How Much Does Light Weigh?

Posted on January 20, 2019 by Josh

Photons are massless particles. They move at the speed of light and do not have an intrinsic mass. And since light is made of photons, we can say that light has no mass. Story over, right?

Did you know that light can exerts a force on objects? This force can cause them to weigh more. Watch this video by Vsauce to see how much a landmass might weigh covered by light as opposed to dark.

Michael Stevens from Vsauce describes the weight of light. Octover 7, 2012. Youtube. For the section we discuss, please watch up to 0:56.

Michael explains that light does carry energy and momentum, which allows it to push objects. If light has momentum, can we assume that light has mass? This assumption is a common misconception. As reference, here is Einstein’s mass-energy equivalence:

E = mc^{2}

The misconception is that light has energy, which relates to mass, “m”. Except that the “m” in this formula actually refers to kinetic mass. Light does not have weight or mass. However, light can push objects, making them heavier.

tl;dr Light does not have weight or mass. Light can push an object or even increase its weight.

We Weigh Less in the Dark, technically

First we assume that a human being is a giant sheet facing the sun, since solar radiation pressure is applied in the direction of sunlight.

In Michael’s video, we learn that the pressure light exerts on a surface is about 1e-9 lbs per square inch. Considering the average human has a surface area of 1.9 meters squared, we can formulate:

\frac{1e^{-9} lbs}{in^{2}} * \frac{1550 in^{2}}{m^{2}}\ * 1.9m^{2} = 3.0 * 10^{-6}

So the next time you weigh yourself, turn off the lights.. You might not notice, but you just shaved a couple millionths of a pound.

sources:

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The Size of the Universe, Relative to the Size of a Picnicker

Posted on January 20, 2019 by luanaisaac1125
Powers of Ten, the video I discuss below

The video begins with a man and a woman out on a picnic, then begins zooming out farther and farther. They start with a focus image 1 x 1 meter wide, then zoom out to a field of vision 10 times larger every ten seconds. So, the first zoom out brings the image to 10m x 10m, then 100m x 100 m, and so on. At 10 million x 10 million meters, the entire earth is enclosed in the square, then at 1,000 million x 1,000 million meters, the orbit of the moon around earth is encompassed as well. At the 1 million million meters (1012) square, the sun and the four rocky planets are within view, and by the next zoom out (1013), the entire solar system is inside the box (save for a clip of Pluto’s orbit). At 100,000 light years (1021), most of the Milky Way galaxy is in the box. The farthest they zoom out is to 100 million light years (1024), at which point our own Milky Way galaxy cannot be seen. The galaxies and galaxy clusters in view are spread out, barely visible dots on the screen. The rest of the video zooms back in, all the way down to the picnickers, and then farther to a subatomic level.

What struck me about this video is just how small it made me feel. It reminded me of what Dr. Neil deGrasse Tyson spoke of in the foreword of our textbook, about the Hayden Planetarium’s “Passport to the Universe” show. This video is essentially a less encompassing version of what he described there. Having said that, the video is still completely captivating. It’s hard not to be drawn in. As the camera zoomed out, I just felt smaller and smaller, more and more insignificant. While I understand that this could sound a little depressing, I found myself getting more and more excited the smaller I felt. The simplest way to explain my stance is this: The universe is huge, and I am tiny. That means there’s so much for me to learn about and explore in all the vast open space around the miniscule portion that I occupy. Humans are insignificant little specs of stardust in the grand scheme of things, but that just means there’s a lot to discover and we have a lot more exploring to do. Although this class only addresses the confines of our own Solar System, it’s a great starting point for someone like me with no past formal education about anything space related. Suffice to say, it made me all the more excited to keep learning about everything this class has to offer.

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The Power of the Moon

Posted on January 20, 2019 by Campbell Flower

The moon has always been a central part of human cultures, whether through film, art, music, or folklore. You have probably heard myths about the full moon and its effects on human (or animal) behavior. Here is some information on many historical beliefs about the power of the moon:

Full moon as seen from Penzance, England on December 13, 2016. This full moon was also a supermoon, meaning the moon was located at the perigee of its orbit and appeared larger in the sky. Image courtesy of Time

Fertility: It was commonly held that a full moon could impact a woman’s menstrual cycle or fertility. There are varying beliefs as to the specific effect, including that a woman’s chances of getting pregnant or giving birth were increased during a full moon or that a full moon could cause a woman to get her period. Studies have found no true correlations, other than that a woman’s cycle (average of 28 days) happens to be similar in length to the moon’s cycle (29.5 days).

Sleep: Can the phase of the moon impact the amount of sleep you get? Studies say that there is no correlation between your ability to sleep and the phase of the moon, although this is not what many believed in ancient times. It was commonly thought that a full moon would result in a sleepless night.

Epilepsy: Many people believed that seizures caused by epilepsy were more common or worse on the night of a full moon. Blame was placed on the moon for impacting those inflicted with this condition. Studies have found a lack of correlation between a full moon and epileptic seizures. In fact, research found the number of seizures is actually lowest during a full moon and highest during the last quarter of the cycle.

