• Bode (1801), Plate 1: Aries Planisphere

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    Uranographia Tab I. Stellatum Hemisphaeri um Arietis

    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 Aries planisphere, centered on the March equinox in Pisces, includes these constellations, among others, which appear high overhead in the night skies of autumn:

    Equatorial:  Orion, Taurus, Harpa Georgii, Cetus, Aries, Pisces, Pegasus, Aquarius, Aquila, Scutum.

    Northern:  Auriga, Perseus, Andromeda, Cassiopeia, Draco, Honores Frederici, Cepheus, Cygnus, Lyra.

    Southern:  Eridanus, Apparatus Chemicus, Machina Electrica, Apparatus Sculptoris, Horologium, Toucan, Phoenix, Grus, Indus, Pavo, Tubus Astronomicus, Octans Nautica, Microscopium, Sagittarius, Globus Aerostatic.

    In March, the Aries-Pisces equinox (the center of the Aries planisphere) is traveling with the Sun, rising in the east in the mornings and setting in the west in the evenings. 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 September equinox. 

  • Equinoxes

    Sunrises and sunsets reach their extreme northerly and southerly positions on the solstices; and occur due east and due west on the equinoxes.

    "Equi-" = same; "nox" = night. Equinox = "equal night."

    On the equinoxes, and only on the equinoxes: 

    • The Sun rises due east and sets due west. 
    • The Sun is located directly overhead at noon as seen from the Earth's equator.
    • Daylight and nighttime are of equal length (12 hours each). 

    There are only two equinoxes each year:

    • September (Autumnal) Equinox: 
      • Occurs around September 22 or 23. 
      • The sunrise and sunset locations are shifting southward along the horizon, relatively fast, perhaps a solar diameter per day.
      • The first day of autumn in the northern hemisphere. Just ahead are cooler days, beautiful fall colors, long starry nights!
    • March (Vernal) Equinox: 
      • Occurs around March 21 or 22. 
      • The sunrise and sunset locations are shifting northward along the horizon, relatively fast, perhaps a solar diameter per day.
      • The first day of spring in the northern hemisphere. Just ahead are warmer, longer summer days.

    Did you know?

    If the Earth were not tilted, every day would be an equinox and there would be no seasons. However, the path of the Sun against the background of fixed stars (the "ecliptic") is tilted with respect to the celestial equator and intersects the celestial equator in only two points (the equinox positions).

    At the North Pole, the Sun sets on the September equinox, the first sunset since the March equinox. The Sun has been located above the horizon throughout the summer, for a total of 186 days, and reached its highest altitude above the horizon on the summer solstice. Once the Sun sets on the September equinox, it will not rise again until the March equinox; there will be 179 days of nighttime at the North Pole. Question: You are an astronomer and wish to book some time using a telescope at the South Pole. What time of year should you go? How many hours a day could you observe the stars?

    When the Sun rises due east, it makes an angle to the horizon equal to 90 minus your latitude. Therefore, at 35 degrees north latitude in Oklahoma, the Sun will rise at an angle of 55 degrees to the horizon.