How Does the Moon Cut His Hair? ECLIPSE IT!

An eclipse is more than just a punch line to a joke; it is a phenomenon that people often hear of and may get the chance to see, but never fully understand.

An eclipse takes place when the Earth passes through the Moon’s shadow, or when the Moon passes through the Earth’s shadow. The darker part of this “shadow” is referred to as the “umbra,” while the lighter portion of the shadow (often more gray than black) is referred to as the “penumbra.”

From: https://www.britannica.com/topic/umbra-eclipse

There are two main types of eclipses: lunar eclipses and solar eclipses.

Lunar eclipses only take place when there is a full moon. An easy way to remember this is by comparing the lunar eclipse to a werewolf. People can only turn into werewolves during the full moon just like lunar eclipses can only take place during a full moon.  Moral of the comparison: Cool things happen during full moons.

The different types of lunar eclipses are penumbral, partial, and total. A total lunar eclipse 

takes place when the Earth’s dark shadow covers all of the Moon’s visible surfaces. A partial lunar eclipse takes place when part of the Moon is partially blocked by the Earth’s shadow, and a penumbral lunar eclipse is when the Moon is in the gray portion of the Earth’s shadow. Most of these lunar eclipses are easily identifiable, except for the penumbral eclipse. 

Total Lunar Eclipse

 From: http://www.space.com/15689-lunar-eclipses.html

Partial Lunar Eclipse

From: https://www.timeanddate.com/eclipse/partial-lunar-eclipse.html

Penumbral Lunar Eclipse

From: http://www.macrokosm.com/gallery/march-penumbral-lunar-eclipse/

Even though these lunar eclipses don’t look alike, remember that they all can ONLY take place during full moons. 

The other type of eclipse is a solar eclipse. Solar eclipses can only take place during new moons. The three different types of solar eclipses are partial, total, and annular. A partial solar eclipse is when the Moon moves between the Sun and the Earth but does not get the opportunity to completely block the Sun. A total solar eclipse is similar to the partial solar eclipse, except for the fact that the Moon completely blocks out the Sun. The last type of solar eclipse is an annular eclipse. In this case, the Moon blocks out the center of the Sun, like a doughnut, and leaves the outer ring of the Sun visible. This visible outer ring is often referred to as a “Ring of Fire.”

The Moon is able to completely block the Sun during a total solar eclipse is because of its close proximity to Earth. When an object, in this case the Moon, is closer, it appears to be bigger, and when it is farther away, it appears to be smaller. During a total solar eclipse, the Moon is closer to the Earth and therefore appears to be big enough to block out the Sun. During an annular solar eclipse, the Moon is farther away and cannot completely block out the Moon, resulting in the "Ring of Fire."

Partial and Annular Solar Eclipse

From: https://mydarksky.org/2010/01/14/15-jan-partial-solar-eclipse-in-malaysia/

Total Solar Eclipse

From: https://www.timeanddate.com/eclipse/total-solar-eclipse.html

An easy way to remember what each solar eclipse looks like is to think of the Earth, the Sun, and the Moon having human-like interactions. Here’s an example:

One day, while Moon is taking his monthly orbit down the street, he sees that Earth is on a date with Sun. Moon isn’t very happy about this so he tries to ruin the date.  First, Moon tries to trip Sun, but doesn’t put his foot out far enough. Sun ends up walking over Moon’s foot with ease and barely notices Moon’s attempt at making him fall (partial solar eclipse). Next, Moon decides to stand in front of Sun. He does this only to discover that Sun is much taller than him and can look over him to continue talking to Earth (annular). In Moon’s last attempt to ruin the date between Earth and Sun, he puffs up his chest with confidence, pushes his shoulders back, and tilts his chin up before stepping in front of Sun, making sure he is closer to Earth's face than before. Moon’s confidence and proximity allows him to be bigger than before and allows him to block out Sun’s appearance on the date (total solar eclipse).  Earth is so impressed that she falls in love with Moon and they live happily ever after.

Though it is true that the Moon never actually changes in size and only moves a bit closer to the Earth, the visual for each solar eclipse should be clear.

