Astronomy, the scientific study of the universe and of the objects that exist naturally in space, is one of the oldest natural sciences to reach a high level of sophistication. The history of this science has impressive continuity and duration, as observed changes would take thousands, millions, and even billions of years.
In 3000 BC, the Greeks became the first to interpret the heavens via models rather than spiritual concepts, and that Earth was surrounded by “spheres/rings.” However, their proposed geocentric model could not explain the exhibited retrograde motion of a number of celestial bodies. This all changed with Copernicus, who made the jump to a heliocentric universe with planets orbiting in perfect circles in the late 1400s. This incorrect assumption was corrected by Tycho, the best naked-eye observer of his time, when his observations planted the seeds for planets orbiting the Sun, and not in perfect circles. His inability to detect parallax led him to conclude that the Earth must remain stationary, which resulted in a model that few people took seriously: the Sun orbiting Earth, and all the other planets orbiting the Sun. Then came Kepler, Tycho’s young apprentice and “diligent calculator,” who trusted Tycho’s observations enough to abandon his previous belief of circular orbits. His key discovery of planetary orbits being ellipses led to his observationally derived Three Laws of Planetary Motion, which serves as a key foundation to modern astronomy today. The Copernican model of the heliocentric universe was finally solidified by Galileo, who had the advantage of the telescopes. This not only allowed him to observe Sun spots, craters of the Moon, and all of Jupiter’s moons, but further enabled him to diffuse any remaining objections to the Copernican view.
Latitude and longitude coordinates are seen everywhere; they’re immensely useful for marking geographic location and helping with navigation. The system is simple enough: latitude is distance north or south from the equator and longitude is distance east or west from the Prime Meridian. But what are the Tropics of Cancer and of Capricorn that are referenced on the map? What is the significance of these specific latitudes?
The region between the Tropic of Cancer and the Tropic of Capricorn encompasses all locations on Earth where the Sun reaches the zenith at local noon, which happens twice a year. The Tropic of Cancer is the northernmost latitude where this occurs, and the Tropic of Capricorn is the farthest south. The sun reaches the zenith at the Tropic of Cancer at the June solstice, marking summer for the northern hemisphere. Likewise, the sun reaches the zenith at the Tropic of Capricorn at the December solstice, marking summer for the southern hemisphere.
But why the references to the constellations of Cancer and Capricorn? Thousands of years ago, when the Tropic of Cancer was named, the June solstice occurred when the Sun was located in Cancer. However, due to the precession of the Earth’s rotational axis, the solstice no longer occurs when the Sun is in Cancer. The likewise is true with the December solstice and Capricorn. Although the timing of the solstices in relation to the stars has changes, it is still much easier to keep the same names rather than constantly renaming these special latitudes.
A solar eclipse occurs when the moon comes in between the path of sunlight and the Earth, casting a shadow on the Earth. Solar eclipses in general are quite rare (only a couple a year), but the moon’s shadow only covers a small portion of the Earth so seeing one is an amazing opportunity. A total solar eclipse, in which the sun is fully blocked by the moon, is even more rare occurring about every year and a half somewhere on Earth. One particular spot on Earth can expect to see a solar eclipse for just a few minutes every 375 years. The next solar eclipse will be on June 21, 2020 and can be seen in a tight strip spanning Africa and Asia. A total solar eclipse will occur on December 14, 2020 and be visible from parts of Chile and Argentina.
A lunar eclipse occurs as the Earth gets in the way of sunlight hitting the moon. The moon turns dark as the Earth’s shadow covers it up. Earth’s atmosphere can make the moon appear red during the eclipse as other colors are absorbed. Lunar eclipses are also very rare due to the tilt of Earth axis causing the Earth, sun, and moon to not line up perfectly every month. Penumbral lunar eclipses are more common than total lunar eclipses and occur when the moon crosses through the large and faint outer part of Earth’s shadow. The next lunar eclipse will be visible from June 5-6, 2020 across Asia, Europe, Africa, and Australia. A total lunar eclipse will be visible on May 26, 2021 in parts of the western US, western South America, and south-east Asia.
