History of the Constellations

Stars and Constellations

Draco

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Contents of this page: | Description | Skylore | Modern Culture | Origin and History | Asterisms | Special Stars | Submit new info... |

Images (at bottom of page): | Draco Chart: (Figure 1) | Hyginus, 1482, page C8v: (Figure 2) | Hyginus, 1482, page D1r: (Figure 3) | Hyginus, 1517, page E1r: (Figure 4) | Ptolemy, 1541-const, page Draco: (Figure 5) | Bayer, 1661, page C: (Figure 6) | Bayer, 1697, page C1v: (Figure 7) | Bayer, 1697, page C2r: (Figure 8) | Bayer, 1697, page C2v: (Figure 9) | Bode, 1801, page l: (Figure 10) | Aspin, 1825, page Draco: (Figure 11) | Images digitized by Hannah Magruder.

Constellation Data

Description

Draco is the 8th largest constellation, occupying over 1,000 square degrees in the sky as it winds from the Pointers of Ursa Minor nearly to Vega in Lyra. Yet it has no bright stars.

Skylore and Literature

To the Babylonians, Draco was Tiamat, a dragon killed by the sun god in the creation of the world.

To the Greeks, Draco guarded the Golden Apples of the Sun in a magical garden.

Modern Culture

Origin and History

Draco is included in the ancient star catalogs of Eudoxos of Knidos, Aratos of Soli, and Ptolemy.

Asterisms

  • Lozenge
  • Head

Special Stars

Gamma-Draconis, or Eltanin, is the brightest star of Draco, magnitude 2.2. Eltanin is part of Draco’s head. It is famous for being the star observed by the 18th-century English astronomer James Bradley when he was trying to detect parallax and so calculate the distance. No parallax was observed (the stars are too far away to be measured in that manner), but during the course of a year, the position of Gamma-Draconis in his telescope moved around in a tiny circle. This was not parallax, but what was it? Bradley had discovered what is called aberration, an effect due to the motion of the Earth. Bradley’s telescope was pointed directly up at the zenith, where Gamma-Draconis was located at his latitude. Consider an analogy between his telescope and an umbrella: Have you ever angled an umbrella forward when walking in the rain to keep dry, lest the rain seem to fall toward your face instead of straight down? Similarly, just as we might walk through the rain, so the Earth moves through space, and the light coming straight down into Bradley’s telescope from above seemed to fall toward his face, just as the rain would get one wet unless one were standing still. Aberration means that a star is not where it may appear to be in a telescope, due to the motion of the Earth which displaces the beam of light as it passes through the telescope--because the telescope is not stationary, but moving with the Earth at great speed just like someone carrying an umbrella slanted forward in the rain.

Draco’s most famous star is Alpha-Draconis, or Thuban, although it is only the 8th brightest star in Draco. Thuban was closest to the north celestial pole in 2830 BC, not long before the Egyptian pyramids were constructed (instead of Polaris; see precession). Magnitude: 3.6, much fainter than Eltanin, although it has been known to vary. Distance: 230 LY.

Two stars of Draco are very near: Chi-Draconis is only 25 LY away; Alrakis (Sigma-Draconis) is only 18.5 LY. It’s a good thing Alrakis is near; it is only about a third as bright as the Sun.

Submit new info...

Many excellent websites provide a variety of information about constellations for amateur astronomers and telescope users (see sidebar links for a few of these). These constellation pages are not intended to duplicate those efforts, but are devoted to two aims: First, they are intended to assist the beginning skywatcher, including students in history of science survey courses, in becoming familiar with Basic Celestial Phenomena (BCP). Second, these pages are devoted to the history of the constellations and the history of astronomy. They are intended to serve as a repository for collaborative use and reference. Do you have additional historical information about the stars or constellation described on this page? Please submit additional information to kmagruder@ou.edu. Submissions will be attributed. Editors for historical information are Kerry Magruder, JoAnn Palmeri, Peter Barker, and Laura Gibbs.

Oklahoma History of Science exhibits: http://hos.ou.edu/exhibits/. Page revised 4/15/04

Bad links, misplaced images, or questions? Contact Kerry Magruder. Thank you.

"If the stars should appear one night in a thousand years, how would men believe and adore, and preserve for many generations the remembrance of the city of God which had been shown. But every night come out these envoys of beauty, and light the universe with their admonishing smile." R. W. Emerson, Nature

Images

Figure 1 Figure 1 - Return to Text

Dra Chart
Figure 2 Figure 2 - Return to Text

Hyginus, 1482

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Hyginus, 1482

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Hyginus, 1517

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Ptolemy, 1541-const

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Bayer, 1661

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Bayer, 1697

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Bayer, 1697

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Bayer, 1697

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Bode, 1801

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Aspin, 1825

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Exhibit credit: Kerry Magruder.

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These teaching resources provided by the History of Science Department at the University of Oklahoma.

Unless otherwise indicated, all images courtesy History of Science Collections, University of Oklahoma Libraries. Image Terms of Use.

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