# Mission Alpha-Centauri

Did you know that Alpha-Centauri was the second nearest star to planet Earth, the first one being the Sun. It is 4.2 light-years away from us!

When astronomers measure the distance of stars (from planet Earth) they do not use the kilometre (km) unit but instead they use the light-year unit. One light-year represents the distance that light travels in one year, at the speed of light (300,000 km/s). The aim of this challenge is to convert the distance between planet Earth and Alpha-Centauri from light-years to km.

To do so we will use a sequencing algorithm based on the following steps:

1. Calculate the number of seconds in a year,
2. Multiply this number by the speed of light,
3. Multiply this number by 4.2 (the distance of Alpha-Centauri from Earth in light-years).
4. Output the result/ distance in km #### Flowchart

The flowchart of this sequencing algorithm is as follows: #### Python Code

You can now implement this sequencing algorithm using Python code:

#### Step 2: using Selection

Your next challenge is to let the user choose a star, and based on their choice, you will output the distance between the selected star and planet Earth, in km using the following data:

 Star Distance from Earth (in light-years) Alpha Centauri 4.24 light-years Barnard’s Star 5.96 light-years Luhman 16 6.59 light-years WISE 0855-0714 7.2 light-years Wolf 359 7.78 light-years

To do so you will use an if, elif and else statements to implement a selection construct. #### Step 3: using Iteration

Finally, using a while loop, you will keep asking the user to choose a star to repeat the above process with the user’s selection, until the user decides to quit the program. Using a while loop is an example of iteration! Tagged with: , ,