The Basics of Reflector Telescopes

One of the most popular telescopes among scientists and amateur stargazers is the reflector. Reflectors are a type of optical telescope that use mirrors to reflect light and produce the image. Reflectors can be compared to refractors, which use lenses to produce the image.

How Reflectors Work

As stated above, reflectors use one or more curved mirrors in order to reflect light and produce their image. A curved primary mirror will be placed in a tube where it creates an image at the focal plane. Depending on the telescope, secondary mirrors may be added to modify different characteristics or to redirect the light.

The mirrors can be ground into a spherical or parabolic shape. Both shapes come with advantages and disadvantages to the viewer. You choose the shape of the mirror based on your observation preferences.

Reflectors differ from refractors because they use mirrors wile refractors use lenses. Mirrors allow for the light to be reflected from the mirror. Lenses, on the other hand, focus on and intensify the light that comes through the end of the tube.


The disadvantages of both shapes come in the form of aberrations. Aberrations are slight distortions from the original image. In total, there are six main optical aberrations: spherical aberration, coma, astigmatism, curvature of field, distortion, and longitudinal chromatic aberration. Reflection causes aberration because light disperses or separates whenever it passes through a prism or lens.

If they are not taken into consideration, aberrations can distort measurements or observations. So, it is important to take your scope’s aberrations into consideration.


The first reflector was made in 1668 by Isaac Newton. His telescope became known as the Newtonian telescope, which is known for its paraboloid primary mirror and flat secondary mirror. Since the 17th-century, many other reflector designs have been made:

  • Gregorian: The Gregorian telescope features a concave secondary mirror. This mirror design was published in 1663 by James Gregory, but Gregory did not make a physical telescope.
  • Cassegrain: The Cassegrain telescope has a primary parabolic primary mirror and a hyperbolic secondary mirror. There are many types of Cassegrain telescopes.
  • Off-Axis Designs: There are several telescope designs where the secondary mirror is either eliminated or moved. The purpose of this is to avoid obstructing the incoming light.
  • Liquid-Mirror Telescopes: Liquid-Mirror Telescopes use a rotating mirror that consists of a liquid metal. As the tray spins, the water creates a paraboloidal surface.

Newtonian Telescope: Reflections with Mirrors

Have you ever wanted a small, portable, and affordable telescope to look at faint objects like the moon or other planets? Newtonian telescopes are great for these purposes because they have a simple design, short focal length, and portable structure.

As the name suggests, the Newtonian telescope dates back to the 17th-century physicist Isaac Newton. In the mid-1600s, Newton noticed that chromatic aberrations occurred when light passed through the lens of a telescope. He theorized that aberrations appear when the light passes through the prism (i.e. lens), causing the colors to separate.

To remove these aberrations, Newton sought to create a telescope that used a mirror in place of a lens. Newton was not the first person to consider using mirrors, though. Galileo Galilei, Giovanni Francesco Sagredo, and others considered using a mirror, but Newton was the first to successfully complete the task. Thus, the telescope, which was completed in 1668, became known as the Newtonian telescope.

Even though Newton aimed to reduce the chromatic aberration from lens telescopes, all Newtonian telescopes come with a coma optical aberration. This aberration makes the stars appear wedge-shaped in short focal length scopes.

Additionally, Newton’s telescope was difficult to construct because the mirrors were difficult to polish into the correct shape. It was not until John Hadley improved Newton’s design by making the mirrors into a parabolic shape.

Newtonian Scopes Today

Today, Newtonian scopes are popular among amateur stargazers. Using Hadley’s design improvement, they are made with a primary concave mirror that is placed in the back of the tube. A secondary piece of the small diagonal mirror reflects the image from the side of the telescope to the eyepiece. Together, these pieces enlarge the image and provide a crisper image.

Since the Newtonian telescope reflects the image, the image is upside down. As a result, Newtonian scopes are mainly used for stargazing and other sky related purposes. More so, Newtonians often have a short focal length, which makes this scope type even more suited for stargazing.

The short focal length also makes Newtonians much smaller than other telescopes. The compact nature of these telescopes, along with their simple design, makes them much more affordable than other scopes. The affordability and compactness make this telescope ideal for amateur stargazers.

Catadioptric Telescopes: The Best of Both Worlds

Many beginner-friendly telescopes use either mirrors or lenses to produce the image you see in the telescope. Reflectors, for example, use mirrors, while refractors use lenses. Catadioptric telescopes, though, use both, making them more error-corrective and ideal for experts and scientists.

