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1 kilometer (km) = 1.05702E-13 lightyear (ly). Kilometer (km) is a unit of Length used in Metric system. Lightyear (ly) is a unit of Length used in Metric system.

Kilometer - Unit of Distance / Length

Unit Symbol/Abbreviation: km

Where the unit used in the World:

The kilometer is used as a unit used to measure distances or lengths.
It's a standard measure for travelled distances, geographical distances and maps in most countries excluding the USA and the United Kingdom where mile is still used for this purpose.
between geographical locations on land, and in most countries is the official unit for this purpose. Primary exceptions are the United Kingdom, Liberia, Myanmar and the United States of America, where the mile remains as standard as a part of imperial system.

Definition of the Unit:

The kilometer (kilometre in UK spelling) is a unit of length/distance in the metric system (SI Unit system) equivalent to one thousand meters.

1 km is equivalent to 0.62137 miles.

History of the Unit:

Although the meter was defined in 1799 in France, the kilometer was first adopted for everyday use by the Dutch in 1817 under local name of the mijl. The myriametre (10000 meters) and "lieues de Poste" (Postal leagues, 4288 meters) were preferred to the "kilometer" for everyday use in France in 19th century. In the mid 19th century the kilometer was already in everyday use in the Italy and in Netherlands and the myriametre was still in use in France. The CIPM (The International Committee for Weights and Measures) officially abolished the prefix "myria-" and the "myriametre" in 1935, leaving the kilometer as the recognised unit of length instead of myriametre.

Where it's used:

The kilometer is commonly used on road signs to indicate the distance to travel to a given location, on maps to indicate scale, for odometer indication in automotive industry. It is also the most popular unit for describing the distance between geographical points and locations.

Equivalents in other units and scales:

• 1 km = 1000000 millimeters (mm)
• 1 km = 100 000 centimeters (cm)
• 1 km = 10000 decimeters (dm)
• 1 km = 1000 meters (m)
• 1 km = 3280.84 feet (ft)
• 1 megameter = 1000 km
• 1 gigameter = 1000000 km
• 1 mile = 1.609 km
• 1 yard = 0.000914 km
• 1 foot = 0.000305 km
• 1 inch = 0.0000254 km
• Units of length in the metric SI system are based on multiples or fractions of a meter.
• There are measurements of length/distance in the metric SI system greater than a kilometer that can be expressed in terms of kilometres.

1 km is equivalent to 0.621371 mi.

The kilometer is unit of length in the metric SI system and is equivalent to one thousand metres.

Lightyear: A Unit of Length

The lightyear is a large unit of length used to express astronomical distances and is equivalent to about 9.46 trillion kilometers (9.46 × 10^¹² km), or 5.88 trillion miles (5.88 × 10^¹² mi). As defined by the International Astronomical Union (IAU), a lightyear is the distance that light travels in a vacuum in one Julian year (365.25 days). The lightyear is most often used when expressing distances to stars and other distances on a galactic scale, especially in non-specialist contexts and popular science publications.

In this article, we will explore the definition, history, usage and conversion of the lightyear as a unit of length.

Definition of the Lightyear

The lightyear is a unit of length that is equal to the product of the Julian year and the speed of light. The Julian year is a unit of time that is equal to 365.25 days or 31,557,600 seconds. The speed of light is a physical constant that is defined as 299,792,458 meters per second. The symbol for lightyear is ly.

The definition of the lightyear can be derived from the following formula:

1 ly = 1 Julian year × speed of light

1 ly = 31,557,600 s × 299,792,458 m/s

1 ly = 9,460,730,472,580,800 m

1 ly = 9.46 × 10^¹⁵ m

History of the Lightyear

The concept of the lightyear as a unit of distance was first proposed by the German astronomer Friedrich Wilhelm Bessel in 1838. He used it to estimate the distance to some nearby stars based on their parallax measurements. Parallax is the apparent shift in position of an object when viewed from different angles. Bessel calculated that the star 61 Cygni was about 10.3 lightyears away from Earth.

The term lightyear was popularized by the British astronomer James Bradley in his book Stellar Movements and the Structure of the Universe (1918). He used it to describe the distances to various stars and galaxies. He also introduced the term parsec as another unit of distance based on parallax.

The lightyear was officially recognized by the IAU in 1976 as part of its System of Astronomical Constants.

Usage of the Lightyear

The lightyear is a unit of length that is used for measuring astronomical distances that are too large to be expressed in other units such as kilometers or astronomical units (AU). An AU is equal to about 150 million kilometers or 93 million miles and is roughly the distance from Earth to the Sun.

The lightyear is commonly used in astronomy and cosmology to describe the distances to stars, galaxies, nebulae and other celestial objects. For example:

• The nearest star to Earth (other than the Sun) is Proxima Centauri, which is about 4.2 lightyears away.
• The center of our galaxy, the Milky Way, is about 27,000 lightyears away from Earth.
• The nearest large galaxy to ours, Andromeda, is about 2.5 million lightyears away.
• The farthest galaxy ever observed by humans, GN-z11, is about 13.4 billion lightyears away.

The lightyear can also be used to measure time intervals in cosmology by relating them to distances traveled by light. For example:

• The age of the universe is estimated to be about 13.8 billion years or about 13.8 billion lightyears.
• The cosmic microwave background radiation (CMB) is a remnant of the early universe that we can observe today. It was emitted when the universe was about 380,000 years old or about 46 billion lightyears away from us.
• The observable universe is a sphere around us that contains all the objects that we can see with our current technology. It has a radius of about 46 billion lightyears.

Example Conversions of Lightyear to Other Units

The lightyear can be converted to other units of length by using different factors and formulas. Here are some examples of conversion for different types of units:

• To convert a lightyear to kilometers, multiply by 9.46 × 10^¹²:

1 ly × 9.46 × 10^¹² = 9.46 × 10^¹² km

• To convert a lightyear to miles, multiply by 5.88 × 10^¹²:

1 ly × 5.88 × 10^¹² = 5.88 × 10^¹² mi

• To convert a lightyear to AU, multiply by 63,241:

1 ly × 63,241 = 63,241 AU

• To convert a lightyear to parsecs, divide by 3.26:

1 ly / 3.26 = 0.31 pc

• To convert a kilometer to lightyears, divide by 9.46 × 10^¹²:

1 km / 9.46 × 10^12 = 1.06 × 10^^-13 ly

• To convert a mile to lightyears, divide by 5.88 × 10^¹²:

1 mi / 5.88 × 10^12 = 1.70 × 10^^-13 ly

• To convert an AU to lightyears, divide by 63,241:

1 AU / 63,241 = 1.58 × 10^^-5 ly

• To convert a parsec to lightyears, multiply by 3.26:

1 pc × 3.26 = 3.26 ly