Humans have never travelled outside of our solar system because we are technologically unable to do so. Yet the solar system is only a tiny fraction of our galaxy, the Milky Way, and the Milky Way Galaxy is only a fraction of the observable universe. There are around 100 billion stars in our galaxy, and there are between 100 and 200 billion estimated galaxies in our observable universe. This means that nearly all possibilities of Solar System development are theoretically possible, causing many scientists to conclude that there is a good chance that extraterrestrial life exists.
Most people (including my past self) think that tides are only caused by the moon. While the moon does have a big impact on the tides. The sun also plays a big role in the way the tides move. The moon and the sun both have gravitational forces that pull on the Earth and cause it to bulge out on both sides. When the moon and the sun are aligned with this bulge the gravitational force is stronger because both forces are pulling in the same direction. This is when the tide changes become more drastic. This is called spring tide. And when the sun and moon forces are perpendicular to each other this causes a more average range of tides which is called neap tide. The image below shows the orientation of the moon and sun’s position that need to be met in order to create the high and low tides.
We usually associate tides with the moon because of its gravitational force acting on the Earth. The gravitational force between the sun and the Earth is much stronger than the force between the moon and the Earth. But the sun is so far away that its pull is not as significant as the one the moon has. The moon has less gravitational force but is closer and orbits the Earth, which allows different parts of the Earth to be affected by this pull from the gravitational force.
After meticulously calculating the data that Tycho Brahe collected, Kepler discovered three different laws that described how planets move.
Kepler’s First Law – The planets orbit in ellipses, not circles nor epicycles. For majority of history, it was thought that planets orbit through epicycles because the orbit of the planets must be perfect. However, the planets actually move in ellipses that have eccentricity very close to 1. They may look like circles, but they are actually ellipses since their eccentricity is not 1.
Kepler’s Second Law – The planet sweeps out equal areas in equal time. In a circle, the centripetal force is pointing towards the center and perpendicular to the velocity. Therefore, the force only changes the velocity’s direction, not its magnitude. However, in an elliptical orbit, the force is direction towards the focal point. Therefore, part of the force is in the same direction as the velocity and part of the force is perpendicular to the velocity. So, the velocity not only changes direction, but also changes in magnitude. The velocity begins to increase. As the velocity increases, the planet travels a greater distance getting closer to the sun. For every unit distance that the planet travels, the area it sweeps out for that unit distance traveled gets smaller. So, if the planet travels faster and covers a greater distance during that time, then it sweeps out a larger area than the unit distance. This all averages out in the end. So, for every unit time, the planet sweeps out equal amounts of area.
Caption: This is image from Wikipedia. The velocity vector is green. The diagonal purple line is the net force, which is pointing to the Sun. The two other purple lines are the components of the force, one in the direction of the velocity, the other perpendicular to the velocity vector. If you look very closely, the white lines chop up the pink area into slices of equal area.
Kepler’s 3rd Law – The square of the period of the planet’s orbit around the Sun is proportional to the cube of the distance from the Sun to the planet. Kepler was only able to show that these values were directly proportional. He was not able to figure out the constant of proportionality. It wasn’t until Newton’s Law of Gravitation that the constant of proportionality was determined. More specifically, the constant of proportionality is 4 times pi divided by the product of gravitational constant and the combined mass of the system.
This term, originally coined in the late nineteenth century, at least with its current connotation, began to speak to me in a unique way in high school. I took a backpacking trip in Northern California, and experienced a dry, warm, cloudless night with no shelter but a mosquito net. The sky was brilliant, and it felt like you could see the cosmos move around the Earth. It was here that I first saw the Banner of Heaven, the distinct and almost colorful band of what looks like nebulas that stretches across the night sky. It was not colorful language, it actually looks like a banner.
Nearly all human beings, from the beginning of the species until the twentieth century, regularly slept and lived under it. But after the large-scale adoption of electric lightbulbs, light pollution began to float into our night skies. So, for all of our technological advancements, and all of our knowledge about the universe, modern people live their everyday more emotionally disconnected from the universe than any other people that have ever existed. This is why when I told my friends about the trip, they also seemed pitifully unfamiliar with how the night sky actually looked.
Here is a map of light pollution in the United States:
While it may look a lot like a population density map, the ramifications are quite tragic: most Americans have never seen the night sky. One could certainly theorize about the impact the theft of this aspect of our natural habitat could have on our health, but you wouldn’t need to, the impacts are undeniable.
The lack of true darkness has interrupted our circadian rhythms, in particular our ability to produce melatonin, which light prevents, resulting in difficulty sleeping, anxiety, headaches, and other health issues. Blue light, in particular, associated with screens and LEDs, stimulates our bodies in unnatural and unhealthy ways at night. But it isn’t just humans.
Animals also have been observed to disrupt migration patterns, disrupt their sleep schedules, and even to lose accuracy in their sense of direction due to light pollution.