Catadioptric Optical System

As stated above, a catadioptric optical system uses both refraction and reflection to create a combined optical system. In most cases, this combined system is made via lenses and curved mirrors. In fact, the name “catadioptric” references both parts of this system. “Dioptric” refers to the study of refraction via lenses, while “catoptrics” refers to the study of reflection via mirrors.

This catadioptric optical system can be seen in many places. Searchlights, headlamps, and early lighthouses all use this system. More so, many telescopes and microscopes use catadioptric optical systems.

Why Catadioptric Telescopes are Superior

Catadioptric telescopes are a type of optical telescope that are known for their precision and clarity. The reason for this is that the mirrors and lenses are used to both create the image and correct any errors that may be produced from the reflection or refraction.

In fact, catadioptric telescopes have a greater overall degree of error correction than either reflectors or refractors. They can even have a wider field of view that is essentially aberration-free. Telescopes without aberrations tend to have full-aperture correctors.

Full-aperture correctors are lenses that are placed in front of a spherical primary mirror. They combine the spherical mirror’s reflection ability with a large lens at the front of the tube. This combination allows the spherical mirror to image objects at infinity.

Catadioptric Designs

There are several catadioptric designs. Here are the four most popular:

  • Schmidt-Cassegrain: This telescope consists of a short tube, spherical primary mirror, full-aperture corrector lens, and a convex secondary mirror. The image is formed behind the primary mirror while the secondary mirror reflects light. The image location is why this telescope is classified as a Cassegrain telescope.
  • Maksutov-Cassegrain: The Maksutov-Cassegrain features a short tube, spherical concave primary mirror, full-aperture corrector lens, and convex secondary mirror. The corrector lens is made from a weak negative meniscus lens. The image is formed behind the primary mirror.
  • Schmidt-Astrograph: this telescope is made of mirrors and accessory lenses. Unlike the previous two telescopes, this scope often lacks a full-aperture corrector lens, though you can purchase a modified Schmidt-Astrograph.
  • Schmidt-Newtonian: This telescope is a cross between a Newtonian telescope and a Schmidt-Cassegrain. This telescope differs from the Schmidt-Cassegrain in that the image is formed on the side of the tube.

Downsides of Catadioptric Telescopes

Obviously, catadioptric telescopes are great for their clarity and error-corrective qualities, but there are several reasons why you would opt for another telescope.

Most notably, catadioptric telescopes are much more expensive than regular refractors or reflectors. The reason for this is that catadioptric telescopes use more materials than the other two telescope types. Additionally, the extra materials make catadioptric telescopes heavier and more burdensome to carry around.

As a result, these telescopes may be more trouble than they are worth if you are new to stargazing.

An Overview of the Cassegrain Telescope

Being able to easily port your telescope around with you everywhere you go is ideal for many scientists and astronomy-enthusiasts. The Cassegrain telescope is one of the best in terms of portability. Between its compact design and excellent optical quality, the Cassegrain telescope is a great all-purpose telescope.

The Cassegrain scope’s portability is due to its genius design, it uses both a concave mirror and a convex mirror. The primary concave mirror is placed at the back of the tube while the secondary convex is placed at the front.

At the center of the primary mirror is a hole. This hole allows for the electromagnetic waves to be captured by the primary mirror’s edges and redirected to the secondary mirror. It is at the secondary mirror that the waves converge and are then refocused to the back of the primary mirror.

This design places the focal point behind the primary mirror, and the secondary mirror adds a telephoto effect, which results in a longer focal length. Together, these two mirrors cause the optical path to fold back onto itself. This folding makes the telescope much more compact and small.

Cassegrain scopes are great options for more serious stargazers. They are great for planetary and sky viewing and astrophotography, but they can cost more than other amateur-favorites such as the Newtonian telescope.

