Pegasus / Andromeda

Great Square of Pegasus

Square of Pegasus

common observer pattern · high confidence

Four second-magnitude corner stars make autumn's large empty-looking square. The northeast corner, Alpheratz, now belongs to Andromeda even though the pattern is still the Great Square.

Central RA: 23^h 37^m 32.4^s
Central Dec: +21° 53′ 26″
Brightest member: V 2.06
Best months from 50°N: September–December evenings
Suggested instrument: naked-eye
Approx. span: 20.6°

Finder context

This wider chart is deliberately schematic: it uses nearby bright-star context and boxes the asterism’s member-star footprint, but it does not draw official constellation boundaries or promise horizon/season precision.

Framing: Approximate member-star span: 20.6°; use at least 28.9° field for context.

Observing and imaging

Naked eye

Primary naked-eye pattern; suburban skies should show the main stars unless the description notes a low horizon or dark-sky need.

Binoculars

Binoculars are optional: use them to check colours, nearby doubles, or richer Milky Way background.

Small scope

A telescope is usually too narrow for the whole shape; use it after the pattern has guided you to a target.

Imaging

Frame as a wide-field scene in/near Pegasus / Andromeda; a field of view around 29° keeps context without claiming exact constellation boundaries.

Tonight from your latitude

Observability from your latitude: uses this asterism’s centroid RA/Dec with a schematic local clock from longitude, astronomical twilight (Sun below −18°), and the 2026 Moon heuristic. Month stays for the seasonal readout.

Latitude 50°NLongitude -114°Date Month Sky darkness Bortle 4 · limit V 6.1

Naked-eye visibility by sky class

Approximate limiting magnitudes: Bortle 3 ≈ V 6.6, Bortle 5 ≈ V 5.6, Bortle 7 ≈ V 4.6. The shape is counted recognisable when at least 70% of defining stars clear the limit.

Bortle 3: 4/4 stars — fully visibleBortle 5: 4/4 stars — fully visibleBortle 7: 4/4 stars — fully visible

Moon impact

Reference year 2026, Oct: 22/31 nights (71%) have a sampled ≥2 h window with Great Square of Pegasus above 20° and the Moon below the horizon. At transit the Moon is up on about 55% of nights; the average moonlight penalty is roughly 0.67 mag of naked-eye limiting magnitude. Good nights below are the deterministic 2026 best-month mini-calendar for 50°N; green means a ≥2 h sampled dark window with the Moon down.

01020304050607080910111213141516171819202122232425262728293031

Member stars

Name	Bayer / Flamsteed	HR	RA J2000	Dec J2000	V mag
Alpheratz	21Alp And	HR 15	00^h 08^m 23.3^s	+29° 05′ 26″	2.06
53Bet Peg	53Bet Peg	HR 8775	23^h 03^m 46.5^s	+28° 04′ 58″	2.42
54Alp Peg	54Alp Peg	HR 8781	23^h 04^m 45.7^s	+15° 12′ 19″	2.49
Algenib	88Gam Peg	HR 39	00^h 13^m 14.2^s	+15° 11′ 01″	2.83

Source and confidence

common observer pattern; high confidence. Commonly used constellation-part or seasonal guide-pattern name, with member-star positions plotted from BSC5.

Citations

Bright Star Catalogue, 5th Revised Ed.: Hoffleit, D. & Warren, W.H. Jr. (1991). Positions, V magnitudes, Bayer/Flamsteed identifiers. source
Star Tales: Ridpath, I. Constellation and asterism notes used to cross-check common sky-pattern names. source
The Hipparcos and Tycho Catalogues: ESA SP-1200 (1997). Used as the modern astrometric reference named by the atlas; the MVP pages expose BSC5 J2000 fields for the plotted bright-star members.