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Since ancient times, humans have been gazing up into the heavens and wondering about our place in the universe. Though we’ve long been mapping and observing the stars and other celestial bodies, it’s only been recent that we could see far enough into the universe to discover many of the hidden secrets it holds.
Today, astronomy is becoming more accessible for more people than ever before. It no longer requires a large budget to acquire the type of equipment you need to explore the cosmos up-close. As a result, interest in astronomy continues to grow. When you get a new telescope, the first question that probably comes to mind is the most obvious — how far can you see with your telescope?
Unfortunately, there’s no one-size-fits-all answer here. Every telescope is different, allowing you to see different distances, varied fields of view, and more. But it’s not just differences in equipment that will affect the distance you can see through your telescope. Several variables can impact your possible viewing distance, from weather to your location and more.
Forget about space for a minute. How far can you see just looking at the horizon? This is going to vary from person to person as we don’t all have equal vision. For humans, 20/20 vision is considered perfect vision. But if your vision isn’t considered perfect, then you’re not going to be able to see as far as others. This will still hold true when peering through a telescope. Though you’ll be able to see farther than normal, you won’t be able to see farther than someone with perfect vision looking through the same lenses.
If you live in a big city, you might notice that there are rarely more than a few stars visible. However, if you take a short trip out to a rural area and peek up at the same sky, it will look wildly different. When you’re away from all the extra lights of a city, the lights from the sky appear many times brighter.
Here’s a good way you can get an idea of how much light pollution a city causes. Pay attention next time you’re driving into a major city at night. Dozens of miles before approaching, you’ll notice that the whole sky is illuminated over that city. The larger the city, the farther you can see its illumination from. When you’re trying to view celestial bodies through a telescope, all of that extra light can put a serious damper on things, preventing you from seeing out into space.
Observing space means you’re looking for faint light emissions in an endless expanse of black sky. But if there’s too much light around you here on Earth, then your ability to see those light emissions will be substantially hampered.
How is your visibility affected by rain? It stops you from seeing as far as you could on a clear day, right? Well, the same is true about many weather phenomena. Obviously, rain clouds and precipitation will prevent you from viewing the heavens as you can’t see through the thick rain clouds. But other weather can wreak just as much havoc on your astronomy plans.
Snowstorms will stop you from seeing. Things don’t have to be drastic though. All it really takes to hinder your view is a bit of humidity. Even the moisture in the air acts as a barrier, stopping you from getting a full view of the cosmos. So, if you want to see as far as possible with your telescope, you’ll need to time your viewing on nights of near-perfect weather.
It should be clear that your equipment will also play a major role in how far into the heavens you can see. If you expect a $50 telescope to show you the same images that researchers manage to pull from the Hubble Space Telescope, then you’ll be severely disappointed.
That was an extreme example, but the concept remains the same. The larger and higher-quality your telescope is, the farther you’ll be able to see with it. For a telescope to see extreme distances, it must be made with superior optics. And as a general rule, the bigger a telescope’s lenses are, the farther it should be able to see.
In truth, you’ll always be limited by your equipment. Even if you get a top-end consumer-grade telescope, it’s never going to match a multi-million-dollar observatory with a roll-off roof. So, try to keep your expectations realistic. That said, even consumer-grade telescopes today can offer an incredible view of many distant celestial bodies that are thousands of light-years away.
Your location is also going to play a major role in how far you can see, regardless of your equipment. Even between two dark-sky sights that are relatively close, your viewing abilities will be different. This is why it’s great to travel with your kit. Sometimes, all it takes is getting to a new place and you’ll open yourself up for a new discovery.
When discussing far-off heavenly bodies, we can’t use our common terminology, such as miles. To describe these distances, we’d have to use scientific notation because these objects are so far away. Instead, we use terms like light-year to describe distance and magnitude to describe brightness. It’s important to understand these terms when discussing such subjects.
Magnitude can be a bit confusing because it’s a unitless measure of brightness. Often, it’s measured only in visible wavelengths. The scale goes down, with brighter objects having lower values of magnitude. The brightest objects in the sky can even have negative magnitude values. For reference, a star with a magnitude of one is 100 times brighter than a star with a magnitude of six.
Because celestial objects are spread so far apart, we can’t measure them using conventional means. So, a new form of measurement was created — the lightyear. A lightyear is the amount of distance that light can travel in a single Earth year. That distance is approximately six trillion miles. You can only imagine how many zeros would be necessary to describe the distance of an object that’s millions of light-years away if we were to use miles!
