Brian Cox is a British astrophysicist who has produced some great BBC documentaries over the past few years. Here is episode 1 of his "Wonders of the Universe" series. Some of us watched part of it on Friday.
http://www.dailymotion.com/video/xyr1ly_wonders-of-the-universe-destiny_shortfilms
He also has a "Wonders of the Solar System" series and a "Wonders of Life" series. All good stuff.
Friday, April 10, 2015
Wednesday, April 8, 2015
Final talk topics
black holes
neutron stars
variable stars
SETI
Drake equation
Supernovae
Galaxy types
end of the universe
Olber's paradox
dark matter
dark energy
origin of the Moon
life on Earth?
Exoplanets
wormholes
relativity / twin paradox
general relativity
NASA
moon landing
radio waves from space - radio astronomy (K. Jansky)
WMAP
inflation (Adam Riess)
James Webb
Hubble (legacy / telescope)
astronaut training
planet colonizing
Mars One
entropy? (2nd law of thermodynamics)
Stars and the Main Sequence
There are 4 fundamental forces of nature:
Strong nuclear - this keeps protons close together
Weak nuclear a responsible for radioactive decay
Electromagnetism - light, electricity, magnetism, etc
Gravity - weakest of all, but furthest reaching
A star (Latin root stella-) is essentially a ball of gas powered by nuclear reactions, held together by gravity.
Stars may appear white, but their color is a conbination of many colors (and non visible e-m waves like uv).
Spectral types are listed in order of decreasing temperature:
O B A F G K M
with a temperature range from 60,000 K down to under 3500 K.
There are further subdivisions (C and S stars under M).
You can learn a lot about a star from where it lies on the Hertzsprung-Russel diagram.
The H-R diagram plots magnitude (brightness, from dim to bright) vs. temperature (high to low, usually as spectral type).
Hottest stars are on the left if the graph - they are normally brighter than cooler stars.
Most stars fall on along a diagonal band from upper left to lower right on the H-R diagram. We call this the Main Sequence, and the stars there are main sequence stars or dwarfs (which is a misleading term).
Stars above and to the right of the MS are giants (including supergiants).
Faint hit objects (white dwarfs) are below and to the left of the MS.
>
Strong nuclear - this keeps protons close together
Weak nuclear a responsible for radioactive decay
Electromagnetism - light, electricity, magnetism, etc
Gravity - weakest of all, but furthest reaching
A star (Latin root stella-) is essentially a ball of gas powered by nuclear reactions, held together by gravity.
Stars may appear white, but their color is a conbination of many colors (and non visible e-m waves like uv).
Spectral types are listed in order of decreasing temperature:
O B A F G K M
with a temperature range from 60,000 K down to under 3500 K.
There are further subdivisions (C and S stars under M).
You can learn a lot about a star from where it lies on the Hertzsprung-Russel diagram.
The H-R diagram plots magnitude (brightness, from dim to bright) vs. temperature (high to low, usually as spectral type).
Hottest stars are on the left if the graph - they are normally brighter than cooler stars.
Most stars fall on along a diagonal band from upper left to lower right on the H-R diagram. We call this the Main Sequence, and the stars there are main sequence stars or dwarfs (which is a misleading term).
Stars above and to the right of the MS are giants (including supergiants).
Faint hit objects (white dwarfs) are below and to the left of the MS.
>
Monday, April 6, 2015
Electromagnetic Waves
Recall that waves can be categorized into two major divisions:
Mechanical waves, which require a medium. These include sound, water and waves on a (guitar, etc.) string
Electromagnetic waves, which travel best where there is NO medium (vacuum), though they can typically travel through a medium as well. All electromagnetic waves can be represented on a chart, usually going from low frequency (radio waves) to high frequency (gamma rays). This translates to: long wavelength to short wavelength.
All of these EM waves travel at the same speed in a vacuum: the speed of light (c). Thus, the standard wave velocity equation becomes:
where c is the speed of light (3 x 10^8 m/s), f is frequency (in Hz) and l (which should actually be the Greek letter, lambda) is wavelength (in m).
Mechanical waves, which require a medium. These include sound, water and waves on a (guitar, etc.) string
Electromagnetic waves, which travel best where there is NO medium (vacuum), though they can typically travel through a medium as well. All electromagnetic waves can be represented on a chart, usually going from low frequency (radio waves) to high frequency (gamma rays). This translates to: long wavelength to short wavelength.
All of these EM waves travel at the same speed in a vacuum: the speed of light (c). Thus, the standard wave velocity equation becomes:
c = f l
where c is the speed of light (3 x 10^8 m/s), f is frequency (in Hz) and l (which should actually be the Greek letter, lambda) is wavelength (in m).
General breakdown of e/m waves from low frequency (and long wavelength) to high frequency (and short wavelength):
Radio
Microwave
IR (infrared)
Visible (ROYGBV)
UV (ultraviolet)
X-rays
Gamma rays
In detail, particularly the last image:
http://www.unihedron.com/projects/spectrum/downloads/full_spectrum.jpg
Don't forget - electromagnetic waves should be distinguished from mechanical waves (sound, water, earthquakes, strings on a guitar/piano/etc.).
Don't forget - electromagnetic waves should be distinguished from mechanical waves (sound, water, earthquakes, strings on a guitar/piano/etc.).
ALL E/M waves (in a vacuum) travel at the SPEED OF LIGHT (c).
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