Cassegrain Variants

Above is a basic description of a Cassegrain telescope, but there many variants to this model. Here are some modern Cassegrain telescope variations:

  • Classic Cassegrain: The classic Cassegrain scope uses a parabolic primary mirror and a hyperbolic secondary mirror.
  • Ritchey-Chretien: The Ritchey-Chretien is a specialized Cassegrain that uses two hyperbolic mirrors. It is best for wide field and photographic observations.
  • Dall-Kirkham: The Dall-Kirkham is a specialized Cassegrain that uses a concave elliptical primary mirror and a convex spherical mirror.
  • Catadioptric Cassegrains: These Cassegrain telescopes use both mirrors and lenses. Schmidt-Cassegrain, Maksutov-Cassegrain, Argunov-Cassegrain, and Klevtsov-Cassegrain are all examples of Catadioptric Cassegrain scopes.

Of these variants, the Ritchey-Chretien telescope is probably the most effective and useful for stargazing purposes. The Ritchey-Chretien uses two hyperbolic mirrors. This design causes the scope to be free of coma and spherical aberration on a flat focal plane. This fact makes the scope ideal for a wide field and photographic observations. The most known Ritchey-Chretien scope is the Hubble Space telescope.

An Overview of Ultraviolet Telescopes

If you went to the beach as a child, your parents probably slathered you with sunscreen in order to protect your delicate skin from the sun’s rays. More specifically, the sunscreen protected your skin from the sun’s ultraviolet (UV) rays.

Ultraviolet radiation is more dangerous than regular light rays because it is more energetic. This energy is a result of ultraviolet radiation’s shorter wavelength. The short wavelengths also cause UV to be invisible to the human eye. As a result, we need special equipment to detect ultraviolet light. It’s used in solar appliances, but we also have special telescopes that detect ultraviolet radiation.

Ultraviolet Radiation

As discussed in the article about infrared telescopes, objects with a temperature over absolute zero emit electromagnetic radiation. Radio waves, microwaves, infrared, visible light, ultraviolet, X-rays, and gamma rays are all types of electromagnetic radiation because they carry electromagnetic radiant energy through the electromagnetic field.

We are constantly in contact with electromagnetic radiation. Most notably, we see visible light, cook using microwaves, and get X-rays at the doctor’s office. As we discussed earlier, we also come in contact with ultraviolet radiation. The sun, stars, and other galaxies are responsible for ultraviolet radiation.

Ultraviolet radiation requires a special telescope for detection because it is invisible. The human eye blocks radiation with wavelengths of 300-400 nm. More so, humans lack the color receptor adaptors needed to see UV. As a result, optical telescopes cannot pick up ultraviolet radiation, which produces the need for ultraviolet telescopes, instead.

How Ultraviolet Telescopes Work

Just like all telescopes, ultraviolet telescopes use mirrors to gather and focus radiation. In fact, the mirror placement and technology are extremely similar to that of an optical telescope. Unlike other telescopes, though, the mirrors on ultraviolet telescopes are coated with a special material. This material makes it possible for the mirrors to reflect the ultraviolet light.

Ultraviolet telescopes also include detectors. Once the ultraviolet light is reflected from the coated mirrors, the detectors can pinpoint the ultraviolet light.

Another difference between ultraviolet telescopes and many other telescopes is that they should be placed outside the earth’s atmosphere. The reason for this is that the high-energy UV photons cannot penetrate the earth’s atmosphere. As a result, the UV would not reach the telescope if it were placed on the earth.

Since ultraviolet telescopes are only effective outside of the earth’s atmosphere, they are only capable through space flight, making them more modern technology.

Optical Telescope Overview

To beginner stargazers, picking out the right telescope can be difficult. There are many telescope types to choose from, and it can be overwhelming trying to figure out the classification of the most popular telescopes. The best place to start is with the optical telescope.

Visible Light

All objects with a temperature over absolute zero emit electromagnetic radiation, which refers to the spectrum of waves that carry electromagnetic radiant energy through the electromagnetic field. Radio waves, microwaves, infrared, visible light, ultraviolet, X-rays, and gamma rays are all electromagnetic waves.

Visible light is the most obvious type of electromagnetic radiation. It falls between infrared and ultraviolet on the electromagnetic spectrum. Unlike the two waves surrounding it, visible light is seen with the human eye. In fact, it is the visible light that you see when you look around.

Optical telescopes specifically work with visible light, and they are the oldest form of telescope. They will not be able to detect ultraviolet or infrared light; both of which require special telescopes.

How Optical Telescopes Work

The most common telescopes are optical telescopes, especially telescopes used by amateurs or beginners. To put it simply, optical telescopes gather and then focuses light by using lenses, mirrors, or both. The focusing of this light can be used to create a magnified image, take a picture, or collect data.

