The Lyra Constellation

Lyra is a small constellation. It is one of 48 listed by the 2nd-century astronomer Ptolemy and is one of the 88 constellations recognised by the International Astronomical Union. Lyra was often represented on star maps as a vulture or an eagle carrying a lyre and hence is sometimes referred to as Vultur Cadens or Aquila Cadens respectively. Beginning at the north, Lyra is bordered by Draco, Hercules, Vulpecula, and Cygnus. Lyra is visible from the northern hemisphere from spring through autumn, and nearly overhead, in temperate latitudes, during the summer months. From the southern hemisphere, it is visible low in the northern sky during the winter months. Covering 286.5 square degrees, it ranks 52nd of the 88 modern constellations in size. It appears prominently in the northern sky during the Northern Hemisphere’s summer, and the whole constellation is visible for at least part of the year to observers north of latitude 42°S. Its main asterism consists of six stars, and 73 stars in total are brighter than magnitude 6.5. The constellation’s boundaries, as set by Eugène Delporte in 1930, are defined by a 17-sided polygon. In the equatorial coordinate system, the right ascension coordinates of these borders lie between 18h 14m and 19h 28m, while the declination coordinates are between +25.66° and +47.71°.

The brightest and by far the most well-known star in the constellation is Vega, a main-sequence star of spectral type A0Va. Only 7.7 parsecs distant, is a Delta Scuti variable, varying between magnitudes −0.02 and 0.07 over 0.2 days. On average, it is the second-brightest star of the northern hemisphere (after Arcturus) and the fifth-brightest star in all, surpassed only by Arcturus, Alpha Centauri, Canopus, and Sirius. Vega was the pole star in the year 12,000 BCE, and will again become the pole star around 14,000 CE. It is one of the most magnificent of all stars, and has been called “arguably the next most important star in the sky after the Sun,” and was the first star other than the Sun to be photographed, as well as the first to have a clear spectrum recorded, showing absorption lines for the first time. The star was the first single main-sequence star other than the Sun to be known to emit X-rays and is surrounded by a circumstellar debris disk, similar to the Kuiper Belt. Vega forms one corner of the famous Summer Triangle asterism; along with Altair and Deneb, these three stars form a prominent triangle during the northern hemisphere summer. It also forms one vertex of a much smaller triangle, along with Epsilon and Zeta Lyrae. Delta Lyrae is an optical double, with the two stars simply lying along the same line of sight east of Zeta. The brighter and closer of the two, Delta2 Lyrae, is a 4th-magnitude red, bright giant that varies semiregularly by around 0.2 magnitudes with a dominant period of 79 days, while the fainter Delta1 Lyrae is a spectroscopic binary consisting of a B-type primary and an unknown secondary. Both systems, however, have very similar radial velocities and are the two brightest members of a sparse open cluster known as the Delta Lyrae cluster. South of Delta is Gamma Lyrae, a blue giant and the second-brightest star in the constellation. The final star forming the lyre’s figure is Beta Lyrae, also a binary composed of a bright blue giant and an early B-type star. In this case, the stars are so close together that the larger giant is overflowing its Roche lobe and transferring material to the secondary, forming a semi-detached system. The secondary, originally the less massive of the two, has accreted so much mass that it is now substantially more massive, albeit smaller, than the primary, and is surrounded by a thick accretion disk.

In orbit around the orange subgiant star, HD 177830 is one of the earliest exoplanets to be detected. A Jovian-mass planet, it orbits in an eccentric orbit with a period of 390 days. A second planet closer to the star was discovered in 2011. Visible to the naked eye are HD 173416, a yellow giant hosting a planet over twice the mass of Jupiter discovered in 2009; and HD 176051, a low-mass binary star containing another high-mass planet. HD 178911, a triple system consisting of a close binary and a visually separable sun-like star. The sun-like star has a planet with over 6 Jupiter masses discovered in 2001, the second found in a triple system after that of 16 Cygni. One of the most-studied exoplanets in the night sky is TrES-1b, in orbit around the star GSC 02652-01324. Detected from the transit of its parent star, the planet has around 3/4 the mass of Jupiter, yet orbits its parent star in only three days. Also discovered by the transit method is WASP-3b, with 1.75 times the mass of Jupiter. At the time of its discovery, it was one of the hottest known exoplanets, in orbit around the F-type main-sequence star WASP-3. Lyra is one of three constellations (along with neighbouring Cygnus and Draco) to be in the Kepler Mission’s field of view, and as such it contains many more known exoplanets than most constellations. In April 2013, it was announced that of the five planets orbiting Kepler-62, at least two—Kepler-62e and Kepler-62f—are within the boundaries of the habitable zone of that star, where scientists think liquid water could exist and are both candidates for being a solid, rocky, Earth-like planet. The exoplanets are 1.6 and 1.4 times the diameter of Earth respectively, with their star Kepler-62 at a distance of 1,200 light-years.

M57, also known as the “Ring Nebula” and NGC 6720, has a diameter of one light-year and is at a distance of 2,000 light-years from Earth. It is one of the best known planetary nebulae and the second to be discovered; its integrated magnitude is 8.8. It was discovered in 1779 by Antoine Darquier, 15 years after Charles Messier discovered the Dumbbell Nebula. Astronomers have determined that it is between 6,000 and 8,000 years old; it is approximately one light-year in diameter. The outer part of the nebula appears red in photographs because of emission from ionised hydrogen. The middle region is coloured green; doubly ionised oxygen emits greenish-blue light. The hottest region, closest to the central star, appears blue because of emission from helium. The central star itself is a white dwarf with a temperature of 120,000 kelvins. It can be found halfway between Gamma Lyrae and Beta Lyrae. Another planetary nebula in Lyra is Abell 46. The central star, V477 Lyrae, is an eclipsing post-common-envelope binary, consisting of a white dwarf primary and an oversized secondary component due to recent accretion. The nebula itself is of relatively low surface brightness compared to the central star and is undersized for the primary’s mass for reasons not yet fully understood. NGC 6791 is a cluster of stars in Lyra. It contains three age groups of stars: 4 billion-year-old white dwarfs, 6 billion-year-old white dwarfs and 8 billion-year-old normal stars. NGC 6745 is an irregular spiral galaxy in Lyra that is at a distance of 208 million light-years. Several million years ago, it collided with a smaller galaxy, which created a region filled with young, hot, blue stars. Astronomers do not know if the collision was simply a glancing blow or a prelude to a full-on merger, which would end with the two galaxies incorporated into one larger, probably elliptical galaxy. A remarkable long-duration gamma-ray burst was GRB 050525A, which flared in 2005. The afterglow re-brightened at 33 minutes after the original burst, only the third found to exhibit such an effect in the timeframe, and unable to be completely explained by known phenomena. The light curve observed over the next 100 days was consistent with that of a supernova or even a hypernova, dubbed SN 2005nc. The host galaxy proved elusive to find at first, although it was subsequently identified. Credit: Wikipedia.