From civil twilight to nautical twilight: Exploring the science of sunrises and sunsets

Sunrise and sunset are two of the most stunning moments of the day, where the sky is painted with shades of pink and orange. However, what happens before and after these moments? GBH meteorologist Dave Epstein recently shared with Morning Edition co-hosts Jeremy Siegel and Paris Alston the science behind the beauty of sunrise and sunset.

Sunrise occurs when the center of the sun’s disk rises above the horizon, while sunset marks the moment when the sun disappears below the horizon. Civil twilight is the period just before sunrise and after sunset, when the sun is zero to six degrees below the horizon. According to Epstein, civil twilight is his favorite time of the day as it is still light, and the sun is not yet fully visible, creating stunning sunrises and sunsets.

Nautical twilight takes place when the sun is six to 12 degrees below the horizon and occurs before civil twilight in the morning and after civil twilight in the evening. During this time, the brightest planets and stars become visible, and animals like deer and coyotes emerge, making it a cautious time for drivers. Following nautical twilight is astronomical twilight, when the sun is between 12 and 18 degrees below the horizon. This period allows for the observation of faint objects like the Milky Way but is still not considered nighttime.

In summer months such as June, astronomical twilight occurs early and late, resulting in a very short nighttime. In northern regions, night may not start until late in the evening, and astronomical twilight may not begin until early morning hours. True nighttime is brief during the longest days of the year due to the timing of astronomical twilight.