If you fly through Shabbat (permitted for business only), you must keep even Shabbat d'rabanan while flying over the area of the earth that is in Shabbat.
If you fly east (such as from Asia to the US, across the Pacific) after Shabbat is over, you will re-enter Shabbat and may not do melacha on the airplane. Say the Shabbat prayers and kiddush at the appropriate local time where you are flying.
 

The International Dateline (IDL), which is 180 degrees away from Greenwich, England, crosses the Pacific ocean from north to south and divides a region of safek/doubt as to which day is Shabbat. This region's eastern boundary is a line 180 degrees east of Jerusalem, which lies between Hawaii and the US mainland; the western boundary is east of Shanghai. All countries in this region of IDL safek/doubt are island countries.
 
In a region of doubt, such as Tasmania, keep normal Shabbat (Shabbat d'rabanan) on local Saturday and keep Shabbat d'oraita on:

• West of mainland USA, but
• East of the IDL, and
• Not attached to the mainland.

• West of the IDL, but
• East of Shanghai, and
• Not attached to the mainland.

Note In all cases, you must still observe regular Shabbat on Friday night/Saturday.
Situation
You are in a place near the International Dateline (IDL) in which you are not sure which day of the week it is halachically: Shabbat or, if you are east or west of the IDL, Friday or Sunday.
What To Do
On the Friday or Sunday in question, there is no shvut (d'rabanan prohibitions, including muktza), so you may do all melacha d'rabanan WITHOUT a shinui. You may:

• Ask or tell a non-Jew to do anything, including a melacha d'rabanan or d'oraita.
• Ride in a cab or car driven by a non-Jew.

• Use electricity--except for heat or light—including turning on a fan or air conditioner (heat and light are forbidden by the Torah).
• Use the telephone. (Using a cellphone may be permissible--ask a rabbi).

• Carry from a private domain (reshut ha'yachid) to another private domain, even through a public domain (reshut ha'rabim); but you may not stop walking in the public domain and you may not put the object down in the public domain unless you use a shinui.
• There is no practical way to light candles, even using a shinui, but a non-Jew may light them for you and and you may say the blessing on the candles.
• Swim, surf, scuba dive, climb, and play all games that do not use melacha. You may not wring out clothes and if you are swimming or scuba diving, your swimsuit or wetsuit must be clean.
• Walk any distance (there is no techum Shabbat d'oraita).
• Kinyan. You may acquire items.

• Fly, including check in and getting on plane if:
  • The pilot is non-Jewish, and
  • You don't do any melacha d'oraita (including any writing) without a shinui.
• Use a computer if it automatically goes to sleep after less than 24 hours of not being used.
• Shower. However:
  • You may not use an “instant on” hot water system in which the water is heated as you use it; you may only use the hot water if it has a holding tank.
  • You may use only liquid soap; hard soap is forbidden.
• Ingest medicine (but you may not smear it on skin).
• Use some make up, such as rouge, mascara, eye shadow. You may not use lipstick.
• Open a refrigerator with light (and all other psik reisha d'la neicha lei).

• You may buy necessities on Friday or Sunday as long as:
  • The store owner is not Jewish (or if he/she is Jewish, does not write or print a receipt),
  • You do not write, and
  • There is no reshut ha'rabim.

You may also do melacha d'oraita if:

• You use a shinui (non-normal way of doing that action--this is forbidden d'rabanan on Shabbat but is allowed on the Friday or Sunday in question), OR
• Two or more people do the melacha together.

 
D'oraita, you may not:

• Cook food.

• Turn on lights (but you may turn them off).
• Carry from domains.
• Boneh – building any permanent structure.
• Write two or more letters of the alphabet.
• Drive--there is no practical way to drive using a shinui.
• Shave--there is no practical way to shave using a shinui.
• Use toothpaste (but you may use tooth-cleaning powder).
• Use skin cream--you may dab it on without smearing it.

However, you may do these following actions with a shinui on the Friday or Sunday in question, as follows:

• Cook food. You must put food in the cooking utensil first, then turn on the heat with shinui. You may turn off the heat even without a shinui.
• Turn on lights (such as with your elbow).
• Stop along the way when carrying from a private domain (reshut ha'yachid) to another private domain, even through a public domain (reshut ha'rabim). As a shinui, you may carry the object in your mouth (as long as it is not food), etc.

