What is a light-year and how is it used?? - NASA Answer: A light-year is a unit of distance It is the distance that light can travel in one year Light moves at a velocity of about 300,000 kilometers (km) each second So in one year, it can travel about 10 trillion km More p recisely, one light-year is equal to 9,500,000,000,000 kilometers Why would you want such a big unit of distance?
Just How Big is this Place - NASA A light year is equal to 9,500,000,000,000 km and is the distance that light travels in one year A light year can be expressed as 9 5 trillion km or in scientific notation as 9 5 x 10 12 km
Parallax - NASA Parallax Astronomers derive distances to the nearest stars (closer than about 100 light-years) by a method called stellar parallax This method that relies on no assumptions other than the geometry of the Earth's orbit around the Sun You are probably familiar with the phenomenon known as parallax Try this Hold out your thumb at arm's length, close one of your eyes, and examine the relative
StarChild: Glossary - NASA L LIGHT YEAR The distance light can travel in one year, which is 9,500,000,000,000 kilometers LUNAR MODULE The section of the Apollo spacecraft designed to land on the Moon LUNAR ROVER The car-like vehicle used by Apollo astronauts while exploring the Moon's surface M MASS The amount of matter in an object MATTER What all things are made of
StarChild: Glossary - NASA L LIGHT YEAR The distance light can travel in one year, which is 9,500,000,000,000 kilometers
Does the Sun move around the Milky Way?? - NASA StarChild Question of the Month for February 2000 Question: Does the Sun move around the Milky Way? Answer: Yes, the Sun - in fact, our whole solar system - orbits around the center of the Milky Way Galaxy We are moving at an average velocity of 828,000 km hr But even at that high rate, it still takes us about 230 million years to make one complete orbit around the Milky Way! The Milky Way
StarChild: Galaxies - NASA Galaxies A light-year is the distance light travels in one year It is 9 5 trillion (9,500,000,000,000) kilometers The size of a galaxy may be as little as a thousand light-years across or as much as a million light-years across
Supernovae - NASA Supernovae At large distances (up to about 1 billion light-years), astronomers can no longer use methods such as parallax or Cepheid variables At such large distances, the parallax shift becomes too small and we can no longer even see individual stars in galaxies Astronomers then turn to a series of methods that use "standard candles", that is, objects whose absolute magnitude is thought to
Cepheids - NASA Cepheids Cepheids, also called Cepheid Variables, are stars which brigthen and dim periodically This behavior allows them to be used as cosmic yardsticks out to distances of a few tens of millions of light-years In 1912, Henrietta Swan Leavitt noted that 25 stars, called Cepheid stars, in the Magellanic cloud would brighten and dim periodically Leavitt was able to measure the period of each
StarChild: The Milky Way - NASA The Milky Way is over 100,000 light-years wide It is called a spiral galaxy because it has long arms which spin around like a giant pinwheel Our Sun is a star in one of the arms When you look up at the night sky, most of the stars you see are in one of the Milky Way arms Before we had telescopes, people could not see many of the stars very clearly They blurred together in a white streak