Just in time for Halloween, my topic this week focuses on electron degeneracy pressure specifically to delve into how “A degenerate gas does not expand when the temperature increases as an ordinary gas does.”
In 1923, Arthur Stanley Eddington derived a formula to relate the luminosity of a star to its mass, and in the same year correctly interpreted high-density, white dwarf stars as being formed of matter so dense that atomic electrons have collapsed from their orbits, a substance we now call degenerate matter. (Levy, p. 116)
Young giant stars of a certain size, between .4 and 2 solar masses, have helium rich cores squeezed by gravitational force into a crystal-like solid. At these pressures, the atoms become completely ionized, separately into nuclei and electrons and are so closely crowded together that become influenced by the Pauli exclusion principle phenomenon. Two identical particles are not allowed to exist in the same place and time. As the electrons are pressed closer and closer together, the exclusion principle forces many of them to move faster and faster so they do not become ‘identical’ (meaning occupying the same space and moving with the same speed of adjacent electrons) and consequently this motion increases the repulsion between the electrons. This state provides pressure in the core preventing it from collapsing and is referred to by astronomers as degeneracy. Thus, low-mass giants with helium-rich cores are supported by electron degeneracy pressure. (Comins, p. 335)
At the end of September I reached that point in the year when I could shake off all my various book club obligatory reading and get down to the serious business of reading the books I bought for myself all year long. Not every year gives me a break where I can read what I want. I often have to squeeze in my ‘must read’ books between the two to three other books I read per month for various discussion groups and book clubs. Don’t get me wrong. I very much enjoy reading outside my comfort zone and would not give up the wonderful discussions and cherished friendships I’ve nurtured through a shared love of reading.
Most years, I read between 75 and 100 books; last year I read 88 and as of today I’ve read 99 thus far in 2017. And only about ten percent make it onto my ‘loved-it’ shelf (the equivalent of a five-star rating). This year had a few more than normal and will probably end with two to three more on the shelf before year’s end (because I’m now reading what I’ve had on hold for most of the year).
And by friends, I’m referring to the Friends of the Lansing Community Library (FotLCL for short), a nonprofit organization that is member supported and advocates, fundraises and provides critical support for my local library, the Lansing Community Library (LCL for short). Their mission, which you can choose to accept as well, is to support LCL in providing free and equal access to information for all citizens through donations of time, talent and resources.
This week I want to discuss “What might cause the closer of two identical stars to appear dimmer than the farther one?”
Apparent Magnitude: A measurement of the brightness of stars without regard to their distance from Earth.
The scale in use today starts with the star Vega and an apparent magnitude of 0.0
Objects brighter than Vega are assigned negative numbers. For example. Sirius, the night’s brightest star, has an apparent magnitude of -1.44
The scale was extended to include the dimmest stars visible through binoculars and telescopes. For example, a pair of binoculars can see stars with an apparent magnitude of +10
Ignoring distance for a moment, all other things being equal, the closer of two identical stars will appear brighter (have a smaller apparent magnitude) to us than the more distant star. When we account for the difference in distance, we use either or two measurements: absolute magnitude and luminosity.
A friend and work colleague of mine who also happens to be a photographer started posting snapshots in her Facebook feed last week. The challenge was to take a photo a day from your life with no people featured in them and provide no explanation. Oh, and they must be black and white photos.
This intrigued me as my first camera back in the early or mid 70s had been a small inexpensive fixed lens camera that used small rolls of black and white film. My dad had a dark room at home but I don’t think we ever developed film that I shot in my camera, at least not until I was much older and part of the yearbook staff in high school.
I decided to revisit my youth and took up the challenge. I also happened to be on vacation this week so I had plenty of time to think of what sites in and around my home would lend themselves to good black and white photography.
Here’s the seven I posted daily on my Twitter and Facebook feed:
And here are all the photos I took in the last week that I used as the pool of photos to choose from:
I’ve reached the halfway point through my Introduction to Astronomy class. This week marks the eighth week of fifteen, sixteen if you count the first week where we just spent time getting to know each other and exploring the textbook and getting the lab software, Starry Night, installed and licensed. Last week, we reached the outer limits in the Kuiper Belt and Oort Cloud of our solar system where only comets and Voyagers I and II have ventured. Now we’ve snapped back to study our closest star, Sol, or more commonly just the Sun. My topic for discussion responds to the following question:
Why is the solar cycle said to have a period of 22 years, even though the sunspot cycle is only 11 years long?
Some surface features on our active Sun vary periodically in an eleven year cycle. The Sun’s magnetic fields which cause the surface changes vary over a twenty-two year cycle. The relatively cool and slightly darker regions, commonly called sunspots, are produced by local concentrations of the Sun’s magnetic field piercing the photosphere. The latitude and number of sunspots on average vary during the same eleven year cycle. But the hemisphere where the Sun’s north magnetic pole anchors during one eleven year cycle will have south magnetic poles during the next. Because it takes a full twenty-two years for the magnetic poles to return to their original orientation astronomers refer to the entire solar cycle. The magnetic dynamo model posits that many transient features of the solar cycle are caused by the effect of differential rotation and convection on the Sun’s magnetic field. The Sun’s differential rotation (different speeds at different latitudes) causes its magnetic field to become increasingly stretched like a rubber band. The bands can’t break so they periodically untangle themselves with the help of trapped gases which leak out (sunspot) and gradually settle back under the photosphere, when the sunspot disappears. The most recent reversal of the Sun’s magnetic field occurred in 2013. We are currently at the tale end of Solar Cycle 24. (Comins, 2015, p. 272-83)
My topic for discussion this week will attempt to answer the question:
Why do astronomers believe that the debris that creates many isolated meteors comes from asteroids, whereas the debris that creates meteor showers is related to comets?
But first, I want to share two things that serendipitously fell from my Twitter feed (@mossjon) today. Today’s APOD (Astronomy Picture of the Day@apod) featured the unusual mountain on Ceres (Comins, 2015, p. 239).
The second thing that immediately caught my eye today was an episode of Astronomy Magazine‘s “The Real Reality Show” entitled “How an Asteroid Killed Off the Dinosaurs” covered late in Chapter 8 of our textbook (Comins, 2015, p. 263-4) and which also bonked me on the head via my Twitter feed:
In this week’s discussion topic, I attempt to answer the question “Why are Uranus and Neptune distinctly bluer than Jupiter and Saturn?”
On Uranus and Neptune, the methane absorbs red, orange and yellow light, reflecting back the blue. In contrast, Jupiter and Saturn have only minor trace amounts of methane and quite a bit more hydrogen and ammonia.