The Milky Way – Timeline

The Milky Way Galaxy

HISTORY

1750: Immanuel Kant: advocated the “lens-shaped” distribution of stars, or an “island universe” with galaxies like the Milky Way

1785: William Herschel + Caroline (wife): made the first attempt to determine the shape of the galaxy; found few stars near the edge  and many stars toward the center; determined the galaxy to be an irregular “grindstone” or hockey puck

1900: If the Sun is at the center of the Universe, why is it not brighter at the center? Gas and gas prevent seeing far toward the center and light absorbed and refracted by Earth’s atmosphere  only allows us to see a small portion of the galaxy

Harlow Shapley and Herbert Curtis

1920: The Curtis- Shapley Debate

Harlow Shapley: rising star and “golden boy” of astronomy

  • Since globular clusters are not uniformly distributed uniformly around the Sun, the center of the Milky Way must be centered 30,000 light years away
  • Concluded that the Milky Way is much larger than previously believed (>100,000 light years in diameter)
  • The “nebulae” seen are not island universes but contained in the Milky Way

Herbert Curtis: established astronomer and respected

  • Spiral nebulae are galaxies out side the Milky Way, with high recessional velocities
  • Predicted that these spiral nebulae are the right size to be galaxies –> “huge” galaxy idea

While Shapley advanced that the Sun is not at the center of the galaxy and the galaxy is much larger than believed, Curtis argued that since spiral galaxies are external, there must be more big galaxies.

Who was right? BOTH. Who was wrong? BOTH.

Shapley was right the Sun is not at the center of the Universe. Curtis was right the Universe is composed of many galaxies. However, the size of the Milky Way was in-between their estimates.

1920s-1930s: Edwin Hubble: With the Hooker Telescope on Mt. Wilson, Hubble observed Cepheid Variable stars in the Andromeda Galaxy (M31); Cepheid Variable stars are 500-10,000 brighter than the Sun (in absolute magnitudes)

  • 1920s: Discovered that M31′s distance is too large to be within the Milky Way; M31 is a galaxy like the Milky Way
  • 1930s: Further understanding of the distances and distribution of globular clusters; the scientific community accepted that they underestimated the size of the Milky Way and the Sun is not at its center

Albert Einstein’s Legacy

ALBERT EINSTEIN (1879-1955)

Albert Einstein

Legacy

  • Reformulated the concept of time and space (E = mc² => special relativity)
    • Time is not an absolute quantity but appears to flow at a different rate depending on relative motion
  • Opened the road to quantum mechanics
    • Light “hits” like a particle
    • Light waves have “quantized” and “discrete” energies, depending on their wavelengths
  • Presented a revised theory of relativity
    • General relativity: space is curved
    • Foundation of modern cosmology

Einstein’s World

  • Reality of atoms and molecules in hot debate
  • Light poorly understood: “What was the medium light traveled in?”
  • Phenomena of radiation
  • Absorption lines in the Sun were observed, but could not be explained

Einstein helped clear these mysteries and began the era of modern physics.

Einstein’s Early Life and Career

Born in Ulm, German Empire in 1879, Albert Einstein excelled in physics and mathematics but failed in other subjects. Einstein dropped out of high school in 1895 and restarted school in Aarau, Switzerland, where he studied Maxwell’s works (~1870), which stated that electricity and magnetism obeyed the same set of physical laws — hence, electromagnetism. Einstein discovered that the velocity of light remained constant no matter the media. Although Einstein was brilliant, he irritated professors as he was too independent. In 1902, Einstein became a patent office clerk at the Swiss Patent Office in Bern. By 1905, Einstein had written six scientific papers, three of which explored the existence of molecules and the “kinetic theory.” For his other three papers, one published in March explained his light-quantum hypothesis (light hits like a particle), a fundamental step of quantum mechanics. For this, Einstein received a Nobel Prize in 1921. Another paper published in June was Einstein’s first paper on Special Relativity that explored light contraction and time dilation approaching the speed of light. In September of 1905, Einstein published his second paper on special relativity, in which he included the famous equation E = mc².