Flip a switch. Turn a knob. Push a button. Look in the sky in the day or at night. Each of these actions will allow you to see light, and most people see light as nothing more than an illuminator. Its purpose in the field of astronomy is much more than illuminating the Universe for us to see. Light is the most significant means of measuring just about everything out there. One specific application is figuring out the composition of objects we are looking at.
This is done through spectroscopy, or getting information from spectra, pictured above. An emission spectrum is obtained when a hot, low-density cloud is shone through a prism. Conversely, an absorption spectrum is obtained when a hot light source is shone through a cooler gaseous cloud through a prism. Analyzing the spectra, we see colored lines on a black background or black lines on a continuous spectrum. What does this tell us?
The presence/absence of colors represent a “fingerprint” of an element. In the picture shown, the spectra represent the “fingerprint” of hydrogen. It may seem simple for us then to analyze the composition of objects in the Universe, but the trick comes when objects are made of multiple elements. The spectra would have colored/black lines all over and we’d have to decipher it. Luckily, computer programs aid in this endeavor but nonetheless, it is an application of using light as measurement.
So next time you flip a switch or look at the stars at night, you can think about what elements are present to emit the light you’re seeing. Impossible is the task of knowing, but interesting enough to wonder about.
An intriguing phenomenon that took millennia for the modern human to explain is gravity. First explained by Sir Isaac M. Newton, gravity as a force as a function of mass is a difficult one for many to wrap their heads around. The reason many non-scientists struggle to understand the basics of gravity is because it only comes into play with extremely massive bodies. For example, electrostatic and magnetic forces can move even tiny atoms, but gravity does not begin to have a noticeable effect on bodies until they are massive. Furthermore, even the “weak” nuclear forces that hold atoms together are 10 to the 25th times more powerful than gravity [read more here].
How, then, does our planet orbit a sun 90 million miles away from us if it’s only bound by gravity? The answer lies in physics. The force due to gravity between two objects can be described by a single equation: F = G*(m1m2)/r^2, where G is a constant, m1/m2 are the masses of the bodies, and r is the distance between the two bodies. Analyzing this formula reveals a very delicate balance between mass and distance. As the two objects separate, the force due to gravity becomes exponentially smaller. But as the objects’ masses increase linearly, the total force due to gravity increases exponentially. This helps to explain why our planet, though so far away from the Sun, is still tethered to the sun–because both the sun and the Earth are incomprehensibly massive.
While astrology is widely disproven as a form of science in our modern age, it has its origins in the beginnings of computational astronomy. As explained by David Lindberg in his book The Beginnings of Western Science,
“By the end of the fifth century B.C., Babylonian celestial divination had expanded to embrace horoscopic astrology, which used planetary positions at the moment of birth (or near the date of birth for such exceptional phenomena as lunar eclipses) to predict individual fortunes.”
By the time the Greeks inherit the Babylonians’ methodology, astrology and astronomy are inseparable.
The specific idea of the 12 zodiacs signs (although a 13th one actually exists as well) comes from the positions not of the planets, but of the Sun. As Earth orbits on the ecliptic, the Sun is positioned “within” a specific zodiac constellation during a specific time in the orbit. For example, between July 23 and August 22, the Sun appears to be within the constellation Leo. This is why my horoscope sign would be Leo, since I was born on August 7th.
However, because of precession, these horoscope signs are actually a lie. These signs are based on the positions of the Sun in relation to these constellations from almost 2000 years ago, when astrology began. Earth’s axis has since moved about 1/13th of the way through its precession cycle in that time, so horoscopes are off by about a month from the actual position of the Sun today.
So instead of being a Leo, I guess I have to start embracing my inner Virgo!
Astronomers have declared that our galaxy, the Milky Way is one of the largest two galaxies in our Local Group, rivaled only by its own twin, Andromeda. However, while technology has advanced greatly within the realm of astronomy, we have not yet reached the point of searching beyond the halo of the Milky Way and observing our own galaxy as outsiders. Considering this then begs the questions: How do we know that we are one of the largest galaxies in our Local Group? What evidence points us to the theory that we are Andromeda’s twin?
