Ballet of the Planets by Benson Donald;

Author:Benson, Donald;
Language: eng
Format: epub
Publisher: Oxford University Press, Incorporated
Published: 2012-03-14T16:00:00+00:00

Figure 6.5 Galileo’s telescopic observations of the phases of Venus supported the heliocentric theory of the solar system. In (c), Venus is greatly magnified. The relationship is shown between the Sun and the positions of Venus and Earth. An orthogonal projection shows the crescent shape of phase 2.

Figure 6.5c is an enlargement of a detail in Figure 6.5b consisting of the triangle formed by the Sun, Earth, and image 2 of Venus, showing the geometry underlying the observations of the phases of Venus. A is Venus, greatly enlarged, image 2 in Figure 6.5b. B is an orthogonal projection of A (a rotation of A by 90°) showing the crescent shape seen from Earth. The angle β represents the apparent distance in the sky between the Sun and Venus. If β, is equal to zero or 180°, Venus is obscured by the glare of the Sun.3

Galileo’s observations did not prove the heliocentric theory of the solar system. They are explained equally well by using a geocentric model.4 The story of Earthship 2 in Section 3.2 shows that the difference between the heliocentric and geocentric theory can never be more than a relative point of view, but Galileo did demonstrate that the geocentric premise was unnecessarily complicated and of little use in any systematic treatment of astronomy. The coming Newtonian theory of dynamics would demonstrate this more convincingly.

Galileo’s observations with his telescope hastened the end of the dogma that the heavens are a region of eternal and immutable perfection. Galileo found pimples and moles on those heavenly bodies—spots on the Sun, craters on the Moon. Today we are comfortable with the idea that Earth is a minute part of an incredibly complex cosmos, but this idea was upsetting in Galileo’s time.

The hearing impaired—I am one of them—do not always welcome a hearing aid. The peace of a gentle ringing in the ears is replaced by a buzzing confusion of traffic sounds, half-heard conversations, and clattering dishes. Galileo augmented our senses, and the universe can never be as it was.

The work of Copernicus and Galileo set the stage for Kepler’s discovery that planetary orbits are elliptical. In preparation, the next chapter discusses abstract properties of the ellipse.

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