A spiral galaxy projected by the Planetarium's Watchout wide-screen video systemFor middle and high school; also suitable for introductory college courses
To arrange a visit for your school group, please call (585) 697-1942.
Go beyond the planets of our solar system in this program for students whose excitement is maturing into challenging curiosity!
We begin with light, the source of most of our information about deep space. See how to manipulate a diffraction grating to produce a spectrum. Next, generalize from visible to invisible forms of light. Compare and contrast telescopes needed to detect different forms of light. Classify stars by color, brightness, mass and ultimate fate. Use ratio, proportion, and appropriate units to communicate astronomical distance scales. See computer models
used by professional astronomers to explore galaxy collisions and the
expansion of the universe. Encounter evidence pointing to the greatest
mysteries in astronomy today, including dark matter and dark energy (gathering and organizing data). Observe stars, constellations and planets visible in the current sky.
NYS Learning Standards: ELA1; MST1MA(1,2); 1SI(1,2,3); 2(1); 3(4,5); 4PS(1,3,4,5); 5(3,4,5); 6(2,3,4); CDOS 3a(5),3b
Download the script for a typical presentation here (52k PDF)------------------------------------------------------------------------
Outline of the Program
The electromagnetic spectrum
Your presenter demonstrates how a diffraction grating
"un-mixes" white light into a spectrum, showing the colors of a rainbow. Each
color is associated with a different wavelength of electromagnetic waves. Human
eyes are sensitive only to a narrow range of wavelengths known as visible
light. Within the visible range, the colors are always in the same order: red,
orange, yellow, green, blue, violet (remember ROY G. BIV). The entire
electromagnetic spectrum includes a wide range of wavelengths, from radio waves
(longest waves, lowest energy) to gamma rays (shortest waves, highest energy).
First look at the sky
The star projector rises on its elevator; we take a first
tour of the brightest stars, constellations and planets visible to the unaided
eye in the current season's sky.
Our Sun: the nearest star
Size: about 109 times as wide as Earth
Rotates once in about 25 days at the equator
Surface temperature: about 10,000 degrees F.
Core temperature estimated to be about 27 million degrees
Some solar features visible to us: sunspots, granulation,
the solar activity cycle, coronal mass ejections
Life cycles of stars
We compare stars of low mass, medium (Sun-like) mass, and
high mass
All stars begin when gravity compresses gas and dust
When the center of the protostar gets hot and dense
enough, nuclear fusion begins
High-mass stars are the rarest type and live the shortest
lives
A high-mass star may explode as a supernova
A Sun-like star lasts much longer and does not explode.
Eventually it uses up hydrogen, turns to helium burning, swells up to become a
red giant, and sheds mass to create a "planetary nebula", leaving a white dwarf
behind
Red dwarfs are the most common stars, but they are so dim
that not even one is visible to the unaided eye. They shine dimly for many
billions of years with little change
White dwarf
Only about as large as Earth
On the surface, a typical person would weigh over 1
million pounds
No longer releasing new nuclear energy
An example of a white dwarf: Sirius B
In X-ray light, Sirius B is brighter than Sirius
Intense X-ray emission indicates
very hot temperature
Neutron star
Forms if a dead star has enough gravity to crush protons
and electrons together
Less than 20 miles across
As dense as compressing all humans on Earth into one
teaspoon
Extremely strong magnetic field
Black hole
According to our current understanding of physics, a
black hole must form if a dead star has enough gravity to overcome nuclear
forces
In an ideal, simple black hole, the singularity at the
center is the point at which gravity and density approach infinity
The event horizon is the boundary from which nothing can
escape, not even light
Anything that crosses the event horizon must fall into
the singularity
The size of a black hole depends on its mass
Star formation
We examine an image of the Orion Nebula taken by the
Hubble Space Telescope
The Orion Nebula
is lit up mostly by a cluster of four stars called the Trapezium
Scattered through the Orion Nebula: dozens of
protoplanetary disks (proplyds)
Looking into a nebula
"Nebula"
is Latin for "cloud" – in space, a cloud of gas and dust
Infrared light can penetrate dust clouds, so an infrared
camera can see stars inside a nebula
Example: compare visible vs. infrared views of the 30
Doradus region
Late stages of a star's life
Red giants
Pictures in astronomy books usually show red giant stars
as plain red spheres
However, computer simulations by Prof. Freytag in Sweden indicate
they could be much more interesting
Planetary nebulas
A red giant star may gently puff its outer layers into space,
maybe multiple times
The resulting shell of gas is confusingly called a "planetary"
nebula because it may resemble a planet when seen through a telescope
Examples: The Helix Nebula, the Cat's Eye Nebula, many
others with nicknames
A supernova remnant: the Crab Nebula
On or about July 4, 1054, Chinese astronomers recorded a "guest
star" in what we call the constellation Taurus. Now we realize they were seeing
a supernova explosion.
Now, at that same location, we see the Crab Nebula
At the center of the Crab Nebula, the neutron star formed
in the explosion has been detected by telescopes sensitive to X-rays, infrared
light, and radio waves.
The neutron star's magnetic field steers particles and
energy outward in narrow beams. As the neutron star spins, the beams sweep past
our line of sight with each rotation. Our radio telescopes see a pulsar – a point
emitting regular pulses of radio energy.
Black holes
If black holes are black, light-absorbing objects against
the black background of the sky, how could we find them? One strategy: look for
binary star systems (two stars orbiting each other) in which one star has
formed a black hole. Matter from the companion star, swirling around the hole,
is heated by friction and pressure to emit flickering X-rays. Thus X-ray
telescopes are important in the search for black holes.
