The Optical Tube
The StarSense Explorer 8” Dobsonian is optically an 8” (203mm) f/6 Newtonian reflector with a focal length of 1200mm. At f/6, there is little to no coma visible at the edges of the field of view at low magnifications, and you don’t need extremely well-corrected wide-angle eyepieces to get sharp images.
Collimation at f/6 is also fairly easy – however, the StarSense Explorer 8” Dob requires that you use tools to adjust both mirrors; the primary is collimated with a set of three easily-stripped Philips head screws while the secondary mirror is adjusted with a hex key. You shouldn’t need to adjust the primary mirror much, and the secondary mirror will likely never need to be adjusted after initially aligning it, but it’s still a major nuisance, especially when you’re on the ground and trying to line up a screwdriver with the back of the scope in total darkness without stripping the soft metal screw head.
The focuser on the StarSense Explorer 8” Dob is the same single-speed 2” Crayford focuser design that is provided with many Orion and Sky-Watcher Dobsonians. It uses thumb screws to grip your eyepieces, and a 2” extension tube (included) is mandatory for reaching focus with most eyepieces. The included 1.25” adapter does, thankfully, include a compression ring, is threaded for 2” filters on the bottom, and the scopes don’t have the separate 1.25” and 2” extension tube shenanigans that plague Sky-Watcher’s Dobsonian lineup.
Accessories
The StarSense Explorer 8” Dob includes a single 25mm Plossl eyepiece providing 48x magnification. This is good to start with, but you’ll want more eyepieces at a variety of focal lengths for different magnifications; a high-power eyepiece for viewing the Moon and planets and a 2” wide-angle eyepiece for sweeping vistas of deep-sky objects are two examples of oculars you’ll probably need right away. The only other accessory you get besides the required extension tube and 1.25” adapter is a standard red dot finder, which is used to aim the telescope by hand when you’re not using the StarSense Explorer app and phone dock.
The Dobsonian Mount
The StarSense Explorer 8” Dobsonian uses a Dobsonian mount which has a lot in common with those from other manufacturers—namely Sky-Watcher and some older Orion products which were produced by the same OEM. Like all Dobsonians, it’s an alt-azimuth design that pivots up/down (in altitude) and left/right (in azimuth) on plastic pads, taking advantage of friction to provide smooth motion without gears or locks.
The scope pivots on a pair of altitude bearings that glide on plastic rollers mounted inside the rocker box. The scope drops onto these bearings and has two brake/clutch knobs that slide into slots in the rocker on each side. These clutch knobs can be used to add friction to the scope’s movement up and down. It’s a slightly better version of the system Sky-Watcher uses on many of their Dobsonians.
However, as with many of the manual Sky-Watcher scopes, the StarSense Explorer Dobsonian’s clutch system is really just a stopgap measure to compensate for balance issues caused by using heavy eyepieces; the tube will otherwise droop when aimed lower in the sky. While technically a solution, tightening the clutch knobs, of course, impedes your ability to smoothly aim and track the telescope across the sky, unlike other measures like being able to slide the bearings along the tube or spring-tensioning to create a larger virtual bearing.
The StarSense Explorer Dobsonians use a base made out of particle board and melamine, which you assemble yourself with a hex key. These scopes are unique, however, in the optimized design of the base. Rather than big blocky pieces, the StarSense Explorer 8” Dobsonian’s base has cutouts designed for use as handles and using the minimum possible amount of material to cut down on weight. The ground board is triangular instead of circular to save weight.
The StarSense Explorer App
Using the StarSense Explorer app and phone dock is extremely simple. After a quick alignment procedure, the app will help you locate thousands of deep-sky objects by showing you where your scope is pointed in the sky in real-time using your phone’s camera and gyroscope data. Accuracy largely depends on the quality of your smartphone, but can be as good as around ¼ of a degree, or half the width of the full Moon. Celestron has improved and updated the app for their Dobsonians, and it sports a far larger database than it used to; the previously tiny database made the StarSense Explorer technology essentially pointless for finding all but the brightest and most obvious targets.
Should I buy a used Celestron StarSense Explorer 8” Dobsonian?
The StarSense Explorer 8” Dobsonian is a relatively new product, so it’s unlikely you’ll find a used one unless it was purchased and never taken outside. However, the usual advice applies: check for damage to the base or mirror coatings. Cosmetic damage or small dents in the tube are fine. A ruined base can be replaced, but doing so requires some carpentry or paying quite a bit for a custom one.
