USAAAO — 2017 First Round

Choose the values (x, y, z) that would best complete the descriptions below for the 3 different types of twilights. i) civil twilight, when the Sun is x° below the horizon. We can start to see the brightest stars and the sea horizon can be clearly seen. At this point it becomes hard to read outdoors without artificial light. ii) nautical twilight, when the Sun is y° below the horizon. It is too dark to see the sea horizon and you can no longer make altitude measurements for navigation using the horizon as a reference. iii) astronomical twilight, when the Sun is z° below the horizon. Scattered sunlight becomes less than the average starlight and it is about the same brightness as the aurora or zodiacal light.