Main sequence

In astronomy, the main sequence is a continuous and distinctive band of stars that appears on plots of stellar color versus brightness. These color-magnitude plots are known as Hertzsprung–Russell diagrams after their co-developers, Ejnar Hertzsprung and Henry Norris Russell. Stars on this band are known as main-sequence stars or "dwarf" stars.

After a star has formed, it generates thermal energy in the dense core region through the nuclear fusion of hydrogen atoms into helium. During this stage of the star's lifetime, it is located along the main sequence at a position determined primarily by its mass, but also based upon its chemical composition and other factors. All main-sequence stars are in hydrostatic equilibrium, where outward thermal pressure from the hot core is balanced by the inward pressure of gravitational collapse from the overlying layers. The strong dependence of the rate of energy generation in the core on the temperature and pressure helps to sustain this balance. Energy generated at the core makes its way to the surface and is radiated away at the photosphere. The energy is carried by either radiation or convection, with the latter occurring in regions with steeper temperature gradients, higher opacity or both.

Main Sequence (horse)

Main Sequence (foaled 13 February 2009) is a Kentucky-bred Thoroughbred racehorse. In his first three seasons he raced in Europe winning his first four races including the Lingfield Derby Trial before losing his unbeaten record when finishing second in the 2012 Epsom Derby. After failing to win in 2013 he was gelded and sent to race in the United States. In 2014 he recorded Grade I victories in his first four American starts, winning the United Nations Stakes, Sword Dancer Invitational Handicap, Joe Hirsch Turf Classic Invitational Stakes and Breeders' Cup Turf.

Background

Main Sequence is a chestnut horse with a narrow white blaze bred in Kentucky by Flaxman Holdings an organisation which deals with the breeding and racing interests of the Niarchos family. His sire Aldebaran, a son of Mr Prospector, began his racing career in Britain before moving to the United States where he won three Grade I races including the 2003 Metropolitan Handicap. Main Sequence is the first foal of his dam Ikat, who won one race and finished second in the Group Three Prix d'Aumale. Ikat's dam, Burning Sunset was a half-sister to the Epsom Oaks winner Light Shift and a granddaughter of the leading French-trained racemare Northern Trick. The colt was sent to race in Europe where he was trained by David Lanigan at Upper Lambourn in Berkshire.