Note Carrying something in your pocket is NOT a shinui.

• Tear paper (such as putting toilet paper across knees and moving the knees apart).
• Write (such as with the opposite hand).

Flying East From Australia on Sunday If You Cross IDL from Friday into Saturday

Shabbat was the goal of Creation. Just as God completed the world's creation on the sixth day and ceased His work on the seventh, so Jews are supposed to imitate God and not do any creative work on the seventh day. Everything we need for living through Shabbat must be prepared ahead so that we do not do any creative activities on Shabbat.
Our observance of Shabbat thus testifies that God created the world. In the Shabbat kiddush, we mention the Exodus from Egypt, too, to testify to the world that God is continuously involved in our lives.
By ceasing our normal efforts to dominate the physical world, we can appreciate the spiritual aspects of our existence.
On Shabbat, all observant (shomer Shabbat) Jews receive an extra “soul.”

Zachor and Shamor

Remember (Zachor) the Sabbath day to make it holy—Exodus/Shmot 20:8
Observe (Shamor) the Sabbath day to make it holy—Deuteronomy/Devarim 5:12
Shabbat has two dimensions:

• Zachor  “Remember,” encompassing positive (“to do”) commandments, and
• Shamor  “Observe,” encompassing negative (“refrain from”) commandments.

Zachor:  Positive Shabbat Commandments
What Are Positive Shabbat Commandments
Positive Shabbat commandments include:

• Lighting candles,
• Making kiddush evening and morning,
• Making havdala,
• Honoring Shabbat (Kivod Shabbat), and
• Enjoying Shabbat (Oneg Shabbat), including eating three meals on Shabbat.

Honoring Shabbat: Special Food and Clothes
Honoring Shabbat includes eating tasty food and wearing nice clothes.

Shamor: Negative Shabbat Commandments
Shabbat Laws from the Torah (Shabbat D'Oraita)
What Are Melachot
On the Jewish day of rest, we refrain from 39 creative activities (melachot) that had been used to build the Tabernacle in the wilderness. These 39 melachot, prohibited by the Torah, are listed in the mishna of Shabbat and in later halacha books.

The word melacha is frequently mistranslated as “work,” but work has nothing to do with the Jewish concept of melacha. Some melachot are physically strenuous (plowing, grinding wheat, skinning an animal) and some are easy to do (drawing, baking). The defining point is whether the activity is one of the 39 creative, value-adding labors. Emptying your pockets before leaving an eruv (so you are not “carrying”) may seem confusing to someone who thinks that resting on Shabbat means refraining only from hard physical labor!

What Are Toldot
Toldot are variations of the 39 melachot. These types of melacha are also prohibited by the Torah.

Intention and Other Considerations
Most Torah (d'oraita) prohibitions of melacha on Shabbat are for cases in which you:
            1) Intend a permanent change.
                Often, actions that may be forbidden when they cause permanent change, will
                be permissible by Torah law if the result is only temporary. Or
            2) Intend or act for a specific purpose.
                Random or unintended actions are generally not prohibited by Torah law.
                (However, actions that are not prohibited by the Torah, may be prohibited
                by Chazal.)

Whether you may benefit from a melacha done on Shabbat depends on intention:

• A Jew who intentionally does a melacha on Shabbat may never benefit from that melacha.

            Note Any other Jew may benefit from that melacha as soon as Shabbat is over.

• A Jew who does melacha on Shabbat by mistake (shogeg) may benefit from that melacha immediately after Shabbat ends.

In order to violate a prohibited melacha d'oraita, the melacha must be done as follows. If any of these do not apply, then the melacha is forbidden d'rabanan but not d'oraita:

• K'darko--The action must be done in a normal way.
• Tzorech tikun—The action must be done for a constructive purpose.
• Tzricha l'gufa--You must need the normal result of that action.
• Asiya b'yachid—The action must be done by one individual (if commonly done by just one person).
• Mit'aseik--You must realize that you are doing a melacha.

