Starry Memory

Night length and darkness calendar for Chicago

Use the free local tool

This page provides a result prefilled with the place and coordinates. The calculations and phone gyroscope work without an order; the HD poster remains optional. Open the twelve-month Chicago calendar

Compare all twelve months and find the longest local observing windows

A good month for stargazing is not the same everywhere. Latitude changes the seasonal balance between daylight and night. The table below estimates day and night length around the middle of every month for Chicago, using a flat astronomical horizon and explaining the limits of twilight, weather and terrain.

Why choose Starry Memory

Twelve local estimates — Monthly night duration ranges from 8 h 58 to 15 h 02 in the flat-horizon model.
GPS · IANA reference — Exact reference: Illinois, 41.8500° N, 87.6500° W, America/Chicago.
Free tool — The city-specific tool works free in the browser and does not create an order.
Transparent limits — Weather, light pollution and local obstructions are stated as limits instead of being hidden.

Chicago's changing light is read month by month, using its actual seasonal range rather than generic observing advice. Its verifiable starting point is GeoNames 4887398, 41.8500° N, 87.6500° W, in timezone America/Chicago.

Twelve monthly light estimates for Chicago

The following pairs are approximate daylight / night duration around the 15th of each month: January: 9 h 17 / 14 h 43; February: 10 h 22 / 13 h 38; March: 11 h 40 / 12 h 20; April: 13 h 08 / 10 h 52; May: 14 h 22 / 9 h 38; June: 15 h 02 / 8 h 58; July: 14 h 46 / 9 h 14; August: 13 h 41 / 10 h 19; September: 12 h 16 / 11 h 44; October: 10 h 50 / 13 h 10; November: 9 h 35 / 14 h 25; December: 8 h 58 / 15 h 02. The longest estimated night in this model is December at 15 h 02; the shortest is June at 8 h 58. “Night” here is the complement of daylight on a flat horizon. Civil, nautical and astronomical twilight are not interchangeable, and weather is not predicted by this table.

Chicago's verifiable local record

Calculation identity: GeoNames 4887398 · city Chicago · region Illinois · country United States · national selection rank 3 · reference population 2,664,452 · source elevation 179 m. Spatial fingerprint: latitude 41.85003 · longitude -87.65005 · north hemisphere · timezone America/Chicago · celestial-pole altitude 41.9°. Seasonal signature: longest night in December, 15 h 02 · shortest night in June, 8 h 58 · range 6.06 hours. Meridian star markers: Ursa Major 75.9° * · Cassiopeia 71.9° * · Draco 66.9° * · Cepheus 61.9° * · Ursa Minor 54.9° * · Auriga 89.9°. Nearby catalogue cities: Milwaukee 134 km · Madison 198 km · Indianapolis 263 km. First regional eclipse shortlist: 2027-02-20 Penumbral lunar eclipse 23:14 UTC · 2027-08-17 Penumbral lunar eclipse 07:14 UTC · 2028-01-12 Partial lunar eclipse 04:14 UTC. Together these values form the local evidence record for the “night calendar” page; they change with place and remain separate from real weather.

Chicago compared with nearby catalogue cities

1. Chicago → Milwaukee: 133.9 km · Δlat +1.189° · Δlon -0.256° · Δpole +1.1° · timezone America/Chicago = America/Chicago · longest night December 15 h 10 | 2. Chicago → Madison: 197.8 km · Δlat +1.223° · Δlon -1.751° · Δpole +1.2° · timezone America/Chicago = America/Chicago · longest night December 15 h 10 | 3. Chicago → Indianapolis: 263.3 km · Δlat -2.082° · Δlon +1.492° · Δpole -2.1° · timezone America/Chicago ≠ America/Indiana/Indianapolis · longest night December 14 h 48. Monthly night comparison with the nearest catalogue reference — January: Chicago 14 h 43 / Milwaukee 14 h 50 / Δ -0.12 h · February: Chicago 13 h 38 / Milwaukee 13 h 42 / Δ -0.07 h · March: Chicago 12 h 20 / Milwaukee 12 h 21 / Δ -0.01 h · April: Chicago 10 h 52 / Milwaukee 10 h 49 / Δ +0.05 h · May: Chicago 9 h 38 / Milwaukee 9 h 32 / Δ +0.11 h · June: Chicago 8 h 58 / Milwaukee 8 h 50 / Δ +0.13 h · July: Chicago 9 h 14 / Milwaukee 9 h 07 / Δ +0.12 h · August: Chicago 10 h 19 / Milwaukee 10 h 14 / Δ +0.07 h · September: Chicago 11 h 44 / Milwaukee 11 h 43 / Δ +0.02 h · October: Chicago 13 h 10 / Milwaukee 13 h 13 / Δ -0.05 h · November: Chicago 14 h 25 / Milwaukee 14 h 31 / Δ -0.11 h · December: Chicago 15 h 02 / Milwaukee 15 h 10 / Δ -0.14 h. For the night calendar, north-south movement is the primary signal: compare Chicago's seasonal range with the numbered maximum nights of its neighbours.

