Tuesday, July 29, 2008

        Went for my evening walk re-listening to an astronomy lecture on galaxies and dark matter. There are different types of galaxies: Elliptical, Spiral, and irregular galaxies with odd shapes that don’t fall into the other two types. Dark matter makes up 90% of the mass in galaxies. No one really understands dark matter and what it consists of, but there are a few ideas floating around. First inferred by Fritz Zwicky of Cal Tech in 1933 when he was observing a galaxy cluster and compared their calculated mass with their motion about each other and found there was four hundred times more mass than should be. Zwicky also came up with the idea of neutron stars. I would like to read more about him!
        Read more of the Richard Feynman book until it was time to do my exercises. Did my stretches, lifted weights, and went for my nightly run. When I got back I took out my telescope to do a little star gazing. The night was clear but the atmosphere was a little unstable. Jupiter was bright in the sky and I watched it and its moons for a while. Two of its moons were very close to the planet and on opposite sides. I could barely make out the two bands of the planet tonight. Then I just did a sweep of Sagittarius looking at a few globular clusters and the rich star fields near the Tea Cup.

Lecture on Neutron Stars

        Went on my evening walk re-listening to an astronomy lecture on Neutron Stars. Neutron stars are formed in type 2 supernovas. During the process of a star’s death where it’s burning through different elements it finally reaches iron 56 which cannot fuse. This iron core builds up pressure to the Chandrasekhar limit and electron degeneracy pressure takes over. Different outer layers keep burning lighter elements until they reach iron 56, which falls into this core (which is the size of the Earth) to exceed this limit. When the Chandrasekhar limit of 1.4 solar masses is exceeded and the pressure of the electron degeneracy pressure can no longer hold up against gravity the core implodes very fast at .01 the speed of light (I think that is the speed he said) and compresses around two solar masses into a sphere ten miles in diameter. As this takes place electrons and protons are squeezed together forming neutrons and it is the neutron degeneracy pressure that takes over the fight against gravity. Neutron stars spin very fast because of the angular momentum it got as it collapse into a smaller area- like a skater pulling in her arms to spin faster. Neutron stars emit high-energy radiation because of the spin and electrons flowing on its surface between its two magnetic poles- like a lighthouse. These are called Pulsars. This was how neutron stars were first found thirty years after Fritz Zwicky anticipated their structure. The next lecture will be on black holes.

Lecture on Supernovas

        Went on my evening walk re-listening to another astronomy lecture about supernovas. There are many ways a star can go supernova but the lecture was on type 1A and type 2. A type 1A supernova is formed in a binary system where one star is a red giant and the other is a white dwarf. The white dwarf accretes matter from the red giant and if the white dwarf exceeds the Chandrasekhar limit of 1.4 solar masses it goes supernova- 5 million times brighter than the Sun. Type 2 is from massive stars with at least nine solar masses and releases so much energy that it out shines the galaxy they implode in. Heavier elements than iron are created in this process by electrons and protons that merge to create neutrons. If it wasn’t for type 2 novas we wouldn’t exist because there wouldn’t be any heavy elements heavier than Iron 56. Oh there is so much more on type 2s that I could write about, but time grows late.

Fate of Stars II

        Went for my evening walk and re-listened to “Fate of Stars II” about the processes that power stars. Hydrostatic equilibrium is where the outgoing thermal pressure is in balance with the gravity of incoming matter. This Hydrostatic equilibrium is caused by the fusion of four hydrogen atoms that overcome the Coulomb barrier (at high temperatures strips away electrons from the hydrogen atom leaving protons) that collide at high velocities forming a new helium atom. The energy left over after this process (a helium atom has less mass than four hydrogen atoms) is released in the form of neutrinos and high-energy photons. These photons eventually slow down as they make their way through to the stars surface and radiate into space. Our Sun converts hydrogen to helium at a rate of four million tons a second. After a star runs low on hydrogen (our Sun in about five billion years from now) will start fusing helium into carbon and oxygen and go off the main sequence of the HR diagram becoming a red giant. At this point blowing off its outer shells creating a nebula, and if it is below 1.4 solar masses, with a white dwarf at its center. Above 1.4 solar masses and depending on how massive the star is you can have a neutron star or a black hole (this will be discussed in the next lecture). The electron degeneracy pressure holds up a white dwarf core. Wow did I just write all this!
        Watched “Science Now” on PBS about Stem cells, filming underwater critters, SETI and the new Allen radio telescopes, and leaches used for modern medical purposes.
        I forgot to add that last night I setup my telescope (as I did tonight) to view Jupiter before the Moon came up. Well last night I believe I saw one of the moons go behind the planet: there was a little bump on Jupiter’s edge that slowly disappeared, cool! Tonight I saw four moons lined up.