The last major fact about eclipses that one should know is that the Earth only has two eclipse seasons each year. This is due to the Moon's orbit in relation to the ecliptic plane. The Moon's orbit is inclined approximately 5 degrees to the Earth's ecliptic plane which causes it to be either above or below Earth's ecliptic plane at most times. The two points of time where the Moon crosses from being below the ecliptic plane to above the ecliptic plane or above the ecliptic plane to below it are called nodes. Only 12 sets (1 set =  2 nodes in 1 lunar cycle) of nodes take place each year, and only 2 of those 12 are properly aligned with the Earth and the Sun to have eclipse seasons. Every eclipse season there is a lunar and solar eclipse. In total, there are 2 solar eclipses and 2 lunar eclipses per year. 

From: http://joe-cali.com/eclipses/PLANNING/TSE2013/

After reading about eclipses, it’s safe to say that eclipses, both solar and lunar, are pretty awesome. Fortunately, one will be available for observation in the United States on August 21, 2017!  If you want to read more about that make sure to check out www.greatamericaneclipse.com .  If you would like to gather more information about eclipses in general, visit the websites listed below!

http://www.mreclipse.com/Special/SEprimer.html

http://www.thetruthseeker.co.uk/?p=60206

https://www.timeanddate.com/eclipse/eclipse-information.html

Seasons: They Have a Reason

The seasons have been a staple of life on earth, influencing the moods and activities of many -- but rarely do we think about why they occur.

The seasons are fascinating, something we take for granted but yet something that has a major impact on our day to day life. A common misconception regarding the 'reason for the seasons', is that it is caused by the distance of earth's rotation around the sun, however the earth's orbit is nearly circular, with a 3% difference from closest to farthest approach to the sun, being nearly negligible in terms of differences in energy recieved. Additionally, if the seasons were merely based on various distances from the sun, the seasons would remain consistent across hemispheres, but they don't.

Rather the underlying cause for the seasons is the tilt of the earth's axis, which allow for the light from the sun to hit the earth's surface more or less directly. Check out this diagram, to help visualize why the tilt of the axis is the reason for the seasons.

Source: http://scinote.tumblr.com/post/109822921304/the-spin-of-the-earth-the-seasons

As one can see, during the summer the northern hemisphere recieves the most energy from the sun, and is consequently the warmest. This is based upon the tilt of the axis.

The severity of the seasons is dependent upon the degree of tilt. If another planet had a more drastic tilt, the seasons would fluctuate much more. As a result of this, the axial tilt of a planet can determine the chance for life on that planet. Scientists believe that reduced seasonality can be linked to the evolution of complex organisms. Rene Heller, a postdoctoral research associate at the Leibniz Institute for Astrophysics, notes that, "axial tilt, or obliquity, is a crucial parameter for climate and the possible habitality of a planet". If this tilt, is lost or altered it could potentially eliminate, or significantly reduce the habitability of a planet. Over the course of a planet's history, many circumstances can affect its axial tilt. This includes: the impacts of celestial bodies, gravitational pulls from neighboring stars and planets, as well as other factors.

To further exemplify the importance of obliquity, we could look at a potential planet in the "goldilocks zone", but one with an obliquity similar to that of Uranus. For this planet, the north pole would face the star they orbit for a quarter, then shift completely away the next quarter. One can imagine the difficulty of survival of complex life with such a large obliquity, causing rapid and extreme fluctations in climate. However, it is also important to maintain an axial tilt. If it erodes, this causes the equators to feel the full force of the sun's radiation, while the poles would recieve even less seasonal shifts than they already do. As a result, there would be bands of differening temperatures based on the planet's latitude. While in theory this could still enable life to persist, it could also spur the collapse of the planet's atmosphere.

This severity of seasons upon earth is also based upon latitude, but to a much lesser extent because of its pronounced obliquity. The equator is least affected by changes in the directness of solar radiation, and thus has the least extreme seasons. On the other hand, at the poles the effect is most pronounced, with dramatic shifts in daylight depending on the season.

As one can see, seasons have a bigger impact on daily life besides the need to shovel your driveway, or turn on the AC -- in fact they are arguably vital to human existence. If you would like more information about the seasons, check out these links!