 
Shabbat Laws from Chazal (Shabbat D'Rabanan)
Chazal instituted additional restrictions, such as:

• Activities that might lead directly to violating a Torah prohibition.
• Use of items not designated for Shabbat use (muktza). For a good explanation of muktza from the TorahTots website, please click here.
• Activities that might lead one to think that a prohibited activity is permissible (mar'it ayin--the appearance of the eye).
• Activities that are not appropriate for Shabbat, even though they are technically permissible according to the Torah (“uvda d'chol”).
• Tircha--Exerting a physical effort to accomplish a result that is not required for Shabbat.

Enjoying Shabbat/Oneg Shabbat
Chazal instituted laws to engender a positive Shabbat atmosphere and experience.  Beyond the actual halachot of shamor and zachor, we have a concept of enjoying Shabbat (oneg Shabbat)—of enhancing our experience of Shabbat by doing whatever each person finds to be enjoyable and relaxing--as long as it is neither destructive nor violates the laws of Shabbat. The criteria are subjective. To fulfill the idea of honoring Shabbat, do things you would not do just for yourself if it were not Shabbat. Take essential life activities such as eating and sleeping and do them more and better and make them especially enjoyable.

Meals as Oneg
On Shabbat, we eat better foods and more types of food than we would normally do on weekdays.
The main idea behind meals for Shabbat is enjoyment (oneg; by contrast, the main idea for Jewish festivals is joy--simcha), so on Shabbat you should eat bread and either fish, poultry, or meat (but only if you enjoy them).
In order to have a special appetite for our Shabbat evening meal, we don't eat a full meal with bread on Friday afternoon.

Special Shabbat Songs (Zmirot)
Special songs (zmirot) are sung at the various Shabbat meals. Some zmirot have an aspect of prayer to them.

Studying Torah
Studying Torah on Shabbat is another way of increasing our spiritual experience. It honors the Shabbat and should bring about enjoyment of Shabbat.

Shabbat and Muktza
For information on Shabbat and muktza, see section below, Shabbat: Muktza.

Weekday Talk
Don't talk about subjects that are forbidden to do on Shabbat (weekday subjects); for example, don't talk about what you will do after Shabbat is over. There is no prohibition about discussing actions from the past as long as no planning is discussed.

Three Shabbat Meals
We are required to eat three Shabbat meals, as a rabbinic (d'rabanan) enactment to enjoy Shabbat (oneg Shabbat). The first Shabbat meal must be at night and the remaining two must be during the day (the third meal must be eaten after halachic midday). Friday night dinner and the first meal on Saturday are preceded by kiddush. For the first two Shabbat meals, say ha'motzi over two complete loaves of bread, each of which is at least 1.3 fl. oz. in volume. For the third meal, the ideal is to use two complete loaves of bread, but the requirement of eating the third meal can also be fulfilled by eating any food other than salt or water.

Source of Saying Shabbat Kiddush

• Saying kiddush on Shabbat night is a commandment from the Torah (d'oraita).
• Saying kiddush on Saturday morning is a rabbinical (d'rabanan) enactment.

Note If you did not say Friday night kiddush, you must say that version of kiddush on Shabbat morning and it is then a requirement from the Torah (d'oraita). Do not begin with va'yechulu; instead, begin with borei pri ha'gafen and say the second blessing of kiddush.

Source of Kiddush Location
Saying kiddush at the place where you will eat your meal is a rabbinical (d'rabanan) enactment.

Shabbat Kiddush-Meal Quantities: Evening

• For evening kiddush, a minimum of 4 fl. oz. (119 ml) of wine must be blessed on and at least half must be drunk.
• For the evening meal, as on Shabbat lunch and all required Jewish festival meals, a minimum of 1.9 fl. oz. of bread must be eaten within four minutes.