The Hertzsprung-Russell (H-R) diagram
The H-R diagram is not a map of star locations in space;
it's a graph that plots the luminosity of a star on the vertical axis and its
color or temperature on the horizontal axis. Most stars fall on a diagonal band
called the main sequence. We see a short video from the Space Telescope Science
Institute explaining the H-R diagram in a clever way: http://bit.ly/epKUwR
Moving out to the realm of the galaxies
We review:
The speed of light: 186,000 miles per second in a vacuum
One light year is the distance light travels in one year,
about 6 trillion miles
Using light travel time to express distance
- Light from our moon takes about 1.3 seconds to reach us,
so we can say the moon is about 1.3 light-seconds away
- The Sun: about 8.3 light-minutes
- Pluto: about 6 light-hours
- The nearest star to the Sun, Alpha Centauri: about 4.2 light-years
- The Spiral Galaxy in Andromeda: about 2.4 million light-years
Types of galaxies
Spiral, elliptical, irregular
A beautiful example of a spiral galaxy
Galaxy M100, photographed by the Hubble Space Telescope.
We note the nucleus and spiral arms
The Milky Way, our home galaxy
We have discovered that we live in a galaxy – the Milky
Way Galaxy
It contains about 300 billion stars in a disk about
100,000 light years across
Our sun is not at the center; we are about two-thirds of
the way from the center to the edge of the disk of stars
Dark Matter
A major discovery of the late 20th century:
Gravity from stars, gas, dust, planets and black holes is
not enough to hold a galaxy together
Most of a galaxy is dark matter, known by its gravitational
pull on stars
A more correct illustration of our Milky Way Galaxy must
include a giant halo of dark matter
Another way to detect dark matter: gravitational lensing
In 1916, Albert Einstein published his general theory of
relativity, which says that gravity is curved spacetime
Spacetime is curved by matter and energy of any kind,
including dark matter
When we look at a photograph of the cluster of galaxies
called Abell 2218, we see curved, distorted images of faraway galaxies behind
the cluster.
The images are distorted as they pass through the cluster
because the space within it is curved by the presence of dark matter. The
cluster acts as a gravitational lens, altering the appearance of objects behind
it.
Gravitational lensing has been used to map dark matter in
thousands of galaxy clusters.
Expansion of the universe
One of the predictions of Einstein's general theory of
relativity was that the entire universe should be either expanding or
contracting. This conclusion was so strange that Einstein himself did not
believe it.
Then, in 1929, American astronomer Edwin Hubble (after
whom the telescope is named) announced his discovery that galaxies are getting
farther and farther from each other. In other words, the universe is indeed
expanding.
If we trace the motion of the galaxies backward in time,
all distances reach zero about 13.7 billion years in the past. We call that
moment the Big Bang; the universe has been expanding since then.
Accelerating expansion and dark energy
In 1998 there was a startling new discovery: the expansion
of the universe is speeding up. The space between galaxies seems to have
repulsive gravity. Repulsive gravity is possible according to Einstein's
equations. The mysterious source of this repulsive force is now called dark
energy, and it comprises most of the energy in the universe.
Our current inventory of the universe:
- Ordinary matter (atoms): 4%
- Dark matter: about 23%
- Dark energy: about 73%
In other words, most of the universe is dark.
Return to the sky
What if we could step outside on a clear night and see
all the known galaxies? The galaxies form a texture of filaments and sheets
that must be explained by any theory of the history of the universe. Remember,
however, that shining galaxies are like lights on an invisible tree of dark
matter.
The Hubble Deep Field
In 1995, engineers in charge of the Hubble Space
Telescope selected a tiny patch of sky (about the size of a dime 75 feet away)
that was blank on star charts. They programmed the telescope's camera to record
everything it could see in this tiny area. More than 1500 previously unknown
galaxies were found. A few years later, with a more sensitive camera installed
by spacewalking astronauts, about 10,000 galaxies were found in this tiny,
unremarkable sample of the sky.
The program ends with a longer tour of currently visible
stars, constellations and planets. After the lights come back up, we encourage
questions from students and teachers.
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Links to further information outside the RMSC website:Hubble Space Telescope: http://www.stsci.edu/outreach/
Chandra X-ray Observatory: http://chandra.harvard.edu or http://chandra.nasa.gov
European Southern Observatory: http://www.eso.org/outreach
National Optical Astronomy Observatory: http://www.noao.edu
W.M. Keck Observatory, Hawaii: http://www.keckobservatory.org
NASA's Microwave Anisotropy Probe (MAP)
mission is gathering information about the early universe. Go to their
web site at http://map.gsfc.nasa.gov and click on "outreach/media" to
find "Cosmology 101," a tutorial on the "Big Bang" idea and the
evidence for it:
NASA's Astronomy Picture of the Day
is a wonderful resource. Links and searching capabilities make it
possible to learn a little or a lot about almost any topic in astronomy
or space exploration: http://antwrp.gsfc.nasa.gov/apod
Students
and teachers who are very interested in cosmology, the Big Bang, and
the early universe will find detailed information and amazing graphics
at these sites:
The Kavli Center for Cosmological Physics at the University of Chicago, http://cfcp.uchicago.edu. Click on "Education and Outreach," then "About cosmology."
The Wilkinson Microwave Anisotropy Probe mission (WMAP) at http://map.gsfc.nasa.gov. Click on "Universe" to find "Cosmology 101."