* General relativity includes gravity, while special relativity does not.

General Relativity and Special Relativity

Special Relativity

  1. The laws of physics are the same in all uniformly moving reference frames, or in all directions
  2. In any uniformly moving reference frame, the velocity of light (c) is the same whether emitted by a body at rest or a body in motion

Time Dilation and Length Contraction

Time Dilation: Time itself doesn’t tick at the same rate approaching the speed of light; instead, the time synchronization veers off; so approaching the speed of light, time appears to tick much slower.

Length Contraction: The lengths of moving objects are contracted when viewed by a stationary viewer

Mass and Energy

  • The mass of a moving body increases compared to its “rest mass” because it takes a bigger force to accelerate
  1. Acceleration: speed gained in a given time
  2. An object accelerating up is smaller because of time dilation; acceleration is harder the more massive the object is
  • Energy is responsible for powering stars, nuclear decay, and nuclear energy

Einstein’s Impact

  • At first, the scientific community met Einstein’s special relativity theory with silence, but Max Planck, who won the Nobel Prize for explaining black body radiation, realized the importance of Einstein’s work and publicized it; from 1906, scientists took notice and visited Einstein to talk about science
  • Einstein’s scientific circles grew stating 1908; became associate professor in 1911 and a professor of the Swiss Federal Institute of Technology in 1912
  • Einstein’s findings demanded a new way of thinking as Newton’s Law of Gravity was only valid from speeds much smaller than light
  • Einstein named the “birth of special relativity” “The Step”
  • 1907: The Equivalence Principle – gravity corresponds to acceleration
  • 1911: Bending of light in a gravitational field, a consequence of the Equivalence Principle, could be checked with astronomical observations
  • 1912-1915: Extend relativity to objects moving in an arbitrary way with respect to one another
  • 1915: General Relativity “Gravity curves space”: there’s no need for the “force” of gravity; all motion is along “straight lines” in curved space-time and matter tells space how to move
    • Evidence: starlight bends around the Sun; Mercury’s orbit will precede at a different rate than Newton predicted
  • 1919: Arthur Eddington leaders solar eclipse expedition and confirms special relativity
  • 1929: Edwin Hubble observes expansion of the Universe
    • Friedmann said that Einstein’s equations supported an expanding Universe, but Einstein proposed the “cosmological constant” to keep the Universe static

In Remembrance: Sally Ride (1951-2012)

SALLY RIDE (May 26, 1951 – July 23, 2012)

Sally Ride, First Woman Astronaut in Space

Sally Ride, the first woman astronaut to travel to space, passed away today at the age of 61 from her 17-month battle with pancreatic cancer. At Stanford University, Ride earned her master’s degree and Ph.D in physics. Ride joined NASA in 1978 and rode the Challenger to space on June 18, 1978 at the age of 32 and again in 1984. She spent 14 days in space!  After NASA, Sally Ride worked at the Stanford University International Security and Arms Control and taught physics at the University of California, San Diego. She later became the director of the California Space Institute and the founder and CEO of Sally Ride Science. Today, President Obama remembered Sally Ride as “a national hero and a powerful role model.”

References

Borenstein, Seth, and Alicia Chang. “Sally Ride, first US woman in space, dies at 61.” Boston.com. Boston.com, 23 July 2012. Web. 23 July 2012.

Early Astronomy History: Timeline

EARLY HISTORY (2700 B.C. – 1600 A.D.)