Shabbat Kiddush-Meal Quantities: First Meal on Saturday
Shabbat day first meal has two separate eating requirements.  They may be combined (say/hear kiddush and start the main meal right away) but are often done separately (say/hear kiddush and then eat some mezonot; the main meal is eaten later in the day).
Note Since eating and drinking requirements on all morning kiddushes (both Shabbat and Jewish festivals) are d'rabanan, the required beverage amount for morning kiddush is only 3.3 fl. oz. (99 ml) instead of the d'oraita 4 fl. oz. (119 ml), which is required for kiddushes for Shabbat evening.
1) Morning kiddush requires a halachically legal “meal” with these elements:
      a) Blessing on a minimum of 3.3 fl. oz. (99 ml) of wine (or other beverage),
      b) Someone's drinking at least 2 fl. oz. of the beverage, followed by
      c) Eating at least 1.3 fl. oz. (39 ml, or 1/6 cup) of some type of mezonot (or bread) within four minutes.
Note If you drink at least 3.3 fl. oz. (99 ml) of wine within 30 seconds, you do not need to eat mezonot.
Note You do not need to drink the wine or other kiddush beverage to fulfill “establishing a meal.” You may hear kiddush and then simply eat the required amount of bread or mezonot. This applies to Shabbat or Jewish festivals, evening or morning.
The kiddush “meal” does not have to satiate.
Note If you have not fulfilled the requirements for kiddush, you may not eat other foods, such as fruit or fish at a kiddush.

2) The real meal (kovei'a se'uda) of Shabbat lunch requires eating at least 1.9 fl. oz. (56 ml) of bread (or matza during Passover!) within four minutes. It should include enough food to satiate.
Note You can simultaneously fulfill the requirement to “establish a meal” and to “eat a meal” by eating one (the same) piece of bread.
For details on fulfilling the first two meals' requirements, see Shabbat: Kiddush.

Shabbat: Eating a Meal Requirement: Third Meal
For details on fulfilling the third meal's requirements, see Shabbat: Third Meal (Se'uda Shlishit).

We are required to eat two meals on Jewish festivals, each preceded by kiddush, one in the evening and one in the morning. For both meals for each Jewish festival day (and all three meals on Shabbat), say ha'motzi over two complete loaves of bread, each of which is at least 1.3 fl. oz. in volume. 

Source of Saying Jewish Festival Kiddush
Some kiddushes are commanded by the Torah (d'oraita); the others are from Chazal (d'rabanan), as follows:
Kiddush d'Oraita

• First night of Jewish festivals
• Night of seventh day of Passover
• Night of Shmini Atzeret.

Kiddush d'Rabanan

• First day of Jewish festival
• Second night of Jewish festival
• Second day of Jewish festival
• Seventh day of Passover
• Eighth night of Passover
• Eighth day of Passover
• Shmini Atzeret day
• Night and day of Simchat Torah.

Source of Jewish Festival Kiddush Location
Saying Jewish festival kiddush at the place where you will eat your meal is a rabbinical (d'rabanan) enactment.
Jewish Festival Kiddush-Meal Quantities: Evening

• For evening kiddush for a first-night (d'oraita) Jewish festival, a minimum of 4 fl. oz. (119 ml) of wine must be blessed on and at least half must be drunk.
• For evening kiddush for a second-night (d'rabanan) Jewish festival, a minimum of 3.3 fl. oz. (99 ml) of wine must be blessed on and at least 2.0 fl. oz. must be drunk.
• For the evening meal, as on the first two Shabbat meals and for all required Jewish festival meals, a minimum of 1.9 fl. oz. (56 ml) of bread must be eaten within four minutes.

Eating Requirements for Jewish Festival Morning Kiddush
There are two separate eating requirements during the daytime. They may be combined (say/hear kiddush and start the main meal right away) but are often done separately (say/hear kiddush and then eat some light foods and beverages; the main meal is eaten later in the day).
Note Since eating and drinking requirements on all morning kiddushes (both Shabbat and Jewish festivals) are d'rabanan, the required beverage amount for morning kiddush is only 3.3 fl. oz. (99 ml) instead of the d'oraita 4 fl. oz. (119 ml) (which is required for kiddushes for Shabbat evening and all first-night Jewish festivals).

