The Guide to Autumn Constellations

Key Constellations of the Northern Autumn

Autumn offers a sky rich in deep-sky objects and mythological figures. Among the most notable constellations are:

• Pegasus (the winged horse), identifiable by its characteristic "square" formed by 4 bright stars (app. mag < 2.5).
• Andromeda, home to the M31 galaxy, visible to the naked eye under dark skies (distance: 2.5 million light-years, according to HST data).
• Perseus, associated with the Perseid meteor shower (peak around October 8).
• Cassiopeia, shaped like a "W", and Cepheus, its celestial neighbor, both circumpolar for observers above 35° north latitude.

Location and Observation

To locate these constellations, use the Polaris star as a starting point:

1. Find the Big Dipper (low on the northwest horizon in autumn).
2. Draw an imaginary line through the "guards" of the Big Dipper (Dubhe and Merak) to reach Polaris.
3. From Polaris, move eastward to find Cassiopeia, then Pegasus.

As noted by astronomer Johannes Hevelius (1611-1687) in his Firmamentum Sobiescianum, "Pegasus seems to gallop westward while Andromeda leaps toward Perseus, echoing their Greek mythology."

Notable Celestial Objects

This season is ideal for observing:

• The Andromeda Galaxy (M31): the only extragalactic object visible to the naked eye from the Northern Hemisphere. Its apparent diameter equals 6 full moons (source: ESA/Gaia, 2023).
• The Double Cluster in Perseus (NGC 869 and NGC 884), two groups of young stars (estimated age: 12-13 million years, study by Charles Messier (1730-1817) revisited by the VLT in 2020).
• The star Algol (β Persei), prototype of eclipsing variable stars (period of 2.87 days, discovered by John Goodricke (1764-1786)).

Comparative Table of Autumn Constellations

Sources: Strasbourg Astronomical Data Center (CDS), The Astrophysical Journal (2024), and International Astronomical Union (IAU).

Observation Tips

To optimize your sessions:

• Prioritize moonless nights (check a lunar calendar).
• Use 10x50 binoculars to distinguish M31 or Perseus clusters.
• Avoid urban areas (light pollution > Limiting Magnitude 4).

As Carl Sagan (1934-1996) pointed out: "Autumn reminds us that we are all travelers among the stars, connected to these celestial patterns by millennia of history."