How Big of a Telescope Do I Need to See Pluto?

Pluto is merely 0.02% of the Earth’s mass. For perspective, Pluto’s width – 1,400 miles – is about 50 percent of the width of the United States. Furthermore, the distance from Pluto to the Sun is about 3.6 billion miles. The distance between Mars and the Sun is around 142 million miles.  

Due to its size and distance from the Earth and the Sun, you need a telescope with significant power to see Pluto. The telescope must have an aperture size of at least 10 inches. You’ll also need multiple factors to be in your favor, especially low light pollution. 

In this article, we share with you what kind of telescope you can use to view Pluto. Additionally, we discuss the factors you must consider and the steps to take when choosing a telescope to observe the dwarf planet. 

Can I view Pluto with a telescope?

You can view Pluto with a telescope, but it must have an aperture of at least 10 inches, although an 8-inch telescope will work if all other conditions are perfect. You’ll also need a night with good seeing, irrespective of the size of your telescope. 

Good seeing means a clear night sky with low light pollution from the Moon and background stars. It is also a night with low humidity and no clouds. You’ll also need a generous dose of patience to have a shot at seeing Pluto. 

What size of telescope is required to observe Pluto?

Visual magnitude is how much light celestial bodies in the solar system reflect from the Sun and the intensity of that reflection by the time it gets to the Earth. The visual magnitude of any solar system object depends on its distance from the Sun and Earth. 

Planet Pluto is very far from the Sun and the Earth. Less light gets to Pluto from the Sun. After Pluto absorbs some light, it reflects some, too. Because Pluto is far from our planet, the intensity of this reflection weakens before it gets to the Earth. 

The visual or apparent magnitude of Pluto ranges between 13.64 to 16.3 depending on where it is in orbit. And the best magnitude the dwarf planet can ever have is 13.64.

This feature of Pluto makes it incredibly hard to see outer planets via telescopes. That is why larger-aperture telescopes are necessary for observing Pluto. 

Can I see Pluto with a 10-inch telescope?

A telescope with a 10-inch aperture is a good option to view Pluto. However, it may not appear as more than a speck in the night sky, similar to a faint star. You’ll also need a map to confirm that what you saw was indeed Pluto. 

Can I see Pluto with a 5-inch telescope?

You cannot see planet Pluto with a 5-inch telescope. Pluto is at the end of the solar system and is exceedingly dim. A 5-inch telescope does not have the power to overcome these challenges.  

If you had asked this question in 1989, the answer would have been “yes.” Pluto had a magnitude of 13.7 then, similar to the brightness of Uranus and Neptune. 

You would have been able to use a 4-5-inch aperture telescope to view the dwarf planet. The next chance this is possible would be well beyond 2100. 

Even though you cannot see Pluto with a 5-inch telescope, you can use them to see other planets, such as the details on Jupiter, cloud belts on Saturn, Cassini Division in Saturn’s rings, and much more. 

One of the best-priced 5-inch telescopes you can get as an amateur astronomer is the Celestron NexStar 5SE Telescope. It has a fully-automated GoTo mount to track and observe planets.

Factors to consider when choosing a telescope for observing Pluto in the night sky

Given the conditions surrounding the dwarf planet, you can’t use just any telescope. 

When choosing a telescope for observing Pluto, you must consider its aperture size, magnification capabilities, mount type, and the quality of optics you seek.

Aperture size

If you slightly open a window, only a small breeze can enter the room. But if you open the window to the end, more breeze comes in. 

The amount of breeze that enters the room is directly proportional to the window size, assuming you open the window to the end. 

Think of aperture size as the size of the window for a telescope. It determines the amount of light that passes through the telescope. In a reflecting telescope, the aperture is the diameter of the primary mirror or the objective lens in a refracting telescope. 

The larger the aperture, the more light the telescope can collect and the clearer the celestial bodies you see. 

The aperture size determines many features of the telescope, especially what you can observe, image resolution, and the details you’ll see. 

Aperture size also determines the weight and cost of the telescope. So you know if you want to see Pluto, you have to splurge the cash. 

Magnification capabilities

The focal length of a telescope contributes significantly to its magnification capabilities. The other factor in the magnification power equation is the focal length of the eyepiece you’re using. The formula for magnification is:

This equation means the magnification you’ll enjoy will vary depending on the eyepiece you use since telescopes have fixed focal lengths. 

That said, all telescopes have a minimum and maximum useful magnification. Below and beyond this magnification power, the telescope’s performance won’t be optimal. 

As a rule of thumb, the minimum useful magnification is 3-4x the telescope’s aperture size in inches. So a 10-inch telescope has a minimum magnification power of 30-40x. 

Maximum useful magnification is 50 times the aperture size. The same 10-inch telescope will have a maximum magnification power of 500x. Note that these figures are just estimates. 

At a magnitude of 14.47, you’ll need at least a magnification power of 450x to spot Pluto. 

Mount type

A mount serves two primary purposes. The first is to serve as an anchor to secure and stabilize your telescope. Your telescope must be steady and balanced because a slight wobble can impact your observation. 

The second purpose is to enable you to move the telescope in the exact direction of the object you want to view. The location of a planetary object is relative to yours. It is necessary to be able to pinpoint your target object with ease. Some mounts are also automated. 

You can adjust the mount manually or electronically through an app if it has electric motors. When the mount rotates or adjusts to where the object is, the whole setup must remain sturdy. 

There are about five types of telescope mounts, including:

1. The Dobsonian mount (Dob)
2. The altazimuth mount (Alt-Az)
3. The equatorial mount (EQ)
4. The computerized GoTo mount
5. The Star trackers

The major difference between all these mount types is the movement mechanism. The altazimuth and Dobsonian are similar, except that the latter can carry larger telescopes than the former. They both allow movement across two axes – horizontal and vertical. 

The equatorial mount, which comes with most premium telescopes, has one axis in alignment with the Earth’s rotation axis. This setup makes tracking the sky object you want to observe easy. You can also attach motor units to EQ mounts to make them semi-automatic.

Learn more about Alt-Azimuth Mount vs Equatorial Mount in this article.

A computerized GoTo mount is fully automatic. You must enter a few parameters (planetary object, date and time, and geolocation) into the system and complete a three-star alignment. 

The equipment takes up the task of pinpointing the object’s exact location. These mounts are pricey and can cost between $4,000-$10,000.  

Star trackers are like GoTo mounts, but they are popular in astrophotography.

Quality of the optics

What level of image quality are you okay seeing? You must determine if your spending on the telescope is worth the image you’ll see. 

The good news is that even if you buy a telescope for Pluto, it’ll most likely work for most sky objects. You’ll only need to select eyepieces with care.

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