UPS PER (Upsilon Persei) = 51 AND (51 Andromedae). The constellations provide a good background for the initial naming and cataloging of stars, but in the long run are insufficient. Proper names (Betelgeuse, Altair) are fine as far as they go, but who can remember thousands, especially when many are so similar to one another. The first person to bring some order out of the chaos was Johannes Bayer, who in his Uranometria of 1602 gave the brighter stars Greek letters attached to the Latin genitives of the constellation names, with the stars ordered by apparent brightness, location, perhaps whimsy. He was followed by John Flamsteed, the first Astronomer Royal, who published his great atlas of 2935 stars in 1725, to which numbers had already been applied to the stars from west to east within the relevant constellation by Newton and Halley. Vega is thus Alpha Lyrae and also 3 Lyrae. As expected the schemes were not without problems. Other astronomers had to complete the work for stars in the far southern hemisphere, and they did not always agree. Bayer also let several individual stars do double duty to complete the outlines of adjoining constellations. Alpha Andromedae is also Gamma Pegasi and Beta Tauri is Gamma Aurigae. (the first of the pairs always the ones used). Constellation boundaries were also individualistic and flexible, and could differ considerably from one astronomer to another. When Eugene Delporte's modern rectangular boundaries were adopted by the International Astronomical Union in 1930, quite a few Flamsteed stars were orphaned into the wrong constellation despite Delporte's heroic attmpts to keep everything in order. Thus Beta Scuti is 6 Aquilae, 3 Arietis is in Pisces, and Gamma Scorpii is also 20 Librae as well as being Sigma Lib. Various astronomers from Ptolemy onward played around with 51 Andromedae, which is also Upsilon Persei in northwestern Perseus. Even though the fairly bright fourth magnitude star (3.57, nearly third) is actually within the confines of Andromeda, it still goes by the name Upsilon Per in the modern literature. Sometimes it's best to use a catalogue that's free of the constellations altogether and just numbers stars to the east from the Vernal Equniox. Beyond that bit of arcane history, Ups Per is not terribly special. At a distance of 111 light years (give or take just 1), Upsilon is yet another class K (K3) helium-fusing giant like so many others that populate the sky. With a temperature of 4380 Kelvin (much of its radiation in the infrared), Upsilon Per shines with the light of 164 Suns, from which we derive a radius of 22.3 times solar and a mass of roughly double solar. Interferometer measures give discordant radii: 22.0 times that of the Sun at visual wavelengths, but 28.6 solar in the deep red. It's quite possible that both are correct, or close to it, as stars, being gaseous, can easily have different opacities (and thus different apparent radii) as measured in different colors. A projected equatorial rotation velocity of 5.9 kilometers per second suggests a rotation period as long as 190 days. Two names it may have, but the star itself seems decidedly single with no companion following along. (Thanks to "Lost Stars," M. Wagman, McDonald and Woodward, Blacsksburg, VA ,for discussion, and to Martin Trevisan for suggesting this star.)
Written byJim Kaler 05/05/17. Return to STARS.