• Morning kiddush requires a halachically legal “meal” with these elements:
  • Blessing on a minimum of 3.3 fl. oz. (99 ml) of wine (or other beverage),
  • Someone's drinking at least half the beverage, followed by
  • Eating at least 1.3 fl. oz. (39 ml, or 1/6 cup) of some type of mezonot within four minutes. 
    Note If you drink at least 3.3 fl. oz. (99 ml) of wine within 30 seconds, you do not need to eat mezonot.
    Note You do not need to drink the wine or other kiddush beverage to fulfill “establishing a meal.” You may hear kiddush and then simply eat the required amount of bread or mezonot. This applies to Shabbat or Jewish festivals, evening or morning.
     

 

• The real meal (kovei'a se'uda) requires eating at least 1.9 fl. oz. (56 ml) of bread (or matza during Passover!) within four minutes. It must include enough food to satiate. 
  Note You can simultaneously fulfill the requirement to “establish a meal” and to “eat a meal” by eating one (the same) piece of bread.

You may directly instruct or ask a non-Jew to do melacha d'rabanan for you on Shabbat, but only:

• To prevent a large financial loss.
  Note A large loss is subjective to the individual's actual wealth and also to that person's perception of what is a large loss. Consult a rabbi.
• For Shabbat needs.
  Example You may ask a non-Jew to unlock an electric hotel door or trigger an entrance door on Shabbat, since this is for a Shabbat need and the action is not prohibited d'oraita.
  Situation A new guest arrives and you need the space on the table occupied by your Shabbat candlesticks.
  What To Do You may not move the candlesticks, but you may ask a non-Jew to do so.
  Situation You left a non-muktza item that you now need for Shabbat on a tree branch (or a child left one in a tree house!).
  What To Do You may not climb the tree to retrieve the item, but you may ask a non-Jew to retrieve it. Example You may ask a non-Jew to turn on air conditioning.
  ExampleYou may ask a non-Jew (directly, no need to hint) to turn off a light if it interferes with someone's sleeping.

  • To allow doing a mitzva.
  • For other pressing (and certainly for life-threatening) needs, such as health, even if the person not sick.

  Note All of these are d'rabanan cases!

As on Jewish festivals, the minimum total volume of Shabbat kiddush beverage that must be drunk--usually by the kiddush-maker (mevareich) but it may even be by several people combined--is a cheekful (m'lo lugmov), as follows:

• 2 fl. oz. (59 ml) within 30 seconds of beginning to drink for d'oraita cases such as Shabbat evening kiddush (as well as first-night Jewish festival kiddush and all havdalas), and
• 1.7 fl. oz. (50 ml) within 30 seconds of beginning to drink for d'rabanan cases such as Shabbat lunch kiddush (as well as first-day Jewish festival lunch kiddush and all second-day Jewish festival kiddushes).

You may ask a non-Jew to open an electric door or to push the button to summon an elevator for you on Shabbat--even if he does not need to get to the floor you want--if you need to get to your room for any mitzva or Shabbat purpose, such as for a nap, to eat, or use the toilet.

Reason Even if a light comes on, it is d'rabanan (you do not need the light) and, therefore, you are permitted to ask the non-Jew to push the button.

Selecting Good from Bad and Bad from Good
Boreir Principle #1: You may eat anything in the manner in which it is normally eaten.
ExamplePeeling an orange.
 
Boreir Principle #2: You may not use a specialized tool.
 
Boreir Principle #3: You may not remove “bad” from “good.”
What To Do  Take good (edible or desired food) from the undesired (bad) components.
Note You may do this only when you are ready to eat it or when you are preparing the food to be eaten soon afterward.
 
Note Boreir is a complicated area of halacha. Because issues of boreir are almost always from the Torah (d'oraita, not d'rabanan), we are stringent in applying restrictions concerning boreir. Consult a rabbi for specific questions.
 
Selecting Undesired from Desired Food
On Shabbat, you may not usually separate totally undesired from totally desired food in a standard way, even without a specialized tool.
    NOTE As on Jewish festivals, an action needed to eat a food normally (derech achila) does not violate the prohibition of boreir on Shabbat. So you may peel a food that is normally separated from its peel or shell in order to be eaten, as long as you do not use a specialized instrument to do so. For example, on Shabbat, you may do the following by hand without a shinu'i:

• Peel an orange
• Remove the shell of a hard-boiled egg
• Separate peanuts from their shells.

