Newton and His Laws

Isaac Newton is a household name for his invention of calculus, laws of motion, and realization that gravity exists in the heavens (contrary to Aristotle’s beliefs!). College students that have studied introductory physics or math may have been exposed to Newton’s three laws of motion, but how exactly are they relevant in the context of astronomy? Let’s restate them and provide some astronomical context:

            Newton’s First Law: an object moves at a constant velocity (or stays at rest) unless acted upon by an outside force. This law explains why the spaceships we launch do not need fuel after they are in space; without air resistance or friction in space, ships can simply move at a constant velocity without a need for thrusters (hint: a net force!). 

            Newton’s Second Law: mass multiplied by acceleration equals force. Large planets can exert a greater gravitational force on, say a comet, than a smaller planet would—mass is a direct factor in the determination of force (stay tuned for a future post on the Universal Law of Gravitation). 

            Newton’s Third Law: each force has an equal and opposite reaction force. Celestial objects, or any objects for that matter, exert forces on each other. You heard that right—that same gravitational force that keeps you grounded to Earth is also being exerted on Earth by you! 

From The Science Explorer

While this brief blog post is not an exhaustive astronomical explanation of Newton’s laws, I do hope it provided a little more context than simply F = m • a.  

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Tidal Friction: a 5 hour long day to a month long day

Due to the Universal law of gravitation, we know that objects of equal mass have a larger gravitation force between them when they are closer together. Because the near side of the Earth is closer to the Moon than the far side of the Earth, the force between the Moon and the near side of Earth is greater than the force between the Moon and the far side of Earth. This difference in forces causes the Earth to stretch along the Earth-Moon line, which causes a bulge on the near side of the Earth and a bulge on the far side of the Earth. This stretching is caused by a “tidal force” and causes the rising and falling of tides on Earth as the Moon continues its orbit.

George Darwin, Charles Darwin’s son, was the first to mathematically illustrate the theory of tidal friction. Tidal friction occurs because, as the Moon continues along its orbit, the Moon’s gravity attempts to pull the bulges right along with it, while the Earth attempts to pull the bulges along with it as it rotates. A torque is produced and a friction between Earth and the tides slows down the rotation of the Earth. Due to the conservation of angular momentum, the Earth’s loss of angular momentum becomes the Moon’s gain of angular momentum1.

This transfer of angular momentum results in the slowing of Earth’s rotation and the growing of the Moon’s orbit. These changes occur very slowly; the length of a day increases by about 1 second every 50,000 years1. However, these seconds add up and it is likely that early Earth had a day of only about five or six hours and the Moon was far closer to the Earth than it is now1. Tidal friction also explains the synchronous rotation of the Moon; as the tidal force from the Earth slowed the Moon down, it eventually rotated at the same rate as its bulges1. Eventually, the Earth could have a synchronous rotation toward the Moon and have days as long as its months. However, this likely would not last consistently due to the tidal forces of the Sun.

[1] Bennett, Jeffery, et al. The Cosmic Perspective: The Solar System. 9th ed., Pearson, 2020.

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Wanderers of Space

In this post we will talk about the concept of retrograde motion. If you watch the movement of planets, it is actually quite complex. The word planet comes from a greek term meaning “wandering star”. Planets typically move eastward throughout the constellations. When there is apparent retrograde motion the planets are moving westward throughout the constellations. The reason why it is apparent is because we aren’t always able to see it happen. These times of retrograde motion can last weeks to months depending on the planets. To explain the concept simply the planet is always is moving east, but as earth catches up to the planet, it appears to be moving backward as we pass it. This cycle repeats as we orbit the earth. The farther or closer away earth is from a planet determines how wide the range of retrograde motion is. What’s interesting is that people who used to believe earth was the center the universe, had a very difficult time trying to explain what was happening. Retrograde motion

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Stonehenge and Archeoastronomy

Sunrise over Stonehenge on the Summer Solstice; Photo by: County Line Magazine

Stonehenge is one of the most easily recognizable sites across the globe. Often designated as one of the wonders of the ancient world, Stonehenge has both fascinated and confounded humanity for centuries. While some may still argue about how Stonehenge came to exist, whether it be aliens, magic, or old-fashioned hard work and sweat, one thing remains almost uncontestable: Stonehenge’s use and significance as an astronomical site. Perhaps the most striking display of Stonehenge’s relation to astronomy comes during the Summer and Winter solstices, when the sunrise and sunset align with the Heel stone, a significant monument in the site’s organization. It has been theorized that this alignment was used by ancient peoples to serve a variety of purposes, from tracking the seasons to ritual and cult practice. What is interesting about this alignment though is that it is not an exact alignment. While this could be an indication of humanity looking too deeply into the significance of the structure, William Stukeley, an 18th century scholar, hypothesized that the alignment may have drifted over the centuries due to changes in the solar system’s ecliptic obliquity. This change is something that Stukeley believed the builders of Stonehenge hadn’t known about, and thus its construction didn’t account for. Whether this is truly the case or not remains unknown, but the striking image of the Summer solstice’s sunrise over the central circle, and its alignment over the heel stone is a sight that is not readily forgotten.

