Technically speaking, our sense of time is based on two things: the earth's rotation on its axis and its revolution around the sun. Our rotation produces a day that we divide into 24 hours. Our revolution takes about 365.24 days.
If you go anywhere else in the galaxy, time is different. A year on Mercury is shorter than three Earth months. If you travel to Venus, a year lasts 224.7 Earth days, but Venus takes 243 days to rotate on their axis, so a day is longer than a year. I have no idea how that plays out with Venusian birthdays.
But on Jupiter, a year lasts more than a decade on Earth, but their day is about 10 hours long. It takes nearly 165 Earth years for Neptune to make a trip around the sun--so since Neptune was discovered it has only been around the sun once (July 2011 marked it's one year birthday).
Planets made of gas, like Neptune, usually don't rotate at a uniform speed. There it takes the equator two hours longer to make a rotation than it does the poles.
If it were possible to travel to the sun would you experience days or years? Would time stand still?
And consider that the light from the sun takes about 8 minutes to reach earth. The light from the next nearest star (Alpha Centauri) takes about four years to reach us. When we look into the night sky, we're looking into the past. If an alien living in another galaxy looked through a powerful enough at Earth today, they would in theory see a prehistoric earth.
Einstein asserted that time is relative--that someone who could theoretically travel in a space ship at the speed of light would age differently than someone on Earth.
Time becomes even more perplexing when we consider that God
has no beginning and no end. He is outside of time. He is in the past,
present, and future simultaneously.
But for something so relative, it is also so central to our way of living. We live by time: Time is money. I'm late. You're early. Your time's up. Wait a second. Got a minute? We get into arguments over time--like how old the earth is (which I wonder if it matters so much from either end when time isn't as universal as we like to think it is).
Sometimes, especially around birthdays or other milestones, it feels like time is against us. We only have so many days of life on this planet. In the Star Trek movie Generations, Captain Picard says, "Someone once told me that time was a predator that stalked us all our
lives. I rather believe that time is a companion who goes with us on the
journey and reminds us to cherish every moment, because it will never
come again. What we leave behind is not as important as how we've lived"
Later in the movie Insurrection, Captain Picard is told by a woman named Anij who has been able to turn back time on her life, "We've discovered that a single moment in time can be a universe in
itself, full of powerful forces. Most people aren't aware enough of the
now to even notice." I wonder if the same single moment in time can hold that full of a potential for us...