Have you heard of the phrase: ‘My Very Educated Mother Just Showed Us Nine Planets? In the late 90s, it was a famous mnemonic used to teach children the names of the nine planets in our solar system.
However, in August 2006, Pluto was removed from its planetary status, lessening our solar system’s planets from 9 to 8. Pluto instead became the founding member of the ‘dwarf planets’ group.
A dwarf planet is one that failed to clear its orbit of debris (remember how planets, while forming, get bigger by attracting smaller rocks around them? Pluto couldn’t do that).
In 2006, scientists found that Pluto’s orbit is littered with rocks of similar sizes to it, which is why the International Astronomical Union (IAU) no longer consider Pluto to be a fully-fledged planet.
Despite the sadness of losing a planet from the solar system, dwarf planets are exciting worlds of their own to learn and observe, which is what we’ll be doing in this article.
The Dwarf Planets
The IAU defines the ground rules for planetary bodies. According to the union, celestial bodies need to satisfy three conditions to be in the ‘planet’ category.
- They should be orbiting a host star. In the case of our solar system’s planets, that star is our Sun.
- The celestial body has to be big enough for its gravity to pull the mass into a spherical shape.
- It also has to be the ‘dominant’ body in its orbit, which means that it has to clear its orbit of debris.
Celestial bodies that don’t satisfy all three categories cannot be named as planets. Instead, those that satisfy 1 and 2 but not 3 are called dwarf planets.
In Pluto’s case, it orbits our Sun and is spherical in shape but hasn’t cleared its orbit of debris, which is why it was removed from the planet category and renamed as a dwarf planet.
In 2014, IAU named five dwarf planets: Ceres, Pluto, Eris, Haumea, and Makemake.
|Diameter miles (km)||1,445 (2,326)||1,476 (2,376)||1,014 (1,632)||889|
|Distance from Sun|
AU (million miles/km)
|67.78 (6,303/ 10,167)||39.47 (3,670/|
|Solar System Position||Scattered Disc||Kuiper belt||Kuiper belt||Kuiper|
Ceres is the closest and the smallest dwarf planet in our solar system. Eris is the farthest but is just beaten for the title of largest dwarf planet by Pluto at 1,476 miles in diameter.
Can I See Pluto With a Telescope?
Yes, you can see Pluto but you’ll need a large aperture telescope!
If you’ve done this before, and have all of the above, then it’s possible to spy Pluto with a 5” telescope. Realistically, you’ll need at least an 8” scope is the best bet to go Pluto-hunting.
As a result of it being so far away, Pluto does not move much against the background of stars. The image below, from SkySafari 6, shows the path it takes between Capricornus and Sagittarius between 2020 and 2022. Click the image for a full-screen version.
The dwarf planet is 3,670 million miles away from the Sun and looks just like another faint star in your telescope. At this point, make use of some of that abundant patience because we are going to observe Pluto and plot its path for consecutive nights.
A good thing about planets and dwarf planets is they move, while stars don’t, at least not as significantly as planets. From the star chart (make sure yours is one that includes magnitude 14 and 15 stars, else Pluto won’t be on the list), take an educated guess as to which star could be Pluto, and plot its changing position for 2-3 consecutive nights.
The dwarf planet moves 1.5 arc minutes a day, and if you can make use of your telescope’s 200X magnification, you’ll be able to see this change clearly.
Voila! You have successfully spotted Pluto using your own telescope!
Can You See Other Dwarf Planets With a Telescope?
Eris has an apparent magnitude of 18.6. Combined with its methane-rich, highly reflective atmosphere, Eris is not bright enough to be seen in an average backyard telescope.
Like Eris, Haumea too has a similar magnitude of 17.3. It is also the third brightest object in the Kuiper belt and can’t be seen with regular backyard scopes.
Makemake is the second-brightest object in the Kuiper belt after Pluto, at a magnitude of 17. Like Eris and Haumea, Makemake can’t be observed with an average-sized telescope.
Although Ceres is the smallest of all five dwarf planets, it is the closest of all to Earth and is easily visible at magnitudes between 6.7 to 9.3. In fact, on perfectly dark nights, you might be able to see it with binoculars.
The SkySafari 6 sky chart below shows its path across Pisces, Cetus, and Taurus in 2021.
Our solar system consists of a rich variety of celestial bodies of varying shapes, sizes, and colors. Scientists have developed some ground rules and classified them into planets, dwarf planets, and rocks or asteroids.
Pluto was once the ninth planet in our solar system but was degraded from its planetary status in 2006. Pluto isn’t the only dwarf planet in our system, four more are currently known and officially recognized: Ceres, Eris, Makemake, and Haumea.
They might look just like tiny specks of light when you see them, even in the biggest telescopes, but it is fascinating to know that they are worlds of their own, complete with moons, atmospheres, and lots of nearby rocks in their orbit to keep them company.
Written by Adam Kirk