A unit of length in the → metric system equal to one millionth of a → meter (10-6 m); symbol μm. Also called → micrometer. The average thickness of a human hair is about 50 μm (30-100 μm). The human eye cannot see anything smaller than 40 μm in size. Other small sizes: white blood cells = 15 μm; red blood cells = 8 μm; bacteria 2 μm.
Coined 1880 in Fr. from Gk. mikron, neutral of mikros "small."
A localized → thermonuclear burst on the surface layers of an → accreting white dwarf. In comparison, classical → nova explosions are caused by global → thermonuclear runaways on the surface of such white dwarfs. Micronovae are less powerful than novae; they have been observed to release up to 1039 ergs of energy, that is approximately 106 times less than the energies released in classical novae (thus the term micronova describing these events). They are also much short-lived, lasting only several hours, while nova outbursts last for weeks. The micronova phenomenon is provoked by the accumulation of accreted matter on the poles of → white dwarfs under the confining effect of strong → magnetic fields (S. Scaringi et al., 2022, arXiv:2204.09073).
Fr.: Omicron Ceti
Another name for → Mira.
Omicron, Gk. alphabet letter; Ceti, → Cetus.
Fr.: Omicron (ο) Lupi
A bright star of → apparent visual magnitude V = 4.3 lying in the constellation → Lupus. Among its other designations: HD 130807, HR 5528, HIP 72683. It is an → early-type star of → spectral type B5 IV and a member of the → Scorpius-Centaurus association. Ο Lupi is in fact a → binary system whose components have an angular separation of 0.043 arcsec, corresponding to a physical separation of 5.3 → astronomical units, with a mass ratio of 0.91.
Two Micron All Sky Survey (2MASS)
An astronomical → survey conducted from 1997 to 2001 of the entire sky in near-infrared J, H, and K bands (wavelengths 1.25, 1.65, and 2.17 microns respectively). The aim was to detect and characterize point sources brighter than about 1 → mJy in each band, with → signal-to-noise ratio greater than 10, using a pixel size of 2".0. Two automated 1.3-m telescopes were used, one at Mt. Hopkins, AZ, and one at CTIO, Chile. 2MASS is currently producing the following data products: 1) A digital atlas of the sky comprising approximately 4 million 8' × 16' images, having about 4" spatial resolution in each of the wavelength bands. 2) A point source catalog containing accurate positions and fluxes for 300 million stars and other unresolved objects. 3) An extended source catalog containing positions and total magnitudes for more than 1,000,000 galaxies and nebulae.