- http://spaceplace.nasa.gov/seasons/en/

- http://www.morehead.unc.edu/Shows/EMS/seasons.htm

- https://www.youtube.com/watch?v=aSNs15sEINM

- http://www.astrobio.net/news-exclusive/high-planetary-tilt-lowers-odds-for-life/

Epicycles and Errors: The Story of the Geocentric Model

Figure 1. Ancient Greek Debate

It begins, as so much else does, with the ancient Greeks and their efforts to explain what they saw in the sky.  The Ancient Greeks were among the first to attempt to scientifically assess the nightly motion of the celestial objects, in part because of a culture that encouraged discussion, disagreement and heated debate! 

Their observations were based on what they could see with their naked eyes – approximately 2000 stars, the Milky Way, Earth’s moon and 5 of the planets – Mercury, Venus, Mars, Jupiter, and Saturn.

Over the course of a night, stars slowly rotate westward across the sky. Over 24 hours, the Sun also moves westward across the sky. Over the course of a year, the sun and other planets move eastward relative to the constellations.
However, the planets observed by the ancient Greeks appeared to move differently over the course of a year. Planets often changed in brightness and sometimes appeared to reverse their direction of motion. Indeed, the word “Planet” is derived from the Greek word for wanderer!

Figure 2. A Geocentric Model

Figure 3. Ancient Celestial Spheres

Greek philosophers primarily believed in a geocentric model of the universe - everything seen in the sky was orbiting an Earth that was fixed in place.  One of the first models of the universe was of the ancient celestial sphere, which explained the nightly motion of the stars. Proposed in about 600 BCE that stars were attached to a spinning celestial sphere, with earth at the center.

The motion of the sun, moon, and planets was explained by placing them on different, offset spheres.  

Figure 4. Retrograde Mars

However, while Greek philosophers were able to explain the motion of stars by using this geocentric model, they were unable to explain the movement of planets as they seemingly reversed their direction, only to reverse back again. This is known as the apparent retrograde motion of planets.  

 Claudius Ptolemy (90-168 C.E.) explained apparent retrograde motion by proposing a geocentric model with the concept of “Epicycles” – mini orbits that planets would follow even as they orbited the Earth.

Figure 5. Claudius Ptolemy

Figure 6. Ptolemy's Epicycles

The idea of Ptolemy’s Epicycles persisted for hundreds of years but by 1500 C.E., astronomers began to his revise his model. The idea of epicycles seemed too complicated and couldn’t easily be proven, which as we know is a disadvantage in science! To better explain the retrograde motion of planets, astronomers began to turn to the heliocentric model, in which the Earth and planets revolve around the sun. Ancient Greek astronomers had considered heliocentric models (indeed, sun-centered models were considered by the Greeks as early as 300 B.C.E.) but dismissed them because of various reasons.

The 150-year period in which the modern heliocentric model began to develop was known as the Copernican Revolution, named after Nicolaus Copernicus (1473 – 1543 C.E.) who proposed a heliocentric model to explain retrograde motion without the need for epicycles.

Figure 7. Planetary Motion Explained!

Other key figures in the Copernican revolution included Johannes Kepler (1571-1630 C.E.), Galileo Galilei (1564- 1642 C.E.), and Isaac Newton (1642-1727 C.E.). Each of these figures refined the heliocentric model.

But how do we actually explain retrograde motion? 

Apparent retrograde motion actually isn’t retrograde motion at all! Today we know that more distant planets orbit the Sun at slower average speeds, meaning that “retrograde motion” is no more than the Earth moving at a different speed than other planets! When planets switch directions in their orbit in respect to fixed background stars (appearing to move from east to west, rather than west to east), what is actually happening is an optical illusion. The Earth makes a complete orbit around the sun in 1 year, while planets father away take a longer time to complete a full orbit. As Earth pulls up to and then passes a planet like Mars in orbit, Mars falls behind and appears to be switching directions, although its orbit actually remains the same. Of course, this explanation of apparent retrograde motion is dependent on both the Earth and Mars orbiting the Sun at different speeds and thus a heliocentric model is necessary.



