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Science and the Universe

Science and the Universe. Nature of Astronomy. The study of the objects that lie beyond the atmosphere of our planet Earth The study of the processes by which these objects interact with one another

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Science and the Universe

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  1. Science and the Universe AST 2010: Prologue

  2. Nature of Astronomy • The study of the objects that lie beyond the atmosphere of our planet Earth • The study of the processes by which these objects interact with one another • Humanity’s attempt to organize the knowledge our universe into a clear history of the universe from the instant of its birth to the present time and beyond • And much more… AST 2010: Prologue

  3. Nature of Science • Science is a method (or process) by which one attempts to understand nature and how it behaves • The ultimate judge in science is the experiment or observation: what nature itself reveals • Science accepts nothing on faith AST 2010: Prologue

  4. Scientific Method Involves… • Many (repeated) observations over a period of time • Analyzing the trends and patterns • The formulation of models of the particular phenomena • Testing the models with further experiments and observations • Iteration of the above process AST 2010: Prologue

  5. Concrete Example of the Scientific Process • Ancient astronomers built a geocentric model of the universe • Better observations required the model to add circles after circles to the movements of the planets to keep the Earth at the center • The geocentric model eventually could no longer explain all the observed facts and was abandoned in favor of a heliocentric model, which fit the experimental evidence better AST 2010: Prologue

  6. Some Remarks about the Scientific Process • New models/ideas are called hypotheses • Contrary to common beliefs, much is yet to be learned in astronomy (and physics in general) • New phenomena are observed constantly, and new hypotheses needed to explain these • Some observational facts are very well understood, but others remain “mysterious” • Typically, new ideas are difficult to test either because the amount of data is small, or because they require observations that are difficult based on current technology AST 2010: Prologue

  7. Some Remarks about Astronomy • Astronomy is an observational science • It’s impossible for an astronomer to experiment with planets or stars in a laboratory on Earth • Much of astronomy is also a historical science • The events being observed have already happened • This is similar to a detective trying to solve a crime that occurred before the detective ever got to the scene AST 2010: Prologue

  8. Laws of Nature • Over the centuries, from experiments and observations, scientists have extracted certain fundamental principles, called scientific laws • Laws are the same everywhere in the universe • Astronomy would be difficult or even impossible without such laws • Laws (models and theories) are constantly refined by scientists to follow new, and typically more comprehensive, observations of nature • Describing the laws of nature requires a precise language: mathematical models and equations AST 2010: Prologue

  9. Numbers in Astronomy • Distances in astronomy are huge • It is convenient to use the power-of-tennotation, sometimes called scientific notation • Examples • 5,200,000 = 5.2 millions = 5.2 x 106 • 0.000125 = 1.25 x 10-4 AST 2010: Prologue

  10. Light Years • Astronomers use a convenient unit called “light-year” to describe distances in the universe • One light-year, abbreviated as 1 LY, equals the distance that light travels in one year • This unit is useful because light (of any color) • always travels at the same speed in vacuum • has the largest speed at which anything can travel AST 2010: Prologue

  11. Speed of Light (in Vacuum) • Light travels at the amazing speed of 300,000 kilometers per second (1 kilometer = 0.6 mile) or • 300,000 km/s = 3 x 105 km/s • 3 x 108 m/s • 1,080,000 km/hour AST 2010: Prologue

  12. One Light-Year (1 LY) • 60 seconds in 1 minute • 3 x 105 km/s x 60 s/min = 1.80 x 107 km/min • 60 minutes in 1 hour • 1.80 x 107 km/min x 60 min/hour = 1.08 x 109 km/hour • 24 hours in a day • 1.08 x 109 km/hour x 24 hour/day = 2.592 x 1010 km/day • 365.24 days in a year • 2.592 x 1014 km/day x 365.24 day/year = 9.46 x 1012 km/year • 1 LY = 9.46 x 1012 km AST 2010: Prologue

  13. How We Learn about Distant Objects • Information about distant objects comes to us almost exclusively via various forms of light • All such light travels at the speed of light (namely, 1 LY every year) • This leads to two consequences … AST 2010: Prologue

  14. Consequence 1 • The fact that light takes time to travel sets a limit on how quickly we can learn about events in the universe • If a star is 10 LY away, the light we see from it tonight left that star 10 years ago • If that star exploded today, we would learn about it only 10 years from now AST 2010: Prologue

  15. Consequence 2 • Since light takes time to travel, an observation of distant objects in the sky is actually an observation of what happened in the past • The further away the objects we look at, the more ancient they are • This is a potential benefit in disguise, providing a way to study the history of the Universe AST 2010: Prologue

