Download 100 Greatest Discoveries in Science

100 Greatest Discoveries in Science - Astronomy (Video Guide)
1. The Planets Move (2000 B.C. – 500 B.C.) A thousand years of observations reveal that there are stars that move in
the sky and follow patterns, showing that the Earth is part of a solar system of planets separate from the fixed stars.
Why is the Venus tablet of Amozogania important?
It’s the earliest record of a planet moving.
Describe the Greeks’ model of the solar system.
Planets move around the Earth.
2. The Earth Moves (1543) Nicolaus Copernicus places the sun, not the Earth, at the center of the solar system.
How was Nicolaus Copernicus’s model of the solar system different than the Greeks’ model?
The sun is the center of the solar system, and the Earth circled the sun like other planets.
Why was it so hard for people to accept his theory?
It didn’t feel like the Earth was moving.
3. Planetary Orbits Are Elliptical (1605 – 1609) Johannes Kepler devises mathematical laws that successfully and
accurately predict the motions of the planets in elliptical orbits.
How was Johannes Kepler’s model of the solar system different than the models of Copernicus and the Greeks?
Planets did not move in circular orbits as Copernicus and the Greeks thought, but rather in an elliptical orbit.
Why was Kepler’s model so important?
It was the first system to accurately predict the movement of the planets.
4. Jupiter Has Moons (1609 – 1612) Galileo Galilei discovers that Jupiter has moons like the Earth, proving that
Copernicus, not Ptolemy, is right. Copernicus believes that Earth is not unique, but instead resembles the other
planets, all of which orbit the sun.
What were some of the things first seen by Galileo Galileo with his new telescope?
Mountains on the moon, star clusters of the Milky Way, Jupiter’s moons
How did Galileo’s discovery of Jupiter’s moons support Copernicus’s model of the solar system?
If moons could orbit Jupiter, then Earth could orbit the sun.
5. Halley's Comet Has a Predictable Orbit (1705 – 1758) Edmund Halley proves that comets orbit the sun like the
planets and successfully predicts the return of Halley's Comet. He determines that comets seen in 1531 and 1607 are
the same object following a 76-year orbit. Halley's prediction is proven in 1758 when the comet returns.
Unfortunately, Halley had died in 1742, missing the momentous event.
What did people in the Middle Ages believe about the appearance of a comet?
It meant that something bad was going to happen.
Edmund Halley studied the orbits of comets and predicted that a particular comet (now named Halley’s Comet)
would return in the year _____ and every _____ years after that.
1758, 76
Why Halley’s Comet a milestone discovery in astronomy?
A superstitious belief was replaced with a rational understanding of the universe.
6. The Milky Way Is a Gigantic Disk of Stars (1780 – 1834) Telescope-maker William Herschel and his sister Carolyn
map the entire sky and prove that our solar system resides in a gigantic disk of stars that bulges in the center called
the Milky Way. Herschel's technique involves taking a sample count of stars in the field of view of his telescope. His
final count shows more than 90,000 stars in 2,400 sample areas. Later studies confirm that our galaxy is disk-shaped,
but find that the sun is not near the center and that the system is considerably larger than Herschel's estimation.
What did William Herschel find as he counted the stars in particular sections of the sky?
First he found the planet Uranus. He also found that the Milky Way was much larger than people knew.
How did this discovery change the study of astronomy?
Our solar system is just an island in a huge universe.
7. General Relativity (1915 – 1919) Albert Einstein unveils his theory of general relativity in which he proposes that
mass warps both time and space, therefore large masses can bend light. The theory is proven in 1919 by astronomers
using a solar eclipse as a test.
Why did the orbit of Mercury puzzle Einstein and other scientists?
Mercury’s orbit could not be correctly predicted by Newton’s Laws of motion.
How can a trampoline help to explain the theory of general relativity?
A bowling ball in the middle sinks in the trampoline, and a marble will orbit around the bowling ball because
the trampoline is pushing the marble in certain directions. This shows that a large mass warps space (and
time).
How did observations taken during a solar eclipse help to prove Einstein’s theory of general relativity?
Pictures taken before, during, and after an eclipse show that light from stars was bent as the light passes by
the Sun.
