Does one have to make up the day and offer expiation if semen is discharged merely by seeing and shaking hands with one's husband returning from travel during Ramadan, or is that considered like a wet dream?

The emission of semen without continuous thought, looking, or direct physical contact does not invalidate the fast, according to the more preponderant opinion among scholars. This is based on the Prophet's (peace be upon him) saying: "Indeed, Allah has forgiven my Ummah for what their souls whisper or think about, as long as they do not act upon it or speak of it." Therefore, there is no need for a compensatory fast (qada') or expiation (kaffarah (definition)).