Due to Earth’s counterclockwise rotation, many objects in the sky like the Sun rise in the east and set in the west. However, planets such as Mars exhibit apparent retrograde motion, where they appear to reverse direction in the sky and move from west to east. This is a result of planets orbitting at different speeds than Earth and thus, Earth passes or is passed by these planets during its orbit. The ancient Greeks noticed this retrograde motion but rejected the possibility of Eart rotating the Sun since they didn’t believe the stars could be far enough to not detect stellar paralax. Instead, figures such as Aristotle developed complex motions for planets that involve an extra loop accounting for retrograde motion. After the Copernician model of the solar system, retrograd motion no longer remained a mystery.
Retrograde motion is one of the apparent motions of planets relative to the background of the stars. If we continue to track a certain planet for a period of time, we will find that it sometimes moves to the east, sometimes stops for a short time, sometimes moves to the west, then makes a short stay, and then moves to the east as it did at the beginning. In order to explain this phenomenon, the epicycle-deferent model was born. This geocentric model dominated for two thousand years until Kepler’s three laws were proposed.
So, what causes the retrograde motion of the planets? Actually, they are not really retrograde. The earth is closer to the sun than many planets, so the earth moves faster. Whenever Earth overtakes a planet, the outer planets appear to start receding in the sky. From Earth, Mercury and Venus appear to oscillate on either side of the Sun. These planets all do circular motion around the sun, it’s just that here on Earth, it looks like the planets are going backwards.
Today I learned about the nuances of thermal energy that answered a forgotten question from my childhood. When I was little I was always afraid to stick my hand inside a hot oven because I knew how badly my tongue gets burned whenever I drink something hot. However, when I finally did stick my hand inside a hot oven for a few seconds, it turns out that it didn’t burn me as much as I thought, and I briefly wondered why. Now, ten years later, I know that even though the temperature looks really high (about 450 degrees Fahrenheit), what really determines whether something is hot or cold is thermal energy. Thermal energy depends not only on temperature, but also the number and density of particles. So the reason why the air didn’t burn as much as the water did is because air is less dense than water, drinking the water meant many more molecules struck my tongue each second, and more thermal energy was transferred.
Light waves travel through electric and magnetic fields that vibrate perpendicular from each other. As an electromagnetic wave, like all waves, light’s vibration has a direction along with its frequency and wavelength. We often imagine waves moving up and down vertically, like a wave on the shore, but this is not always the case. Specifically, the polarization of an electromagnetic wave is the orientation of vibration of the electric field.
You may own sunglasses that mitigate glare, which is often caused by light with a horizontal polarization reflected off of a horizontal surface. This type of sunglasses contains a polarizer, which absorbs incoming light that vibrates horizontally and transmits vertical light.
In 2019, the Event Horizon Telescope captured the first ever photo of a black hole. The same black hole, centered in the Messier 87 galaxy some 50 million light-years away, was captured again in 2021 with polarimetric imaging tools that recovered and visualized the light’s polarization. This new perspective allows astronomers to measure how magnetic fields influence matter near the event horizon of the black hole. While the original photo depicts the brightness of the surrounding light, the second depicts its direction.
Astronomy is a science. This means that in astronomy we make predictions, test hypotheses, and use findings to continuously build and refine our theories. Interestingly, astronomy was very likely the first science. Humans, ever since the ancient civilizations, have looked to the sky and pondered its mysteries.
What use would such people have in astronomical science? Consider the importance of keeping time. Keeping time has a broader goal than being able to tell what hour of the day it is. Time is important for farmers and their crops—the changing of the seasons dictates what can grow. Time is also important for religious holidays that must fall at the same time each year. Time is also important for further astronomical observations, and we see it as a variable in many relevant equations.
Here is a photo of an ancient Egyptian sundial, used to keep time. It is taken from Wikipedia.
Tides are definitely one of the most mesmerizing phenomena in the world. The tides are the rise and fall of the sea level caused by the gravitational pull of the Moon and the Sun. The Moon has a strong gravitational pull that causes tidal ocean currents while the sun’s pull is way weaker because it is farther away.
An interesting fact about tides is that they can affect and play a role in the movement of some objects in our solar system. For example, a recent study showed that the tides on Jupiter’s largest moon, Ganymede, generate a good amount of heat, which contributes to its overall internal warmth. Tide could show us that there might be life outside Earth. For example, the observed tides on the Saturnian moon, Enceladus, shows that hat geyser-like jets spew water vapor and ice particles from an underground ocean beneath the icy crust of Enceladus. So this made it a promising object to study creating hope for a possibility of extraterrestrial life.
In class, we’ve been diving into the world of gravity and light. We have covered Newton’s laws of motion and the effects of gravity in our universe. As well, we’ve explored how light behaves and travels through space.
Now I want to introduce another intriguing topic that combines the two –gravitational lensing!
Broad Visualization of Gravitational Lensing. Source: NASA/ESA
Gravitational lensing occurs when light is magnified or distorted by the gravitational pull of incredibly massive bodies (i.e galaxy clusters).
As a result, we can see distant objects that would otherwise be invisible. This effect also gives us a unique way to study the distribution of matter in the universe.
On the simplest level, gravitational lensing occurs when there is a single concentration of matter that redirects light from a distant galaxy to produce multiple images of the background galaxy. Perfectly symmetrical lensing results in a complete circle of light, which is called an Einstein ring.
Gravitational lensing has some powerful uses for astronomers. Currently, it is being used to map the distribution of dark matter in galaxy clusters. As well, the observations of gravitational lensing have extended our views deeper into the universe by amplifying the light from distant galaxies!