Mental State: Definitely one of the most popular beliefs, it was commonly thought that the moon could influence a person’s mental state. Many fear that the full moon can lead someone to crazy and erratic behavior. Many even believe the moon possesses transformative capabilities, which I am sure you are all familiar with (cue the werewolf howl). A possible explanation was that a full moon was so bright a person couldn’t sleep, and therefore was driven mad. Studies have not found this to be true.

Animals: Many believed the psychological effects of the moon also applied to animals. Therefore, many feared that animals would attack on the night of a full moon. Studies have actually found mixed results on this topic. The British Medical Journal reported an increase in the number of animal bites on the night of a full moon, while other studies reported no such increase. A study did conclude that the number of animal injuries resulting in trips to the vet does increase with a full moon, showing that animal behavior (not necessarily increased aggressiveness) is potentially impacted by the moon.

Surgery: Many doctors have refused to operate and many patients have refused to be operated on during a full moon. This is because it was commonly believed that a full moon would result in blood loss and death during surgery. However, studies have found no difference in surgical success rates based on the phase of the moon.

Most of the information from this post was obtained from Bustle and Live Science . Have you found yourself impacted by the full moon or believing in these or any other effects?

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Where the Zodiac Signs Come From

Posted on January 20, 2019 by richardtli
12 Zodiac Signs

What’s your sign? This is a common question you may have encountered in your life. While most people aren’t too deep into astrology, chances are that most of us have looked into our daily horoscope at least once for fun. However, a lot of people don’t really know where these signs come from, or why they exist in the first place. If you are curious, keep reading.

The twelve zodiac signs come from the way the sun moves across the sky throughout the year. As each day passes, the sun will slightly shift its position among the stars. Due to Earth’s orbit, the sun will cycle around the stars in nearly the same pattern every year. The twelve zodiacs get their names from the constellations that the sun appears in front of during the year. Although the sun actually crosses over a thirteenth constellation Ophiuchus, it unfortunately does not a place in astrology.

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The 13th Zodiac

Posted on January 20, 2019 by reallyroyalqueen
The Zodiac Constellations

When NASA formally announced in 2016 that there is a 13th Zodiac Constellation, people everywhere were so shocked. They felt that NASA had been withholding information from the public. Cosmopolitan, an entertainment news outlet that does daily horoscopes for its users, published a story immediately providing the new borders for the zodiac symbols. Later in the month, Cosmopolitan edited the post to correct that NASA had not hidden anything. Since Babylonian times, the 13th zodiac, Ophiuchus, has been scientific knowledge. They just ‘did the math’. Using only 12 was easier to match with the lunar calendar. Many people feel as if everything they had assumed to be true is wrong, but the recognition of Ophiuchus deals with astronomy and constellations, not how we perceive our signs, astrology. Take a look and see if yours has changed!

Capricorn: Jan 20 – Feb 16

Aquarius: Feb 16 – March 11

Pisces: March 11 – April 18

Aries: April 18 – May 13

Taurus: May 13 – June 21

Gemini: June 21 – July 20

Cancer: July 20 – Aug 10

Leo: Aug 10 – Sept 16

Virgo: Sept 16 – Oct 30

Libra: Oct 30 – Nov 23

Scorpio: Nov 23 – Nov 29

Ophiuchus: Nov 29 – Dec 17

Sagittarius: Dec 17 – Jan 20

OPHIUCHUS
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Traveling at the Speed of Light

Posted on January 20, 2019 by Aaron Molotsky

Have you ever imagined what it would be like moving at the speed of light? To have the ability to travel that quickly (think ~300,000,000 m/s) would be incomprehensible — you’d experience a host of different effects, including time dilation (how more rapidly moving objects experience time more slowly), relativistic aberration (how your field of view distorts as a result of moving at such high speeds), and even the Doppler effect (changing light frequencies from high speeds). In essence, things would be very different if you chose to start traveling at around the speed of light!

 

However, what’s interesting is that physics dictates that it’s actually physically impossible for humans to travel at the speed of light. As a result of Einstein’s Theory of Special Relativity (E = mc^2), an object moving at the speed of light must have an infinite mass (which doesn’t seem right). So, even though humans can’t actually travel the speed of light, they can travel “almost” the speed of light, causing the host of effects listed in the paragraph above.

speedoflightpic
This picture represents an artist’s rendition of what traveling at around the speed of light could look like. You can find this picture at the following website.

And, as a brief overview, the speed of light represents a fundamental physical constant used throughout Astronomy and Physics. It’s not only used in quantitatively-based equations — it’s also commonly used to describe vast distances between objects in space (as constants we use on Earth would be orders of magnitude too small to describe the distances). All in all, the speed of light serves as a significant physical quantity that manifests itself in all sorts of different parts of the sciences.

