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Saturn from Cassini Astronomy 161:
An Introduction to Solar System Astronomy
Prof. Richard Pogge, MTWThF 2:30

Lecture 3: The Starry Night

Key Ideas:

About 6000 stars are visible to the naked eye


Uses of Constellations

Star Names
Note: This lecture uses a lot of graphics, unfortunately many of them (the paintings and photos) are copyrighted, and cannot be reproduced on these web pages. To get the full visual effect, you have to come to lecture.

The Starry Night

From a dark site, about 6000 stars are visible to the naked eye on a moonless night.

This represents only a tiny fraction of the nearly 200 Billion stars that make up the Milky Way Galaxy in which we reside.


From time immemorial, people have seen patterns and drawn figures in the sky by connecting the bright stars.

These starry figures are the Constellations

All peoples have populated the night sky with constellations.

Figures in the Sky

Most constellations are composed of bright stars that stand out from the others.

Many look like what they are named

Peoples greatly separated in distance and/or time often made the same connections. A few common examples:

[Look for Orion in the winter sky, it rises in the east/southeast around sunset beginning in late December].

The Classical Constellations

The oldest known constellations (Leo, Taurus, Scorpius) appear in cuneiform tables dating from 3000 BC, but may be older still.

The Greek constellations and associated star lore were described in the Phaenomena of Eudoxus of Cnidos (c. 366 BC), and likely derived from Babylonian (Assyrian?) lore of c. 1100 BC.

The Greek astronomer Ptolemy made a catalog of 48 "classical" constellations in the 2nd century AD:

All of the classical constellations are those visible from the middle latitudes of the northern hemisphere.

Populating the Sky

16th & 18th century travelers to the southern hemisphere filled in the rest of the sky.

Map makers invented new constellations to add to the Classical 48 of Ptolemy:

There are now 88 Modern Constellations with boundaries and figures defined by the International Astronomical Union (IAU). This work was completed in 1888.

Role of Constellations

Constellations have served many purposes among the peoples that created them. A few of the major ones are:

As Story-telling Mnemonics

Religious and Ritual Uses

Navigational Aids

High Art

This "purpose" is purely aesthetic. Constellations and views of the night sky have figured in the arts in all ages and cultures:

Star Names

The brightest stars visible to the naked eye have all been given proper names.

In the western tradition, these names are mostly Arabic & Greek, revealing the chain of transmission of the western astronomical tradition:

Mesopotamia -> Classical Greece -> Roman Empire 
-> Islam -> Renaissance Europe -> Today

Other cultures have also named some of the brightest stars, though these names are not in common use today.

Common Names of Stars

The common names of stars in use today are mainly Arabic, but there is a mix of Greek and Latin for a few famous stars


Extra Info: Names of Stars

This is really a topic that becomes more relevant when we talk about the stars themselves in Astronomy 162, but it fits in context. I've added it here as extra information, but will not include it on the exams.

Bayer (Greek Letter) Names

In 1601, German astronomy Johannes Bayer developed a system of naming stars using lower-case Greek letters in approximate order of brightness (though he didn't always get it right). A "Bayer Name" for a star consists of two parts
  1. Greek letter to indicate brightness, in order of brightest to faintest.
  2. Genitive (possessive) form of the constellation name

Examples: Orion

And so forth.

After you run out of Greek letters (there are 24 letters), stars are given "Flamsteed Numbers" (e.g., 61 Cygni), taken from a great catalog of naked-eye stars created by John Flamsteed in the 18th century.

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Updated: 2007 September 16
Copyright Richard W. Pogge, All Rights Reserved.