Starry Memory

Night length and darkness calendar for San Antonio

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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 San Antonio 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 San Antonio, 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 08 to 13 h 53 in the flat-horizon model.
GPS · IANA reference — Exact reference: Texas, 29.4241° N, 98.4936° 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.

San Antonio's changing light is read month by month, using its actual seasonal range rather than generic observing advice. Its verifiable starting point is GeoNames 4726206, 29.4241° N, 98.4936° W, in timezone America/Chicago.

Twelve monthly light estimates for San Antonio

The following pairs are approximate daylight / night duration around the 15th of each month: January: 10 h 19 / 13 h 41; February: 10 h 59 / 13 h 01; March: 11 h 47 / 12 h 13; April: 12 h 43 / 11 h 17; May: 13 h 28 / 10 h 32; June: 13 h 52 / 10 h 08; July: 13 h 43 / 10 h 17; August: 13 h 04 / 10 h 56; September: 12 h 10 / 11 h 50; October: 11 h 16 / 12 h 44; November: 10 h 29 / 13 h 31; December: 10 h 07 / 13 h 53. The longest estimated night in this model is December at 13 h 53; the shortest is June at 10 h 08. “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.

San Antonio's verifiable local record

Calculation identity: GeoNames 4726206 · city San Antonio · region Texas · country United States · national selection rank 7 · reference population 1,526,656 · source elevation 198 m. Spatial fingerprint: latitude 29.42412 · longitude -98.49363 · north hemisphere · timezone America/Chicago · celestial-pole altitude 29.4°. Seasonal signature: longest night in December, 13 h 53 · shortest night in June, 10 h 08 · range 3.75 hours. Meridian star markers: Draco 54.4° * · Cepheus 49.4° * · Ursa Minor 42.4° * · Boötes 89.4° · Lyra 83.4° · Gemini 82.6°. Nearby catalogue cities: Austin 118 km · Corpus Christi 210 km · Houston 305 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.

San Antonio compared with nearby catalogue cities

1. San Antonio → Austin: 118.4 km · Δlat +0.843° · Δlon +0.751° · Δpole +0.9° · timezone America/Chicago = America/Chicago · longest night December 13 h 56 | 2. San Antonio → Corpus Christi: 209.9 km · Δlat -1.624° · Δlon +1.097° · Δpole -1.6° · timezone America/Chicago = America/Chicago · longest night December 13 h 45 | 3. San Antonio → Houston: 305.0 km · Δlat +0.339° · Δlon +3.130° · Δpole +0.4° · timezone America/Chicago = America/Chicago · longest night December 13 h 54. Monthly night comparison with the nearest catalogue reference — January: San Antonio 13 h 41 / Austin 13 h 45 / Δ -0.06 h · February: San Antonio 13 h 01 / Austin 13 h 04 / Δ -0.04 h · March: San Antonio 12 h 13 / Austin 12 h 13 / Δ -0.01 h · April: San Antonio 11 h 17 / Austin 11 h 16 / Δ +0.02 h · May: San Antonio 10 h 32 / Austin 10 h 28 / Δ +0.06 h · June: San Antonio 10 h 08 / Austin 10 h 04 / Δ +0.07 h · July: San Antonio 10 h 17 / Austin 10 h 14 / Δ +0.06 h · August: San Antonio 10 h 56 / Austin 10 h 54 / Δ +0.04 h · September: San Antonio 11 h 50 / Austin 11 h 50 / Δ +0.00 h · October: San Antonio 12 h 44 / Austin 12 h 45 / Δ -0.02 h · November: San Antonio 13 h 31 / Austin 13 h 34 / Δ -0.05 h · December: San Antonio 13 h 53 / Austin 13 h 56 / Δ -0.06 h. For the night calendar, north-south movement is the primary signal: compare San Antonio's seasonal range with the numbered maximum nights of its neighbours.

The astronomical fingerprint of San Antonio

San Antonio is represented by 29.4241° N, 98.4936° W, in Texas, using the IANA zone America/Chicago. This is a tropical viewpoint: the relevant celestial pole stands about 29.4° above its horizon. GeoNames record 4726206 supplies the geographic reference; its population field is 1,526,656 and is used for catalogue selection, not presented as a live census. The source elevation is 198 metres; terrain can hide a low object even when the geometric calculation says it rises.

Latitude-screened constellations for San Antonio

Each entry below gives an approximate maximum altitude at meridian transit and a practical season; an asterisk means circumpolar in this simplified centroid model: Draco: 54.4°, all year *; Cepheus: 49.4°, all year *; Ursa Minor: 42.4°, all year *; Boötes: 89.4°, spring; Lyra: 83.4°, summer; Gemini: 82.6°, winter; Andromeda: 81.4°, autumn; Cygnus: 79.4°, summer; Taurus: 78.6°, winter; Auriga: 77.4°, winter; Leo: 75.6°, spring; Perseus: 74.4°, winter; Orion: 65.6°, winter; Ursa Major: 63.4°, 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 San Antonio, twilight shortens fully dark conditions, especially near the longest days.

Can I replace the centre of San Antonio 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 San Antonio 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 San Antonio calendar