Star Trip
You are on a super-fast spaceship that travelled from Earth to Neptune, our outermost planet, in one week. (This is more than 600 times as fast as the Apollo moon missions travelled; almost 22 thousand times the speed of sound). How long will it take you to get to Alpha Centauri, the nearest star, at this speed?

Answer: 170 years. (Be sure to pack plenty of food and water!)

Calculation: The distance to Alpha Centauri is 4.24 light years. (Technically Alpha Centauri is a trinary star system - 3 stars/suns orbiting each other. 4.24 light years is the distance to the nearest of the three to us. The distance to the center of the star system is 4.37 light-years.) A light-year contains 5.88 x 10¹² miles. Therefore Alpha Centauri is 4.24 x 5.88 x 10¹² = 2.49 x 10¹³ miles.
The distance to Neptune is 2.8 billion miles (i.e., 2.8 x 10⁹). (Actually this is the distance from Neptune to the sun, but the distance from the Earth to the sun is less than a tenth of a billion miles. Since I did not stipulate exactly where the Earth and Neptune were in their orbits when we made this one-week trip, and the Earth could be either farther from or nearer to Neptune by this amount, I will simply use the "average" of 2.8 billion miles.) Therefore the number of weeks to travel to Alpha Centauri at this speed is 2.49 x 10¹³ / 2.8 x 10⁹ = 8,893 weeks. Dividing by 52.18 weeks/year gives 170 years.

And, yes, this is travelling 2.8 x 10⁹ miles in one week (= 7 x 24 = 168 hours). That is 2.8 x 10⁹ / 168 = 16,666,667 mph. The top speed of the Apollo missions was 24,791 mph, so this is 16,666,667 / 24,791 = 672 times the speed of the fastest Apollo mission.

The speed of sound is 768 mph (in dry air at 20^oC). So this is 16,666,667 / 768 = 21,701 times the speed of sound.