The Leo Minor Constellation

Leo Minor is a small and faint constellation in the northern celestial hemisphere. Its name is Latin for “the smaller lion,” in contrast to Leo, the larger lion. It lies between the larger and more recognisable Ursa Major to the north and Leo to the south. Leo Minor was not regarded as a separate constellation by classical astronomers; it was designated by Johannes Hevelius in 1687. It is a small constellation bordered by Ursa Major to the north, Lynx to the west, Leo to the south, and touching the corner of Cancer to the southwest. The official constellation boundaries, as set by Eugène Delporte in 1930, are defined by a polygon of 16 sides. In the equatorial coordinate system, the right ascension coordinates of these borders lie between 9h 22.4m and 11h 06.5m, while the declination coordinates are between 22.84° and 41.43°. Ranked 64th out of 88 constellations in size, Leo Minor covers an area of 232.0 square degrees or 0.562 per cent of the sky. It culminates each year at midnight on February 24, and at 9 p.m. on May 24.

There are only three stars in the constellation brighter than magnitude 4.5, and 37 stars with a magnitude brighter than 6.5. Leo Minor does not have a star designated Alpha because Baily erred and allocated a Greek letter to only one star, Beta. At magnitude 3.8, the brightest star in Leo Minor is an orange giant of spectral class K0III named 46 Leonis Minoris or Praecipua. Situated 95 light-years from Earth, it has around 32 times the luminosity and is 8.5 times the size of the Sun. It was also catalogued and named as o Leonis Minoris by Johann Elert Bode, which has been misinterpreted as Omicron Leonis Minoris. Beta Leonis Minoris is a binary star system: the primary is a giant star of spectral class G8 and an apparent magnitude of 4.4. It has around double the mass, 7.8 times the radius and is 36 times the luminosity of the Earth’s Sun. Separated by 11 seconds of arc from the primary, the secondary is a yellow-white main sequence star of spectral type F8. The two orbit around a common centre of gravity every 38.62 years, and lie 154 light-years (47 parsecs) away from the Solar System. Around 98 light-years (30 parsecs) away and around ten times as luminous as the Sun, 21 Leonis Minoris is a rapidly rotating white main-sequence star, spinning on its axis in less than 12 hours and very likely flattened in shape. Of average apparent magnitude 4.5 and spectral type A7V, it is a Delta Scuti variable. These are a short period (six hours at most) pulsating stars which have been used as standard candles and as subjects to study astroseismology.

Two stars with planetary systems have been found. HD 87883 is an orange dwarf of magnitude 7.57 and spectral type K0V 18 parsecs distant from Earth. With a diameter three quarters that of Earth’s sun, it is only 31 per cent as luminous. It is orbited by a planet around 1.78 times the mass of Jupiter every 7.9 years, and there are possibly other smaller planets. HD 82886 is a yellow dwarf of spectral type G0 and visual magnitude 7.63. A planet 1.3 times the mass of Jupiter and orbiting every 705 days was discovered in 2011.

Regarding deep-sky objects, Leo Minor contains many galaxies. Located 3 degrees southeast of 38 Leonis Minoris, NGC 3432 is seen nearly edge-on. Known as the knitting needle galaxy, it is of apparent magnitude 11.7 and measures 6.8 by 1.4 arcminutes. Located 42 million light-years away, it is moving away from the Solar System at a rate of 616 km per second. In 2000, a star within the galaxy brightened to magnitude 17.4 and had since been determined to be a luminous blue variable and supernova impostor. NGC 3003, a SBbc barred spiral galaxy with an apparent magnitude of 12.3 and an angular size of 5.8 arcminutes, is seen almost edge-on. NGC 3344, 25 million light-years distant, is face-on towards Earth. Measuring 7.1 by 6.5 arcminutes in size, it has an apparent magnitude of 10.45. NGC 3504 is a starburst barred spiral galaxy of apparent magnitude 11.67 and measured 2.1 by 2.7 arcminutes. It has hosted supernovae in 1998 and 2001. It and the spiral galaxy NGC 3486 are also almost face-on towards Earth; the latter is of magnitude 11.05 and measures 7.1 by 5.2 arcminutes. NGC 2859 is an SB0-type lenticular galaxy. At least two pairs of interacting galaxies have been observed. Arp 107 is a pair of galaxies in the process of merging, located 450 million light-years away. NGC 3395 and NGC 3396 are a spiral and irregular barred spiral galaxy, respectively, that are interacting, located 1.33 degrees southwest of 46 Leonis Minoris. The unique deep-sky object known as Hanny’s Voorwerp was discovered in Leo Minor in 2007 by Dutch school teacher Hanny van Arkel while participating as a volunteer in the Galaxy Zoo project. Lying near the 650-million-light-year-distant spiral galaxy IC 2497, it is around the same size as the Milky Way. It contains a 16,000-light-year-wide hole. The voorwerp is thought to be the visual light echo of a quasar now gone inactive, possibly as recently as 200,000 years ago.

Discovered by Dick McCloskey and Annette Posen of the Harvard Meteor Program in 1959, the Leonis Minorid meteor shower peaks between October 18 and October 29. The shower’s parent body is the long period comet C/1739 K1 (Zanotti). It is a minor shower, and can only be seen from the Northern Hemisphere. Credit: Wikipedia.