Early Astronomy: Predicting Eclipses, Determining Equinoxes and Solstices

2700 B.C. (Stonehenge, England) - stones marked solstices and equinoxes; Aubrey holes predicted eclipses

2000 B.C. [Sumerians] - earliest constellations (bull, lion, scorpion); base 60 system

2000 B.C. [Babylonians] - Pythagorean Theorem

1000 B.C. [Egyptians] - helical rising of Sirius; 12 month, 30 day calendar; sundial

1000 B.C. [Chinese] - counting boards

700 B.C. – 50 A.D. [Babylonians] - planetary positions and eclipses

600 B.C [Pre-Greek: Thales of Miletus] - solar eclipse prediction, Saros Cycle; constellations as known today

600 B.C. (Miletus, Greece) [Anaximander] - shadow from stick t calculate the length of the year; life originated in water, evolved from simpler forms

500 B.C [Pythagoras of Samos] - spherical moon, spherical-moving Earth

450 B.C [Empodocles] - water thief to argue that air must be so finely divided that it’s invisible

400 B.C. [Chinese] - sunspots

400 B.C. [Democritus] - atoms, large number of other worlds, Milky Way aggregates of light from other galaxies

4th Century B.C [Plato] - proposed Uniform Circular Motion of Planets; spherical Earth

350 B.C. (Athens, Greece) [Aristotle]- model of the solar system: spherical universe centered on solid spherical Earth (geocentric view); moon between Earth and Sun; all objects are from the four elements – earth, water, fire, and air; earth and heaven to be subject to two different sets of laws

300 B.C. (Alexandria) [Euclid] - most prominent mathematician; “Elements”: geometry; conic sections

310-250 B.C. [Aristarchus of Samos] - relative distances and sizes of the Moon and the Sun; Sun at the center of the solar system (heliocentric view); used Earth’s shadow to measure the size of the moon

200 B.C. (Alexandria) [Eratosthenes] - measured earth’s size using simple geometry and scientific process

130 B.C. [Hipparchus of Rhodes] - star maps; star catalog of 850 stars, precession; epicycles

150 A.D. [Ptolemy] - fixed Aristotle’s model with the epicycle theory: planets move in epicycles (small circular paths around which the planets move); the centers pf epicycles are along the deferent (big circle)

250 A.D. [Mayans] - “place-value” number system

500 A.D [Hyptia] - first known woman astronomer, librarian of Alexandria

500 A.D. [Chinese] - solar wind; comets: tail of comets always point away from the Sun

6th – 9th Century A.D. [Persian and Arabic Astronomy] - “Al-Sufi”: Book of Stars Showing Orion Nebula; “Al-Battani”: Non-circularity of Earth’s Orbit

10th Century A.D. [Mayans] - Dresden Codex, Venus tables, eclipse tables

10th Century A.D. [Chinese] - star map showing 26 sections

1054 A.D. [Chinese] - supernova: remnant traced to Crab Nebula

1100 A.D. [Pueblo Native Americans] - Sun Dagger

1270 A.D. [Samarkand] - star catalog

Mid-1400′s A.D. (Germany) [Regiomontanus] - “Ephemeris”; “The Nuremberg Chronicle” – planetary positions and comet charts

Prehistoric Astronomy

Prehistoric Astronomers

As one of the oldest sciences, astronomy flourished in prehistoric times. Hunter-gatherers realized the importance of recognizing seasons, moon phases, annular events, and the apparent movement of the Sun. The early peoples divided the skies into the North Celestial Pole, a single point about which stars move around in the sky, and the South Celestial Pole. The Celestial Equator is the half-way line between the Celestial Poles and also a projection of Earth’s equator into the sky. 3,000 years ago, the Babylonians discovered the 360° circle, which is a base 60 system that originated from 365 days in a year. The five ancient planets are Mercury, Venus, Mars, Jupiter, and Saturn. The North Star is the star closest to the North Celestial Pole— currently Polaris. Because of precession, or the wobble of Earth’s rotational axis that sweeps out a circle in 26,000 years, the extension of Earth’s North Pole points to a different North Star during the motion. Helical rising is the first day each year when a particular star can first be seen just before dawn; helical setting, then, is the last day of the year when the star can be seen at dusk.  The ecliptic is the apparent path of the Sun in the sky and the zodiac is the path of planets within a zone of 18 degrees wide-centered on the ecliptic. Hunter-gatherers and early settlers utilize knowledge of these ideas to farm, navigate, and survive.