ปีแสง
การใช้คำศัพท์

ระยะทางที่แสดงเป็นปีแสงรวมถึงระยะทางระหว่างดวงดาว ในพื้นที่ทั่วไปเดียวกัน เช่น ระยะทางที่อยู่ในแขนก้นหอยเดียวกันหรือ กระจุกดาวทรงกลมกาแล็กซีเองมีขนาดเส้นผ่านศูนย์กลางตั้งแต่ไม่กี่พันปีจนถึงไม่กี่แสนปีแสง และอยู่ห่างจากกาแล็กซีและกระจุกกาแล็กซีเพื่อนบ้านเป็นระยะทางหลายล้านปีแสง ระยะทางไปยังวัตถุต่างๆ เช่น ควาซาร์ และ สโลนเกรตวอลซึ่งมีระยะทางหลายพันล้านปีแสง
| สเกล (ปีแสง) | ค่าของสิ่งต่าง ๆ | สิ่งต่าง ๆ |
| --- | --- | --- |
| 10−9 | 4.04×10−8 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 | 1.58×10−5 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. |
| 10−6 | 1.27×10−4 ly | The <i id="mw3w">Huygens</i> probe lands on Titan off Saturn and transmits images from its surface, 1.2 billion kilometres from Earth. |
| 10−6 | 5.04×10−4 ly | New Horizons encounters Pluto at a distance of 4.7 billion kilometres, and the communication takes 4 hours 25 minutes to reach Earth. |
| 10−3 | 2.04×10−3 ly | The most distant space probe, Voyager 1, was about 18 light-hours (130 au,19.4 billion km, 12.1 billion mi) away from the Earth ข้อมูลเมื่อ October 2014. It will take about 17500 years to reach one light-year at its current speed of about 17 km/s (38000 mph, 61 200 km/h) relative to the Sun. On 12 September 2013, NASA scientists announced that Voyager 1 had entered the interstellar medium of space on 25 August 2012, becoming the first manmade object to leave the Solar System. |
| 10−3 | 2.28×10−3 ly | Voyager 1 as of October 2018, nearly 20 light-hours (144 au, 21.6 billion km, 13.4 billion mi) from the Earth. |
| 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 ≈ 0.8 ly, with its outer edge at 100000 au ≈ 1.6 ly. |
| 100 | 2.0×100 ly | Approximate maximum distance at which an object can orbit the Sun (Hill sphere/Roche sphere, 125000 au). Beyond this is the deep ex-solar gravitational interstellar medium. |
| 100 | 4.24×100 ly | The nearest known star (other than the Sun), Proxima Centauri, is about 4.24 light-years away. |
| 100 | 8.6×100 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. |
| 100 | 1.19×101 ly | Tau Ceti 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. |
| 100 | 2.05×101 ly | Gliese 581, a red-dwarf star with several detectable exoplanets. |
| 100 | 3.1×102 ly | Canopus, second in brightness in the terrestrial sky only to Sirius, a type A9 bright giant 10700 times more luminous than the Sun. |
| 103 | 3×103 ly | A0620-00, the second-nearest known black hole, is about 3000 light-years away. |
| 103 | 2.6×104 ly | The centre of the Milky Way is about 26000 light-years away. |
| 103 | 1×105 ly | The Milky Way is about 100000 light-years across. |
| 103 | 1.65×105 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 million light-years away. |
| 106 | 3×106 ly | The Triangulum Galaxy (M33), at about 3 million light-years away, is the most distant object visible to the naked eye. |
| 106 | 5.9×107 ly | The nearest large galaxy cluster, the Virgo Cluster, is about 59 million light-years away. |
| 106 | 1.5×108 – 2.5×108 ly | The Great Attractor lies at a distance of somewhere between 150 and 250 million light-years (the latter being the most recent estimate). |
| 109 | 1.2×109 ly | The Sloan Great Wall (not to be confused with Great Wall and Her–CrB GW) has been measured to be approximately one billion light-years distant. |
| 109 | 2.4×109 ly | 3C 273, optically the brightest quasar, of apparent magnitude 12.9, just dimmer than R136a1. 3C 273 is about 2.4 billion light-years away. |
| 109 | 4.57×1010 ly | The comoving distance from the Earth to the edge of the visible universe is about 45.7 billion light-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 here for why this is possible. |