**ELI5 How do we know how long light has been traveling**

14/12/2018 · For most space objects, we use light-years to describe their distance. A light-year is the distance light travels in one Earth year. One light-year is about 6 trillion miles (9 trillion km).... 4/05/2017 · How do I calculate light years to years? Dec 20, 2009 #1 So if we're seeing a planet 2.7 times the size of earth with liquid water on it, and it's 40 light years away, how do you calculate how far into the past we are seeing this planet? If it is 40 light years away, then the light we see reveals the planet as it was 40 years ago. Last edited by a moderator: May 4, 2017. sylas, Dec 21

**How do they measure that some star is at 100 light years**

The exact distance to Deneb is not known for certain, but the currently accepted distance of around 2,600 light-years. That makes Deneb one of the most distant stars we can see with the eye alone.... The result was the light year, which covers the distance that light travels in one year. That distance is nearly 6 trillion miles, but a light year conveys time more than it does actual distance. For instance, if you are running late to meet a friend, you might say, “I’m 20 …

**Speed of Light Space - Distance Calculator**

20/11/2007 · About 4 1/2 light-hours from Earth. So, if you went the speed of light, it would take that long to get there, (about the same amount of time it takes to drive from L.A. to Las Vegas. So, if you went the speed of light, it would take that long to get there, (about the same amount of time it takes to drive from L.A. to Las Vegas. how to make your bulge look bigger By using the light signature of various known objects (galaxy, super nova, common element like hydrogen) in a way that is analogous to the "star catalogs" from the 2nd method, you can determine by how much the light was redshifted and find out how long it traveled.

**Parallax Georgia State University**

Astronomical unit - a unit of length that is roughly equal to 150 million kilometers, the average distance from the Earth to the Sun. Other units of length used in astronomy are based on the speed of light and the time it takes light to cover a specific distance. how to find the side of square info area Astronomical unit - a unit of length that is roughly equal to 150 million kilometers, the average distance from the Earth to the Sun. Other units of length used in astronomy are based on the speed of light and the time it takes light to cover a specific distance.

## How long can it take?

### Luminosity and the Distance to Stars

- How are astronomers able to measure how far away a star is
- Lightyears conversion calculators tables and forumas
- Distances---Inverse Square Law Astronomy Notes
- Speed of Light Space - Distance Calculator

## How To You Find The Distance Using Light Years

The distance travelled by light in one second is 300000 km(3 followed by five zeros!!).Sparing you the mathematical work, the total distance travelled by light in one year is 9460800000000 kms !. This distance is termed as one Light year.

- z tells you the number of years the light from the object has traveled to reach us, however this is not the distance to the object in light years, because the universe has been expanding as the light traveled and the object is now much farther away.
- Harlow Shapley, an American astronomer using a larger number of Cepheids, recalibrated the absolute magnitude scale for Cepheids and revised the value of the distance to the SMC to 95,000 light years.
- The method of measuring distance to stars beyond 100 light-years is to use Cepheid variable stars. These stars change in brightness over time, which allows astronomers to figure out the true brightness. Comparing the apparent brightness of the star to the true brightness allows the astronomer to calculate the distance to the star. This method was discovered by American astronomer Henrietta
- You want to cast things to an int. Example: int(raw_input("Enter the distance (meters, feet, miles, or light years): ")). After that, things get a bit unclear. As Akash1993 is mentioning, you should review how you are handling this data and the units you are using.