Search results
Results From The WOW.Com Content Network
The planetary hours are an ancient system in which one of the seven classical planets is given rulership over each day and various parts of the day. Developed in Hellenistic astrology , it has possible roots in older Babylonian astrology , and it is the origin of the names of the days of the week as used in English and numerous other languages.
Each of the 'planetary' dials used complex clockwork to produce reasonably accurate models of the planets' motion. These agreed reasonably well both with Ptolemaic theory and with observations. For example, Dondi's dial for Mercury uses a number of intermediate wheels, including: a wheel with 146 teeth, and a wheel with 63 internal (facing ...
Mercury and Venus are visible only in twilight hours because their orbits are interior to that of Earth. Venus is the third-brightest object in the sky and the most prominent planet. Mercury is more difficult to see due to its proximity to the Sun. Lengthy twilight and an extremely low angle at maximum elongations make optical filters necessary ...
Sidereal time was defined such that the March equinox would transit the meridian of the observatory at 0 hours local sidereal time. [ 7 ] Beginning during the 1970s, the radio astronomy methods very-long-baseline interferometry (VLBI) and pulsar timing overtook optical instruments for the most precise astrometry .
[4] The treatise is lost, but the answer to the question is known; see planetary hours. [ citation needed ] The Ptolemaic system of planetary spheres asserts that the order of the heavenly bodies from the farthest to the closest to the Earth is Saturn , Jupiter , Mars , Sun , Venus , Mercury , and the Moon ; objectively, the planets are ordered ...
For solid objects, such as rocky planets and asteroids, the rotation period is a single value.For gaseous or fluid bodies, such as stars and giant planets, the period of rotation varies from the object's equator to its pole due to a phenomenon called differential rotation.
A sidereal year (/ s aɪ ˈ d ɪər i. əl /, US also / s ɪ-/; from Latin sidus 'asterism, star'), also called a sidereal orbital period, is the time that Earth or another planetary body takes to orbit the Sun once with respect to the fixed stars.
A convention used by spacecraft lander projects to date has been to enumerate local solar time using a 24-hour "Mars clock" on which the hours, minutes and seconds are 2.75% longer than their standard (Earth) durations. This has the advantage that no handling of times greater than 23:59 is needed, so standard tools can be used.