• Hya - Hydra the Water Snake

    IAU Constellation

    Size

    1 of 88

    Astronomical Regions

    Intro and Visual description

    Hydra the Water Snake is the largest and longest of the constellations, stretching from Cancer to Libra. Several constellations and asterisms ride on its back; from head to tail they are Sextans the Sextant, Crater the Cup, Corvus the Crow, and Noctua the Owl.

  • Vir - Virgo the Maiden

    IAU Constellation

    Size

    2 of 88

    Astronomical Regions

    Intro and Visual description

    Continue past Arcturus on the curve from the Dipper’s handle ("Arc to Arcturus, then speed on to Spica"). To "Speed on to Spica," go the same distance as it took to reach Arcturus. If it’s not below the horizon, Spica is the brightest star of the constellation Virgo the Maiden. Although Virgo is the second largest constellation in the sky, the rest of its stars are faint. Yet don’t be surprised if you often see a bright visiting planet nearby.

  • Bode (1801), plate 2: Libra Planisphere

    Image

    Uranographia Tab II. Stellatum Hemisphaeri um Librae

    Bode included two planisphere plates. They are not southern and northern hemispheres; each one has Polaris at the top and the south pole at the bottom. Each one is centered upon an equinox point (where the ecliptic or path of the Sun and the celestial equator intersect). The March equinox point was in Aries in antiquity; by Bode’s time, due to the precession of the equinoxes, it had shifted to Pisces. The September equinox point was in Libra in antiquity; by Bode’s time it had shifted to Virgo.  Bode titled the plates as the Aries and Libra planispheres.

    The Libra planisphere, centered on the September equinox in Virgo, includes these constellations, among others, which appear high overhead in the night skies of spring:

    Equatorial:  Ophiuchus, Serpens, Libra, Virgo, Crater, Corvis, Hydra, Sextans, Leo, Cancer, Monoceros.

    Northern:  Hercules, Quadrans Muralis, Bootes, Canes Venatici, Ursa Major, Telescopium Herschelii, Gemini, Lynx, Ursa Minor.

    Southern:  Scorpius, Tubus Astronomicus, Lupus, Centaurus, Apis, Chameleon, Crux, Argo Navis, Robur Caroli II, Circinus (sector compass), Canis Major, Pixis Nautica (magnetic compass), Machina Pneumatica (air pump), Officina Typographica (printing press).

    In September, the Libra-Virgo equinox (the center of the Libra plate) is traveling with the Sun, rising in the east in the morning and setting in the west in the evening.  Imagine the center of the planisphere has the Sun pinned to it for that day, and that’s how it would move across the sky. Therefore the constellations near the center of this planisphere are invisible in the daytime sky at that time unless there is a solar eclipse.  They would be visible directly opposite the Sun at the March equinox.