So far, all of this has essentially been theory. But what’s the farthest thing we’ve actually seen with a telescope to date? As of 2021, the farthest documented finding in the cosmos was found by the Hubble Space Telescope in 2016. It’s a galaxy called GN-z11.
What’s amazing about GN-z11 is that it’s currently about 32 billion light-years away from Earth. Viewing this galaxy is like looking back through a time machine because of how long its light takes to reach us. When we view this distant galaxy, the light we’re seeing was emitted 13.4 billion years ago. At that point in time, the universe was just 3% of its current age.
Of course, that’s an entire galaxy, which is much easier to spot than a single heavenly body. If you’re wondering about the farthest celestial body ever observed through a telescope, it’s a blue star that goes by the nickname of Icarus. This star first became visible in 2016 when gravity from a nearby massive galaxy cluster magnified the light from the star.
Aside from Icarus, the next nearest star we can see is 100 times closer, so Icarus is really a special case. The light we see from this star has taken 9 billion years to make it to Earth. That means we’re seeing the light that was emitted when the universe was just 30% of the age it is now.
This is a tricky question. As we’ve already discussed, there are many variables that affect how far your telescope can see. Some of those variables are about your own eyes, making this type of estimation even more difficult. Truthfully, we can’t give you a straight answer about how far you can see through a telescope. But we can give you a few celestial bodies to look for that should be at the extent of what your telescope is capable of.
M49 is an elliptical galaxy with a magnitude of 8.4. In the Virgo Galaxy Cluster, M49 is the brightest member. If you don’t know, the Virgo Galaxy Cluster is the nearest group of galaxies beyond our own.
In perfect conditions, when the weather is ideal and you’re far away from the light pollution of a busy city, you can faintly spot this galaxy with a pair of 10×50 binoculars, though it will appear as a faint smudge of light, nothing more.
This is considered the distance barrier for binoculars, but you can see more with a decent telescope. For instance, using an 8-inch reflector telescope with 100x magnification will make the M49 galaxy appear as a wide oval smudge spanning 10 arcminutes, with a bright core at the center.
But how far is M49? You might be surprised to find out that this galaxy is located 72 million light-years away! And while you certainly can’t make out any details, even with a decent telescope, you can observe and identify it.
Moving out, the Coma Cluster, which also goes by the names of Abell 1656 and the Coma Berenices Galaxy Cluster, is about 300 million light-years from Earth. This cluster is best viewed in April and May when it’s most visible.
You won’t be able to even see a smudge of this galaxy with binoculars. It’s far past the distance barrier of such optics. Even with a 4-inch reflector at 90x-100x magnification, you’ll be at the very edge of sight distance. With such equipment, you’ll be able to make out very faint dots representing the Coma Cluster, but nothing more.
With a magnitude of +12.8, 3C 273 is the brightest quasar in the sky. At 2 billion light-years from away, it’s also one of the farthest celestial bodies you’ll be able to see with any telescope. Of course, massive telescopes like the Hubble space telescope can see many times farther, but without multi-million-dollar observatories and equipment, this is about as far as you can hope to see at the moment.
To ee this quasar, even though it’s incredibly bright, you’ll need a 10-inch reflector. You should be able to find it on any clear evening in the springtime, though it represents the distance barrier for most amateur astronomers.
Many factors affect how far you can see through a telescope. Even your own eyes can be a barrier, not to mention the equipment, weather, light pollution, and more. Still, we can see a great distance into the heavens with a telescope. With just a pair of binoculars, you can view a galaxy that’s 72 million light-years from us. And if you have a good 10-inch reflector telescope, you can even spot the 3C 273 quasar from 2 billion light-years away. Of course, none of that can match the Hubble Space Telescope, which first observed the GN-z11 galaxy at a distance of 32 billion light-years back in 2016.
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Featured image credit: FSchiller, Pixabay
Robert’s obsession with all things optical started early in life, when his optician father would bring home prototypes for Robert to play with. Nowadays, Robert is dedicated to helping others find the right optics for their needs. His hobbies include astronomy, astrophysics, and model building. Originally from Newark, NJ, he resides in Santa Fe, New Mexico, where the nighttime skies are filled with glittering stars.
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