Prepositions of Time: at, in, on

In English we use in before months, years, centuries and parts of the day:

• in 1997           I was born in 1984.
• in January          In England, it often snows in December.
• in the 20th century          There should be a lot of progress in the next century.
• in the morning          I usually meet my friends in the evening.
• in the Ice Age          Mammoths became extinct in the Ice Age.
• in the summer          
• in the 1990s          
• in the past/future          Do you think we will go to Jupiter in the future?

We use on before days or dates:

• on Monday          We play tennis on Saturdays.
• on 21st September          Her birthday is on 20th November.
• on Monday morning         I learn German on Monday morning. 
• on Christmas Day          In Poland we open presents on Christmas Eve.
• on my birthday          
• on New Year's Eve          Where will you be on New Year's Day?

We use at before time and a period of a few days:

• at 4:00          I have a meeting at 9am.
• at noon          He woke up at noon.
• at bedtime          
• at sunrise
• at sunset
• at mignight          The shop closes at midnight.
• at lunchtime          Jane went home at lunchtime.
• at the weekend        I'm going to my friend at the weekend. 
• at the moment         I'm writing a letter at the moment. 
• at Christmas (2-3 days)          We visit our family at Christmas.