to Voyager 1. The Voyager 1 space probe was launched by NASA in 1977, and it is the human-made object that is furthest from Earth. The webpage contains dropdown bars for the Solar System, Planets, Moons, and Asteroids, Comets, & Meteors. These options make it easy to quickly explore essential elements of space and learn about them in depth. For example, from reading into some planets and asteroids, I found that each individual page contains the same key sections; Overview, In Depth, Exploration, and Galleries. When comparing it to other websites that provide similar information, I believe that the NASA Solar System Exploration website is the best site to reference. It is easy to navigate and provides an abundance of information in a format that isn’t too overwhelming. I would recommend it to anybody trying to build a foundation of knowledge about space!
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An animation illustrating how the Earth precesses, or “wobbles,” on its axis. This gif was created by me using footage from a Youtube video published by Steven Sanders.
What if I told you that in a couple thousand years from now, your Zodiac sign would no longer be your Zodiac sign? It may be devastating to devout followers of astrology, but the relative positions of the Zodiac constellations are changing very, very slowly, at least from our viewpoint. This is due to a process called precession, the continuous, gradual wobble that changes Earth’s axial orientation in space. The Earth really is like a spinning top – just an extremely slow one. In fact, this top only makes a complete spin every 26,000 years.
Because Earth protrudes at its equator, the planet is not quite a perfect sphere. The equator is also tilted with respect to the ecliptic plane, and as a result, the gravitational attractions of the Sun and the Moon attempt to draw the equatorial bulge into the ecliptic plane. In simpler words, gravity from the Sun and the Moon tries to pull the Earth into straightness. However, because Earth tends to keep rotating, gravity fails to straighten out the Earth and instead causes the axis to precess.
It is not likely that we will see any major changes during our lifetimes, but the night sky will look a lot different thousands of years from now. The North Celestial Pole is pointed toward the star Polaris now, but in 3,000 BC, the North Star was actually Thuban, a star in the constellation Draco. In roughly 12,000 years, Vega, a star in the constellation Lyra, will be the new North Star. Precession also alters the points in Earth’s orbit at which equinoxes and solstices occur; this means that in 13,000 years, the seasons on Earth will have switched times of year.
An animation that illustrates how the North Celestial Pole (NCP) moves in relation to the North Ecliptic Pole (NEP) over a 26,000 year period. This gif was created by me using footage from a Youtube video published by Steven Sanders.
Matchbox Twenty’s Bright Lights. CeeLo Green’s Bright Lights Bigger City. My personal favorite is Sara Bareilles’s Bright Lights and Cityscapes.
There is no shortage of songs about bright lights–perhaps it’s a testament to how prevalent we’ve made them. Think about it for a moment: We love candles and think they improve any occasion. We’re scared of dark alleys, so we’ve dotted them with streetlights. All of this, however, comes at a cost.
Light Pollution
What is light pollution? It is a familiar concept disguised in a term that not everyone might know. Light pollution is simply the phrase to describe excessive light in an area and all the consequences that come along with it. There are four main components to it:
This component of light pollution is often the most familiar to people and simply describes the brightening of the sky around highly populated areas. In the picture above, you see that the area of cloud immediately above the city is a light orange and fades closer to black as you move away from the city. You might be surprised to learn that a certain amount of sky glow actually comes from natural sources! These include sunlight reflecting from the moon and starlight scattering in the atmosphere, but don’t really come into play with the type of light pollution we’ll be talking about. Most of the negative effects of sky glow come from man-made light such as streetlights or building lights. Interestingly enough, the brightening effect becomes exaggerated in dusty or cloudy environments as the light bounces off the tiny particles in the air. This means that the areas with poor air quality (many particles in the air) will experience more sky glow from less light.
This is the component of light pollution that most affects astronomers. Over time, skies have only gotten brighter and fewer areas than ever are able to see the Milky Way Galaxy. It also means all but the brightest stars are no longer available to a casual backyard observer. For many, this means that any sky-watching session requires at least a half hour drive from home.
2. Light Trespass
This is a component of light pollution that affects your personal health–it describes light that crosses boundaries into areas where it is no longer desired. You may have experienced this firsthand on a sleepless night as a light outside your bedroom window streamed mercilessly through your blinds. If so, then you understand how this type of light pollution can hurt our quality of life. Luckily, it is easy to cut down on this type of light pollution by changing the shape and types of lamps that we use along our streets.
Unfortunately, we are not the only victims of light pollution. When unnatural light reaches places it should not, wildlife can be harmed in the process as well. Countless sea turtles, who rely on moonlight to guide them home, have been led astray by streetlights along the Florida coastline. Many other animals who rely on the natural light and dark cycle have also developed irregular feeding and mating behavior.
3. Glare
Glare is another type of light pollution that can be detrimental to our personal happiness. This is an unpleasant type of lighting that can bother you even if you’re not trying to sleep, because it affects your vision at night. It is an irony of light pollution as extra brightness results in lowered visibility. Glare is the result of excessively bright lights and forces you to squint. The uncontrolled light becomes the brightest object and actually interferes with your ability to see important things such as a driveway or the sidewalk. The key detail of this component is that it causes physical discomfort in people. It can be annoying, or even painful.
This last type of light pollution is a combination of the last three. When too many lights are placed too close together, it becomes distracting and difficult to understand what you’re looking at. It results in a generally brighter ambiance in an area and prevents our eyes from ever becoming fully dark-adapted.
This and other types of light pollution can be dangerous in urban areas because, without dark-adapted vision, any area that isn’t well-lit becomes disproportionately dangerous. The distraction that the excessive lights create can also lead to accidents when drivers can’t figure out what they’re seeing in time.
While most of us know of light pollution as something that only affects those who want to see more stars from their backyard. By breaking down all the types of light pollution that exist, however, we see that light pollution is more than that and is detrimental to many different aspects of our lives. It is not only a tremendous waste of resources, but also harms our quality of life. Whether or not you’re an astronomer, light pollution has an effect on you.
and you can download it 
