Sky Map (Star Chart): October 2018

Look for two of Ptolemy's original constellations: Camelopardalis and Lacerta!

By Jeff DeTray from AstronomyBoy.com
SkyMap October 2018

See this printable sky map for October to navigate the skies and look for Camelopardalis and Lacerta—plus, find helpful stargazing tips.

Click-and-Print Sky Map

Just click here or on the image below to open the printable map—then bring outside!

October printable sky map

 

Documenting the Stars

As human beings, it is in our nature to seek order from chaos, to find patterns where none exist. We look for ways to organize our world, from properly arranging books on a shelf to making sense of the stars in the sky. It’s no surprise, then, that no matter how far we look back into recorded history, we find ancient peoples drawing sky maps and giving names to what they’ve observed. 

Inevitably, ancient observers of the sky saw patterns in the stars—patterns that we now call constellations. Beginning at least 7,000 years ago, early astronomers started documenting mythological creatures, supernatural beings, even ordinary tools and weapons, all composed of stars. Across the millennia, the names and even the patterns of most constellations have changed as different cultures applied their own mythology to the stars. In fact, the 88 constellations that we recognize today were finally agreed upon less than 100 years ago.

For most of recorded history, only the brightest or most distinctive star patterns were recognized as constellations. Some parts of the sky belonged to no constellation at all. This was the case in the 2nd century, when the renowned Greco-Roman astronomer Claudius Ptolemy produced one of history’s most important scientific writings, the Almagest. This colossal work comprised 13 books, each devoted to a different aspect of astronomy.

Books VII and VIII concerned the stars and identified 48 constellations. Of Ptolemy’s 48 constellations, all but one are still recognized today.

Finding New Constellations

Over the next many centuries, astronomers slowly invented additional constellations from stars that Ptolemy had failed to include in his original 48. This month’s sky map shows two of them.

In 1612, Dutch astronomer Petrus Plancius invented the constellation Camelopardalis, the Giraffe, from a jumble of faint stars between Ursa Major and Perseus. The constellation Lacerta, the Lizard, was created in 1690 by Polish astronomer Johannes Hevelius from otherwise unassigned stars between Cepheus and Pegasus. A prolific constellation inventor, Hevelius created seven new constellations where none had been recognized before. The star pattern of Camelopardalis looks nothing like its namesake, but the stars of Lacerta can be imagined as a lizard of sorts.

Throughout the 16th, 17th, and 18th centuries, new constellations were invented to fill in those parts of the sky where none existed. Occasionally, there were conflicts, such as when Edmond Halley (of Halley’s Comet fame) invented a new constellation to honor King Charles II of England. Other astronomers rejected the idea of naming constellations for contemporary persons.

The question of constellations was one of the matters discussed by the International Astronomical Union (IAU) at its first General Assembly in 1922. The IAU determined that there would be 88 constellations and that their boundaries would be drawn so that every part of the sky lies within a constellation. No more unassigned stars! All but one of Ptolemy’s original 48 constellations made the modern list of 88. Because every point in the sky must lie within a constellation, the boundaries of some constellations (Camelopardalis, for example) resemble a gerrymandered Congressional district.

October 2018 Sky Map

Click here or on image below to enlarge this map (PDF).

October 2018 Sky Map
Sky map produced using Chris Marriott’s Skymap Pro

Note: How to Read the Sky Map

Our sky map does not show the entire sky. Instead, the monthly map focuses on a particular region of the sky where something interesting is happening that month. The legend on the map always tells you which direction you should facing, based on midnight viewing. For example, if the map legend says “Looking Southeast,” you should face southeast when using the map.

The map is accurate for any location at a so-called “mid northern” latitude. That includes anywhere in the 48 U.S. states, southern Canada, central and southern Europe, central Asia, and Japan. If you are located substantially north of these areas, objects on our map will appear lower in your sky, and some objects near the horizon will not be visible at all. If you are substantially south of these areas, everything on our map will appear higher in your sky.

The items labeled in green on the sky map are known as asterisms. These are distinctive star patterns that lie within constellations. When getting your bearings under the stars, it’s often easiest to spot an asterism and use it as a guide to finding the parent constellation.

The numbers along the white “Your Horizon” curve at the bottom of the map are compass points, shown on degrees. As you turn your head from side to side, you will be looking in the compass direction indicated by those numbers. The horizon line is curved in order to preserve the geometry of objects in the sky. If we made the horizon line straight, the geometry of objects in the sky would be distorted.

Leave a Comment