|
Lunar Time
Timekeeping on the Moon is an issue of synchronized human activity on the Moon and contact with such. The two main differences to timekeeping on Earth is the length of a day on the Moon, being the lunar day or lunar month, observable from Earth as the lunar phases, and the differences between Earth and the Moon of how differently fast time progresses, with 24 hours on the Moon being 58.7 orders of magnitude (time), microseconds (0.0000587 seconds) faster, resulting from the different masses of the Moon and Earth, the effect being called gravitational time dilation. As of early 2024, there is no lunar time standard. Instead, the time on the Moon is different for each country involved. Thus, American activities on the Moon run on the time zone of their mission control centre, while Chinese activities on the Moon run on China Standard Time. As more countries are active on the Moon and interact with each other, a different, unified system will be needed. In 2024, the White House as ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Moon
The Moon is Earth's only natural satellite. It is the fifth largest satellite in the Solar System and the largest and most massive relative to its parent planet, with a diameter about one-quarter that of Earth (comparable to the width of Australia). The Moon is a planetary-mass object with a differentiated rocky body, making it a satellite planet under the geophysical definitions of the term and larger than all known dwarf planets of the Solar System. It lacks any significant atmosphere, hydrosphere, or magnetic field. Its surface gravity is about one-sixth of Earth's at , with Jupiter's moon Io being the only satellite in the Solar System known to have a higher surface gravity and density. The Moon orbits Earth at an average distance of , or about 30 times Earth's diameter. Its gravitational influence is the main driver of Earth's tides and very slowly lengthens Earth's day. The Moon's orbit around Earth has a sidereal period of 27.3 days. During each s ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Air & Space Magazine
''Air & Space/Smithsonian'' is a quarterly magazine published by the National Air and Space Museum in Washington, D.C., United States. Its first publication was in April 1986. Articles in the magazine involve topics related to aviation and space travel, historical and current. It also covers military aviation and aeronautical technology. References External links * 1986 establishments in Washington, D.C. Bimonthly magazines published in the United States History magazines published in the United States Aviation magazines Magazines established in 1986 Magazines published in Washington, D.C. Smithsonian Institution publications {{hist-mag-stub ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Sidereal Time
Sidereal time (as a unit also sidereal day or sidereal rotation period) (sidereal ) is a timekeeping system that astronomers use to locate celestial objects. Using sidereal time, it is possible to easily point a telescope to the proper coordinates in the night sky. In short, sidereal time is a "time scale that is based on Earth's rate of rotation measured relative to the fixed stars", or more correctly, relative to the March equinox. Viewed from the same location, a star seen at one position in the sky will be seen at the same position on another night at the same sidereal time. This is similar to how the time kept by a sundial (Solar time) can be used to find the location of the Sun. Just as the Sun and Moon appear to rise in the east and set in the west due to the rotation of Earth, so do the stars. Both Solar time and sidereal time make use of the regularity of Earth's rotation about its polar axis: solar time following the Sun while, roughly speaking, sidereal time fol ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Nautical Time
Nautical time is a maritime time standard established in the 1920s to allow ships on high seas to coordinate their local time with other ships, consistent with a long nautical tradition of accurate celestial navigation. Nautical time divides the globe into 24 nautical time zones with hourly clock offsets, spaced at 15 degrees by longitudinal coordinate, with no political deviation. Nautical time keeping dates back to the early 20th century as a standard way to keep time at sea, although it largely only applied to military fleets pre–World War 2. This time-keeping method is only used for radio communications and to account for slight inaccuracies that using Greenwich Mean Time (GMT) may lead to during navigation of the high seas. It is typically only used for trans-oceanic travel, as captains will often not change the timekeeping for short distances such as channels or inland seas. History of nautical time Establishment The establishment of nautical standard times, nautical ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
International Celestial Reference System And Its Realizations
The International Celestial Reference System (ICRS) is the current standard celestial reference system adopted by the International Astronomical Union (IAU). Its origin is at the barycenter of the Solar System, with axes that are intended to "show no global rotation with respect to a set of distant extragalactic objects". This fixed reference system differs from previous reference systems, which had been based on Catalogues of Fundamental Stars that had published the positions of stars based on direct "observations of heirequatorial coordinates, right ascension and declination" and had adopted as "privileged axes ... the mean equator and the dynamical equinox" at a particular date and time. The International Celestial Reference Frame (ICRF) is a realization of the International Celestial Reference System using reference celestial sources observed at radio wavelengths. In the context of the ICRS, a reference ''frame'' (RF) is the physical realization of a reference ''system, ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Timekeeping On Mars
