An image of distant galaxies captured by the NASA/ESA Hubble Space Telescope. Credit: ESA/Hubble & NASA, RELICS; Acknowledgment: D. Coe et al. For most space objects, we use light-years to describe their distance. A light-year is the distance light travels in one Earth year. One light-year is about 6 trillion miles (9 trillion km). That is a 6 with 12 zeros behind it! When we use powerful telescopes to look at distant objects in space, we are actually looking back in time. How can this be? Light travels at a speed of 186,000 miles (or 300,000 km) per second. This seems really fast, but objects in space are so far away that it takes a lot of time for their light to reach us. The farther an object is, the farther in the past we see it.
Looking Back in Time
Our Sun is the closest star to us. It is about 93 million miles away. So, the Sun's light takes about 8.3 minutes to reach us. This means that we always see the Sun as it was about 8.3 minutes ago.
The next closest star to us is about 4.3 light-years away. So, when we see this star today, we’re actually seeing it as it was 4.3 years ago. All of the other stars we can see with our eyes are farther, some even thousands of light-years away.
Stars are found in large groups called galaxies. A galaxy can have millions or billions of stars. The nearest large galaxy to us, Andromeda, is 2.5 million light-years away. So, we see Andromeda as it was 2.5 million years in the past. The universe is filled with billions of galaxies, all farther away than this. Some of these galaxies are much farther away.
An image of the Andromeda galaxy, as seen by NASA's GALEX observatory. Credit: NASA/JPL-Caltech
In 2016, NASA's Hubble Space Telescope looked at the farthest galaxy ever seen, called GN-z11. It is 13.4 billion light-years away, so today we can see it as it was 13.4 billion years ago. That is only 400 million years after the big bang. It is one of the first galaxies ever formed in the universe.
Learning about the very first galaxies that formed after the big bang, like this one, helps us understand what the early universe was like.
This picture shows hundreds of very old and distant galaxies. The oldest one found so far in GN-z11 (shown in the close up image). The image is a bit blurry because this galaxy is so far away. Credit: NASA, ESA, P. Oesch (Yale University), G. Brammer (STScI), P. van Dokkum (Yale University), and G. Illingworth (University of California, Santa Cruz)
article last updated August 27, 2020
Absolutely, when it comes to the vast cosmos and our understanding of distant celestial objects, I'm quite well-versed. Let's break down the concepts and information highlighted in the article about the NASA/ESA Hubble Space Telescope and the distant galaxies it observed.
Light-years and Distance Measurement:
The article discusses the use of light-years as a measurement unit for distances in space. A light-year represents the distance that light travels in one Earth year, roughly equal to 6 trillion miles or 9 trillion kilometers. This remarkable distance helps contextualize the enormous scale of the universe.
Time and Space Observation:
One fascinating aspect is how observing distant objects actually means looking back in time. Light, though incredibly fast at 186,000 miles (or 300,000 km) per second, takes considerable time to reach us from distant celestial bodies. The farther an object, the further back in time we perceive it. This principle allows us to witness objects as they were in the past.
Proximity and Perception:
The article explains that our closest star, the Sun, is approximately 93 million miles away, meaning it takes about 8.3 minutes for its light to reach us. Consequently, we see the Sun as it was over eight minutes ago. The next closest star is about 4.3 light-years away, so when we observe it today, we're essentially looking at it as it existed 4.3 years in the past.
Galaxies and Their Distance:
Stars are grouped into galaxies, vast collections containing millions or even billions of stars. The Andromeda galaxy, our closest large neighbor, is around 2.5 million light-years away. Hence, observing Andromeda means viewing it as it existed 2.5 million years ago.
Farthest Observable Galaxies:
The Hubble Space Telescope, in 2016, detected the farthest known galaxy, GN-z11, located 13.4 billion light-years away. This incredible distance means we perceive GN-z11 as it was 13.4 billion years ago, merely 400 million years after the big bang. Studying such ancient galaxies offers crucial insights into the early universe and its formation.
Implications for Understanding the Universe:
Analyzing these distant galaxies, especially the earliest ones like GN-z11, provides valuable clues about the universe's infancy. This information helps in constructing a more comprehensive picture of how the cosmos evolved after the big bang.
The images captured by the Hubble Space Telescope and other observatories allow us to peer into the ancient past, unraveling the mysteries of the universe's formation and evolution. This continual exploration advances our understanding of the cosmos and our place within it.