Images Used: 

http://cf.mp-cdn.net/54/aa/efa2e24344fe58ec66a9243cc6be-in-ancient-greece-debate-played-a-significant-role-in-citizenship-is-this-true-of-american-society.jpg

https://en.wikipedia.org/wiki/Geocentric_model#/media/File:Bartolomeu_Velho_1568.jpg

https://en.wikipedia.org/wiki/Celestial_spheres
http://www.sciography.com/images/ptolemy.gif
http://apod.nasa.gov/apod/ap100613.html

https://en.wikipedia.org/wiki/Deferent_and_epicycle

http://www.splung.com/content/sid/7/page/earlymodels

Interstellar Travel: The Prospects of Exploring the Unexplorable

Interstellar space travel: the act of going beyond our solar system to reach our oh so familiar yet ever so distant companions in our galaxy — the stars. Now, we are already incredibly well acquainted with one star, which holds our entire solar system in its gravitational grasp. That star is, of course, our sun which provides us with the energy necessary to create and perpetuate life. Not to mention, it is 500 times more massive than every other planet in our solar system -- combined.

http://pics-about-space.com/star-sizes-compared-to-the-sun?p=1

 Now, to an observer of the night sky reliant solely on his/her own perception, the stars that pepper the night sky appear hobbit-like when compared to the sun. In truth, these stars appear so small by virtue of how far away they are from us. Our galaxy alone, let alone our universe, proves absolutely enormous. The 10 billion-to-one scale model is useful for beginning to conceptualize the massiveness of the galaxy and the distance between us and the stars we see at night sans the sun. The model reduces the moon earth system down to the size of our palm where as the closest star system would be all the way on the coast of California, from the east coast. The sun is, to be sure, an exceptional star by virtue of the fact that it gives way to life itself, but, in terms of size, the sun is a rather ordinary star dwarfed by some of the supergiant stars present in our galaxy . Still, there are larger stars visible to the naked eye and even larger ones that are not. All in all, there are over 100 BILLION stars in our galaxy.

http://wallpaperswide.com/galaxy_5-wallpapers.html

 With each star emerges the possibility for planets, moons and other celestial objects around them. NASA has already identified many planets with conditions similar to earth that reside around stars in our galaxy. In fact, just recently we discovered a new planet, Proxima Centauri B, that has a mass similar to earth's and orbits the sun at a habitable distance -- not to mention it orbits the star that is closest to us in distance (Click here to further explore this exciting development).  Interstellar travel could be the outlet through which we discover the answer to that vital question: are we alone in this universe. So, why have we not explored these leads further? One simple answer: sheer distance. Even the most familiar stars we see every single night range from fifty to one hundred light years away from earth. Currently, our fastest spacecrafts travel around 100,000 times slower than the speed of light, meaning that a voyage to the nearest star with our current technology would exhaust millenniums.

http://www.quotidianogiovanionline.it/Sceltipervoi/Esploso/12935/-Il-primo-vero-gemello-della-Terra

Now, when one thinks of the crowning achievements in the history of human space travel, their mind immediately flies towards Neil Armstrong’s first steps on the moon. As a species, we love to think about a physical human conquering the expanses of space by traveling through it. In the case of interstellar travel, we may have to turn to the movies to satiate this need. The practicality of human space travel has diminished rapidly over the past decades as technological innovation has ramped up exponentially. Humans are simply not well equipped for space travel; millions of years of evolution adapted our bodies and minds to earth and not space. We need food and water, emit waste, are extremely susceptible to radiation and, above all, require a return journey when our robotic friends require only a one way ticket. 

http://memeburn.com/2015/11/10-reasons-why-2001-a-space-odyssey-stands-as-the-best-sci-fi-movie-ever-made/

What does this mean for the future? One thing is certain: achieving interstellar travel would provide incredible insights into the nature of our galaxy and universe. As such, we are going to continue to strive towards the stars. As previously stated, our current spacecrafts are too slow to entertain Interstellar travel without planning that spans thousands and thousands of years into the future. Due to our finite resources, this type of undertaking is simply not practical. There are, however, alternate solutions that have been proposed by leading astrophysicists. While still in theoretical stages, these ideas and insights may be what propels us to the stars. For example, Freeman Dyson’s Orion Project aims to employ nuclear explosions, in combination with a pusher plate, to propel a spacecraft to incredible velocities, even nearing the speed of light. This project has been shrouded in controversy and divisive opinions, which you can explore further here. 