  16. An Imaginary Journey from Home • Earth • Planets • Solar System • Star Clusters • Galaxy • Galaxy Clusters • Galaxy Super-clusters • The Universe! AST 2010: Prologue

  17. Planet Earth • A nearly spherical planet about 13,000 km in diameter • Distinguished by the large amount of liquid water it has, which covers 2/3 of its surface • Supports “intelligent life” • Has one natural satellite: the Moon AST 2010: Prologue

  18. The Moon • The Moon’s diameter is about 3476 km • The Moon-to-Earth distance is about 30 times the Earth’s diameter • Light travels from the Moon to the Earth in about 1.3 seconds Photo by John French, Abrams PlanetariumMichigan State University AST 2010: Prologue

  19. More about the Earth • The Earth revolves around the Sun • The period of revolution is 3 x 107 s (1 year) • The average Earth-to-Sun distance is about 150 million km • This defines a unit of distance called 1 astronomical unit (AU) • The Earth travels at about 110,000 km/hour in its orbit around the Sun • Light takes 8 minutes to travel from the Sun to the Earth • Our latest news from the Sun is always 8 minutes old! AST 2010: Prologue

  20. Solar System (1) • The solar system consists of the Sun at its center and nine planets orbiting the Sun • The Earth is one of the nine planets • The Sun is a star • Its diameter is 1.5 million km • A planet is a body of significant size that orbits a star and does not produce its own light • A star is large body which (at some point during its life) produces light by nuclear reactions AST 2010: Prologue

  21. Solar System (2) • The other 8 planets are visible from Earth because of the (Sun’s) light they reflect towards us (albedo) • The 9 planets are located at enormous distances from the Sun as illustrated here AST 2010: Prologue

  22. Jupiter • Being the largest planet in the solar system, Jupiter has a diameter of 143,000 km • 11 times Earth’s size • Its distance to the Sun is about 5 AU • Like many other planets, it has a number of natural satellites or moons AST 2010: Prologue

  23. The Milky Way (1) • The Sun is our local star • Other stars are also suns: typically enormous balls of glowing gas that generate vast amounts of energy and light via nuclear reactions • Other stars look small and faint compared to our sun because they are extremely distant from us • The nearest star beyond the Sun is Proxima Centauri, which is 4.3 LY away • The stars we see at night are part of a gigantic complex of stars called the Milky Way • The Milky Way is a Galaxy AST 2010: Prologue

  24. The Milky Way (2) • The Sun is about 30,000 LY from the center of our Galaxy • From our location within the Galaxy, we cannot see through its far rim because the space between stars is not empty, but contains (an extremely sparse distribution of) interstellar dust or gas which absorbs visible light • The interstellar gas and dust are believed to be the raw material for future formation of stars AST 2010: Prologue

  25. The Milky Way (3) • There is indirect evidence that much of our Galaxy is made of material that cannot be observed with present-day instruments • Thus, much of our Galaxy seems to consist of dark matter • Stars in a number of places form clusters, eachcontaining up to hundreds of thousands of stars and taking up a volume of space hundreds of light years across • Stars have a long, but not infinite, life (billions of years) • They die or collapse in spectacular ways AST 2010: Prologue

  26. Nearby Objects • Our Galaxy, the Milky Way, is not alone • Many other galaxies have been discovered and studied, and most are at enormous distances from ours • So many galaxies have been found that it would be foolish to give them all proper names -- they are usually given a catalog number • The Magellanic Clouds are two of the small galaxies nearest to ours • The nearest large galaxy is Andromeda, or M31 The two Magellanic Clouds NOAO/AURA/NSF AndromedaNOAO/AURA/NSF AST 2010: Prologue

  27. Local Group of Galaxies • M31 is part of a small cluster of over 40 galaxies which is called the Local Group • At distances of about 10 to 15 million LY, one finds other small galaxy groups or clusters • At about 50 million LY, one finds a very large cluster containing thousands of galaxies — called the Virgo Cluster • Some of the observed clusters appear to form superclusters • Our Local Group and the Virgo Cluster are part of one such supercluster which stretches over a diameter of 60 million LY Center of Virgo Cluster AST 2010: Prologue

  28. And beyond… • At even greater distances, galaxies are too dim to see, and one finds spectacular objects called quasars • Quasars are brilliant centers of galaxies, glowing with enormous intensities • One theory suggests that a giant black hole is swallowing whole neighborhoods of raw material to produce the observed huge and intense emissions • Quasars allow us to probe the universe 10 billion or more LY away and, thus, 10 billion years in the past! • This may bring us closer to the earliest times of the universe, and even its beginning! AST 2010: Prologue

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