Zmanim: Jewish prayer times that follow the sun

What Risetime does for zmanim

Risetime is a clock app for Android: alarms at a fixed time or following the sun, and timers that repeat and chain. No ads ever and completely offline.

Risetime does not set your prayer times: communities count them in different ways, and choosing between them is not its place. You pick the conventions your community follows, and Risetime rings at them. Unsure which to follow? Ask your rabbi. Risetime is a clock, not an authority.

What are zmanim?

Zmanim (Hebrew for “times”) are the moments of the day that Jewish law ties to the Sun: the earliest time for some prayers, the latest time for others, the start and end of the day itself. They are counted from dawn, sunrise, solar noon, sunset and nightfall, never from a fixed hour.

That is why a printed timetable is only good for one place, and why it changes every day. In New York, sunrise comes at about 07:17 on 21 December and about 05:25 on 21 June: a zman counted from sunrise moves with it.

In Risetime, each of these zmanim is an anchor: a moment of the solar day that the app calculates again every day for your location. You then set your own alarms on the anchors you choose: at the anchor, or a number of minutes before or after it.

You will also see these names spelled in other ways: alos or alot hashachar, tzais or tzeit hakochavim, shma or shema, chatzos or chatzot. They are the same moments.

Why do Jewish calendars give different times?

Because they start from different definitions of the day. Two families cover most calendars:

• The Gra (the Vilna Gaon): the day runs from sunrise to sunset.
• The Magen Avraham: the day runs from dawn to nightfall, so it is longer. Dawn and nightfall are themselves counted in two ways: a fixed 72 minutes before sunrise and after sunset, or the moment the Sun is 16.1° below the horizon.

Most zmanim of the morning and afternoon are a fraction of that day. Change where the day starts and ends, and every one of them moves. With 72 minutes on each side, the arithmetic is exact:

Neither column is “the right one”. They are two readings, each with a long tradition behind it. Your shul’s calendar follows one of them; Risetime can follow either.

What is a proportional hour (sha’ah zmanit)?

A proportional hour is one twelfth of the day, however long that day is. In winter the hours are short, in summer they are long.

In London, a Gra day lasts about 7 h 50 on 21 December and 16 h 38 on 21 June: a proportional hour is then about 39 minutes in winter and 83 minutes in summer. So “three hours into the day”, the latest time for the morning Shema in the Gra’s reckoning, falls around 10:01 in London on 21 December and around 08:53 on 21 June, summer time: two hours before noon in winter, four in summer. A clock alarm cannot follow that; an alarm on a fraction of the day can.

Dawn and nightfall: an angle, or minutes?

Alot HaShachar (dawn) and Tzeit HaKochavim (nightfall, “the stars come out”) are the two ends of the night, and each has two schools:

• An angle of the Sun below the horizon: 16.1° for dawn, the angle that matches the Magen Avraham’s 72 minutes at the Jerusalem equinox; 8.5° for nightfall (the angle most communities use; some calculators label it “Geonim”). The angle follows the sky itself, so the gap to sunrise or sunset grows in summer and away from the equator.
• A fixed number of minutes: 72 minutes before sunrise for dawn (Magen Avraham), 72 minutes after sunset for nightfall (Rabbeinu Tam). Some use a fixed number of minutes after sunset: Rabbi Moshe Feinstein gave about 50 minutes for New York (45 to 51 in Igrot Moshe), and 40 to 42 minutes is also used.

The two schools meet where the minutes were measured: around the equinox in Jerusalem, 16.1° falls 72 minutes before sunrise. Elsewhere they part ways. In London on 21 December, 16.1° comes about 112 minutes before sunrise; in New York on 21 June, about 109 minutes.

How do I set an alarm for a zman?

• Chatzot and sunset are ready to use: set an alarm on Noon or Sunset, with an offset if you want one.
• Dawn and nightfall at an angle: create an anchor of the solar angle kind, at −16.1° in the morning or −8.5° in the evening.
• A proportional zman: create an anchor of the fraction of the day kind, choose where the day starts and ends, and how far into it the zman falls.

How anchors and offsets work — or let this page create them for you, further down.

Far from the equator, some summer nights have no dawn at 16.1°

In June the Sun stays shallow below the horizon at northern latitudes. In London it never gets to 16.1° below from about 4 June to 8 July: on those nights there is no dawn at 16.1°, and no zman counted from it. On those days the alarm does not ring, rather than ring at a time the sky never produces.

Communities at those latitudes have their own answer for those weeks. Your rabbi will know it.

Then paste them into Risetime

1. Copy your links, above.
2. In Risetime, open Settings › Anchors › Advanced › Import anchors.
3. Paste your links in the Paste anchor links field, and import. More on importing anchors.

Something missing, or a mistake?

These conventions come from public sources and I may have missed one, or got one wrong. If so, please write to me: I will fix it.

What an anchor can and cannot do

• An anchor gives the time computed for your location. That time changes every day with the Sun.
• One link describes one anchor. It is a rule, not a table of times: Risetime computes a new time each day.
• It follows no calendar: it rings on the days you set it to ring.
• Fixed offsets are in whole minutes.

What it costs

Risetime is free for up to three alarms and three timers – forever. Need more? Use those three first, and see if it’s worth your support: supporters get unlimited alarms and timers, yearly or once. If not, I’ll be happy to read your message. A full day of zmanim takes more than three alarms.