Since the optical telescope is a broad category of telescope, there are three primary types of optical scopes:

  • Refractors, which use lenses
  • Reflectors, which use mirrors
  • Catadioptric telescopes, which use both lenses and mirrors
  • Characteristics

    Optical telescopes have specific characteristics that relate to their performance. The most important characteristics to know are the focal length, magnification, and field of view.

    The focal length of an optical scope measures how strongly the scope converges or diverges light. Typically, this is measured by the distance that the rays must be brought into focus. Generally, a shorter focal length is stronger because they bring the rays to a focus in a shorter distance.

    The magnification is how much larger a telescope can make an object appear while limiting the field of view. Magnification does not always correlate to the performance or strength of a telescope since magnification reduces the quality of the image. It is important to choose a correct magnification for your optical scope depending on the objects you want to observe.

    The field of view is how much you can see at one point through the instrument. Depending on the object you want to observe, you may want a larger or smaller field of view. Typically, the higher the magnification, the smaller the field of view.


    Whenever you’re using an optical telescope, there will be some kind of distortion to the image. This distortion is called aberrations. In total, there are six main optical aberrations: spherical aberration, coma, astigmatism, curvature of field, distortion, and longitudinal chromatic aberration.

    The reason that aberrations appear is that light disperses or separates whenever it passes through a prism or lens. Different lens types will create different types of aberrations.

    It is important to know about the aberration your telescope produces since the aberration can distort measurements or observations if they are not taken into consideration. So, it is important to research the type of aberration your optical scope produces.

    Infrared Telescopes: Detecting the Invisible

    When you were little, you may have heard of infrared telescopes and thought that they give the viewer superpowers. In a way, infrared telescopes do give us superpowers because they allow us to pinpoint infrared radiation, which is invisible to the naked eye. That’s pretty super!

    Infrared Radiation

    All objects with the temperature over absolute zero emit electromagnetic radiation. Electromagnetic radiation refers to the spectrum of waves that carry electromagnetic radiant energy through the electromagnetic field. Radio waves, microwaves, infrared, visible light, ultraviolet, X-rays, and gamma rays are all part of this spectrum.

    Every day, we interact with electromagnetic radiation. Visible light is the most obvious type of electromagnetic radiation. We interact with infrared radiation too, but it is felt and not seen. The reason that infrared is invisible to our eyes is that infrared photons have lower energies than that of visible light.

    All sorts of objects emit infrared radiation. Nebulae, young stars, and other galaxies all emit this radiation, and it is with the infrared telescope that scientists find these objects in the distance.
    Infrared radiation requires a special type of telescope since it is not visible. As a result, optical telescopes will not be able to show you infrared radiation.

    How Infrared Telescopes Work

    Infrared telescopes always come with a camera. This camera includes a special solid-state infrared detector that detects the infrared radiation. This detector is how scientists are able to pinpoint and estimate the distance from the infrared radiation source.

    Infrared telescopes work similarly to optical telescopes. Just like in the optical telescope, the infrared telescope uses a combination of lenses and mirrors to gather and focus radiation onto the detector. There, the detector determines the position and distance of the infrared source.

    The reason that infrared telescopes work so similarly to optical telescopes is that infrared radiation and visible light are both part of the electromagnetic spectrum. This means that both are waves that can be manipulated or observed in similar fashions.

    One big difference between optical telescopes and infrared telescopes, though, is that infrared telescopes are designed to minimize the amount of heat emitted from the telescope.
    In order to detect infrared radiation, infrared telescopes can be based on the ground, air, or space. Ground- and air-based infrared telescopes are stifled and encounter interference from the earth’s atmosphere. Space-based scopes, on the other hand, face no interference since they are outside the earth’s atmosphere.

    Making Sense of MOND, an Alternative Theory of Gravity

    Galaxies are strange beasts: simply put, they rotate faster than they’re supposed to. At the speeds stars orbit the center, their centrifugal force (okay, not actually a real force) should overwhelm gravity and send them flying off into space.

    One way to explain this is to assume the existence of a kind of matter we can’t see, which significantly raises the total mass of the galaxy and therefore its gravitational pull. This, called the dark matter theory, explains some phenomena but struggles with others, while something that doesn’t emit, reflect or even absorb any kind of electromagnetic radiation just seems a little weird to some. Another hypothesis, which also works in some cases but not all, is called Modified Newtonian Dynamics, or MOND for short.

