The best way to understand this is to look at what’s in the universe and then look where we are in it. First, let’s start with the number of galaxies in the known universe. This is challenging because the estimate of the number of galaxies has a very broad range. Astrophysicists are continually debating this, but the estimate I see most frequently is between 200 billion to 2 trillion galaxies in the known universe.
Let’s get a little more local and look at our home, the Milky Way Galaxy. The Sun is one star in the Milky Way, and the Milky Way is one of over thirty galaxies in the Local Cluster. The Milky Way has an estimated 100-400 billion stars rotating around a supermassive black hole called Sagittarius A. The Milky Way has a diameter of 105,700 light-years which is a staggering 620 quadrillion miles!
Unfortunately, these numbers are just too large to comprehend, so let’s get even more local and look at our solar system. Our solar system consists of one star (the Sun) and eight planets. Earth is the third planet from the Sun, and the furthest planet is Neptune (poor little Pluto got the boot a few years ago). To understand how big our solar system is, let’s look at how long it took the Voyager 2 probe to reach some of these distant worlds.
Voyager 2 was launched by NASA on August 20, 1977, and flew by Jupiter on July 9, 1979, flew by Saturn on August 26, 1981, flew by Uranus on January 24, 1986, and finally flew past Neptune on August 25, 1989. As of this writing, Voyager 2 has extended its mission and will study Interstellar Space as it has now left the solar system.
Since the launch of Voyager 2, rocket technology has significantly advanced. Currently, NASA’s Juno Spacecraft is the fastest human-made object ever recorded at 165,000 mph, so let’s see how long it would take it to reach our distant neighbors (distances are averages since the distance varies due to the elliptical orbit of the planets around the Sun):
Earth to the moon is 238,900 miles and would take 4 hours to get there.
Earth to the Sun is 92.2 million miles and would take 23 days.
Earth to Jupiter is 444 million miles and would take 112 days.
Earth to Neptune is 2.77 billion miles and would take one year and 333 days.
Pretty good improvement, but now let’s look at the time it would take to get to our nearest star (Alpha Centauri) and our galaxy neighbor (Andromeda):
Alpha Centauri is 4.3 light-years (ly) from Earth and would take 17,296 years to get there.
Andromeda is 2.5 million ly and would take 16 billion years to get there.
Bottom line, our little solar system is cosmic dust once you enter the stellar and galactic scale, let alone universal scale. It’s a bit like the famous Dr. Seuess book Horton Hears a Who!
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