Crux dominant stars, descending in clockwise order by magnitude: Beta, Gamma (one of the closest red giants to Earth), Delta and Epsilon Crucis. Many of these brighter stars are members of the Scorpius–Centaurus Association, a large but loose group of hot blue-white stars that appear to share common origins and motion across the southern Milky Way. The constellation contains four Cepheid variables that are each visible to the naked eye under optimum conditions. Crux also contains the bright and colourful open cluster known as the Jewel Box (NGC 4755) and, to the southwest, partly includes the extensive dark nebula, known as
Crux 67 degrees south declination for the middle of the constellation. But in AD 18000 or BC 8000 Crux will be and was less than 30 degrees south declination making it visible in Northern Europe. Even by AD 14000, it will be visible for most parts of Europe and the whole United States. In the Southern Hemisphere, the Southern Cross is frequently used for navigation in much the same way that Polaris is used in the Northern Hemisphere. Alpha and Gamma (known as Acrux and Gacrux, respectively) are commonly used to mark south. Tracing a line from Gacrux to Acrux leads