Distances in Light-years
Distances measured in fractions of a light-year (or in light-months) usually involve objects within a star system. Distances measured in light-years include distances between nearby stars, such as those in the same spiral arm or globular cluster.
One kilolight-year, abbreviated "kly", is one thousand light-years (about 307 parsecs). Kilolight-years are typically used to measure distances between parts of a galaxy.
One megalight-year, abbreviated "Mly", is one million light-years (about 307 kiloparsecs). Megalight-years are typically used to measure distances between neighbouring galaxies and galaxy clusters.
One gigalight-year, abbreviation "Gly", is one billion light-years (about 307 megaparsecs)—one of the largest distance measures used. Gigalight-years are typically used to measure distances to supergalactic structures, including quasars and the Sloan Great Wall.
| Scale (ly) | Value | Item |
|---|---|---|
| 10−9 | 40.4×10−9 ly | Reflected sunlight from the Moon's surface takes 1.2–1.3 seconds to travel the distance to the Earth's surface (travelling roughly 350000 to 400000 kilometres). |
| 10−6 | 15.8×10−6 ly | One astronomical unit (the distance from the Sun to the Earth). It takes approximately 499 seconds (8.32 minutes) for light to travel this distance. |
| 127×10−6 ly | The Huygens probe lands on Titan off Saturn and transmits images from its surface 1200 million kilometres to the Earth. | |
| 10−3 | 1.95×10−3 ly | The most distant space probe, Voyager 1, was about 17 light-hours away from the Earth as of December 2012. It will take about 17,500 years to reach one light-year (1.0 ×100 ly) at its current speed of about 17 km/s (38000 mph) relative to the Sun. On June 15, 2012 NASA scientists stated that Voyager 1 may be very close to entering the interstellar medium of space, becoming the first manmade object to leave the Solar System and is expected to do so before 2015 |
| 100 | 1.6×100 ly | The Oort cloud is approximately two light-years in diameter. Its inner boundary is speculated to be at 50000 AU, with its outer edge at 100000 AU. |
| 2.0×100 ly | Maximum extent of the Sun's gravitational dominance (hill sphere/roche sphere, 125000 AU). Beyond this is the deep ex-solar gravitational interstellar medium. | |
| 4.22×100 ly | The nearest known star (other than the Sun), Proxima Centauri, is about 4.22 light-years away. | |
| 8.60×100 ly | Sirius, the brightest star of the night sky. Twice as massive and 25 times more luminous than the Sun, it outshines more luminous stars due to its relative proximity. | |
| 11.90×100 ly | HD 10700 e, an extrasolar candidate for a habitable planet. 6.6 times as massive as the earth, it is in the middle of the habitable zone of star Tau Ceti. | |
| 20.5×100 ly | Gliese 581g, the first discovered extrasolar candidate for habitable planet. Three or four times as massive as the Earth, it is in the middle of the habitable zone of star Gliese 581. | |
| 310×100 ly | Canopus, second in brightness in the terrestrial sky only to Sirius, a type F supergiant 15000 times more luminous than the Sun. | |
| 103 | 26×103 ly | The centre of our galaxy, the Milky Way, is about 26 kilolight-years away. |
| 100×103 ly | The Milky Way is about 100000 light-years across. | |
| 165×103 ly | R136a1, in the Large Magellanic Cloud, the most luminous star known at 8.7 million times the luminosity of the Sun, has an apparent magnitude 12.77, just brighter than 3C 273 | |
| 106 | 2.5×106 ly | The Andromeda Galaxy is approximately 2.5 megalight-years away. |
| 3×106 ly | The Triangulum Galaxy (M33), at about 3 megalight-years away, is the most distant object visible to the naked eye. | |
| 59×106 ly | The nearest large galaxy cluster, the Virgo Cluster, is about 59 megalight-years away. | |
| 150×106 – 250×106 ly | The Great Attractor lies at a distance of somewhere between 150 and 250 megalight-years (the latter being the most recent estimate). | |
| 109 | 1.2×109 ly | The Sloan Great Wall (not to be confused with the Great Wall) has been measured to be approximately one gigalight-year distant. |
| 2.4×109 ly | 3C 273, optically the brightest quasar, of apparent magnitude 12.9, just dimmer than R136a1. | |
| 45.7×109 ly | The comoving distance from the Earth to the edge of the visible universe is about 45.7 gigalight-years in any direction; this is the comoving radius of the observable universe. This is larger than the age of the universe dictated by the cosmic background radiation; see size of the universe: misconceptions for why this is possible. |
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Famous quotes containing the words distances in and/or distances:
“I was surprised by Joe’s asking me how far it was to the Moosehorn. He was pretty well acquainted with this stream, but he had noticed that I was curious about distances, and had several maps. He and Indians generally, with whom I have talked, are not able to describe dimensions or distances in our measures with any accuracy. He could tell, perhaps, at what time we should arrive, but not how far it was.”
—Henry David Thoreau (1817–1862)
“I was surprised by Joe’s asking me how far it was to the Moosehorn. He was pretty well acquainted with this stream, but he had noticed that I was curious about distances, and had several maps. He and Indians generally, with whom I have talked, are not able to describe dimensions or distances in our measures with any accuracy. He could tell, perhaps, at what time we should arrive, but not how far it was.”
—Henry David Thoreau (1817–1862)