A well-established Halacha requires one to stand in the presence of his father or mother (Shulhan Aruch – Yore De’a 240:7). One must stand throughout the time that the parent is within viewing distance, until the parent either sits or stands in his/her place, or until the parent is no longer in view or has entered a different domain. If the parent pauses temporarily as he/she makes his/her way toward his/her place, the child must continue standing.
This obligation applies regardless of where the child is when the parent walks in, whether the parent enters the room in the synagogue, the home, a social function, and so on.
The authorities debate the question of how we define "viewing distance" with respect to this Halacha. Some authorities maintained that one must stand when a parent comes within 128 meters, whereas the Hazon Ish (Rabbi Avraham Yeshaya Karelitz, Lithuania-Israel, 1879-1954) held that one must stand within 160 meters (or 525 feet). Rav Yishak Yosef writes that one should follow the stringent view of the Hazon Ish.
It should be obvious that a child must stand if his parent speaks to him while standing. It is very disrespectful for a child to remain seated while his parent, who is standing, speaks to him.
This obligation also applies if a child sits on a bus, train or airplane and the father or mother enters; he must stand at that point until the parent reaches his or her seat. Of course, if there are no available seats for the parent, the child must offer the parent his seat.
When one stands for his parent in fulfillment of this Halacha, he may not lean on a wall or other structure, since leaning does not qualify as standing with respect to this obligation. One may, however, lean slightly, such that he would not fall if the wall would be removed.
It is customary to stand in the synagogue when one’s father goes to the Torah for an Aliya. Strictly speaking, one is required to stand only until his father reaches the Torah. The prevalent practice, however, is to remain standing until the father returns to his place; Hacham Yishak Yosef writes that one should follow this custom. It is also customary to kiss one’s father’s hand after his Aliya to the Torah. Although kissing is generally forbidden in the synagogue, kissing one’s father hand is permissible, as it serves as an expression of respect and honor, rather than as a sign of affection.
Summary: One must stand when one’s father or mother enters the room, and remain standing until the parent is out of view, goes into a different domain, or stands or sits in his/her place. One may not lean on a wall or piece of furniture while standing in one’s parent’s honor. It is proper to stand in the synagogue when one’s father is called for an Aliya to the Torah, until he returns to his place.