    Newton Spinning in His Grave

    It may seem absurd for scientists in search of knowledge to make up stuff apparently at random. Both of these somewhat kooky theories, however, fit the data we have reasonably well. The same can be said for the double-helix structure of DNA, the Schrödinger equation and how atoms arrange themselves into benzene rings. All of these involved a level of creative thinking that must have seemed insane, to some and at the time, but they could all be proven eventually, and each kicked off an entirely new branch of science.

    It’s already well-known that size matters: subatomic particles behave completely differently to volleyballs. It’s also true that the laws of physics change when something is going very fast or under the influence of a very strong gravitational field. It is therefore possible that making a “small” alteration to the math we have to describe gravity, which only becomes relevant on very large scales, can eliminate the need for something like dark matter to exist.

    How It Works

    The basic idea behind MOND is that, when it comes to large distances and low accelerations, star motion can be explained better by either changing the famous F=ma to F=ma2, or writing the gravitation equation F=Gm1m2/r2 as F=Gm1m2/r instead. This has since lead to a number of more detailed interpretations of MOND, both relativistic and non-relativistic.

    There’s no inherent reason to assume that this is accurate, but it does help to explain a number of things that otherwise require dark matter. It’s also worth pointing out that we’ve only really tested our current theory of gravity within the solar system; for all we know, there could be space gremlins further out who like messing with the laws of physics.

    Arguments for and Against

    In our solar system, Mercury’s orbit is the smallest and fastest at only 88 days, while Pluto didn’t make it around the sun once in the 76 years between being discovered and fired from its job as a planet. This makes sense: the more gravity acts on an object, the faster it accelerates.

    With entire galaxies, however, the outer rim rotates at the same speed as stars closer to the center. Dark matter can explain this, but only by assuming that it’s spread around fairly evenly instead of crowding around the core like visible matter. This is what you’d expect something with mass to do. MOND provides a much simpler, more elegant and more accurate explanation…but only for individual galaxies. Once you get to a system the size of a galaxy cluster, it breaks down and dark matter seems to be the winner.

    There’s also the matter of the cosmic microwave radiation, a leftover from the Big Bang. This is generally uniform, but varies slightly in intensity and color temperature. These tiny fluctuations, with the help of some pretty impressive software, can be analyzed to produce a kind of sky map. The results are consistent with something up there that’s the same density dark matter is supposed to be. MOND offers no comparable answer.

    Overall, in terms of the ability to make (correct) predictions, dark matter seems to be the stronger theory. Most cosmologists (who are obviously most concerned with very large-scale systems) regard modified Newtonian dynamics as a kind of mathematical curiosity. Several people are still doing work on it, though. It could just be that distance really does affect gravity in more ways than decreasing it at an inverse-square rate.

    Related Information:
    Dark Matter
    More about the standard (but still unproven) way of explaining why galaxies seem to weigh more than they should.
    A little about how astronomical research is conducted.

    Dark Matter – Why Is Most of the Universe Invisible?

    One of the biggest scientific mysteries of our time is why the galaxy doesn’t simply fall apart. Yeah, that’s right: we know that planets and indeed stars are kept in their orbits by gravity and not some kind of magical force. The problem is that, once you’ve added together the mass of the stars, interstellar gas, dust and all the objects we know about…there just isn’t enough gravity to go around. Not by a long shot: we should actually be seeing about 85% more stuff.

    Sneaky Little Particles, Hiding all Over the Place

    This is pretty much a certainty: between Newton and Einstein, we have a fair idea of how gravity works. Measuring the mass of a planet or asteroid, which determines how much gravitation it emits, is not very difficult. So, why doesn’t this number match the actual amount of gravity?

    The most popular hypothesis among astronomers is that the “stuff” is in fact there, we just can’t observe it directly, hence the name dark matter. Even the name of this website is a kind of inside joke: there really is no such thing as a dark matter telescope.

    No one has ever found so much as a cupful of the stuff. We don’t have a clue what it consists of, though some kind of quark soup seems like a strong possibility. Since we don’t know, we might as well call all the matter we can’t observe through radio waves, visible light or other kinds of radiation “dark”.