Those most active and concerned about it, of course, are astronomers. Though it may seem crippling, strategically placed telescopes have become the main sources of data-driven observation for astronomy, so the ability for them to observe themselves is not an issue. What is an issue, however, is that if people themselves are not inspired to look at the sky, especially when they are young, they will not grow the curiosity that it necessary to maintain healthy astronomy communities.
There are many different ways to visualize how gravity functions. However, one of the best way I have found to visualize gravity is with strings and using the center of mass. Gravity is the weakest force of the four fundamental forces, however, it works over an infinite amount of distance. I put this in perspective by assuming every object, especially celestial objects, are connected by a long string— regardless of distance. So, every object, even if it’s at a minuscule scale, is being pulled towards one another. If we think about this in terms of a clump of objects, such as a galaxy, I visualize it more as a tug-of-war between two galaxies. The heavier galaxy is going to win but they both will still be pulled to each other.
The center of mass comes into effect when two massive bodies are close enough together that the force of gravity is strong enough to cause a noticeable physical reaction. If two bodies are approximately the same mass, are connected by an invisible string, and close enough for the force of gravity to cause a noticeable effect, they will begin to orbit each other. Because the two bodies are equal size, neither are winning the tug-of-war so, they will orbit around the middle of the two of them. Likewise, if one of the celestial objects is twice the mass of the other, the larger massed object will have a smaller tighter orbit around the center of mass as the lighter one. If we have a scenario where one object is significantly heavier than the other (such that M>>m) then the heavier object will have such a small and tight orbit that it is nearly undetectable, while the smaller object seems to orbit around the larger one (such as the earth and the sun). There are examples of these as can be seen here. This is the fundamental way that I view gravity.
Pages 48-50 of the Dresden Codex showing some of the Venus Table.
Thousands of years before telescopes and computers, the ancient Mayans had the ability to predict eclipses and track retrograde motion. They are some of the most advanced astronomers of the ancient world. Astronomy was a central part of Mayan culture. Calendars were based on the movements of the Sun, moon, and planets and festivals, rituals, and sacrifices were held on certain days corresponding with these movements.
They also had rich mythology surrounding the cosmos. Venus was especially important within their culture. There are regional variations, but the planet is often affiliated with the god of war and there are tales of battles between the Sun and Venus. The Mayans observed the morning/evening star cycles of the planet with incredible precision and even corrected their calculations over time as the days gradually shifted. Details of their calculations and stories are found in the few surviving codexes from that time, most famously the Dresden Codex.
Even some of their architecture was based on the movements of Venus. At the site of Uxmal, there is a building known as the Governor’s Palace. It is adorned with statues of Chac, a Mayan rain deity, with the symbol for Venus under his eyes. Another site was found directly to the south, and when Venus is at its northernmost point around May and views from here, it’s positioned right above the Governor’s Palace. There is a theory that on this day people gathered at this site to signify the beginning of the rainy season.
To learn more about the Mayans and their astronomical achievements, ask in the comments or check out this article in Science!
The effects of human-induced climate change are becoming more and more apparent over time. Some of the most highly impacted areas are those on the water, who, when facing spring tides, can experience dangerous levels of flooding. Spring tides occur when the Sun and the Moon are exerting gravitational force on the same line, both combining to increase the “bulge” of the water and thus, the extremity of the tides. Neap tides, on the other hand, occur when the Sun and Moon are exerting forces perpendicular to each other, thus counteracting each other and reducing the bulge. At a few points every year, the Earth and Moon are especially close together, and the increased gravitational force creates what are referred to as “king tides,” or more extreme versions of spring tides. It is the king tides that present the biggest threat to areas such as Fort Lauderdale, and show us why we need to pay more attention than ever to the growing threat of climate change. You can read more about how Fort Lauderdale is currently trying to manage these tides here. As a result of glacial melting and extreme weather conditions brought about by climate change, the seas will continue to rise, making the king tides capable of washing away entire cities.
One thing that has always fascinated me is how gravity and time are interlocked. Specifically, people at higher altitudes experience time relatively faster than people at sea level. This is due to a concept called gravitational time dilation. Time dilation comes from Newton’s theory of relativity. Basically, the more gravity you feel, the slower you experience time relative to someone who is experiencing less gravity.
The photo above helps put it into perspective. It shows how people on the International Space Station (ISS) loose roughly 24 microseconds a day due to this effect. Now in the grand scheme of things 24 microseconds a day is nothing relative to a human life, but the whole principle has some funny applications. For instance, if you take a plane flight you are actively speeding up your life.
I remember when I was first made aware of the concept of time dilation. I was watching some documentary or listening to a podcast, I cannot remember specifically, and the person was saying, if you were being sucked into a black hole, and look out towards the rest of the universe, you would be able to see it rapidly aging due to the high gravity you are experiencing. He continued the thought experiment saying, assuming that you are invincible, as you reach the center you would be able to see the heat death of the universe.