The Fate of Stars 1

Went on my evening walk re-listening to another astronomy lecture on “The Fate of Stars”, about what happens to a star when it leaves the main sequence of the HR Diagram, and also emission and reflective nebulae: Young hot stars with temps of 13,900C excite the atoms and cause them to re-emit the UV light that they absorb when they cascade down to a lower energy state drive emission nebulas. Reflective nebulas, on the other hand, are particle clouds near a star with a temp less than 13,900C and the light is reflected. The emission nebulas are the most colorful.

Exoplanets

Went for my evening walk re-listening to another astronomy lecture on exoplanets or extra solar planets. At this time there are 307 that have been found. Most exoplanets have been discovered using the Radial Velocity or Doppler Method by studying spectral lines and looking for blue and red shifts as the star and its planets orbit around a common center of gravity called a barycenter that create a wobble- a stars blue shift is coming at us, and the red shift is going away. Astronomers need to use computers to sort this out because the shifts are so minuscule. Then Professor Bloom went on to discuss the formations of planets around protostars that form out of the gas and particles of nebulas. By loosing angular momentum these particles fall into the protostar by the effects of gravity that then creates a flat disk. These particles begin to heat, which causes pressure, and depending on the gasses makeup- heavier particles closer to the central mass and lighter particles in farther orbits and their closeness to the central mass determines when a cohesion process starts to bind them to one another. Astronomers have found these protoplanetary disks in other star systems. I think I got this right.

Spectrum and Blackbody Radiation

I re-listened to lecture three about spectrum and blackbody radiation. As I understand it a blackbody absorbs light- like a black surface is hotter than a white surface heated by the Sun. If you took the atmosphere away from the Sun it would be a perfect black body- this was where I got confused: why is something that radiates light a black body? Well maybe if we looked at the hot back surface heated by the Sun in infrared wavelengths we would see that it was radiating- as I’m writing this I think I just now understand why the sun would be a perfect black body without its atmosphere now! Okay this leads us to where we get into absorption lines- the Sun’s atmosphere has gasses whose electrons absorb energetic photons at certain wavelengths which create a dark line on the absorption spectrum. And we can use these dark lines to find what elements are present in a star.

July 01 2008

        Went outside with the binoculars when it got dark. I was looking to the western part of the sky when I eyed what I believed to be Mars. So I got out the telescope to check it out, and it was Mars (last time I saw Mars it was in the horns of Taurus). I also saw a beautiful binary system with an orange and yellow star, but I didn’t know what constellation it was in, so I took out my laptop and ran the astronomy program, and found it was Algieba about 126 light years away. Funny that I didn’t recognize Leo the constellation Algieba lies in, but my excuse is that Leo laid sideways in the western horizon. I also noticed that Saturn was nearby, had it sighted and focused when a faint satellite came zipping across my field of view. So I followed it till it vanished into the west. Cool! I didn’t realize at the time that I had been using a 6mm eyepiece so the satellite must have been very, very small. Maybe it was Ed White’s space glove he lost in his 1965 spacewalk! Nah! Well maybe!
        Got inside just in time to watch “Seeing in the Dark” by author Timothy Ferris. I’ve seen it before and really liked it, so I made it a point to see it again tonight. One item I missed last time was when he was talking about the Andromeda Galaxy being 2.5 million light years away. When we are viewing the whole galaxy, the light from the nearest edge gets to us one hundred thousand years before the light from the back does! Now that gave me pause to think of scale, and just how immense our universe is! And there are billions upon billions of these galaxies in every direction we look. Great show!

old cheap equatorial mount

        I got back home and went for my evening walk. It was too windy to listen to a lecture but I think I want to pause on the lectures until I learn as much as my little brain can absorb of the Spectra: the absorption and emission lines that the last two lectures talked about.

        Went outside to setup an old cheap equatorial mount I had lying around. I must have done something wrong somewhere and I think it was the polar alignment. I haven’t done this since college but that was on a more professional mount. This one’s RA and Dec setting circles are so small that it was hard for me to read. Anyways I was able to follow Jupiter using the fine adjustment cables, but not very well. I’ll have to go online later to find some documentation and see what I’m doing wrong. The seeing wasn’t very good with all the particulates suspended high in the air from the fires in northern California scattering light. It made the sky appear like a quarter Moon was out and I didn’t need a flashlight to navigate around. So I got out the binoculars and sat back trying to name some of the constellations I know. There was Hercules high overhead, Corona Borealis, Bootes, and several others. The asterism “Summer Triangle” with Vega (in Lyra), Deneb (in Cygnus), and Altair (in Aquila), was making its way up in the eastern sky. I used Kstars on the laptop to help me find some of the other constellations I’m not that familiar with. All in all it was a productive night and it feels good to get outside and try to recall the names of the constellations and stars.