    Detecting Dark Matter

    Just about all we understand about dark matter is that it has mass. A little bit of detective work therefore allows astronomers to see its effects. In particular, scientists had suspected for decades, and finally proved it in 1979, that light passing near a massive object is deflected somewhat like the lens of a refractor telescope does:

    A red galaxy directly between us and a blue galaxy causes light from the blue one to appear as a ring.

    (A true geek will tell you that the light is still traveling in a straight line; it’s the structure of space itself that gets bent. The more you know…) This means that tiny distortions in the way we see distant astronomical objects give us clues about how much dark matter may lie along the path traveled by its light.

    Additional observations tally with these gravitational lensing experiments. Dark matter is one of the easiest ways to explain the shape and size of far-off galaxies: if there weren’t some extra substance of unknown composition in there, they would look very differently, rotating much more slowly or being less crowded. To put this into perspective, our sun orbits the center of the milky way at about 500,000 m.p.h, yet still takes 230 million years to go around once.

    Perhaps the most visually interesting evidence for the existence of dark matter comes from observing collisions between and within galaxies. Galaxies are, of course, almost completely made up of empty space, but when stars are forced into relatively close proximity, they do have an effect on one another.

    A colliding galaxy; observations show that there are large masses of dark matter near the green gas cloud formed by the collision.

    As it turns out, dark matter basically ignores the ordinary kind except when it comes to gravity. Intriguingly, however, it seems that it does somehow interact with itself, occasionally making large clumps of invisible material form and separate from what we can see. These can be detected, including by the methods mentioned above.

    A Good Concept, But Far from Certain

    While dark matter seems plausible enough for a ton of money and effort to be spent on looking for it, the hypothesis (which is what you call a scientific explanation that agrees with the available evidence, but hasn’t been adequately tested through experiment) is not universally accepted. Some observations can be interpreted in favor of its being true, others seem to argue against this.

    What we can conclude is the following: either our theories of astrophysics aren’t 100% complete yet, or something really interesting exists out there. Whatever science fiction has told you about dark matter, the truth is probably stranger. If so, there’s a whole new field of knowledge out there waiting to be discovered.

    Related Information:
    Deep Space Telescope
    A little more about the instruments used to search out cosmological phenomena.
    One of the theories that tries to explain gravitational anomalies without exotic forms of matter.

    Orbital Telescopes: The Cutting Edge of Observational Astronomy

    It is perhaps an astronomy nerd’s greatest dream – telescopes viewing space from space itself. These scopes are launched from the surface and orbit the Earth as satellites. Up there, their sight is unobstructed by any atmospheric disturbance, meaning pollution, weather and normal air turbulence, and they can therefore observe points in the sky in great detail. Getting above the atmosphere has another advantage, too: many wavelengths of radiation are simply blocked by the earth’s ionosphere, ozone layer and air, meaning the only way to “see” some kinds of non-visible light is from the vacuum of space.

    What makes things even more exciting is that NASA and other organizations don’t spend millions on sending a cheap scope you can buy at any supermarket into the sky. Space telescopes are constructed with the most advanced mirror and imaging technology available.

    Perhaps the king of these scopes is the Hubble. Loads of fanfare accompanied the launching of this scope and it has actually caused a minor revolution in the astronomy world. Since 1990 when the scope was placed into orbit by the space shuttle Discovery, the Hubble has produced a cornucopia of images that have been published around the world, such as its beautiful close up of the Eagle Nebula:

    Eagle Nebula

    This didn’t occur without a setback or two – within weeks of it going online, a tiny flaw was discovered in its mirror, which led to another shuttle being dispatched to give the scope a set of “glasses” to correct its vision.

    The Hubble has allowed scientists to peer farther into the galaxy than ever before. Its images of really deep-space objects have shown us galaxies billions of light years away, which has helped answer questions about the formation and the overall composition in the universe.

    Penny-Wise, Pound-Foolish

    While this is very impressive, space telescopes remain controversial. They are very, very expensive to build and maintain and new ground-based technologies are making these telescope less competitive. Saying that the money should rather be spent at home is short-sighted, though. Sometimes, the only way to get the benefits of science is to actually invest in it, and technologies ranging from cellphones to MRI machines would never have been invented if it weren’t for discoveries made by astronomers.

    Related Information:
    Dark Matter
    Mysterious and difficult to detect, dark matter is one of the scientific puzzles space telescopes may help to solve.
    Many amateur telescopes are of the refractor type and not intended to work in vacuum; learn more about them here.