1. A person is obligated to refrain from Melacha (activities prohibited on
Shabbos) and light candles at least half an hour before the appearance of
[three medium-sized] stars (that is, nightfall) (1).
Even if it is as much as two hours before nightfall (2), if the
congregation has already recited Psalm 92, "Mizmor Shir L'Yom HaShabbos"
("A Song for Shabbos"), (3) in the synagogue, Shabbos is considered to have
begun for [all the members of the community,] even the minority [who are
not in the synagogue], and all are forbidden to perform any prohibited
labors. This applies even to a person who comes [to the communtiy] from
another city. When there are two synagogues within a community, the members
of one synagogue are not influenced by the actions of the other.
(1) It is obviously impossible for us to determine the exact moment that
Friday ends and Shabbos begins. According to most authorities, once the sun
sets ( "Shkiah"), we enter a period of time in which we are uncertain as to
whether or not it is "day" or "night." This period is called "Bein
Hashemashos," and it is forbidden during this time of uncertainty to
perform Melacha (Torah-prohibited labor) as well as most Rabbinically
prohibited acts (certain Rabbinically prohibited acts may be performed in
pressing circumstances or for the sake of a Mitzvah). However, some
authorities rule that we don't enter the period of uncertainty until
sometime after the sun has set, and its clear that, in this Halacha, the
Kitzur Shulchan Aruch concurs with these authorities, and therefore sets
candle-lighting time at a half an hour before nightfall, rather than a
similar period before sunset. According to all authorities, the appearance
of three medium-sized stars signals the beginning of the "night."
According to the authorities who rule that the period of uncertainty begins
at sunset, it should be permissible to light Shabbos candles until a moment
before sunset. However, the custom in most communities is to light-candles
and begin Shabbos about 18 minutes before sunset; there are two possible
reasons for this practice. Firstly, most authorities rule that it is a
Mitzvah (derived from the Torah) to begin Shabbos while it is still
definitely "daytime," i.e. before sunset. This concept is called "Mosif
Mechol Al HaKodesh" (lit: "adding part of the non-holy to the holy," in
other words, adding part of the weekday to Shabbos ). Secondly, even those
authorities who rule that it is not an actual Mitzvah to begin Shabbos
early, still rule that everyone should refrain from performing prohibited
acts a short time before sunset, because if one got into the habit of
waiting until a moment before sunset to begin Shabbos, one could easily end
up performing a prohibited act after sunset (See Shulchan Aruch 261 and
(2) It is permissible to begin Shabbos anytime after "Plag HaMincha" on
Friday afternoon, which is always one and a quarter Halachic hours before
sunset (a Halachic "hour" is equal to one twelfth of the time from sunrise
to sunset (some say from dawn to dark) ) (See Rema 261:2).
(3) According to the Mishna Berura (261:30), when the congregation in
Synagogue sing the words "Boie Challah" ("Welcome Bride") in the song
"Lecha Dodi," they are accepting Shabbos upon themselves, and prohibited
activities may not be performed by any member of the congregation (even
those not in Synagogue), from that point onwards.