What are zmanim, and how does GPS change them?
Zmanim are the times that shape a Jewish day. Your latitude changes every single one of them.
The Jewish day is not measured in flat, 24-hour blocks. It bends around the sun. Sunrise, sunset, and the moments between are the scaffolding for prayer, fasting, Shabbat, and holidays — and every one of them moves as you move across the Earth.
That is why a printed calendar from a community three hundred miles away is a rough approximation, not the truth of your day. Zmanim tuned by GPS are simply zmanim measured where you actually are.
The core zmanim, plainly defined
Most of Jewish law that touches time is anchored to a handful of moments. Learn these seven and the day suddenly has a shape:
Alot Hashachar — the first light of dawn, well before sunrise. The earliest point at which many daytime mitzvot can begin. Netz Hachama — sunrise proper, when the top of the sun clears the horizon. The ideal moment to begin Shacharit for those who daven vatikin.
Sof Zman Kriat Shema — the latest time to say the morning Shema. Calculated as the end of the first quarter of the daylight, but which "daylight" you use depends on your tradition (more on that below). Chatzot — solar noon, the exact midpoint between sunrise and sunset.
Mincha Gedola and Mincha Ketana — the earliest and preferred times to begin the afternoon Mincha service. Shkiah — sunset, when the sun dips below the horizon. Tzeit Hakochavim — nightfall, when three medium stars are visible; the definitive end of the Jewish day.
Why 6:12 PM is not the same moment everywhere
A friend in Jerusalem tells you Shabbat comes in at 6:12 PM. Your friend in Brooklyn says the same. Your friend in Buenos Aires says the same. All three are correct — and none of the three describes the same moment.
Every zman is a function of two things: where the sun is relative to the horizon at your latitude, and how you define the day. Move a few degrees north or south and the sun's arc lengthens or flattens. Move a few degrees east or west and every event shifts by roughly four minutes per degree. A modern app does this arithmetic quietly, from your GPS coordinates, on a horizon model that respects local topography.
"A printed calendar is a snapshot of one place. GPS zmanim are the truth of yours."
Where traditions honestly differ
Even given the same sun, traditions disagree on how to slice the day — and those disagreements are old, principled, and preserved. Two of the most common:
Magen Avraham vs. the GRA. The Magen Avraham begins the day at Alot Hashachar and ends it at Tzeit Hakochavim, stretching the definition of "daylight" and pulling Sof Zman Kriat Shema noticeably earlier. The GRA counts daylight from sunrise to sunset, giving you more time in the morning. Neither is wrong; each belongs to a lineage.
Tzeit at 72 minutes vs. 3 degrees below the horizon. Some communities set nightfall as a fixed 72 minutes after sunset (Rabbeinu Tam and derived customs). Others use a solar-depression angle — commonly 3, 6, or 8.5 degrees — which produces different clock times in summer than in winter. MyJewishGuide lets you set your own opinion and stops trying to average the world.
What to do next
Open the app. Grant location once, choose your tradition, and today's zmanim appear — Alot, Netz, Sof Zman Shema, Chatzot, Mincha, Shkiah, and Tzeit, all tuned to where you are and how your community counts the day. No spreadsheet, no PDF calendar, no guessing.
Keep going in the app.
The moment you close this tab, this is where the practice lives.