• Space/Science
  • GeekSpeak
  • Mysteries of
    the Multiverse
  • Science Fiction
  • The Comestible Zone
  • Off-Topic
  • Community
  • Flame
  • CurrentEvents

Recent posts

A Taste of Armageddon RobVG July 2, 2025 8:00 am (CurrentEvents)

We've got company ER July 2, 2025 7:50 am (Space/Science)

All Along the Watchtower ER July 1, 2025 9:13 pm (CurrentEvents)

Birthright Citizenship RobVG June 29, 2025 3:34 pm (CurrentEvents)

To be blunt, NASA is now dead RL June 27, 2025 11:56 am (Space/Science)

Musk trashes his own AI after it chose a liberal worldview. RobVG June 23, 2025 9:56 am (CurrentEvents)

Psyche keeps its date with an asteroid BuckGalaxy June 22, 2025 5:21 pm (Space/Science)

Just for the record... ER June 22, 2025 8:59 am (CurrentEvents)

The Three Unknowns After the U.S. Strike on Iran BuckGalaxy June 22, 2025 12:58 am (CurrentEvents)

There are only nine meals between mankind and anarchy. BuckGalaxy June 22, 2025 12:29 am (Flame)

Not ready for prime time BuckGalaxy June 19, 2025 12:18 pm (Space/Science)

hypocrisy ER June 15, 2025 2:30 pm (Flame)

Home » Space/Science

Astronomy Domine August 7, 2017 11:07 am ER

Today is 7 August and if you go out tonight at sunset you will see a FULL moon rising in the east. It will be overhead at midnight, and set at sunrise. It makes sense, sun, earth and moon are in a straight line, so sun and moon are as far apart in the sky as possible (in degrees). The moon will be in partial (about 25%) eclipse tonight, as it nicks the edge of the earth’s shadow. This eclipse will be visible in the W Pacific, Asia, Antarctica, Africa and most of Europe.

Exactly a fortnight later (21 August), the NEW moon will be on the opposite side of its orbit, between earth and sun, and we will be directly under its shadow. Eclipses tend to come in pairs, one solar and one lunar, for obvious reasons due to the geometry. There aren’t always eclipses at new and full moon because sometimes the three bodies don’t line up precisely. The moon’s orbit is inclined about 5 degrees to the ecliptic (the sun’s path in the sky), and the ecliptic is inclined about 23.5 degrees to our equator. The earth and moon sometimes go above or below each other’s shadow as a result, but sometimes, like this month, the alignment is right on.

I know you can figure that out without my help, but sometimes it helps to point those things out. The geometry of the celestial sphere is not that complicated, but it took us thousands of years as a species to get it straight because from our point of view inside the system it is hard to untangle all the motions. But the funny thing is that we’ve been accurately predicting eclipses for thousands of years, even long ago when we believed the earth was the center of the universe and everything orbited around it. You can tell time, and devise a good calendar without a true knowledge of how the planets move. You can even determine a ship’s position with a sextant and still believe the earth is the center of the solar system.

Its a good thing to keep in mind. You don’t need to know exactly how things work to figure out how to predict the way they’ll turn out. It explains how we sometimes get things right, and still fuck up big time every now and then.

  • Eclipse by SDG 2017-08-14 16:43:17

    Search

    The Control Panel

    • Log in
    • Register