comets – Neville’s Phantastic Physics Phun

On March 25th amateur astronomer Michael Mattiazzo discovered Comet SWANN (C/2020 F8) using the Solar and Heliospheric Observatory’s SWAN (Solar Wind Anisotropies) camera. (skyandtelescope.org) Viewers in the Northern Hemisphere should be able to view the Comet SWAN beginning in Mid May. The discovery of this previously unknown comet got me thinking a bit about these celestial objects. This comet has only been recently discovered so we don’t yet know much about it. I wanted to give a brief description of comets and talk a little about what we do know about these fascinating objects.

According to solarsystem.nasa.gov “Comets are cosmic snowballs of frozen gases, rock and dust that orbit the Sun.” This certainly doesn’t seem like much to get excited about. Let’s look a little closer at these “cosmic snowballs”. Think back to your days in middle school and high school science class when you learned about atomic structure. One of the things that stood out to me is how similar each atom was varying only by number of electrons and/or neutrons. It was easy to draw an atom of any element using the Bohr model because they all had the same basic structure, a positively charged nucleus containing some protons and neutrons, and electrons with their negative charges orbiting the positively charged nucleus. It turns out that active comets which are close to the sun have all have similar structure as well, meaning they all have the same component parts but may vary from comet to comet in size, composition, and place of origin.

The Structure of Active Comets

The structure of active comets all contain several distinctive features. The nucleus of a comet is the portion which contains mostly ice and gas with trace amounts of dust and other particles and is generally 1 to 10 km in size. It is possible, however for a comet to have a nucleus of up to 100 km. The nucleus of an active comet is mostly in a solid state and fairly stable. The coma is a cloud of water, carbon dioxide and various other gases which are converted directly from solid to gas as they are heated as the comet approaches the sun. This part of the comet may be over a thousand times larger than the nucleus. The nucleus along with the coma form the head of the comet. The hydrogen cloud or envelope is yet another feature of comets, this is an extremely large cloud of hydrogen which envelopes the comet. This cloud may be in the vicinity of millions of kilometers in diameter. Active comets that are nearing the sun have two distinct tails. The dust tail, which is the most obvious and visible feature to the unaided eye, is composed of mainly dust and other gases and may be upwards of 10 million kilometers long. Interestingly, the dust tail always points away from the sun. The dust tail reflects light from the sun making it the most visible portion of the comet. The second tail, the ion tail is composed of plasma and other particles related to the comets interaction with the solar winds associated with the sun. This tail may be much longer than the dust tail reaching lengths of several hundred kilometers.

28+ [ Comet Diagram ] | schematic diagram of a typical comet the ... — Courtesy of http://0osr12g1.adtddns.asia/comet-diagram.html

The Path of a Comet around the Sun

Comets, like planets orbit around the sun. The orbit of a comet follows a much more elliptical path than do planets. The length of time it takes an object to complete one orbit is called a period. The period of the Earth’s rotation around the sun is 365.25 days and the period about its axis is 23 hours and 56 minutes. The period of the moon is 27 days which is the amount of time it takes to orbit the Earth. Comets in general have much longer periods. Any comet with a period of less than 200 years is referred to as short period comets. These comets originate from the Kuiper Belt. In case you were wondering, the Kuiper Belt is “a donut-shaped region of icy bodies beyond the orbit of Neptune. (solarsystem.nasa.gov) If the period of a comet is greater than 200 years it is called a long period comet and originates from the Oort cloud which is “is believed to be a giant spherical shell surrounding the rest of the solar system and is the most distant region of our solar system. Even the nearest objects in the Oort Cloud are thought to be many times farther from the Sun than the outer reaches of the Kuiper Belt.” (solarsystem.nasa.gov) Halley’s comet is perhaps one of the most famous comets of all time and has a period of 76 years making it a short period comet. The Hale Bop comet is a long period comet with a period of over 2500 years.

An article featured on Space.com, author Joe Rao wrote about the period of comet SWAN where he stated “for fun, I fed its orbital elements, which includes the eccentricity of its path around the sun, into an orbital simulator. My simulation suggests Comet SWAN is traveling around the sun in a period of about 25 million years. (space.com) The discovery of this comet is so new that the actual period of orbit remains to be seen but this certainly would be a fascinating development. We would be the very lucky few of humankind to be able to view this very long period comet.

