Stars as History

Rachael Beaton explains why studying astronomy is studying the past.

Arts & Sciences asked Rachael Beaton, “What does it mean to be able to see back to the beginning of the universe?”

When you look through a telescope with large light collecting power, you are actually looking in both distance and in time. Since light has a finite velocity (i.e., the speed of light, 186,282 miles per second), it takes time for the light from distant objects to reach us on Earth. Hence, often Astronomers will use the unit “light-years,” which denotes the time that the light has been traveling to reach us. So, when astronomers take measurements of the universe, they are not taking measurements in real time. Instead, we observe what the astronomical object looked like when the light was emitted. This, of course, can be a significant limitation of observation!

It is a very interesting way to study the universe, that the farther we can “see” in distance, the further back we look in time. Thus, as we are able to look at galaxies farther and farther away, we are effectively viewing galaxies at different phases of general galaxy evolution (and the evolution of the universe as a whole). One can propose the question, “Did galaxies look different in the early universe?” and actually go and seek those answers somewhat directly. It’s very similar to how archaeologists can dig deeper into the Earth to study the evolution of Homo sapiens (and before). Astronomical facilities like Hubble and the LBT that push our ability to delve farther into the universe (and, of course, also to study more nearby objects in greater detail) directly push our ability to understand the evolution of the universe. Indeed, in the notable Hubble Ultra Deep Field, a composite of 11.3 days of observations with Hubble, the light from the most distant objects is more than 13 billion years old. (The image contains more than 10,000 galaxies and is only a tiny, tiny fraction of the sky).

This, however, is still younger than the age of our universe!

Learn more about the earliest galaxies and see the images captured by NASA Hubble Space Telescope via Hubble Ultra Deep Field, the deepest portrait of the visible universe ever achieved by humankind.