107 PSC (107 Piscium). The naked-eye sky is made almost entirely of stars more luminous - really much more luminous - than the Sun. Otherwise stars are so distant that you would not see them. Put the Sun - a pretty standard class G dwarf - at 30 light years and it would be about bright as the faintest stars of the Little Dipper. The constellations are made mostly of hot class A and B hydrogen-fusing dwarfs above 9000 Kelvin and cool orange evolved class K Proxima Centauuri. Even class K dwarfs are rare and faint, the outstanding exception being Alpha Centauri B, the K1 companion to brighter G2 Alpha Cen. By itself, Alpha Cen B would be the third brightest star in the sky. Among the most famed of K dwarfs is the K5-K7 double star 61 Cygni, whose distance was first measured via parallax. Others of note are the (again) binary K0-K5 70 Ophiuchi and Epsilon Indi. Almost all K dwarfs are less massive than the Sun. Their importance is in the study of magnetic fields and cycles and how they relate to those of the Sun. Here's another. In far eastern Pisces we find the fifth magnitude (5.24) class K (K1) dwarf 107 Psc; since the Flamsteed numbers go just to 109 Psc, it must be close to the Aries border. To be visible to the naked eye, 107 Psc must also be close, and it is, just 24.6 light years (give or take just 0.1) away. With a temperature of 5196 Kelvin, 107 Psc shines with the light of just 0.45 Suns. The radius comes out to be 0.81 times that of the Sun. Interferometric observations give 0.76 times solar, in decent agreement. The mass appears then to be about 90 percent that of the Sun, though one study gives 1.01 Suns with a 4.6 billion year age. From the variation in its chromospheric (the "chromosphere" the layer just outside the photospheric surface), the star has a rotation period of 33.7 days with a 9.8 year starspot or magnetic cycle. A projected equatorial velocity of 1.7 kilometers/sec indicates an axial tilt to the plane of the sky of about 45 degrees. Sort of approaching us, 107 Psc will eventually come to within 15 light years of us, when it will shine about a magnitude brighter. A pair of 12th magnitude companions hover some 1 and 3 minutes of arc away, but their motions suggest that they are just line of sight coincidences. There seems to be no dusty disk around the star that might indicate a planetary system"

Written byJim Kaler 2/28/17. Return to STARS.