Travelling across the Milky Way ( 120,000 LY) with a space craft capable of flying at half the speed of light. Are the numbers correct?

If we can build a space ship that can travel as fast as half the speed of light at 1.5E8 m/s , the time it will take to escape our Milky Way galaxy at a diameter of 120,000 lightyears is 120,000 x 9.4607E15 meters or 7,568,560,000,000 seconds or 239,997.5 years. As for observers and families on planet Earth, the time dilation that would have occurred ( the time passed for everyone else on Earth) is 7,568,560,000,000/(sqrt(1-(1.5E8)^2)/(3E8)^2)= 1.00914E13 seconds or 319996.2 years. The time difference between the astronauts and observers on Earth is approximately 79,998.7 years!

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