Dawn, also known as daybreak, is the time of morning when the first light appears in the sky prior to sunrise, which is the appearance of the top of the sun over the horizon. Dawn occurs roughly 30 minutes before sunrise at sea level.
Light from the sun is refracted over the Earth's atmosphere, causing light to appear before the sun is visible and to linger after the sun sets. The interval of time between dawn and sunrise is known as morning dusk or morning twilight. Morning dusk lasts longer than 30 minutes in areas where the horizon is at a higher altitude than the observer. Conversely, morning dusk lasts for a shorter period of time in areas where the horizon is lower than the observer. Atmospheric pressure and temperature can also affect the length of time morning dusk lasts. For example, a high atmospheric pressure combined with a low atmospheric temperature causes sunrise to occur earlier by less than a minute. Since the time of sunrise can vary depending on atmospheric conditions and the location of the observer, specific times for sunrise are given during local weather reports and forecasts. These sunrise times can also be found from any source that specializes in updated weather or astronomy information.