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The Hubble Space Telescope

The Hubble Space Telescope is one of humanity’s greatest achievements. Deployed in 1990, the telescope is responsible for many of the discoveries made about distant solar systems and galaxies. According to the Nasa website, the Hubble “has made more than 1.4 million observations.” Without this great invention, we would still in be in the dark when it comes to a visual representation of our Universe.

The Hubble Space Telescope

Following the launch of the Sputnik by the Soviet Union in 1957, the United States began devoting more time and money into space travel and research, in an effort to beat the USSR to the Moon (which we did). However, even after the Moon landing was a success, the United States remained interested in space exploration. In 1977, the United States Congress approved funding for the Large Space Telescope project. As the construction and planning for the telescope began, Nasa was simultaneously training astronauts for future telescope service mission. In 1983, the telescope was officially named after late astronomer Edwin Hubble, who made the important discovery that other galaxies in the universe existed and that they were travelling away from the Milky Way. Finally, in April 1990, the Hubble Telescope was deployed and it took its first pictures about a month later.

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Examining Historical Astronomy Through the Lens of Fiction

Humans have been studying the skies for millennia with our theories about how space works evolving and growing over the same amount of time. Today, our understanding of astronomy is based primarily on natural and mathematical laws that allow us to evaluate and understand the heavens objectively. However, humanity’s understanding of astronomy has not always been so scientific. I want to look closely at a few historical conceptions of astronomy, namely celestial spheres, the geocentric model of the universe, and astrology, and evaluate them through the lens of a piece of fiction in which all of these now-debunked concepts hold true: The Elder Scrolls V: Skyrim.

The Elder Scrolls V: Skyrim is a fantasy RPG video game set in an entirely fictional universe ruled by magic rather than science. The world in which this game takes place is filled to the brim with rich and complex lore, including lore about how astronomy works in-game. Consider this illustration that depicts the actual model of the cosmos in The Elder Scrolls universe.

This awesome illustration was created by the artist Okiir. You can find this piece, as well as the artist’s other works, at their DeviantArt site.

The Elder Scrolls universe is an example of a geocentric universe, with Nirn (The Elder Scroll‘s version of Earth) lying right in the center of the cosmos. Moreover, the “celestial spheres” model of cosmology is also utilized, with stars being holes in the celestial sphere called Aetherius, rather than actual fusion-powered balls of plasma as they are in our universe.

What’s most interesting is the power and influence of astrology in The Elder Scrolls. There are thirteen constellations, each with their own corresponding months; those born within a constellation’s month are considered to born under the sign of that constellation. Unlike our own universe’s astrology, which has been reduced to a pseudoscience, one’s astrological sign in The Elder Scrolls has a major influence on one’s characteristics and life path. For example, those born under the sign of The Lady are kind and tolerant, while those born under the sign of The Thief are risk-takers who seldom live as long as those born under other signs. (If you are curious and want to know more about the zodiac of The Elder Scrolls, you can find more information here.)

It’s interesting to note just how many hoops the creators of The Elder Scrolls had to jump through to make a geocentric universe comprised of celestial spheres in which astrology dictates the course of people’s lives and personalities. I’ve read lots (and lots and lots) of articles and in-game books trying to explain the function of The Elder Scrolls cosmos scientifically, but it’s pretty much impossible. All of the deviations from our own universe are pretty much just brushed under the rug under the guise of “magic”. Of course, the magic (and all that the existence of magic entails) is really what makes The Elder Scrolls V: Skyrim so fun, but it also makes it wildly scientifically inaccurate.

Examining the connections between The Elder Scrolls and real astronomical theories of history makes me appreciate our modern understandings of the universe so much more. Instead of being condemned to an early grave by my astrological sign or being burnt to a crisp by a dragon, I can spend my time studying astronomy as a science rather than a pseudoscience. I certainly love The Elder Scrolls, but I couldn’t be happier to live in a universe that actually makes scientific sense!

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Gravity of a Mysterious Object

Credit: Caltech/R.Hurt (IPAC)

We know that there are 8 planets in the Solar System. This is a fact. You would be crazy to think that there is a 9th planet out there orbiting beyond Pluto. After all, if there was a 9th planet, why haven’t we seen it yet? Well, meet Konstantin Batygin, a professor of planetary science at Cal Tech. He believes that there is a huge planet 5 times the size of Earth that has not been discovered yet.

The first question that must be addressed of course is why we haven’t seen the mysterious planet. To answer this, we need to discuss light and telescopes. With the planet so far away, it only reflects a very small portion of the Sun’s light, and thus can only be seen with the Subaru Telescope in Hawaii. In class, Dr.G mentioned how it is difficult to get time on large and powerful telescopes. This is the same case with the Subaru Telescope, as Professor Batygin only gets 3 days out of the year to search the entire sky for an extremely small light source.