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The Cosmic Calendar

Posted on January 20, 2019 by kylebward
The Cosmic Calendar

The Cosmic Calendar is a method used to visualize and better understand the timeline of the universe. Midnight, January 1st, is when the Big Bang occurred, and December 31st, 23:59:59, is modern time. On the Cosmic Calendar, the early development of the universe ranged from January 1st to September 6th and the first known biotic life on Earth formed on September 14th. Dinosaurs lasted from December 25th to December 30th, 6:24. What is very interesting is the existence of primitive humans, starting on December 31st, 22:24, with the development of agriculture on 23:59:32. From this point on, from the end of the Ice Age to the start of Modern History, our history has lasted for less than 30 seconds on the Cosmic Calendar. Dinosaurs roamed the Earth for 5 days on the Cosmic Calendar, significantly more time compared to our short 7 seconds since the Iron Age. Despite the short while we have existed, we have discovered, learned, and created so much that has impacted Earth and the species on it in significant ways, for better or for worse.

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Time Travel

Posted on January 20, 2019 by dillonplageman3

While transporting a human from 2019 to the age of the dinosaurs might be a little ways off in terms of technological development, there is another form of time travel that occurs every day and all it takes to appreciate is a glance at the sky.

One of the more thought-provoking aspects of the universe is its immense size and scale. Considering our minuscule place in the all-encompassing beauty of the cosmos, one might ponder about the reach of light and whether what we see if actually accurate. On Earth, the speed of light is fast enough that distance is largely inconsequential; however, as we look further outward this definite speed begins to factor in to our perception of distance celestial objects. One light year, the distance light can travel in one year (9.46 x 1012 km), is typically used to refer to objects as they stand in space. Given the vast separation of even our galaxy, much of what we see in the night sky is distorted. For example, the closest star system to out solar system, Alpha Centauri, is about 4.37 light years away from Earth. Due to the speed of light, as we look at these stars we are actually seeing them as they were 4.37 years ago. This simple fact can be expanded and becomes even more consequential as objects are further and further from the center of our observable universe. Take the Andromeda galaxy, located 2.5 million light years away, if a major event in that galaxy were to occur in the last 2.5 million years, we would not become aware until the light from that instant travels throughout space to reach us. In this sense, as we look further into the depths of space, we catch a glimpse into the past.

wordlessTech

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Picture the enormous universe

Posted on January 20, 2019 by Yihao Yan
A logarithmic illustration of the universe, with solar system in the center and CMB at the edge. Image from Business Insider.

The vast size of universe is so hard to picture in one image because its size is unbelievably enormous compared to human and Earth. Our planet Earth has the size around 12,742 km diameter. And the nearest object to us is moon which is approximately 384,400 km from us. The number is already huge in our sense. But the size of our solar system is about 287.46 billion km and the Milky Way is around 950,000,000,000,000,000 km wide, or 105,700 light-years as the number is too large to use km as unit. It will take light 105,700 years to travel across the whole Milky Way! Consider that human has been around for only 200,000 years. And the size of Milky Way is not unique. In fact, some large galaxy can have size way bigger than Milky Way. IC1101, the largest galaxy has been found, is 6 million light-years in diameter.

Amazingly, astronomers estimated that there are around two trillion galaxies in the observable universe which is 92 billion light-years wide. So the only way to picture such enormous size in an image is to use logarithmic scales. As the picture above shows, each chunk of the circle represent a field of view several orders of magnitude larger than the one before it.  So the whole observable universe is now in a single image.

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Stellarium: a Great Planetarium Program

Posted on January 19, 2019 by Jiayu Kang

Wanna know what the sky looks like today? Here’s an amazing computer program where you can know everything about the sky without walking out of the door!

It is simple to download Stellarium at stellarium.org and follow the instructions. After you install the program and open it, you can input any time and location you want by clicking on the icons on the left side of the screen as shown below.

Screenshot by me

One of the most exciting things about this program is that it provides you with a much clearer view of the universe than what you can observe with the naked eye. Stellarium can line up the constellations and label all the planets, stars, constellations in the sky. In fact, you can even see the sky on the other side of the Earth by turning off the “ground” on the bottom menu, which would make you feel like the ground just turned into glass and you can see through it! Below is a screenshot of today’s sky in Nashville at 17:33 (I dragged on the picture to adjust the view so that it shows the view from lying on the ground and looking up at the sky!)

Today’s sky in Nashville (screenshot by me)

There’s a lot more to explore. I was wondering what the sky is like in my hometown, so I just set the location to Nanjing, China. Then there comes a totally different image because Nanjing is nearly at the opposite side of the Earth. You may notice that is it day time in China, but with the assistance of Stellarium, you can easily figure out which constellations are high in the sky by turning off the “atmosphere” on the bottom menu.

Today’s sky in Nanjing, China (screenshot by me)

Then more and more questions come to mind. What constellation is closest to the Sun right now? How does stars’ relative position to the Sun change during the course of a year? Download Stellarium for free and figure those questions by yourself!

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