In all, gravitational lensing is a captivating part of astronomy that combines our understanding of light and gravity. I am eager to learn more about these topics and explore the ways in which they showcase the workings of our universe.
(If anyone wants to read more in-depth – click here!)
The ancient Mayan civilization, which existed from approximately 2000 BCE to 1500 CE in present day Mexico and Central America, had a highly advanced understanding of astronomy. They used their astronomical knowledge for many things, including religious rituals, calendar systems, and timekeeping. Their primary focus was on tracking the movements of the sun, moon, and planets, especially the cycles of Venus. Their astronomers managed to calculate the cycle of Venus to within 2 hours of its actual orbit.
The Mayans built many structures to support their astronomical observations, including pyramids, temples, and observatories. The most famous of these structures is the Temple of the Sun in Palenque, Mexico, which is aligned with several solar events. These various events created different sunlight effects within the temple, which the Mayans used to determine when to plant and harvest crops, among other things. They also created accurate calendars that were based on astronomical observations and were used to track the passage of time, as well as to mark significant events such as eclipses, solstices, and equinoxes. The Mayan astronomical knowledge was so advanced that they had accurate eclipse predictions before almost any other world cultures, and their body of observations rivaled the Ancient Greeks.
The short tide video we saw in class made me curious about tides. I looked into the relationship between the tides and the Moon, similar to what we had to do at the end of Homework 4. I wanted to share some of my findings.
Both the Moon and Sun contribute to tides on Earth. However, the Moon has a greater impact on tidal motion. This implies that tides cannot be a result of gravitational force as the Sun’s influence is significantly larger than that of the Moon. Like we found out in Homework 4, the gravitational force of the Moon changes with location on the Earth. This is because the Moon is relatively close to the Earth so distances between the near and far side of the Earth make up a small, but noticeable portion of the overall distance. This difference in gravitational force coupled with the orbit of the Moon are actually what cause tides. Water is constantly influenced by the Moon with the result being the bulging on the closest and farthest side from the Moon. High tides occur at these bulges. One rotation is the equivalent to one day, so usually there is the occurrence of two high tides and two low tides per day.
As I mentioned at the beginning, the Sun also contributes to tides. The difference between the gravitational pull of the Sun at different locations on the Earth is negligible. This means that tides resulting from the Sun remain fairly consistent. As seen in the figure, the Moon’s pull is more variable causing greater differences in tide. This provides insight into the question: what would happen to tides if there was no moon? The Sun would be contributing to tides, so they would still exist. The tides would just be much smaller and the difference between high and low tide would be much smaller as well.
Now that I have discussed the difference between lunar and solar tides, I want to explain the result of having both. This is a simple vector addition problem. When the Sun and Moon are in line with each other, the vectors of their forces are going to be added together meaning the high tides will be higher and low tides will be lower. This is called spring tide. When are the Sun and the Moon aligned? Full and New Moon. This means the moon phases can be used to determine the strength of the tides. Applying this logic, lower high tides and higher low tides will occur when the Moon and Sun’s force vectors are at a right angle with each other. The Sun and Moon are at this right angle during First Quarter and Third Quarter Moon. This is called neap tide. Refer to the above figure from NASA Science to visualize how these vectors influence the resulting tide. Their website also has some other figures which help with understanding tides. The result of both the Moon and the Sun’s gravitational forces is a change in tidal movement both throughout the day and throughout the moon’s phases.
In the late 16th century, a young man by the name of Giordano Bruno set out on a journey of discovery, one that would take him to the very frontiers of scientific knowledge and beyond. Bruno was a man of incredible intelligence and curiosity, driven by a deep passion for the mysteries of the universe. He was a man who was not afraid to challenge the prevailing wisdom of his time and to explore new ideas, no matter the consequences.
Bruno’s quest for knowledge led him to the field of astronomy, where he began to delve into the mysteries of the cosmos. He was fascinated by the stars and the infinite expanse of space that surrounded him, and he longed to understand the nature of the universe and its place in the grand scheme of things.
Bruno’s ideas were bold and revolutionary. He believed that the universe was infinite, with no center and no edge, and that there were countless other suns and planets, each with its own unique set of inhabitants. He also believed that the stars were not simply distant lights in the sky, but were in fact suns, much like our own, with their own set of planets and life forms. This idea is also known as Cosmic Pluralism
Bruno’s views were in stark contrast to the prevailing wisdom of his time, which held that the universe was limited and finite, with the Earth at its center. His ideas were deemed heretical by the Catholic Church, and he was soon accused of heresy and brought before the Inquisition.
Despite the danger, Bruno refused to recant his beliefs. He stood steadfast in the face of persecution, declaring that his ideas were the result of his own observations and the fruits of his own intellect. He refused to compromise his beliefs, even as he was subjected to the harshest forms of torture and imprisonment.
In the end, Bruno was brought to trial, where he was convicted of heresy and sentenced to be burned at the stake. On February 17, 1600, Bruno was led to the Place de Grève in Paris, where he was tied to a stake and burned alive, his body consumed by the flames as he remained steadfast in his beliefs to the very end.
Bruno’s death was a tragedy, a cruel and unjust end to a life of extraordinary promise. But despite his cruel fate, Bruno’s legacy lives on, a testament to the power of the human spirit and the unquenchable thirst for knowledge that drives us all. He was a man ahead of his time, a visionary who dared to look beyond the confines of his world and to imagine a universe that was far grander and more magnificent than anything anyone had ever imagined. And his sacrifice serves as a reminder of the power of the human spirit, and the unending quest for knowledge that drives us all.