Alternative Recommendations
There aren’t other telescopes with directly comparable technology to the StarSense Explorer Dobsonians, but if you’re interested in something different, we have a few picks.
Under £550
- The StellaLyra 8” f/6 Dobsonian is a fantastic option, offering numerous features the StarSense Explorer 8” Dobsonian lacks such as a dual-speed Crayford focuser, a built-in cooling fan, and a wide range of premium accessories, including a 2” wide-angle eyepiece and a 9×50 finder scope. However, it is worth noting that this telescope is slightly larger and heavier than the StarSense Explorer 8”.
- The Bresser Messier 8″ telescope offers comparable performance and accessories to the StarSense Explorer 8″, but boasts a better-designed mount with features such as balance adjustments and a reflex sight finder. However, it does not offer the same level of accessories as the StellaLyra, nor does it have Celestron’s StarSense Explorer technology.
- The Ursa Major 8” Dobsonian is a basic but affordable 8” Dobsonian, with simple features such as a single-speed 2” Crayford focuser, 9×50 finder scope, and a pair of quality Plossl eyepieces to get you started.
- The Sky-Watcher Virtuoso GTi 150P is a highly portable telescope with a fully motorized mount featuring GoTo technology, controllable via a smartphone app or manually aimed by hand. While it has a smaller aperture than the StarSense Explorer 8” Dobsonian, its compact design makes it an excellent choice for those who value portability and ease of use. The manual Heritage 150P is also a great scope if you don’t mind the loss of computerized functionality.
£550-£800 Range
- The StellaLyra 10” f/5 Dobsonian shares the excellent features of its 8” counterpart, including its high-quality focuser and accessories, but with the added benefit of a larger aperture. Despite this increase in aperture, the overall size and weight of the telescope remain only slightly larger due to the similar dimensions of the base and tube.
- The Bresser Messier 10” Dobsonian boasts a smooth and sturdy mount, along with high-quality 10” optics and a decent reflex sight finder, making it a solid choice for those looking for a reliable telescope. However, it lacks some of the other useful accessories found in other models.
- The Explore Scientific 10” Ultra Light Dobsonian boasts a more compact design compared to solid-tubed Dobsonians like the StarSense Explorer and StellaLyra Dobsonians, making it a great option for those looking for a more portable telescope. However, it requires more assembly and comes with fewer accessories. The 10″ aperture, on the other hand, offers superior performance and is sure to deliver breathtaking views.
Over £800 Range
- The StellaLyra 12″ f/5 Dobsonian is a powerful telescope with an impressive selection of accessories, providing excellent value for the money, just like its smaller StellaLyra Dobsonian counterparts. However, its solid tube may be challenging to move around without a dolly, and a large vehicle is necessary for transportation to dark sky locations. If your budget allows, a more expensive collapsible or truss 12″ model may be a better choice for easier transportation and setup.
- The Explore Scientific 12″ Ultra Light Dobsonian features an optimized truss design, large altitude bearings, and all-metal components, ensuring compactness and lightweight storage with smooth movements free of springs, clutches, or other aids, along with a dual-speed 2” Cryaford focuser and all the performance to be expected from a 12” telescope. However, it lacks accessories or electronic features, and assembly can be more complex compared to other scopes of similar size.
- The Sky-Watcher Skyliner 300P FlexTube is an impressive 12” Dobsonian, with the FlexTube design providing a balance between the intricacies of a truss tube and the challenges of transporting or storing a solid-tubed scope of this size while the 12” of aperture provides more than twice the light-collecting power of an 8” and 44% more than a 10” Dobsonian.
- The Celestron StarSense Explorer 10” Dobsonian offers the same excellent features as the 8” model, but with the added benefit of a larger aperture and easier collimation adjustments. Despite this increase in performance, the telescope remains relatively lightweight and compact compared to other 10” Dobsonian models.
Aftermarket Accessory Recommendations
In order to fully utilise the range of magnifications and field of view options with the Celestron StarSense Explorer 8″ Dobsonian telescope, it is vital to purchase a selection of additional eyepieces. Our first pick, and an absolute must-have, would be a medium to high power ocular since the StarSense Explorer 8” Dobsonian only includes a single low-power 25mm Plossl eyepiece. A 9mm goldline/redline (133x), or alternatively the more expensive 10mm UWA (120x) is a perfect choice and provides an optimal magnification for viewing the Moon, planets, double stars, and smaller deep-sky objects like globular clusters even on so-so nights with the StarSense Explorer 8” Dobsonian.
