Search results
Results from the WOW.Com Content Network
Blue hour at the Old Cathedral of the Holy Name of Jesus, Bragança in Portugal. The blue hour (from French l'heure bleue; [1] [a] pronounced [lœʁ blø]) is the period of twilight (in the morning or evening, around the nautical stage) when the Sun is at a significant depth below the horizon.
A US Navy sailor lowers day shapes "ball, diamond, ball", signaling the end of restricted maneuvering Day shapes are designed to correspond to the various navigation lights required to be shown at night, and are required to be complied with by day from sunrise to sunset.
Three different concepts of "night" are referred to in the Federal Aviation Regulations in the US. These include the periods from sunset to sunrise - used for nav lights,; the end of evening civil twilight to the beginning of morning civil twilight (this is the "standard definition of night", given in FAR Section 1.1) - used for logging night flight,
Sunrise, sunset, or sun position for any location – U.S. only; Sunrise, sunset and day length for any location – Worldwide; Rise/Set/Transit/Twilight Data – U.S. only; Astronomical Information Center; Converting Between Julian Dates and Gregorian Calendar Dates; Approximate Solar Coordinates; Algorithms for Computing Astronomical Phenomena
Twilight occurs according to the solar elevation angle θ s, which is the position of the geometric center of the Sun relative to the horizon. There are three established and widely accepted subcategories of twilight: civil twilight (nearest the horizon), nautical twilight, and astronomical twilight (farthest from the horizon).
There the sun is seen mid-way between sunrise and sunset. A vertical plane including sun and observer is perpendicular to the plane of the sun's course. Its intersection with the surface of the earth is a meridian, a line passing through a geographical pole. If the sun is in the southern half of the sky, the zenith bearing points true south; if ...
A new Navy command, now called the USNO Flagstaff Station (NOFS), was established there. Those operations began in 1955. [22] Within a decade, the Navy's largest telescope, the 61 inch "Kaj Strand Astrometric Reflector" was built; it saw light at Flagstaff in 1964. [23] USNO continues to maintain its dark-sky observatory, NOFS, near Flagstaff.
Most sun charts plot azimuth versus altitude throughout the days of the winter solstice and summer solstice, as well as a number of intervening days.Since the apparent movement of the Sun as viewed from Earth is nearly symmetrical about the solstice, plotting dates for one half of the year gives a good approximation for the rest of the year.