Starry Memory

Night length and darkness calendar for Jacksonville

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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 Jacksonville 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 Jacksonville, 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 10 h 03 to 13 h 57 in the flat-horizon model.
GPS · IANA reference — Exact reference: Florida, 30.3322° N, 81.6556° W, America/New_York.
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.

Jacksonville's changing light is read month by month, using its actual seasonal range rather than generic observing advice. Its verifiable starting point is GeoNames 4160021, 30.3322° N, 81.6556° W, in timezone America/New_York.

Twelve monthly light estimates for Jacksonville

The following pairs are approximate daylight / night duration around the 15th of each month: January: 10 h 15 / 13 h 45; February: 10 h 56 / 13 h 04; March: 11 h 47 / 12 h 13; April: 12 h 44 / 11 h 16; May: 13 h 32 / 10 h 28; June: 13 h 57 / 10 h 03; July: 13 h 47 / 10 h 13; August: 13 h 06 / 10 h 54; September: 12 h 10 / 11 h 50; October: 11 h 14 / 12 h 46; November: 10 h 26 / 13 h 34; December: 10 h 03 / 13 h 57. The longest estimated night in this model is December at 13 h 57; the shortest is June at 10 h 03. “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.

Jacksonville's verifiable local record

Calculation identity: GeoNames 4160021 · city Jacksonville · region Florida · country United States · national selection rank 10 · reference population 1,009,833 · source elevation 5 m. Spatial fingerprint: latitude 30.33218 · longitude -81.65565 · north hemisphere · timezone America/New_York · celestial-pole altitude 30.3°. Seasonal signature: longest night in December, 13 h 57 · shortest night in June, 10 h 03 · range 3.90 hours. Meridian star markers: Cassiopeia 60.3° * · Draco 55.3° * · Cepheus 50.3° * · Ursa Minor 43.3° * · Boötes 89.7° · Lyra 84.3°. Nearby catalogue cities: Orlando 201 km · Tampa 276 km · Atlanta 459 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.

Jacksonville compared with nearby catalogue cities

1. Jacksonville → Orlando: 201.3 km · Δlat -1.794° · Δlon +0.276° · Δpole -1.8° · timezone America/New_York = America/New_York · longest night December 13 h 49 | 2. Jacksonville → Tampa: 276.4 km · Δlat -2.385° · Δlon -0.803° · Δpole -2.4° · timezone America/New_York = America/New_York · longest night December 13 h 46 | 3. Jacksonville → Atlanta: 458.9 km · Δlat +3.417° · Δlon -2.732° · Δpole +3.4° · timezone America/New_York = America/New_York · longest night December 14 h 14. Monthly night comparison with the nearest catalogue reference — January: Jacksonville 13 h 45 / Orlando 13 h 38 / Δ +0.12 h · February: Jacksonville 13 h 04 / Orlando 12 h 59 / Δ +0.08 h · March: Jacksonville 12 h 13 / Orlando 12 h 12 / Δ +0.02 h · April: Jacksonville 11 h 16 / Orlando 11 h 19 / Δ -0.05 h · May: Jacksonville 10 h 28 / Orlando 10 h 35 / Δ -0.11 h · June: Jacksonville 10 h 03 / Orlando 10 h 11 / Δ -0.14 h · July: Jacksonville 10 h 13 / Orlando 10 h 21 / Δ -0.13 h · August: Jacksonville 10 h 54 / Orlando 10 h 59 / Δ -0.08 h · September: Jacksonville 11 h 50 / Orlando 11 h 50 / Δ -0.01 h · October: Jacksonville 12 h 46 / Orlando 12 h 42 / Δ +0.06 h · November: Jacksonville 13 h 34 / Orlando 13 h 27 / Δ +0.11 h · December: Jacksonville 13 h 57 / Orlando 13 h 49 / Δ +0.14 h. For the night calendar, north-south movement is the primary signal: compare Jacksonville's seasonal range with the numbered maximum nights of its neighbours.

The astronomical fingerprint of Jacksonville

Jacksonville is represented by 30.3322° N, 81.6556° W, in Florida, using the IANA zone America/New_York. This is a mid-latitude viewpoint: the relevant celestial pole stands about 30.3° above its horizon. GeoNames record 4160021 supplies the geographic reference; its population field is 1,009,833 and is used for catalogue selection, not presented as a live census. The source elevation is 5 metres; terrain can hide a low object even when the geometric calculation says it rises.

Latitude-screened constellations for Jacksonville

Each entry below gives an approximate maximum altitude at meridian transit and a practical season; an asterisk means circumpolar in this simplified centroid model: Cassiopeia: 60.3°, all year *; Draco: 55.3°, all year *; Cepheus: 50.3°, all year *; Ursa Minor: 43.3°, all year *; Boötes: 89.7°, spring; Lyra: 84.3°, summer; Andromeda: 82.3°, autumn; Gemini: 81.7°, winter; Cygnus: 80.3°, summer; Auriga: 78.3°, winter; Taurus: 77.7°, winter; Perseus: 75.3°, winter; Leo: 74.7°, spring; Orion: 64.7°, winter. 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 Jacksonville, twilight shortens fully dark conditions, especially near the longest days.

Can I replace the centre of Jacksonville 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 Jacksonville 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 Jacksonville calendar