For low power viewing, a 38mm OVL PanaView (32x magnification) or a similarly inexpensive 2″ super wide angle (SWA) eyepiece will provide the lowest magnification and nearly the widest true field of view achievable with the StarSense Explorer 8″ Dobsonian. For intermediate magnifications between the included 25mm and 10mm eyepieces, we suggest a 16mm Ultra Wide Angle (UWA) eyepiece (75x magnification) or, as a more budget-friendly alternative, a 15mm redline/goldline ocular (80x magnification) suitable for the StarSense Explorer 8″ Dobsonian.
A 2x Barlow lens combined with a 9mm/10mm eyepiece, or a dedicated 4mm UWA or 4mm planetary eyepiece (300x), will yield the highest magnifications likely to be significantly useful with the StarSense Explorer 8″ Dobsonian, assuming the atmospheric conditions permit such observations.
A narrowband Ultra High Contrast (UHC)/OIII nebula filter is a must-have accessory that will notably boost your views of nebulae, for example, the Orion Nebula, when utilised with virtually any telescope capable of providing decent deep-sky views, such as the StarSense Explorer 8” Dobsonian. This filter also heightens the visibility of planetary nebulae by decreasing the apparent brightness of surrounding stars, making it less challenging for you to identify the tiny planetary nebulae hiding between them at low magnification. You’ll also be able to spot the fantastic Veil Nebula and other faint objects which are otherwise invisible without a filter provided your sky conditions are otherwise fairly dark.
What can you see with the Celestron StarSense Explorer 8″?
The StarSense Explorer 8”, as with any good telescope with an aperture of 8”, is a powerhouse for viewing all kinds of objects. Even under light-polluted conditions, you can see a wide variety of open star clusters like M11 or M35, resolve individual stars in globular clusters like M13 and M15, split countless double stars, and, of course, view Solar System objects. The phases of Mercury and Venus are easy to see, and you’ll be able to resolve thousands of craters and mountain peaks on the Moon.
The StarSense Explorer 8” can show you a few dark markings on Mars along with its polar ice caps and any dust storms – careful observing techniques may also allow you to see its tiny outer moon Deimos. You’ll be able to see Jupiter’s cloud belts, the Great Red Spot, and its four large moons, which appear as tiny disks alongside their jet-black shadows whenever they transit in front of Jupiter and cause an eclipse over the planet’s cloud tops. Saturn’s rings are easy to see, along with the Cassini Division in the rings and a few cloud belts on Saturn. Up to 7 of Saturn’s moons can be seen under good conditions, though none are anything more than star-like pinpoints. Uranus is a turquoise disk; its 4 main moons are just at the limit of what you might be able to see with an 8” scope under dark skies. Neptune looks like a tiny blue dot, but its moon Triton is fairly conspicuous next to it, shining at magnitude 13. You might be able to see Pluto, but it’s fairly dim, even under dark skies, and it appears as nothing more than a star-like point.
The overall quality of any telescope’s views of deep-sky objects largely depends on your light pollution conditions; typical suburban light pollution (Bortle 5/SQM 20.5 or worse) will essentially wipe out galaxies altogether and significantly impair nebulae, while very light-polluted skies will make viewing everything but star clusters a frustrating task. Moderately dark (Bortle 4/SQM 21.2 or better) skies are needed for viewing galaxies and nebulae to their fullest extent with any telescope. The StarSense Explorer 8” will show you hundreds of colorful open star clusters and a few dozen globulars, most of which can be resolved into individual stars with a high-magnification eyepiece. Nebulae like Orion (M42) and the Lagoon (M8) are big and bright even under mediocre skies and are enhanced by a UHC filter; the Veil Nebula is spectacular under dark skies with a UHC or Oxygen-III filter, while a good UHC or H-Beta filter brings out the Horsehead and Flame Nebulae in Orion’s belt.
The Celestron StarSense Explorer 8” will easily show all of the galaxies in the Messier and Herschel 400 lists, and you can start to pick out features in brighter and more detailed galaxies. The spiral arms of M51 can be faintly glimpsed at medium magnification, while the dust lanes in M82, M64, and the gigantic Andromeda Galaxy (M31) are strikingly obvious even under light-polluted conditions thanks to their high contrast. Galaxy groups in Virgo, Coma Berenices, Ursa Major, Pegasus, and Fornax show dozens of members, some as far as a few hundred million light-years away – and if you’re going for a distance record, a few quasars – active black holes at the centers of galaxies billions of light-years away – can be seen as star-like points with an 8” telescope if you know where to find them.