NOTE If peanut shells are then put into a container that also has unshelled peanuts, you may not remove the empty shells from that mixture!
SITUATION You want remove dirt from a carrot's surface on a Shabbat.
WHAT TO DO You may remove the dirt with an altered method (shinu'i), such as scraping the peel with a knife (which is a tool not specialized for separating food)-- but not by using a peeler.
REASON The normal way to eat the carrot is to peel it.
 Selecting Desired from Undesired Food
 
While eating food (and some time before--within the amount of time you would normally need to prepare a meal), you may select desired food from undesired (or inedible) substances by hand or non-specialized tool. You may not use a specialized implement.
EXAMPLE You may remove fish from its skeleton even before eating it, but you may not remove the skeleton from the fish (because you have removed bad from good).
NOTE Once Shabbat has begun:

• You may remove fish bones from fish while you are eating the fish, but not before you are eating the fish.
• You may cut open a melon such as a cantaloupe and shake the seeds out (this is because some of the seeds remain), or take a bite of the melon and spit out the seeds. But you may not remove any remaining seeds using your hand or an implement.

EXCEPTION If you take undesired elements along with the desired food, it is not considered to be separating:  you may use a specialized tool and it does not have to be eaten soon (within the normal food-preparation time).

As on Jewish festivals, the minimum volume of kiddush beverage on which you may say Shabbat kiddush (or havdala) is a revi'it, as follows:

• 4 fl. oz. (119 ml) for d'oraita cases such as Shabbat (or first-day Jewish festival) evening kiddush, and
• 3.3 fl. oz. (99 ml) for d'rabanan cases such as kiddush for Shabbat lunch.

You make take medicines for any reason on d'rabanan Jewish festivals--even medicines not allowed on the first day of Jewish festivals--except:

• Medicines that you smear on skin.
• If the Jewish festival falls on Shabbat (which can only be second day of Shavuot).
  Note The d'rabanan Jewish festivals are the second day of Jewish festivals except Rosh Hashana (actually, the second day of Rosh Hashana IS d'rabanan but has the status of d'oraita), plus the last day of Passover and Sukkot outside of Eretz Yisrael.

As on Shabbat, the minimum volume of kiddush beverage on which you may say Jewish festival kiddush (or havdala) is a revi'it:

• 4 fl. oz. (119 ml) for d'oraita cases such as the first night of Jewish festivals (or Shabbat evening) kiddush, and
• 3.3 fl. oz. (99 ml) for d'rabanan cases such Jewish festival lunch and evening/daytime meals on the second Jewish festival day (as well as kiddush for Shabbat lunch).

Issues of boreir are almost always d'oraita, not d'rabanan, and therefore we are stringent in applying restrictions concerning boreir.
Unlike on Shabbat (when you must remove some good along with the bad so as not to violate the melacha of boreir), on Jewish festivals you may remove the bad from the good if it is easier to take the undesired food from the desired food.

You may select desired food from undesired (or inedible) substances if you follow these two rules:

• Food from other food, or
• Food from other substances.
  Note You may remove dirt from a carrot's surface by scraping the peel with a knife (a tool not specialized for separating food), but not by using a peeler.
  Exception As on Shabbat, an action necessary to eat a food normally (derech achila) does not violate the prohibition of boreir. So you may peel a food that is normally separated from its peel or shell in order to be eaten, as long as you do not use a specialized instrument to do so.

• You may peel an orange by hand, with or without a knife.
• You may remove the shells from peanuts by hand.
• You may remove the shell from a hard-boiled egg by hand.

• Remove fish bones from fish while you are eating the fish or just before eating it.
• Cut open a melon such as a cantaloupe and remove any seeds normally.

Although human dignity (kavod ha'briot) cannot override Torah commandments, kavod ha'briot allows violating some d'rabanan laws in order to avoid embarrassment.
Examples

• Tearing Toilet Paper
  Situation You need to use toilet paper on Shabbat but none is torn.
  What To Do You may tear some toilet paper using any non-standard method or change from the normal way (shinu'i), such as not using your hand, or dropping something on the paper.
• Hearing Aid
  Situation You may speak to someone who uses a hearing aid on Shabbat to avoid embarrassing him or her.