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a A regularly pulsating variable star whose prototype is 8 Cephei.

b An irregular variable characterized by sudden decreases in light caused by ejection of an obscuring, carbon-rich shell.

c Superimposed on the longer cycle is a 0m24-amplitude variation over a period of 110 days;eclipse appears to be due to a disk surrounding a hot, unseen companion.

d Multiple star system;"Aab" refers to double-lined spectroscopic binary making up visual component A;there may be additional variations due to sporadic episodes of pulsation of component b (amplitude 0!"05;P = 0i*3). e Betelgeuse's cyclicity varies from epoch to epoch;longer cyclicities are noted.

f Spectroscopic binary of P = 0i26;variations due to one or more shells. There is a close visual companion also.

g In an emission nebula and near an open cluster, this massive, young star has an expanding dust shell. Maximum light was seen in 1843;since 1880, the visual brightness has been in the range 5!"9-7!"9. h A cycle of 30-day length is also reported.

i Flared for 40 minutes in 1965;usual range: 6m67-6m76;in an open cluster. j Brightest in 1600;since 18th century, range has been 4!"6-5!"6. k Flared for ~10 minutes in 1972;dimmed to 3m5 in 1847;usual range: 2m29-2m44. l Variation possibly due to starspot modulation. Spectroscopic binary with P = 20i*6.

a A regularly pulsating variable star whose prototype is 8 Cephei.

b An irregular variable characterized by sudden decreases in light caused by ejection of an obscuring, carbon-rich shell.

c Superimposed on the longer cycle is a 0m24-amplitude variation over a period of 110 days;eclipse appears to be due to a disk surrounding a hot, unseen companion.

d Multiple star system;"Aab" refers to double-lined spectroscopic binary making up visual component A;there may be additional variations due to sporadic episodes of pulsation of component b (amplitude 0!"05;P = 0i*3). e Betelgeuse's cyclicity varies from epoch to epoch;longer cyclicities are noted.

f Spectroscopic binary of P = 0i26;variations due to one or more shells. There is a close visual companion also.

g In an emission nebula and near an open cluster, this massive, young star has an expanding dust shell. Maximum light was seen in 1843;since 1880, the visual brightness has been in the range 5!"9-7!"9. h A cycle of 30-day length is also reported.

i Flared for 40 minutes in 1965;usual range: 6m67-6m76;in an open cluster. j Brightest in 1600;since 18th century, range has been 4!"6-5!"6. k Flared for ~10 minutes in 1972;dimmed to 3m5 in 1847;usual range: 2m29-2m44. l Variation possibly due to starspot modulation. Spectroscopic binary with P = 20i*6.

letter R and proceed to Z; then they begin again with RR, RS, ..., RZ; then, SS, ST,..., SZ; and so on until ZZ; when they start again with AA, AB,..., AZ, then, BB,..., BZ, etc., but avoiding combinations involving J, until QZ. Thereafter, the designations proceed in an uninterrupted numerical order: V335, V336, and so on. The nomenclature is thus a series of compounded mistakes based on inadequate appreciation of the number of variable stars in the sky—possibly a carryover from Greek notions of immutability in the skies by people unaware of their implicit assumptions. The suffix A or B after the name indicates the brightest or second brightest member of a visual double star, respectively. Such visual doubles need not be physical binaries, but simply lie along the same line of sight. For low-amplitude variability, as seen in these cases, the relationship between amplitude in magnitudes, Am, and the proportional light variation, A€/€, is

Because some variable stars are recorded in ancient literature, we are obliged to describe the classes of variables. First, we distinguish between stars with periodic and nonperiodic variations.

The two major types of periodic variable stars are eclipsing binaries and pulsating variables.

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