https://en.wikipedia.org/wiki/Project_Orion_(nuclear_propulsion)

 This engages Einstein’s fascinating Theory of Special Relativity which speculates that for an object traveling near the speed of light, time actually slows down. A person traveling at the speed of light for 100 years would only have aged the equivalent of 10 years on Earth. Stephen Hawking has proposed his own solution which involves accelerating stamp-sized probes to the speed of light with a super-laser. Finally, there is the potential solution explored in sci-fi films like “Interstellar” and “Star Trek”: the wormhole. Hypothetically, a wormhole would allow us to manipulate the very fabric of the time-space fabric and pop out to the other side of hole, bypassing light years of travel across or even out of the galaxy. 

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Here, however, there is much scientific debate on whether these wormholes even exist, if they can be navigated safely and stably, or if we can harness the energy necessary to engage or produce one. While much debate surround the validity and practicality of these methods, they are incredibly exciting to speculate about and follow. They may just hold the key to the safe containing the answers to our most inquisitive questions about our universe. If you want to explore this prospect beyond the realm of this blog, click here. 

How large is our universe really ?

Ever felt the walk to your local grocery store or even the dining hall was too long ? Have you ever thought it takes a long time just to visit Boston from Colby ? All these distances and travel times are extremely small when compared to the scale of the universe. The observable universe as we know it stands at roughly 93 billion light years(light years are a measure of the distance light travels in a year) in diameter, but how did we come to this conclusion ?

To answer this it is vital to understand that the universe is expanding. We can observe distant galaxies moving away from earth in all directions. However an important distinction to make is that earth is not at the centre of the universe and all galaxies are moving apart from each other, therefore suggesting an expanding universe. A good visualisation of this is if you take an uninflated balloon and draw dots around the surface of the balloon, after inflating the balloon all the dots are further away from each other. Despite a uniform expansion, dots separated further away from each other travel at a greater speed, this same phenomenon is observed in our universe.

Picture used from: http://frigg.physastro.mnsu.edu/~eskridge/astr101/kauf28_1.JPG

Using the distance of the galaxies and the expansion rate we have been able to figure out that the universe is roughly 14 billion years old. Due to the expansion of the universe, the universe has expanded over its 14 billion year old life to a current state of roughly 46.5 billion light years in radius or the 93 billion light years in diameter.

The size of the universe can exists on such large scales that it is often hard to comprehend. Take our own solar system: if we shrink the solar system by a factor of 10 billion to 1 then our sun would be the size of a grapefruit, and the earth would only be the tip of a ballpoint pen, furthermore the distance between the sun and the earth would still be over 15 metres and lastly the nearest star object similar to the sun would be all the way in California if the sun was placed here at Colby College. Even after shrinking our very own solar system by a factor of 10 billion the vastness of space is hard to fully comprehend. Even after creating a scale model of 10 billion to one it is not possible to understand the magnitude between galaxies. Thus to grasp the separations that exist in space we can reduce the scale by another factor of 1 billion(scale of 1 to 10^19). At this scale every light year becomes just 1 millimeter and the Milky Way galaxy gets shrunk to roughly 100 metres or approximately the length of a football pitch. Now the distance to our neighbour Alpha Centauri becomes less than the width of your finger and millions of stars would be within the reach of your arms.

Picture taken from: http://i.ebayimg.com/images/g/xeUAAOSw3ydVkUp3/s-l300.jpg

You can follow the link to find out more about the process of figuring out the size of our universe : http://www.bbc.com/earth/story/20160610-it-took-centuries-but-we-now-know-the-size-of-the-universe

Telescope or Time Machine?

http://thecareernation.com/scientists-slow-down-the-speed-of-light/

Light travels at a finite speed, which is about 300,000 kilometers a second. To help to understand how fast this is, we say that if light went in circles it could go around earth eight times in just one second.  Even with such a high speed, it still takes light time to travel vast distances. 

http://vesmir.stoplusjednicka.cz/jak-dlouhy-je-svetelny-rok-parsek

The farther we go into space, the longer light takes to reach us. For example, light from the moon takes one second to reach us while light from the Andromeda Galaxy about 2.5 million years to reach us. 

