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ormation. The second way we try to keep numbers simple is to use a consistent set of units—the metric International System of Units, or SI (from the French Système International d’Unités). The metric system is summarized in Appendix D (see Example 1.2). 16 Chapter 1 Science and the Universe: A Brief Tour Watch this bri... |
ant size that orbits a star and does not produce its own light. (If a large body consistently produces its own light, it is then called a star.) Later in the book this definition will be modified a bit, but it is perfectly fine for now as you begin your voyage. Figure 1.8. Our Solar Family. The Sun, the planets, and so... |
her small galaxy groups, and then at about 50 million light- years there are more impressive systems with thousands of member galaxies. We have discovered that galaxies occur mostly in clusters, both large and small (Figure 1.14). 26 Chapter 1 Science and the Universe: A Brief Tour Figure 1.14. Fornax Cluster of Galaxi... |
sents a classic overview of astronomy by an astronomer who had a true gift for explaining things clearly. (You can also check out Sagan’s television series Cosmos: A Personal Voyage and Neil DeGrasse Tyson’s current series Cosmos: A Spacetime Odyssey.) 30 Chapter 1 Science and the Universe: A Brief Tour Tyson, Neil DeG... |
al Equator To help orient us in the turning sky, astronomers use a system that extends Earth’s axis points into the sky. Imagine a line going through Earth, connecting the North and South Poles. This is Earth’s axis, and Earth rotates about this line. If we extend this imaginary line outward from Earth, the points wher... |
Pluto are actually tilted so much that they orbit the Sun “on their side.” Figure 2.7. The Celestial Tilt. The celestial equator is tilted by 23.5° to the ecliptic. As a result, North Americans and Europeans see the Sun north of the celestial equator and high in our sky in June, and south of the celestial equator and l... |
he Egyptians. The Chinese also recorded comets, bright meteors, and dark spots on the Sun. (Many types of astronomical objects were introduced in Science and the Universe: A Brief Tour. If you are not familiar with terms like comets and meteors, you may want to review that chapter.) Later, Chinese astronomers kept care... |
rence must be 50 × 5000, or 250,000 stadia. Figure 2.11. How Eratosthenes Measured the Size of Earth. Eratosthenes measured the size of Earth by observing the angle at which the Sun’s rays hit our planet’s surface. The Sun’s rays come in parallel, but because Earth’s surface curves, a ray at Syene comes straight down w... |
ns had to be circular. However, we shall see in Orbits and Gravity that the planets, like Earth, travel about the Sun in orbits that are ellipses, not circles. Their actual behavior cannot be represented accurately by a scheme of uniform circular motions. In order to match the observed motions of the planets, Ptolemy h... |
of tests are all the same: there is no evidence that natal astrology has any predictive power, even in a statistical sense. Why, then, do people often seem to have anecdotes about how well their own astrologer advised them? Effective astrologers today use the language of the zodiac and the horoscope only as the outwar... |
a roughly correct scale for the solar system. Copernicus could not prove that Earth revolves about the Sun. In fact, with some adjustments, the old Ptolemaic system could have accounted, as well, for the motions of the planets in the sky. But Copernicus pointed out that the Ptolemaic cosmology was clumsy and lacking th... |
as identical to what he saw up close. Only then could he begin to believe that the miraculous phenomena the telescope revealed in the heavens were real. Beginning his astronomical work late in 1609, Galileo found that many stars too faint to be seen with the unaided eye became visible with his telescope. In particular,... |
g the system of stellar magnitudes, and discovering precession from the apparent shift in the position of the north celestial pole. Ptolemy of Alexandria summarized classic astronomy in his Almagest; he explained planetary motions, including retrograde motion, with remarkably good accuracy using a model centered on Ear... |
h the Sun is a minor star on the outskirts of one galaxy among billions. Discuss some of the cultural and philosophical implications of each point of view. This OpenStax book is available for free at http://cnx.org/content/col11992/1.8 Chapter 2 Observing the Sky: The Birth of Astronomy 67 29. The north celestial pole ... |
circle, ellipse, parabola, and hyperbola are all formed by the intersection of a plane with a cone. This is why such curves are called conic sections. 72 Chapter 3 Orbits and Gravity You might recall from math classes that in a circle, the center is a special point. The distance from the center to anywhere on the circ... |
is 0.72 AU. Earth’s orbital period is 1.00 year, and its semimajor axis is 1.00 AU. Solution We can use the equation for Kepler’s third law, P2 ∝ a3. For Venus, P2 = 0.62 × 0.62 = 0.38 year and a3 = 0.72 × 0.72 × 0.72 = 0.37 AU (rounding numbers sometimes causes minor discrepancies like this). The orbital period (0.38... |
ry), powered by three fuel engines burning liquid oxygen and liquid hydrogen, with two solid fuel boosters, demonstrates Newton’s third law. (credit: modification of work by NASA For more about Isaac Newton’s life and work, check out this timeline page (https://openstaxcollege.org/l/30IsaacNewTime) with snapshots from ... |
Newton must have felt to realize he had discovered, and verified, a law that holds for Earth, apples, the Moon, and, as far as he knew, everything in the universe Calculating Weight By what factor would a person’s weight at the surface of Earth change if Earth had its present mass but eight times its present volume? So... |
he dwarf planet Pluto is inclined about 17° to the ecliptic, and that of the dwarf planet Eris (orbiting even farther away from the Sun than Pluto) by 44°, but all the major planets lie within 10° of the common plane of the solar system You can use an orbital simulator (https://openstaxcollege.org/l/30phetorbsim) to de... |
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