Classroom Technique!: WebLog

Nell Shipman

Fri, 30 Jan 2009 11:10:51 -0600

So, I've begun my World of Cinema class. In class on Wednesday, earlier in the week, we watched a film called Back to God's Country, directed by Nell Shipman, a Canadian writer/director/actress from the early 20th century. Back to God's Country is a silent film, made in 1919. What a fascinating film about a virtuoso female filmmaker!

Final Is Today - Study Notes!

Wed, 12 Dec 2007 13:52:03 -0600

New Moon - When Moon is between Sun and Earth (when conditions right - solar eclipse)

Full Moon - When Earth is between Moon and Sun (when conditions right - lunar eclipse)

Conservation of angular momentum - angular momentum cannot change unless an external twisting force is acting on it

Conservation of momentum - momentum does not change unless an external force is action on it.

The Beginning of Time

Mon, 03 Dec 2007 20:14:28 -0600

What are the timeline of events related to the big bang?

The Planck Era - the time before which we have no understanding of the universe - ~10-43 second

GUT Era - Elementary Particles - ~10-38 second

Electroweak Era - Elementary particles - Electromagnetism and weak force dominant - ~10-10 second

Particle Era - Elementary particles (antimatter common) - ends at .001 second.

Era of Nucleo-Synthesis - Protons, neutrons, electrons (antimatter rare)- 3 minutes

Era of Nuclei - Atoms and plasma (stars begin to form) - 1 billion years

Era of Galaxies - Stars, galaxies, and clusters of galaxies (atoms and plasma) - 14 billion years

What is a quasar?

Tue, 27 Nov 2007 20:29:43 -0600

Quasars are the most luminous examples of an active galactic nucleus. They are found very far away from us, and some quasars are millions of times brighter than our Sun but occupy a very small region of space. Quasars are powered by the energy created as gravitational potential energy turns into kinetic energy as matter falls into a black hole.

How to Obtain the Distances to Galaxies

Mon, 26 Nov 2007 13:58:13 -0600

Method 1: Main Sequence Fitting (finding distances by comparing main sequence stars of different clusters).

1. Identify a nearby cluster with known distance (from parallax), and thus get the luminosities of its main sequence stars - standard candle.
2. Take a faraway cluster's main sequence stars and compare their brightness to the std. candle.
Since stars of the same color have the same luminosity, the difference in their apparent brightness would be proportional to the distance between them.

Method 2: Cepheid Variables

Cepheid stars are very luminous and vary in brightness with periods ranging from days to months. Cepheid variable stars with longer periods have greater luminosities (Period-Luminosity Relation).
Because the period of a Cepheid variable star tells us its luminosity, we can use these stars as standard candles. Gives distances up to 100 million ly.

Method 3: White Dwarf Supernovae As Standard Candle

White-dwarf supernovae can also be used as standard candles, because they happen in similar stars and hence should have similar luminosities.
Apparent brightness of white-dwarf supernova tells us the distance to its galaxy (up to 10 billion light-years)

Method 4: Tully-Fisher Relation:

Entire galaxies can also be used as standard candles galaxy luminosity is related to rotation speed: as both are related to mass in the galaxy (higher the mass, the more luminosity, as well as rotational speed).

Spacetime

Thu, 08 Nov 2007 16:50:17 -0600

Curvature of Spacetime

Is gravity really the curvature of three space dimensions and one time dimensions? Still trying to grasp that concept.

More Special Relativity Ideas

Tue, 06 Nov 2007 18:27:40 -0600

Good 'ol Albert E. -
Genius of massive proportions (no pun intended) and a humanitarian to boot -
What would he think of "Plutonian Marmalade"?

The Absolutes of Relativity:

The laws of nature (physics) are the same for everyone

The speed of light is the same for everyone

Einstein claimed that light should move at exactly c in all reference frames

Photons of Light

Relativity's Effect On Our View of Time & Space:

Time is not absolute.

Time almost halts for objects nearing the speed of light

Since all motion is relative, flashes of light that are simultaneous in your reference frame may not be that way in someone else's reference frame

Length of objects moving by you are shorter in their direction of motion than they would be if objects were at rest- the faster the objects are moving, the shorter the length

Theory of Special Relativity

Tue, 06 Nov 2007 13:33:53 -0600

The above image was taken from the Wikipedia article on Special Relativity and is meant to show that the speed of any object except light depends upon the reference frame of the observer.

Quite honestly, this is not the most interesting aspect of astronomy to me, so for me it involves rote memorization. Here is what I know so far:

Key Ideas of Special Relativity:

Special Relativity does not involve effect of gravity

No material object can travel faster than light

If you observe something near the speed of light, its time slows down, its length contracts in direction of motion, its mass increases

Whether or not two events are simultaneous depends on your perspective

Motion can be defined with respect to a particular reference frame

Black Hole

Wed, 31 Oct 2007 21:45:12 -0500

Artist's Rendering of a Black Hole

A black hole is essentially a region in space of extreme gravity, where no light can escape.

It's mass strongly warps space and time in the vicinity of the Event Horizon- the boundary surrounding the black hole.

Einstein's Theory of General Relativity explains that at the Event Horizon- the gravitational field of a black hole continues to infinity, and time dilation also becomes infinite.

Scientists know that black holes can form from the core of a dying star collapsing on itself under extreme gravity. Scientists also theorize that black holes can also happen naturally as matter collides under enormous pressure from all sides, squeezing and shrinking it till it stays that way forever.

Star Formation

Tue, 30 Oct 2007 18:08:50 -0500

Star Formation

The following are the reasons where and why stars form:

Stars form in dark clouds dusty gas in interstellar space, in between what is called InterStellar Medium

We determine composition of ISM from its absorption lines

70%H, 28%He, 2% Heavier Elements

Some pockets are cool & dense where stars form, while others are some are hot and less dense

The cool, dense parts are the areas where it is cool enough to form molecular clouds made up of H2, CO, NH3, etc.

1% of molecular clouds are made of dust

Stars form as a result of tempering thermal pressure with gravity where gravity has upper hand

Contraction of the gas/dust cloud converts gravitational potential energy into thermal energy

If excess thermal energy not gotten rid of, pressure would increase and contraction would come to a halt

Emission lines from molecules in a cloud can prevent a pressure buildup by converting thermal energy into infrared and radio photons

Fragmentation of the molecular cloud - growing strength of gravity over pressure in dense lumps fragment the cloud, and each lump can go on to form one or more

Isolated star formation - gravity can overcome pressure in relatively small cloud if the cloud is unusually dense

Trapping of thermal energy - Gravity packs molecules and dust particles of a cloud fragment close together, which makes it harder for infrared and radio photons to escape

Thermal energy builds up, increasing internal pressure

Contraction slows down, and center of cloud fragment becomes a protostar

Growth of a protostar and blowing off the remaining gas: Matter from the cloud continues to fall onto the protostar until the protostar blows the surrounding gas away, likely via stellar wind