I've heard that the Oort Cloud contains trillions of icy bodies ... — Courtesy of astronomymagahttps://astronomy.com/magazine/ask-astro/2018/04/the-oort-clouds-icy-bodieszine.com

How to View Comet SWAN

The best time to view SWAN will be in the evening hours or just before dawn beginning on May 23rd until June 10th according to skyandtelescope.org. The comet currently is visible using binoculars as well as the unaided eye to those in the Southern Hemisphere. Curious stargazers wishing to view the comet with the unaided eye in the Northern Hemisphere shouldn’t have to wait much longer as it will be visible to you by late May. The comet will reach perihelion, which is its closest distance to the sun around May 27th. At perihelion the SWAN comet will be roughly 64 330 000 km from the sun and the closest it will be to Earth will be on May 12-13th when it will be a mere 83 330 000 km from Earth.

Stay tuned to your favorite astronomy magazine or website to learn more about this newly discovered comet. Michael Mattiazzo, the amateur who discovered this comet has discovered a total of 8 comets dating back to 2004. Keep your feet on the ground, eyes open and head to the heavens and maybe you will discover the next comet or other astronomical object.

Heinrich Wilhelm Olbers

Wilhelm Olbers was a German astronomer and physician who was born in 1758 and died in 1840. Olbers’ had several noteworthy contributions to the field of astronomy including developing a method to calculate the parabolic orbit of comets. Olbers’ primary focus was in searching for comets. According to Encylopedia Britannica a comet is ” a small body orbiting the sun with a substantial fraction of its composition made up of volatile ices.”

Olbers’ was the first to propose that a comet’s tail is always pointed away from the sun as a result of radiation pressure from the sun itself. Olbers’ is also credited with discovering a total of 5 comets as well as two asteroids, Pallas and Vesta. On March 6th, 1815 Olbers’ discovered a comet with a period of approximately 72 years. The period of the comet was calculated by his friend and colleague Carl Friedrich Gauss and verified by other astronomers of the time. Olbers comet, 13P/Olbers, next perihelion, which is its closet proximity to the sun, will be on June 6th, 2024.

A Scientific Paradox

A paradox, according to Merriam-Webster, is “a statement that is seemingly contradictory or opposed to common sense and yet is perhaps true.” Science is certainly not immune to experiencing a paradox. One of the most famous paradoxes is the grandfather paradox which appears to be a way for nature to forbid time travel to the past. It goes like this, suppose you go back in time and murder your grandfather before he and your grandmother conceive your father. By doing this your father and consequently, you will not be born. If you are not born then you could not have gone back in time to murder your grandfather so then you will be born. A resolution to this paradox is that if you kill your grandfather, you are actually killing him in different universe. Another possible resolution is based on quantum mechanics and the superposition of states. You can watch a short video from minute physics to see the description of the grandfather paradox and possible resolutions to the paradox. https://www.youtube.com/watch?v=XayNKY944lY This is just one example of a paradox in science there are many others you can find by executing a quick google search.

Olber’s Paradox

In 1826 Heinrich Wilhelm Olbers asked a deceptively simple question which became known as Olber’s Paradox. That question was “why is the night sky dark?” If the universe is both endless and populated with bright stars then the night sky should be blindingly bright at least as bright as the sun because every single line of sight must end at a star. If the universe is infinite then we should be able to see a star in every direction. Even if some stars that were further away were dimmer there would be more of them so the result should be a consistent luminosity across the sky.

So why isn’t the night sky uniformly bright?

Perhaps the most reasonable factor in the resolution to Olber’s paradox is that the universe is finite and that light from stars that are more than 13.7 billion years old are to far away for their light to have reached us yet. A second factor is that because the universe is not static but rather is expanding, light from distant galaxies is red-shifted into the non visible portion of the electromagnetic spectrum. The farther away a galaxy is from the earth the higher the red-shift of the visible light. So light from galaxies that are past a certain distance from us is red-shifted to the infrared portion of the spectrum which we can’t detect with our eyes. In summary, because the universe had a beginning, there aren’t stars in every direction, light from stars that are older than 13.7 billion years old hasn’t reached us yet, and because of the expansion of the universe resulting in red-shifting of visible light the night sky looks dark.