When a website states that sunrise is at 6:30 AM, it typically means that this is the time at which the center of the sun is expected to cross the horizon and become visible. However, it's important to note that the exact definition of sunrise can vary depending on the source or context.
In general, before the time specified as sunrise, the sky gradually begins to lighten up due to the scattering of sunlight in the atmosphere. This period is known as twilight, and it can be further divided into three phases: civil twilight, nautical twilight, and astronomical twilight.
Civil twilight begins before sunrise and ends after sunset. During this phase, there is enough natural light for most outdoor activities to be conducted without artificial lighting. Nautical twilight occurs before civil twilight and is characterized by a darker sky. It is primarily used by sailors to navigate at sea. Astronomical twilight is the darkest phase of twilight, preceding nautical twilight. In this phase, the sky is dark enough for astronomers to observe celestial objects without interference from the sun's light.
To summarize, if a website mentions that sunrise is at 6:30 AM, it means that the sun is expected to rise above the horizon at that time. Prior to that, the sky will gradually lighten up during the twilight phases, with civil twilight typically starting earlier.