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  2. Horizon - Wikipedia

    en.wikipedia.org/wiki/Horizon

    Geometrical basis for calculating the distance to the horizon, tangent-secant theorem Geometrical distance to the horizon, Pythagorean theorem Three types of horizon. If the Earth is assumed to be a featureless sphere (rather than an oblate spheroid) with no atmospheric refraction, then the distance to the horizon can easily be calculated. [6]

  3. Earth's circumference - Wikipedia

    en.wikipedia.org/wiki/Earth's_circumference

    Posidonius calculated the Earth's circumference by reference to the position of the star Canopus.As explained by Cleomedes, Posidonius observed Canopus on but never above the horizon at Rhodes, while at Alexandria he saw it ascend as far as 7 + 1 ⁄ 2 degrees above the horizon (the meridian arc between the latitude of the two locales is actually 5 degrees 14 minutes).

  4. Empirical evidence for the spherical shape of Earth - Wikipedia

    en.wikipedia.org/wiki/Empirical_evidence_for_the...

    Graphs of distances to the true horizon on Earth for a given height h. s is along the surface of Earth, d is the straight line distance, and ~d is the approximate straight line distance assuming h << the radius of Earth, 6371 km. In the SVG image, hover over a graph to highlight it.

  5. Observable universe - Wikipedia

    en.wikipedia.org/wiki/Observable_universe

    For example, the current distance to this horizon is about 16 billion light-years, meaning that a signal from an event happening at present can eventually reach the Earth if the event is less than 16 billion light-years away, but the signal will never reach the Earth if the event is further away. [9]

  6. Line-of-sight propagation - Wikipedia

    en.wikipedia.org/wiki/Line-of-sight_propagation

    R is the radius of the Earth, h is the height of the transmitter (exaggerated), d is the line of sight distance. Assuming a perfect sphere with no terrain irregularity, the distance to the horizon from a high altitude transmitter (i.e., line of sight) can readily be calculated.

  7. December’s full moon will soon reach peak illumination. Here ...

    www.aol.com/news/december-full-moon-soon-reach...

    December’s full moon, dubbed the cold moon, will reach the crest of its full phase early Sunday. Here’s the best way to view the last full moon of 2024.

  8. Lunar distance - Wikipedia

    en.wikipedia.org/wiki/Lunar_distance

    In contrast, the Lunar distance (LD or ), or Earth–Moon characteristic distance, is a unit of measure in astronomy. More technically, it is the semi-major axis of the geocentric lunar orbit . The lunar distance is on average approximately 385,000 km (239,000 mi), or 1.28 light-seconds ; this is roughly 30 times Earth's diameter or 9.5 times ...

  9. Zenith - Wikipedia

    en.wikipedia.org/wiki/Zenith

    Diagram showing the relationship between the zenith, the nadir, and different types of horizon. The zenith (UK: / ˈ z ɛ n ɪ θ /, US: / ˈ z iː n ɪ θ /) [1] is the imaginary point on the celestial sphere directly "above" a particular location. "Above" means in the vertical direction opposite to the gravity direction at that location . The ...