Though no standard exists, numerous calendars and other timekeeping approaches have been proposed for the planet Mars. The most commonly seen in the scientific literature denotes the time of year as the number of degrees from the northern vernal equinox, and increasingly there is use of numbering the Martian years beginning at the equinox that occurred April 11, 1955.). Mars has an axial tilt and a rotation period similar to those of Earth. Thus, it experiences seasons of spring, summer, autumn and winter much like Earth. A sol, or Martian day, is less than an hour longer than an Earth day. A Mars year is almost twice as long as Earth's, though its orbital eccentricity is considerably larger, which causes those seasons to vary significantly in length. Sols The average length of a Martian sidereal day is (88,642.663 seconds based on SI units), and the length of its solar day is (88,775.244 seconds). The corresponding values for Earth are currently and , respectively ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Lunar Year
A lunar calendar is a calendar based on the monthly cycles of the Moon's phases (synodic months, lunations), in contrast to solar calendars, whose annual cycles are based only directly on the solar year. The most commonly used calendar, the Gregorian calendar, is a solar calendar system that originally evolved out of a lunar calendar system. A purely lunar calendar is also distinguished from a lunisolar calendar, whose lunar months are brought into alignment with the solar year through some process of intercalation. The details of when months begin vary from calendar to calendar, with some using new, full, or crescent moons and others employing detailed calculations. Since each lunation is approximately days, (which gives a mean synodic month as 29.53059 days or 29 days 12 hours 44 minutes and 3 seconds) it is common for the months of a lunar calendar to alternate between 29 and 30 days. Since the period of 12 such lunations, a lunar year, is 354 days, 8 h ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Feet Per Second
The foot per second (plural feet per second) is a unit of both speed (scalar) and velocity (vector quantity, which includes direction). It expresses the distance in feet (ft) traveled or displaced, divided by the time in seconds (s). The corresponding unit in the International System of Units (SI) is the meter per second The metre per second is the unit of both speed (a scalar quantity) and velocity (a vector quantity, which has direction and magnitude) in the International System of Units (SI), equal to the speed of a body covering a distance of one metre in .... Abbreviations include ft/s, fps, and the scientific notation ft s−1. Conversions See also * Foot per second squared, a corresponding unit of acceleration. * Feet per minute References Units of velocity Customary units of measurement in the United States {{United States Customary Units ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Computer Time
A computer is a machine that can be programmed to carry out sequences of arithmetic or logical operations (computation) automatically. Modern digital electronic computers can perform generic sets of operations known as programs. These programs enable computers to perform a wide range of tasks. A computer system is a nominally complete computer that includes the hardware, operating system (main software), and peripheral equipment needed and used for full operation. This term may also refer to a group of computers that are linked and function together, such as a computer network or computer cluster. A broad range of industrial and consumer products use computers as control systems. Simple special-purpose devices like microwave ovens and remote controls are included, as are factory devices like industrial robots and computer-aided design, as well as general-purpose devices like personal computers and mobile devices like smartphones. Computers power the Internet, which links bi ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Clock Cycle
In electronics and especially synchronous digital circuits, a clock signal (historically also known as ''logic beat'') oscillates between a high and a low state and is used like a metronome to coordinate actions of digital circuits. A clock signal is produced by a clock generator. Although more complex arrangements are used, the most common clock signal is in the form of a square wave with a 50% duty cycle, usually with a fixed, constant frequency. Circuits using the clock signal for synchronization may become active at either the rising edge, falling edge, or, in the case of double data rate, both in the rising and in the falling edges of the clock cycle. Digital circuits Most integrated circuits (ICs) of sufficient complexity use a clock signal in order to synchronize different parts of the circuit, cycling at a rate slower than the worst-case internal propagation delays. In some cases, more than one clock cycle is required to perform a predictable action. As ICs become more ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Quartz Oscillator
A crystal oscillator is an electronic oscillator circuit that uses a piezoelectric crystal as a frequency-selective element. The oscillator frequency is often used to keep track of time, as in quartz wristwatches, to provide a stable clock signal for digital integrated circuits, and to stabilize frequencies for radio transmitters and receivers. The most common type of piezoelectric resonator used is a quartz crystal, so oscillator circuits incorporating them became known as crystal oscillators. However, other piezoelectricity materials including polycrystalline ceramics are used in similar circuits. A crystal oscillator relies on the slight change in shape of a quartz crystal under an electric field, a property known as inverse piezoelectricity. A voltage applied to the electrodes on the crystal causes it to change shape; when the voltage is removed, the crystal generates a small voltage as it elastically returns to its original shape. The quartz oscillates at a stable re ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
.svg "Click for more on -> Moon")
.svg "Click for more on -> Quartz Oscillator")