Night sky viewing lets you see about 6,000 stars with your naked eye. But, of course, the sky opens up when you move beyond just using your eyes! You can see many more stars from a dark area (no light pollution) and even more from a dark area with a telescope (We prefer a local park.) And space observatories can see even more.
The observable universe refers to the portion we can observe from our vantage point on Earth. The distance that light has had time to travel since the Big Bang limits our observable universe, given the finite speed of light. When we look at light from distant stars and galaxies, we’re actually stepping into a “time machine.” The time machine shows us what was happening in the universe billions of years ago.
Since the universe has expanded since its formation, the observable universe is also continually growing. The estimated size of the observable universe is about 93 billion light-years in diameter.
However, it’s important to note that the observable universe is not the same as the entire universe, as there may be regions beyond our visible reach due to the expansion of space and the limitations of our observational tools.
How Many Stars Are Observable in the Universe?
Estimating the exact number of stars in the observable universe is challenging due to its vastness and the limitations of our observations. However, scientists have made estimates based on the known properties of galaxies and the average number of stars they contain.
Astronomers estimate there could be around 1 to 2 trillion galaxies in the observable universe. If there are an average of 100 billion stars per galaxy (which is a rough estimate based on our own Milky Way), this would suggest that there is approximately 100 sextillion (10^23) to 200 sextillion (2 x 10^23) stars in the observable universe.
These numbers give us a glimpse of the staggering abundance of stars scattered throughout the vast expanse of the observable universe.
NASA and ESA Missions
NASA and ESA missions don’t specifically count individual stars in the observable universe since its scale and vastness make it impossible to count every star directly. However, the space agencies have launched missions and telescopes that contribute to our understanding of the universe, including studying stars.
Some notable missions include the Hubble and Kepler telescopes and the Gaia mission.
Hubble Space Telescope
The launch of the Hubble Space Telescope began the revolution of our understanding of the universe. Since 19990, it has captured stunning images of distant galaxies, providing valuable data on their composition, structure, and stellar populations.
Kepler Space Telescope
The Kepler mission operated from 2009 to 2018 and focused on discovering exoplanets by monitoring the brightness of stars. Although its primary goal was to find planets, it indirectly provided valuable data on the number and characteristics of stars in various regions of the galaxy.
Launched by the European Space Agency (ESA) with participation from NASA, Gaia is a mission dedicated to creating a detailed 3D map of our Milky Way galaxy. It precisely measures the positions, distances, and motions of stars, which helps us understand the distribution and characteristics of stars in our galaxy.
While these missions contribute to our knowledge of stars and galaxies, the direct counting of individual stars in the observable universe remains an enormous challenge due to the skies’ vastness and current technology’s limitations.