If the law would be straightforward like R. Tam [which is the opinion of almost all Rishonim and Rav Hai Gaon], then on Friday night one would light the olive oil for the Festival of Lights right before 59 minutes after sunset. But since the Gra (and Rav Sharira Gaon)held the night begins at 18 minutes after sunset it makes sense to light before that time, and simply put in enough olive oil to last for the 72-102 minute period after sunset.
There is one question on R.Tam that I can not answer very well. It is that almost all stars can be seen about 45 minutes after sunset. So according to that no one comes out OK. If the Gra would be correct then one medium sized star would be visible right at sunset. That simply does not happen. If R. Tam would be right then medium stars would begin to be visible after 58.5 minutes. And then three medium stars at 72 minutes.
Just for some background to R. Tam the night starts at 72 minutes after sunset and the twilight doubt period at 58.5. To the Gra night is 3/4 a mil [24 min.] after sunset, 18 minutes. Or if a mil is 18 minutes then night is 13.5 minutes after sunset.
There is one question on R.Tam that I can not answer very well. It is that almost all stars can be seen about 45 minutes after sunset. So according to that no one comes out OK. If the Gra would be correct then one medium sized star would be visible right at sunset. That simply does not happen. If R. Tam would be right then medium stars would begin to be visible after 58.5 minutes. And then three medium stars at 72 minutes.
Just for some background to R. Tam the night starts at 72 minutes after sunset and the twilight doubt period at 58.5. To the Gra night is 3/4 a mil [24 min.] after sunset, 18 minutes. Or if a mil is 18 minutes then night is 13.5 minutes after sunset.
