We do astronomy during the night. Can we do it the day? Yes, in a sense.
Diurnal astronomy[]
Because the sun hides stars' light, we can't see stars, but some heavenly bodies pierce the sun rays.
What to observe the day?[]
Only planets, the moon and the Sun can be observed the day with the naked eye. When?
At a moment of the month, the Moon rises during the day.
Venus, Mercury and maybe Mars and Saturn are visible at a moment of the year at the sunset/sunrise, and Jupiter which can be observed also during the night.
Warning[]
Never see the sun directly. Use material for indirect observation, or don't observe it at all.