The modulation level is 50 percent for the steady tones, 50 percent for the BCD time code, 100 percent for the second pulses and the minute and hour markers, and 75 percent for the voice announcements. The signals broadcast by WWV use double sideband amplitude modulation. This sloping skirt functions as the lower half of the radiating system and also guys the antenna.
The bottom half of each antenna consists of nine quarter-wavelength wires that connect to the center of the tower and slope downwards to the ground at a 45 degree angle. The top half of each antenna is a quarter-wavelength radiating element. The shortest tower, for 20 MHz, is about 7.5 m tall. The tallest tower, for 2.5 MHz, is about 60 m tall. Each antenna is mounted on a tower that is approximately one half-wavelength tall. Each antenna is connected to a single transmitter using a rigid coaxial line, and the site is designed so that no two coaxial lines cross. There are antennas at the station site for each frequency. The WWV antennas are half-wave vertical antennas that radiate omnidirectional patterns. The variety of frequencies makes it likely that at least one frequency will be usable at all times. Although each frequency carries the same information, multiple frequencies are used because the quality of HF reception depends on many factors such as location, time of year, time of day, the frequency being used, and atmospheric and ionospheric propagation conditions. Each frequency is broadcast from a separate transmitter. The station radiates 10 000 W on 5 MHz, 10 MHz, and 15 MHz and 2500 W on 2.5 MHz and 20 MHz. WWV operates in the high frequency (HF) portion of the radio spectrum. The broadcast information includes time announcements, standard time intervals, standard frequencies, UT1 time corrections, a BCD time code, and geophysical alerts. WWV is located near Fort Collins, Colorado, about 100 kilometers north of Denver. Page Go to NASA Lunar Eclise Page Go to NASA Planetary Transit Page Go to NASA Eclipse Resource PageĮmail: NASA Representative: Robert M.NIST radio station WWV broadcasts time and frequency information 24 hours per day, 7 days per week to millions of listeners worldwide. Through Time - National Institute of Standards and
įor more information on time reckoning and time zones, check out To convert any eclipse predictions from UT to local time (i.e. Will see that your local time is 5 hours earlier than UT. Once noted, use this number to convert all eclipse prediction timesįor example, if you are in the Eastern Standard Time zone, you How many hours different your local time is from Universal Time. The official source of time used in the United States is the In order keep it in sync with UT (which varies due to Earth's Occasionally, a "leap second" is added to UTC Is synchronized and adjusted to stay within 0.9 seconds of Just remember that you'll need toĬheck with your travel agent or with a guide book to find out if Daylight Saving Time is practicedĬoordinated Universal Time (or UTC) is based on atomic time. Zone Map courtesy of HM Nautical Almanac Office, Time zones for countries around the world can be determined with So the eclipse will begin at 16:25 (=4:25pm) local time. Saving Time in June, we must ADD one more hour to the above Pacific Standard Time (PST) = UT - 8 hoursĮffect in the time zone, you must ADD one hour to the aboveįor example, let's assume that an eclipse begins in Toledo, Ohio Mountain Standard Time (MST) = UT - 7 hours For North Americans, the conversion from UT to local time is as follows:Ītlantic Standard Time (AST) = UT - 4 hoursĮastern Standard Time (EST) = UT - 5 hoursĬentral Standard Time (CST) = UT - 6 hours In order to convert eclipse predictions from UT to local time, you need to know what time zone you are in. Like most other astronomical calculations, eclipse predictions are usually presented in terms of Universal Time.
It's also approximately equal to mean solar time from Greenwich. Universal Time is actually based on the mean sidereal time as measured in Greenwich, England. Although their exact definitions differ, most readers can assume that Universal Time is equivalent to Greenwich Mean Time or GMT. Universal Time or UT is the precise measure of time used as the basis for all civil time-keeping. Finally, we can measure time through the oscillations of atoms (International Atomic Time). Or we can measure time based on the rotation of Earth on its axis with respect to the stars (Universal Time). For instance, we can measure the passage of time via the orbital motion of Earth and other planets in the solar system (Dynamical Time). Time can be measured in a number of ways.
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