Beginner Exercism • javascript

Space Age

Challenge Overview

Given an age in seconds, calculate how old someone would be on a planet in our Solar System.

Introduction

The year is 2525 and you’ve just embarked on a journey to visit all planets in the Solar System (Mercury, Venus, Earth, Mars, Jupiter, Saturn, Uranus and Neptune). The first stop is Mercury, where customs require you to fill out a form (bureaucracy is apparently not Earth-specific). As you hand over the form to the customs officer, they scrutinize it and frown. “Do you really expect me to believe you’re just 50 years old? You must be closer to 200 years old!”

Amused, you wait for the customs officer to start laughing, but they appear to be dead serious. You realize that you’ve entered your age in Earth years, but the officer expected it in Mercury years! As Mercury’s orbital period around the sun is significantly shorter than Earth, you’re actually a lot older in Mercury years. After some quick calculations, you’re able to provide your age in Mercury Years. The customs officer smiles, satisfied, and waves you through. You make a mental note to pre-calculate your planet-specific age before future customs checks, to avoid such mix-ups.

If you're wondering why Pluto didn't make the cut, go watch [this YouTube video][pluto-video].

[pluto-video]: https://www.youtube.com/watch?v=Z_2gbGXzFbs

Instructions

Given an age in seconds, calculate how old someone would be on a planet in our Solar System.

One Earth year equals 365.25 Earth days, or 31,557,600 seconds. If you were told someone was 1,000,000,000 seconds old, their age would be 31.69 Earth-years.

For the other planets, you have to account for their orbital period in Earth Years:

Planet	Orbital period in Earth Years
Mercury	0.2408467
Venus	0.61519726
Earth	1.0
Mars	1.8808158
Jupiter	11.862615
Saturn	29.447498
Uranus	84.016846
Neptune	164.79132

The actual length of one complete orbit of the Earth around the sun is closer to 365.256 days (1 sidereal year).
The Gregorian calendar has, on average, 365.2425 days.
While not entirely accurate, 365.25 is the value used in this exercise.
See [Year on Wikipedia][year] for more ways to measure a year.

[year]: https://en.wikipedia.org/wiki/Year#Summary

Source: Exercism javascript/space-age

💡 View Solution

export const age = (planet, seconds) => {
  const earthYear = 31557600;
  const ratios = {
    mercury: 0.2408467, venus: 0.61519726, earth: 1, mars: 1.8808158,
    jupiter: 11.862615, saturn: 29.447498, uranus: 84.016846, neptune: 164.79132
  };
  return parseFloat((seconds / (earthYear * ratios[planet])).toFixed(2));
};