8. The Universe Is Expanding (1924 – 1929) Edwin Hubble determines the distance to many nearby galaxies and
discovers that the farther they are from us, the faster they are flying away from us. His calculations prove that the
universe is expanding.
The “white nebulae” found by William Herschel turned out to be what we call today _________.
galaxies
A shift toward the blue end of the spectrum in the color of a star showed the star was moving
_____________________; a shift toward the red end of the spectrum in the color of a star showed the star was
moving _______________________.
closer to Earth, away from Earth
Edwin Hubble found that almost all stars showed a _____-shift, meaning that the universe is _________________.
red, expanding
Measuring backwards from the expansion led astronomers to propose the _____________ theory where a huge
explosion started the universe expanding.
Big Bang
9. The Center of the Milky Way Emits Radio Waves (1932) Karl Jansky invents radio astronomy and discovers a
strange radio-emitting object at the center of the Milky Way. Jansky was conducting experiments on radio
wavelength interference for his employer, Bell Telephone Laboratories, when he detected three groups of static; local
thunderstorms, distant thunderstorms and a steady hiss-type static. Jansky determines that the static is coming from
an unknown source at the center of the Milky Way by its position in the sky.
What did Karl Jansky’s static observations end up showing at the middle of the Milky Way galaxy?
A black hole
How were Jansky’s observations the start of a new kind of astronomy?
He was the first to use radio waves (which can’t be seen) to study astronomy.
10. Cosmic Microwave Background Radiation (1964) Arno Penzias and Robert Wilson discover cosmic microwave
background radiation, which they suspect is the afterglow of the big bang. Their measurements, combined with Edwin
Hubble's earlier finding that the galaxies are rushing away, make a strong case for the big bang theory of the birth of
the universe.
What were Robert Wilson and Arno Penzias trying to measure with the spare microwave antenna?
They wanted to measure the temperature of the gas halo around the Milky Way galaxy.
How is the steady state theory of the universe different than the Big Bang theory?
The steady state theory said that the universe had no beginning or end, and is always expanding.
How did the work of Wilson and Penzias help to support the Big Bang theory?
The “extra” 3-4 degrees measured by Wilson and Penzias showed energy that was left over from the Big Bang
theory.
11. Gamma-Ray Bursts (1969 – 1997) The two-decade-long mystery of gamma-ray bursts is solved by a host of
sophisticated ground-based and orbiting telescopes. Gamma-ray bursts are short-lived bursts of gamma-ray photons,
which are the most energetic form of light and are associated with nuclear blasts. At least some of the bursts have
now been linked with distant supernovae — explosions marking the deaths of especially massive stars.
Contrast the understanding of gamma ray bursts in the 1960’s with today’s understanding of gamma ray bursts.
In the 1960’s scientists believed that gamma ray bursts were caused by supernova explosions. Today we
believe that gamma ray bursts are very powerful and may have caused past extinctions on the Earth.
Why was it so hard to study gamma ray bursts?
They happened so fast that they were over before scientists could get a telescope focused on that area of
space.
12. Planets Around Other Stars (1995 – 2004) Astronomers find a host of extrasolar planets as a result of improved
telescope technology and prove that other solar systems exist, although none as yet resembles our own. Astronomers
are able to detect extrasolar planets by measuring gravitational influences on stars.
How do scientists look for planets orbiting other stars? Why can’t scientists look for the planet itself?
To find another planet, you watch the star to see if it wobbles (using the Doppler effect) due to the planet’s
gravitational pull on the star. Scientists don’t look for the planets because they don’t create their own light
and are very dim.
How many “extra solar” planets (planets outside our solar system) have been found so far?
Around 130
What qualities would a planet need to support life?
The star the planet orbits should be similar to our sun; the planet needs to have a temp that allows liquid
water.
13. The Universe Is Accelerating (1998 – 2000) Unexpectedly, astronomers find that instead of slowing down due to
the pull of gravity, the expansion of the universe at great distances is accelerating. If these observations are correct
and the trend continues, it will result in the inability to see other galaxies. A new theory of the end of the universe
based on this finding has been called the "big rip."
Why is the discovery that the universe expansion is speeding up so important?
The acceleration of the universe expansion doesn’t fit with our current understanding of how the universe
works.
What is one possible explanation for the accelerating universe expansion?
There may be some type of “dark energy” that causes the universe to expand faster and faster.