![]() It meant that the stars must be fantastically distant. One of the greatest delays in switching from a geocentric to a heliocentric model of the solar system was in part tied to the lack of an observable motion in the stars - a measurable stellar parallax - as the Earth orbited. At the time, this reasoning implied a universe thousands of times larger than previous estimates! Guessing that they were all stars like the Sun, he recognized the enormous three-dimensional depth of space. ![]() Galileo used this reasoning when he pointed his telescope at the Milky Way and saw the gauzy light resolve into many pinpoints of light. ![]() Even so, this is an example of how a simple physical idea - the way that light dims as it spreads through space - can be used to deduce remarkable information about the distance to the stars. Also, these estimates only give typical distances rather than accurate distances for individual stars. The brightest stars in the sky are much more luminous than the Sun, so they are much more distant than we would calculate by assuming that they resemble the Sun. Simple distance estimates based on the relative brightness of the Sun and the stars are flawed for one simple reason: stars come in many luminosities. In 1829, English scientist William Wollaston used the inverse square law to estimate that most typical stars must be at least 100,000 (or 10 5) times more distant than the Sun, since the inverse square law indicates that dimming 10 billion times corresponds to increasing distance 100,000 times (which is accurate for some stars). Mistakes continued into more modern times. Unfortunately, the relative brightness of the Sun and other stars is impossible to measure accurately without equipment. The brightest stars have values of apparent brightness that are about 10 billion (or 10 10) times fainter than the Sun. S represents an ideal source of electromagnetic radiation and A represents an arbitrary segment of the surface of a sphere of radius r.īoth these men were trying to use a crude method for estimating the distance of stars inverse square law for the propagation of light. Newton concluded that the bright stars are about 18,000 times farther away than the Sun (which is simply wrong, for the same reason Huygen was wrong neither of them knew that most bright stars in the night sky are intrinsically much brighter than the Sun).Ī diagram illustrating the Inverse Square Law. He guessed the percentage of the Sun's light that Saturn reflects and assumed that bright stars have similar absolute brightness to the Sun. Around the same time, Issac Newton tried to use Saturn as a sort of reflecting mirror to measure the intensity of sunlight. Since the pinhole admitted 1/27,000 of the light of the Sun, Huygens concluded that Sirius was 27,000 times farther away than the Sun (it is actually 543,900 times farther away and substantially more luminous than the Sun). He varied the size of the pinhole until the image seemed equal in brightness to an image of Sirius, the brightest star. In the late 17th century, Dutch scientist Christian Huygens made an image of the Sun through a pinhole in a darkened room. Early distance estimates were no more than educated guesses.
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