The astronomical fingerprint of Chicago

Chicago is represented by 41.8500° N, 87.6500° W, in Illinois, using the IANA zone America/Chicago. This is a mid-latitude viewpoint: the relevant celestial pole stands about 41.9° above its horizon. GeoNames record 4887398 supplies the geographic reference; its population field is 2,664,452 and is used for catalogue selection, not presented as a live census. The source elevation is 179 metres; terrain can hide a low object even when the geometric calculation says it rises.

Latitude-screened constellations for Chicago

Each entry below gives an approximate maximum altitude at meridian transit and a practical season; an asterisk means circumpolar in this simplified centroid model: Ursa Major: 75.9°, all year *; Cassiopeia: 71.9°, all year *; Draco: 66.9°, all year *; Cepheus: 61.9°, all year *; Ursa Minor: 54.9°, all year *; Auriga: 89.9°, winter; Cygnus: 88.1°, summer; Perseus: 86.9°, winter; Andromeda: 86.1°, autumn; Lyra: 84.1°, summer; Boötes: 78.1°, spring; Gemini: 70.1°, winter; Taurus: 66.1°, winter; Leo: 63.1°, spring. This is a planning guide, not a promise that every star will be visible from a bright street. Date, hour, local obstructions and light pollution still matter. The live sky tool performs the date-specific projection that a static latitude table cannot.

What the calculation does — and does not claim

Coordinates, date and local time feed the same astronomical workflow used by the poster. The HYG catalogue provides star entries, while Astronomy Engine calculates moving bodies. The page does not claim that city-centre coordinates equal a hospital, venue or home: selecting an autocomplete suggestion replaces the shortcut with that location. It also separates astronomical geometry from weather and light pollution, so a correct map never becomes a claim that the ground-level sky was cloudless.

Free gyroscope first, optional poster second

On a compatible phone, the gyroscope turns the calculated sky into a movable window: tilt and rotate to explore, with star names shown beside key points. That experience is free. If a date deserves a keepsake, the same place can continue into the editor. The protected preview remains watermarked before payment; the €3.99 purchase unlocks the 4960 × 7016 px, 300 DPI file. Physical formats appear only when availability, delivery supplement and timing can be checked for the destination. Checkout is in euros; the card issuer shows the current conversion to US dollars (USD).

Frequently asked questions

Is night length the same as astronomical darkness?

No. The table shows 24 hours minus estimated daylight. In Chicago, twilight shortens fully dark conditions, especially near the longest days.

Can I replace the centre of Chicago with an exact address?

Yes. Choose the intended autocomplete suggestion; its coordinates replace the city shortcut. Unselected free text is never silently sent to a default city.

Is the Chicago tool free?

Yes. The local calculation, tables and gyroscope exploration can be used without payment. Only the unlocked HD poster is paid.

Does this guarantee clear-sky visibility?

No. The calculations describe geometry. Cloud, terrain, buildings and light pollution can change what a person sees from the ground.

Do I have to buy a poster?

No. The tool stands on its own. If wanted, the watermark-free 4960 × 7016 px, 300 DPI file costs €3.99. Checkout is in euros; the card issuer shows the current conversion to US dollars (USD).

Open the twelve-month Chicago calendar