Let’s first discuss the evidence that tells us that the Milky Way is one of the largest in our local group (so large that other galaxies actually orbit around us!). In the 1920s, it was first believed that the Universe was 300,000 light years across. This was revised shortly after to only 30,000 light years across. However today, astronomers are fairly confident that the Milky Way spans 100,000 to 150,000 light years in diameter. This was discovered by the complex tools of distance measurements that astronomers call “the cosmic distance ladder.” One of the first steps in this ladder is radio waves which are shot out to distances even beyond our solar system so that astronomers can measure the time is takes for the radio waves to come back. The next step in the ladder to uncovering the large size of our galaxy is parallax, which allows scientist to gather distances of close stars within the galaxy. Following this, astronomers use main sequence fitting ( a technique that compares the brightness and color of a far away star to that of a near star) to find the distance to stars that are of even greater lengths from us. Using these techniques, astronomers are able to measure to the ends of the galaxy and get a pretty good idea of how grand our galaxy truly is in comparison to others (Baraniuk).
Yet, this still does not answer how astronomers came to believe that the Milky Way and Andromeda are twins. Previous theories presented Andromeda as three times the size of the Milky Way. Nevertheless, this changed Australian astronomers published an academic article denouncing the previous theory and replacing it with the idea that Andromeda is less than or equal to the size of the Milky Way. Using a measurement technique that measured a the necessary escape velocity of a star leaving the galaxy’s gravity, these astronomers discovered the true size of our neighbor (Parks).
Furthermore, scientist came to discover that the Milky Way is also a spiral galaxy through many clues, the first being the disk of stars that we see in our night sky. This disk of compressed stars can be seen with the naked eye at night and leads scientist to believe that this image is really a look into the disk of our galaxy. Another clue as to the shape of our galaxy is the movement of our stars. Through locating stars’ locations by their rotational velocities, scientist discovered that these stars are located in concentrated spiraling branches, or the “arms” of our galaxy (Peshin). These clues (plus the “duck test” which you can read more on at https://www.scienceabc.com/eyeopeners/how-do-we-know-the-milky-way-is-a-spiral-galaxy.html) give way to the theory that, just like Andromeda, our Milky Way is a large spiral galaxy.
The Voyager 2 is a space probe that was launched by NASA in 1977 in order to study the outer planets. It is still traveling and is now sending back information about the outer solar system and is around 13 billion miles away from earth. There is a record inside the voyager made to display life and the diversity of life on earth. The record comes with directions for playing the record as well as earth’s location. The record can be found here; the beginning of the record is of people of different cultures speaking, and after a few minutes the record gets even weirder. Give it a listen!
Many people have talked about the feeling of walking outside, looking up at the night sky, and feeling small. You look out into the cosmos, see seemingly countless stars, and think that everything you do on earth is just immeasurably small. Despite many people feeling that way, few truly understand the real scope of the universe. Take our own solar system. Personally, as you may know, I’m a big fan of Pluto. Yet Pluto, when compared to the earth, is tiny, not coming close to taking up even half of our size. But it doesn’t stop there. As shown in the picture above, the Earth is barely a spec in comparison to the sun. That might make someone think the sun is a relatively large object in space, and might be fairly important. While that thought process feels right, in reality it is rather laughable. As demonstrated in the video, the sun is barely even measurable compared to other stars, and those other stars are next to nothing when compared to the Milky Way. The Milky Way is about a hundred thousand light years across, a number which seems unfathomable, that there could be anything so large that it takes light hundreds of thousands of years to travel. Yet the Milky Way, when compared to the rest of the universe is also merely a spec. The size and scope of how big things really are is simply beyond comprehension, especially when you have people who think the walk between Commons and Main Campus is far. The universe is bigger than people often think, and it’s important to put that into perspective.