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
Hydrogen sulfide sulfide solution. Hydrogen sulfide generated in this process is typically converted to elemental sulfur using the Claus Process. Hydrogen sulfide is a highly toxic and flammable gas (flammable range: 4.3–46%). Being heavier than air, it tends to accumulate at the bottom of poorly ventilated spaces. Although very pungent at first, it quickly deadens the sense of smell, so victims may be unaware of its presence until it is too late. For safe handling procedures, a hydrogen sulfide safety data sheet (SDS) should be consulted. Hydrogen sulfide is a broad-spectrum poison, meaning that it can poison several different systems in the