By noon - a deadline. For example you have to hand in the report by noon = before noon or at the latest at noon. At noon - at 12:00. For example you meet your friend at noon at your favourite restaurant, for lunch.

"at noon" means 12:00 pm. "by noon" means 12:00 pm or before. Let's meet for lunch at noon = We are meeting for lunch at 12:00 pm I have to get my homework done by noon = My homework must be done before 12:00 pm. I always say "at night". I would understand "in the night" to mean "at night" but that sounds awkward to me.

Hey ali sirous, how are you? 1) ''At'': You use ''at'' when you are mentioning a precise time. E.g.: ''He arrived at noon.'' E.g.: ''At 2.30 a.m. he returned.'' E.g.: ''The train leaves at 9 a.m.'' * You can also say that something happened or will happen 'at dawn', 'at dusk', or 'at night'. E.g.: ''She had come in at dawn.'' E.g.: ''It was ten o'clock at night.'' E.g.: ''She left at dusk.'' 2) ''By'': it is used to mean ''not later than''; ''around/near the time/hour concerned''. So, if something happens ''by'' a particular time, it happens at or before that time. E.g.: ''She said she would be arriving by noon.'' E.g.: ''We all had agreed upon starting our meeting by 09:30 a.m.''. As regards your second question, you should know that ''at night'' and ''in the night'' are completely different expressions. In that regard, they should not be used interchangeably: 1) ''Night'' is the period during each twenty-four hours when it is dark. If something happens regularly during this period, you say that it happens ''at night''. E.g.: ''The doors were kept closed at night.'' E.g.: ''I used to lie awake at night, listening to the rain.'' * If you wish to make it clear that you are talking about a particular time in the early part of the night rather than the morning, you add ''at night''. E.g.: ''This took place at eleven o'clock at night on our second day.'' 2) If something happened during the night before the present day, you say that it happened ''in the night'', ''during the night'', or ''last night''. E.g.: ''I did not hear her in the night. E.g.: ''I had the strangest dream last night.'' * If you are talking about a day in the past and you want to say that something happened the night before that day, you say that it happened ''in the night'', ''during the night'', or ''the previous night''. E.g.: ''His father had died in the night.'' E.g.: ''This was the hotel where they had stayed the previous night.'' Hope that helps! :)