Zmanim · The moments of the day
What is tzet hakochavim (nightfall)?
Tzet hakochavim is nightfall: the moment three medium-sized stars become visible. With it the night begins, a new Jewish day opens, and Shabbat comes to its close.
When three stars appear
The name means צאת הכוכבים, tzet hakochavim (the going-out of the stars). The tradition marks the true beginning of night not by the clock but by the sky: when three medium-sized stars can be seen together, the day that was is over and a new one has begun. In the Jewish reckoning the date turns in the evening, so this is also the birth of tomorrow.
Where this is taught
The Talmud, in tractate Shabbat (35b), is where the Sages describe the emergence of the stars as the sign of nightfall. Today that same moment is expressed in degrees of the sun below the horizon, which is how it can be calculated for any place on earth.
What to do
Because tzet hakochavim marks the end of Shabbat, one waits for it before making havdalah (the blessing that separates Shabbat from the week) and before returning to weekday activity. The exact time shifts with your latitude and the season, so rely on the moment computed for your own city.
Source: Talmud, tractate Shabbat 35b.
To see when the stars come out over your own city, and when Shabbat begins and ends, let Kimá (the Jewish clock: your city's zmanim and candle times) keep the count for you.
Open Kimá