“Does anyone know what Helios is?”
Robert's oldest student, Jim, called out from the third row, “Wasn't it an unmanned spacecraft we sent out sometime in the 70s?”
“You are correct, and probably the only one in this room who was alive when that happened,” he chuckled. “Helios traveled at about 157,000 miles per hour. The sun is on average, 93 million miles away from earth. If an astronaut was charting his travel plans to a planet outside of the solar system and even capitalized on the sun as a gravitational slingshot, there would still be some very tough obstacles to overcome. Traveling at our current maximum achievable speed, it would still take about 26 days just to reach the sun to grab that gravitational slingshot. The astronauts would already have been en voyage for nearly a month … and they wouldn't have even started towards their actual destination yet!
“Did you know that the nearest star to Earth (other than the Sun) is Proxima Centauri?” he wrote on the board, “Also known as Alpha Centauri C, it's about four light years away.” To the class he asked, “Now, can anyone explain what a light year is?” Robert listened for a moment and verbally summarized several of their responses so that everyone could hear: “A light year is the distance traveled at the speed of light for one solid Earth year, twenty-four hours a day. An Earth year is really just how long it takes the Earth to orbit Sol (Earth’s sun) one time.”
“But how fast is light speed?” Robert peered out from the under the bright lights of the auditorium. Jim again raised his hand. “Yes, Jim?”
“About 186,000 miles per hour,” he replied confidently.
“186,282 miles per second,” Robert corrected. Any guesses on how fast that would be per hour?”
A voice from the back row called out, “Very fast?”
“Hit the nail on the head,” Robert laughed agreeably. “It's an astounding 670.6 million miles per hour.” He wrote those numbers on the board.
“Getting to this nearest star outside our solar system at light speed would still require covering approximately 6 trillion miles every year for 4.3 years.
"Here,” he pointed to the board, “let me write the total number of miles on the board.” he scribbled '26' with 12 zeros after it. “That's roughly how many miles it is to Proxima Centauri.” Robert paused. “That's the nearest star to Earth other than the sun.”
A few surprised murmurs made their way through the auditorium as they thought about the stars they’d seen in the Milky Way galaxy for comparison.