RR Lyrae distance estimate of . This type of low-mass star has consumed the hydrogen at its core, evolved away from the main sequence, and passed through the red giant stage. Energy is now being produced by the thermonuclear fusion of helium at its core, and the star has entered an evolutionary stage called the horizontal branch (HB). The effective temperature of an HB star's outer envelope will gradually increase over time. When its resulting stellar classification enters a range known as the instability strip—typically at stellar class A—the outer envelope can begin to pulsate. RR Lyrae shows just such a regular
Water gas of the carbon dioxide formed when carbon monoxide reacts with water. Water gas Water gas is a mixture of carbon monoxide and hydrogen produced from synthesis gas. Synthesis gas is a useful product, but requires careful handling due to its flammability and the risk of carbon monoxide poisoning. The water-gas shift reaction can be used to reduce the carbon monoxide while producing additional hydrogen, resulting in water gas. Synthesis gas is made by passing steam over a red-hot carbon fuel such as coke: The reaction is endothermic, so the fuel must be continually re-heated to keep the reaction going. In