Byr
Encyclopedia
Byr was formerly used in English-language geology
and astronomy
as a unit of one billion year
s. The "B" is an abbreviation for "billion" (meaning 1,000,000,000), with "yr" simply an abbreviation for "year". Today, the term gigaannum (Ga) is also used, but Gy or Gyr are still sometimes used in English-language works (at the risk of confusion with the gray
). Astronomers use Gyr as an abbreviation for Gigayear. Specifically, one Gyr is equal to 109 year
s.
Because a billion
means 1000 million in some countries but can mean a million million in others its use is deprecated in favour of giga- which unambiguously means 109 and annum which for precision may be qualified by (sidereal
), (Julian
), etc.
Geology
Geology is the science comprising the study of solid Earth, the rocks of which it is composed, and the processes by which it evolves. Geology gives insight into the history of the Earth, as it provides the primary evidence for plate tectonics, the evolutionary history of life, and past climates...
and astronomy
Astronomy
Astronomy is a natural science that deals with the study of celestial objects and phenomena that originate outside the atmosphere of Earth...
as a unit of one billion year
Year
A year is the orbital period of the Earth moving around the Sun. For an observer on Earth, this corresponds to the period it takes the Sun to complete one course throughout the zodiac along the ecliptic....
s. The "B" is an abbreviation for "billion" (meaning 1,000,000,000), with "yr" simply an abbreviation for "year". Today, the term gigaannum (Ga) is also used, but Gy or Gyr are still sometimes used in English-language works (at the risk of confusion with the gray
Gray (unit)
The gray is the SI unit of absorbed radiation dose of ionizing radiation , and is defined as the absorption of one joule of ionizing radiation by one kilogram of matter ....
). Astronomers use Gyr as an abbreviation for Gigayear. Specifically, one Gyr is equal to 109 year
Year
A year is the orbital period of the Earth moving around the Sun. For an observer on Earth, this corresponds to the period it takes the Sun to complete one course throughout the zodiac along the ecliptic....
s.
Because a billion
Long and short scales
The long and short scales are two of several different large-number naming systems used throughout the world for integer powers of ten. Many countries, including most in continental Europe, use the long scale whereas most English-speaking countries use the short scale...
means 1000 million in some countries but can mean a million million in others its use is deprecated in favour of giga- which unambiguously means 109 and annum which for precision may be qualified by (sidereal
Sidereal
Sidereal, of the stars, may refer to:* Measurements of time:** Sidereal time** Sidereal day** Sidereal month** Sidereal year* Sidereal period of an object orbiting a star* Sidereal astrology...
), (Julian
Julian calendar
The Julian calendar began in 45 BC as a reform of the Roman calendar by Julius Caesar. It was chosen after consultation with the astronomer Sosigenes of Alexandria and was probably designed to approximate the tropical year .The Julian calendar has a regular year of 365 days divided into 12 months...
), etc.
See also
- MyrMyrThe symbol myr was formerly used in English-language geology, and remains as the standard usage in astronomy, as a unit of one million years.It is an abbreviation for 'million years' and lower case is used in geology, while upper case is used in astronomy....
- annum
- Before PresentBefore PresentBefore Present years is a time scale used in archaeology, geology, and other scientific disciplines to specify when events in the past occurred. Because the "present" time changes, standard practice is to use AD 1950 as the origin of the age scale, reflecting the fact that radiocarbon...
- Gigaannum or Ga
- GyaGyaIn astronomy, geology, and paleontology, Gya or Ga is a year multiplied by one of the SI prefix multipliers. It is often used as a unit of time to denote length of time before the present...
- mya (unit)
- Orders of magnitude (time)#Years