Collins Stars and Planets Guide by Ian Ridpath

Author:Ian Ridpath
Language: eng
Format: epub
Publisher: HarperCollins Publishers
Published: 2017-11-28T05:00:00+00:00

Virgo – The Virgin

The second-largest constellation in the sky (only Hydra is bigger), and the largest in the zodiac. Virgo is usually identified as Dike, the goddess of justice, the scales of justice being represented by neighbouring Libra. But another legend sees her as Demeter, the corn goddess, and in the sky she is pictured holding an ear of wheat (the star Spica). The Sun passes through the constellation from mid-September to early November, and thus is within Virgo’s boundaries at the time of the September equinox each year, when the Sun moves south of the celestial equator.

Virgo contains the nearest major cluster of galaxies to us, which spills over into neighbouring Coma Berenices; the area is sometimes known as ‘the realm of the galaxies’. The Virgo Cluster lies 55 million l.y. away and contains about 3000 members, several dozen of which are visible in apertures of 150 mm or so, although they appear as little more than hazy patches; some of the brightest members are mentioned below. Another famous feature in Virgo, unrelated to the Virgo Cluster of galaxies, is the optically brightest quasar, 3C 273, located at 12h 29.1m, +2° 03′. It appears as a 13th-mag. blue star and is estimated to lie about 3000 million l.y. away.

α (alpha) Virginis, 13h 25m −11°.2, (Spica, ‘ear of wheat’), mag. 1.0, is a blue-white giant or subgiant star 250 l.y. away. It is a spectroscopic binary, tidally distorted by its companion so that it varies slightly with a period of 4 days as it rotates, although by no more than 0.1 mag.

β (beta) Vir, 11h 51m +1°.8, (Zavijava), mag. 3.6, is a yellow-white main-sequence star 36 l.y. away.

γ (gamma) Vir, 12h 42m −1°.4, (Porrima), 38 l.y. away, is a celebrated double star. Together, the stars shine as mag. 2.7. But a small telescope reveals γ Vir to consist of a matching pair of white stars, of mags. 3.4 and 3.5. They orbit each other every 169 years and were last closest in 2005, when a 250-mm telescope was needed to split them. Now moving apart rapidly, the two stars are divisible in the smallest apertures and will remain so for the rest of the 21st century. See the orbit diagram.

δ (delta) Vir, 12h 56m +3°.4, mag. 3.4, is a red giant 198 l.y. away.

ε (epsilon) Vir, 13h 02m +11°.0, (Vindemiatrix, ‘grape gatherer’), mag. 2.8, is a yellow giant 110 l.y. away.

θ (theta) Vir, 13h 10m −5°.5, mag. 4.4, is a blue-white star 316 l.y. away with an unrelated 9th-mag. companion visible in a small telescope.

τ (tau) Vir, 14h 02m +1°.5, mag. 4.3, a blue-white star 218 l.y. away, forms a wide optical double for small telescopes with a mag. 9.4 companion.

ϕ (phi) Vir, 14h 28m −2°.2, 118 l.y. away, is a yellow subgiant of mag. 4.8 with a 10th-mag. companion, difficult to see in the smallest telescopes because of the brightness contrast.

M49 (NGC 4472), 12h 30m +8°.0, is an 8th-mag. elliptical galaxy visible as a rounded glow in a 75-mm telescope under low power.

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