Welcome to Astronomy
workshop:
I will use this page as a
note pad which I will update as the course progresses. Here you will find links for web pages you
will need review before the next class.
I will include thoughts and
comment supplementing what we covered in class.
Clear Skies!
Jim Lawrence
Scales and tools of
measurement used in our normal terrestrial lives are insufficient when dealing
with the vast distances separating the planets, the stars in our home galaxy,
distances between galaxies in our local group and the vast distances between
galactic groupings which form the large scale structure of the universe.
http://www.ifa.hawaii.edu/~barnes/ast110_06/sosat.html
introduces scientific notation and clarifies the difference between linear and
logarithmic scales. Left click on a page
to step forward rather than scrolling. Powers
of Ten link is broken, but Worlds Within link is good, and provides
a view of the universe from macrocosm to microcosm in base 10 logarithmic
steps. Note the controls on this animation – you can adjust the presentation
speed or step through the animation at your own pace.
The speed of light
provides a basis for measuring the cosmos. It takes light approximately 1 1/3
seconds to travel to us from the moon, and accordingly we see the moon as it
was 1
1/3 seconds in the past.
We see the nearest star as it was 4 years in the past and the Andromeda Galaxy
as it was over 2 million years ago, in each example, defining how long light
takes to travel from each object to us on earth.
http://www.krysstal.com/scale.html
takes the observer successively further from our home planet and, successively
further back in time.
This short flash movie
introduces constellations and shows position of bright planets: http://amazing-space.stsci.edu/tonights_sky/
Here is a brief
description of commonly used telescope types: http://www.stargazing.net/naa/scope2.htm
We have developed a scale
model of the universe and it becomes apparent that the distances are so vast
that interstellar travel is not within our immediate reach. Here’s a web application which allows you to
try different scales to get a “feel” for the distances astronomy deals with: Build a Solar System.
Tonight we have a full
moon which showcases the large lava fields or maria and the major impact
craters. Here’s a nice moon map with
major features: moon map
Impact sites on the moon
remain unchanged (excepting modification from later impacts) for eons. It is reasonable to conclude that large
impacts as seen on the moon have occurred here on earth at intervals. This is supported by the discovery of ancient
impacts on earth heretofore “hidden” and only recently found through modern
technology.
Bright stars can be small
stars very close or large stars quite distant.
Parallax is a means of determining the distance of stars within about
150 light years. Parallax - Wikipedia, the free
encyclopedia provides a good overview of parallax.
Astronomical measurement
begins with the Astronomical Unit or AU which is distance from earth to sun
– a bit over 93,000,000 miles or 8.4
light minutes. The next unit of
measurement is the Light Year or LY which equals 63,241 AU. The next unit commonly used is the parallax
second or parsec which represents the distance at which a star has a parallax
of one arc second as seen against distant background stars. A parsec equals 3.262 light years.
Scroll down to the bottom
of sketches and see my drawing of the
lunar crater Eratosthenes. Many lunar
features are named for individuals who contributed to our astronomical
knowledge. Eratosthenes was a Greek ahead of his time who figured out the
diameter of the earth. Eratosthenes
is a link which details how he did it.
Aristarchus, who also has
a lunar crater in his name, was able to estimate the size of the moon. This
site tells how he did it. In basic terms, if the moon were the same size as
the earth, its image would be the same diameter as the earth’s shadow.
Through our tools, we are
able to do things thought impossible but a few years ago. Here
you can see what a Martian sunset really looks like and also watch Jupiter and
earth appear in the evening Martian
sky.
Binary stars “go around
each other” in ways you might not expect, governed by their respective masses
and distances from each other. Go here and
scroll down and run the Java applet which will allow you to experiment with
orbiting stars.
Here are links to Youtube short movies concerning gravity and
spacetime. You may note that gravity and
spacetime are often mentioned together; and that is because the two concepts
are intertwined – a basic grasp of spacetime and gravity will leave you with a
perspective of the universe quite different from that held by “the man on the
street.”
YouTube - fun in a gravity
well
YouTube -
The Elegant Universe - Einstein's Relativity
We talked about Kepler who
found that planets travel in elliptical orbits rather than circular
orbits. Here is a good animation showing
the changes in orbital velocity arising from an elliptical orbit.
Although much smaller than
earth and twice as far from the sun as we are, Mars has fascinated man for a
very long time. Mars beckons for us to visit.
Volunteers
wanted for trip to 'Mars'
If we were asked to make a
scale model of the Milky Way Galaxy on a gymnasium floor, using sand – the
questions arise– how much sand to represent our 200 billion stars and how much
of the gym floor would we need to spread out the sand? It has been calculated that a railway box car
full of sand would just be enough and the gym would be too small – you would
need spread the sand out over 125,000 miles, or about half way to our
moon. The 125,000 mile circle of sand
grains would model the true diameter of our home galaxy – about 90,000 light
years. On the same scale, our nearest
neighboring island universe, the Andromeda Galaxy, 2,500,000 light years away,
would be found 28 times further than the halfway point to the moon, or 3
million 500 thousand miles away - and it
would be just another boxcar full of sand spread out in a whispy disc. Edwin Hubble found that all galaxies are
receding from us – the further away a galaxy is found, the faster it is fleeing
– so we conclude that spacetime itself is expanding and the galaxies like spots
on a balloon being blown up, get further and further apart as the balloon
expands. By playing this movie
backwards, it was concluded that at a point in time about 15 billion years ago,
the universe was a very tiny place which began to expand and is continuing to
do so. Here’s some information about
Hubble, after whom the Hubble Telescope was named.
