The Hubble Space Telescope is many things. It’s an observatory,
a satellite, and an icon of cultural and scientific significance – but
you might be surprised to find out that Hubble is also a time machine!
No, no, no, not like that!
With Hubble’s position just above Earth’s murky atmosphere, its clear view literally lets us
witness our universe’s past. It allows us to travel back in time and see things as they were…
1.3 seconds ago…
33 minutes ago…
An hour ago…
Or even a little bit older than that!
But how does that work? After all, Hubble doesn’t travel beyond our solar system,
or even our home planet’s gravity. So how can it “see” the past?
The answer is light. The term “light-year” shows up a lot in astronomy. This is a measure
of distance that means exactly what it says – the distance that light travels
in one year. Given that the speed of light is 186,000 miles per second,
light can cover some serious ground over the course of 365 days: almost 6 trillion miles worth!
Hubble works by gathering light from objects in our universe – some as close as our Moon
or comets coming into the inner solar system, and some as distant as galaxy clusters that
are billions of light-years away. All that light takes time to reach the telescope,
just as it takes time for light to travel from its source to our eyes.
For example, our Sun is located about 93 million miles from Earth. That means that
it takes roughly eight minutes for its light to reach us here on our planet,
so when we look at the Sun we see it exactly as it was eight minutes in the past.
Cosmically speaking, the 93 million miles between us and the Sun are nothing. We
orbit around just one of billions of stars in the Milky Way Galaxy,
which is one of countless trillions of galaxies in the universe. With that in mind,
time travel gets more intense when Hubble observes objects beyond our star system.
Think about what you were doing four years ago today. What type of sandwich you were eating,
what song you were listening to, what work or school assignment you had, or the car you drove.
Keep those images in your head as you now think about the next closest star to us named Proxima
Centauri. It’s about four light-years away, which makes it a close neighbor on a universal scale.
So right when you ate that ham, tuna, and peanut butter sandwich four years ago, the light from
Proxima Centauri just left the surface of that star and began zooming out towards us. And here
we are, four years and many, many sandwiches later, and that light has finally arrived.
Now, think about what you were up to 700 years ago. Or… at least imagine what your
great great great great great great… add 30 or so more “greats” and you’ll get the point,
great great Grandparents were doing in the 1300s.
If they were in Europe they might have been a brave knight fighting for their king and country. (Or money.)
If they were in Japan they might have
been an early samurai helping to overthrow the Kamakura shogunate.
If they lived in Africa, they might have been collecting gold from Mansa Musa,
or maybe your ancestor even WAS Mansa Musa, arguably the richest human of all time.
During all of those events, the light from the giant star Betelgeuse left its surface.
And all that time from the 1300s up until today that light was traveling at 186,000
miles per second towards us. This means that when Hubble looks at Betelgeuse,
the star appears exactly as it was 700 years ago.
Wanna go even further back in time? Well our next stop is the
Andromeda Galaxy! The Andromeda Galaxy is a whopping 2.5 million light-years away,
but that’s just the closest major galaxy to us here in the Milky Way.
Things were so much simpler back during the Paleolithic period, weren’t they? Dinosaurs
had only been extinct for 62.5 million years as opposed to 65 million years ago. Sandwiches
weren’t even invented yet, let alone peanut butter for sandwiches, let alone sliced bread
for peanut butter sandwiches on sliced bread, and the very earliest humans were just figuring
out how to be… human. Smartphone technology was still quite a few years away though.
Perhaps some of Hubble’s most legendary observations are its deep field images,
which collect light from thousands of galaxies that are billions of light-years away.
With this type of imagery, we can better understand how our universe changes over
time by puzzling out how galaxies evolve. The farther back we look with Hubble, the closer we
get to the big bang, when the universe began – so the most distant galaxies observed by Hubble
often appear to us as the “youngest” ones – giving us a sneak peek at the universe in its infancy.
Because these galaxies emitted their light when they were young,
we get to witness them in their early stages.
These young galaxies are actually old galaxies now as they have evolved over
the time this light has taken to reach us. Hubble has observed galaxies as far back as
13.4 billion years in the past! That’s just 400 million years away from the big bang itself!
So hopefully you’ve enjoyed this time traveling trip with the Hubble Space
Telescope. But remember, you can time travel all on your own without a fancy space telescope
as well. The next time you’re outside at night, remember to look up at the stars;
you’re seeing those stars as they were hundreds, if not thousands of years ago.
Those photons of light have been traveling very far and very fast over a very long period of
time to reach your eyes at that one special moment, so don’t blink or you’ll miss it!