As for the evidence to why a 9th planet could exist, the answer lies in gravity. We know from Kepler’s laws that gravity affects the orbits of celestial objects. Batygin and his team discovered that Sedna, an object 3/4ths the size of Pluto, has an irregular orbit that takes 11,000 years to complete. This means that Sedna was being influenced by an additional gravitational force other than the Sun. 6 other Kuiper belt objects were found to be pulled in the same direction as Sedna, indicating a massive external gravitational force exerting itself on these objects. Batygin believes that this object could be another planet, while other scientists have proposed the source as a primordial black hole. If this object is indeed another planet, our Solar System will again regain its status as a 9-planet system.

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Blog #2: Archaeoastronomy at El Castillo

Image of El Castillo Temple in Chichen Itza

El Castillo, also known as The Temple of Kukulcan, is a ceremonial structure in service to the Mayan deity of Kukulcan, ” the feathered serpent god”. The mesoamerican temple is the central architectural structure of the Chichen Itza archeological site located in the Yucatan peninsula of Mexico, and was constructed by the Maya around 800 CE. This structure although religiously significant to the Maya, also demonstrates their astronomical knowledge. First of which, the structure acts as a physical demonstration of their Mayan Calendar. On each of the 4 sides of the building there is a set of staircases, facing the cardinal directions, with exactly 91 steps leading to top and final communal stair for a total of 365 stairs or the total number of days in their calendar. Also the structure is compose of 18 terraces equalling the number of months in their year.

Also, on the Fall and Spring equinoxes the position of the Sun cast an image over the stairs of the temple. During those periods the sun is at such an angle where the terraces of the temple block the Sun’s light only allowing certain sections of light to pass through and illuminate segments along the staircase. These areas passing down the staircase form the body of a serpent and as they reach the end of the stairs they meet with a sculpted snake head at the base of the monument to form the full serpent. This occurrence, know as the descent of the serpent, is seen in the photo below.

Image of El Castillo during the “serpent’s descent”
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Eppur Si Muove

… were the words (supposedly) quietly uttered by Galileo following his trial with the Catholic church. The Church disapproved of his support of the Copernican system which depicted the Sun being at the center of our solar system with Earth orbiting it. This contrasted with the Church’s view that we were at the center of our universe and that all things, including the Sun, revolved around us.

            But in contrast to the classic science vs. religion clash, the man responsible for the Copernican system, Nicolaus Copernicus, actually maintained a very positive relationship with the Church for much of his lifetime. In fact, according to The Christian Science Monitor, Copernicus even spent time serving as “a canon of the cathedral chapter of Frombork … and he served the church of Warmia as a medical advisor”. Contrary to popular belief, the Catholic church initially accepted Copernicus’ ideas surrounding heliocentricity but, following criticism and opposition from the Protestant church, the Catholic church ultimately banned Copernicus’ book in 1616. Oddly enough, as more evidence supporting heliocentricity arose, the Protestant church began to support Copernicus’ work but the Catholic church did not follow suit until 1822, when the bans were lifted on Copernican views.

Nikolaus Kopernikus.jpg
Nicolaus Copernicus via Wikipedia

            Learning this lead me to wonder why there is such heavy emphasis on the Church vs. science conflict when, in reality, the dynamics were not as black and white as often presented. Additionally, I wonder about what caused the Catholic church to hold on to Copernicus’ beliefs for so long, but later, be so hesitant to return to them. What are your thoughts? Please share below (:

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waves and particles and dualities oh my

What is light? It’s a simple question, really. And simple questions have simple answers, right?

Sometimes they do, yes.

Pink Floyd’s The Dark Side of the Moon cover art depicting light refracting through a prism

But, tragically, this time it doesn’t.

Most people know light acts light a wave. It refracts (thanks Pink Floyd), reflects, and diffracts just light waves are supposed to. Similarly, the electromagnetic spectrum illustrates the wave-like properties of light. Different forms of light (infrared, visible, ultraviolet, etc.) have different wavelengths and frequencies which can found in the glorious equation of fλ = c, where f is frequency, λ is wavelength, and c is the speed of light.

So light acts like a wave – this much we know. But is that the end of this unfortunately long story. By now I hope you can guess that no, it is not.

illustration of the photoelectric effect

The light-as-only-a-wave theory worked very well until some scientists discovered the photoelectric effect. Essentially, an experiment showed that when light was shined onto a sheet of metal, some of the electrons that were initially on the sheet were ejected off in response to the stream of light. This ejection of electrons was then called the photoelectric effect. Given the photoelectric effect, scientists hypothesized that light existed in discrete packets of energy, called photons. When these photons struck the metal sheet, their energy was absorbed by an electron, which was then ejected from the sheet. Therefore, people concluded that light, in addition to acting as a wave, acts like a particle.

So, is light a wave? Yes.

Is light a stream of discrete particles? Also yes.

It is both? Technically, also yes.

Is it neither? At this point, honestly who knows.

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