Therefore, when we see the light from these objects, we are in fact looking back in time. When we see the light from the Andromeda Galaxy, we are seeing it as it was 2.5 million years ago. We are looking back in time when we see these far objects in the sky because light can only travel so fast and some of these objects are so far away from us it takes millions or even billions of years to reach us. This topic can be difficult to comprehend, but it is necessary to that when we observe the universe we can not separate space and time. For a lot of objects in the night sky, we are viewing a much younger universe. If a star was to die today, we would not know for years.

http://www.slideshare.net/sarahjones78/the-universe-35449770

Scientist therefore can use their telescopes as a sort of time machine to discover more about the characteristics of the universe in the past. Galaxies take a long time to evolve so we cannot watch a galaxy change overtime. However by comparing past (more distant) galaxies to the (closer) galaxies of today scientist can see how they evolve as seen in the picture below.

http://www.science.tamu.edu/news/story.php?story_ID=1381

Phases of the Moon

PHASES OF THE MOON

How the sun illuminates the moon in different locations around Earth
Figure from http://www.moonconnection.com/moon_phases.phtml

The lunar phases of the Moon are based on the Moon’s position relative to the Sun around the Earth. In the photo above you can see that the Sun illuminates the Moon at all times, but we don’t see the full Moon everyday because it is in different positions around the Earth. It takes the Moon 29 ½ days to complete each cycle of the lunar phases, but only takes 27.3 days for it to orbit around the Earth. The roughly two day difference is due to the fact that the Earth is also orbiting the Sun at the same time that the Moon is orbiting the Earth and therefor it needs those two extra days to catch up to the Earth's new location in the orbit.

Full Strawberry Moon in June
Figure from www.space.com

FUN FACT: The word “month” was formed by the term “moonth” because each complete cycle of the lunar phases takes about 29 ½ days.

Since the cycle takes around a month to complete that means that there is a full moon every month. Here are some fun facts regarding that concept:

FUN FACT: Each Full Moon of the year has its own name based off of the month that it falls in. For example, the Full Moon in June is called the Strawberry Moon and the Full Moon in April is called the Pink Moon.

FUN FACT: About every 19 years the month of February does not have a Full Moon.

When the Moon is closest to the Sun (between the Sun and the Earth) it is called a New Moon and is not visible on Earth. This is because the Sun is illuminating the side of the Moon facing it and from Earth we see the backside of the Moon. When the Moon is furthest from the Sun (the Earth in between) we see the Full Moon because the Sun illuminates the side of the Moon that is facing towards the Earth. When the Moon goes from New Moon to Full Moon it is considered “waxing”, meaning that it is increasing in visibility, and when it goes from Full Moon to New Moon it is considered “waning”, meaning that it is decreasing in visibility. The phases just before and after the New Moon are referred to as “crescent” and the phases just before and after the Full Moon are referred to as “gibbous”.

The Moon’s phases are also directly related to where it rises and sets. A Full Moon rises at sunset and sets at sunrise, whereas a New Moon rises at sunrise and sets at sunset making it not visible. The moon also sets later each night, allowing the waxing phases to be visible in the afternoon and early evening and the waning phases to be visible in the late evening and early morning. 

All the phases of the moon
Figure from http://astropixels.com/ephemeris/phasescat/phasescat.html

A common misconception is that there is a "dark side" of the moon, when in actuality the Moon is rotating so every part of the Moon is illuminated at some point during the phases. Another idea people often aren't aware of is that we only see one side of the Moon because the Moon orbits the Earth and rotates fully one time per orbit. This is called synchronous rotation. To see a demonstration of this concept I would recommend watching this Youtube video:
https://www.youtube.com/watch?v=OZIB_leg75Q

Occasionally when the Moon, the Sun, and the Earth all fall together in a straight line there is an eclipse. For more information about eclipses check out Tabreya's blog post here:
http://as151.blogspot.com/2016/09/how-does-moon-cut-his-hair-eclipse-it.html