Celestron

The StarSense Dobsonian tube slides into the mount’s sideboards for quick assembly. Just add an eyepiece, and mount the phone into the dock to begin observing. When aimed at the zenith, the eyepiece height is 44 inches (1.12 meters). Credit: Alan Dyer

Celestron expands their StarSense technology to more serious telescopes with greater aperture.

When I reviewed Celestron’s first StarSense Explorer telescopes (see my test at AGT of the DX 102AZ, a four-inch refractor), I thought, “Wouldn’t this technology be great on a larger Dobsonian reflector?”

It’s all very well having computer-aided pointing on small scopes made for beginners. But what about us more experienced observers? Can’t we have the convenience of computer-aided finding on a serious telescope, one with enough aperture to show us deep-sky objects in detail?

Enough people thought the same that many have been buying low-cost StarSense scopes just to cannibalize them for the phone bracket or “dock,” and the “unlock code” needed to activate the app. They then fasten the dock to their own Dobsonian telescopes to create home-brew StarSense Dobs.

The StarSense dock itself clamps into a holder that comes bolted to the tube. To prevent it being damaged, remove the dock when transporting the telescope. The telescope comes with a cloth bag for storing the dock. Credit: Alan Dyer

Well, that’s no longer necessary. Celestron has at last brought out StarSense-equipped versions of new Dobsonian reflectors in two popular sizes: 8- and 10-inch. I tested the 8-inch f/6 StarSense, using a unit sent by Celestron for review before its official announcement.

What is StarSense?

StarSense is technology unique to Celestron that works so well I think it somewhat obsoletes all other entry-level telescopes.
StarSense allows “push-to” finding of objects — an app on your phone shows you where to move the telescope to locate an object you have selected, and then indicates when you are on target.

The dock’s mirror has a plastic protective cover (left). With the phone in place (right), its camera looks into the mirror to see the sky. The dock’s adjustable cradle can accommodate large phones, but not tablets. Credit: Alan Dyer

Unlike all previous push-to scopes, StarSense does not use hardware encoders on the telescope axes, nor does it need to be input with your location, date and time, nor aimed at and aligned on several stars to begin the night’s viewing. It does not require a specialized and costly computer, because it uses the computer you already own, your phone, which always knows where and when it is.

The StarSense app (free for Apple iOS and Android devices) uses the camera in your phone to image the night sky and do what is called “plate solving.” It sees the pattern of stars overhead, identifies them, and figures out where all other objects of interest are in the sky. It does this without needing a connection to the internet.

Arrows point the way to selected targets. When on target, a green box appears. In red screen “night mode,” the box alone indicates you’re there. Also note the messages! Credit: Alan Dyer

Tap on a target and arrows direct you to it as you move the telescope. Remarkably, when the app says it is on target and your object is now visible in the eyepiece, it’s right! In testing this telescope, I found objects were always within the field of the Dobsonian’s supplied 25mm (48x) eyepiece.

It does take a little patience — as you turn the telescope closer to the target, you have to stop moving the scope for a few seconds to allow it to take another sighting of the sky to finalize the precise pointing. The app’s messages prompt you — ignore them and in your haste to locate an object it’ll miss it. Wait a moment and you’ll see the chart and pointing indicator refresh with a new, more accurate position. A square box flashes up to indicate when you’re on target.

Just to be clear — the StarSense scopes are not GoTo scopes. There are no motors to move the scope, nor provide any tracking. You push the scope around the sky and, like most Dobsonians, once you are on target you need to nudge the scope every few moments to keep objects centered.

What the StarSense tech provides is the ability to quickly and easily find objects, with your phone screen acting as a digital finder scope, but with guided pointing.

Each telescope comes with a unique code to activate the StarSense Explorer app so it can begin finding objects. The entry is required only once per device. Credit: Alan Dyer

Using the StarSense

You can download the StarSense Explorer app for free (don’t confuse it with Celestron’s other app called Sky Portal) and use it as a basic planetarium program. However, to activate the app’s pointing ability, you must unlock it with the code that comes with each telescope. The unique code will allow you to use the app on up to five devices.

I tested the StarSense Dob with an iPhone 11 Pro. Celestron says the app is compatible with iPhone 6 and later, and Android phones running v7.1.2 and later. A full compatibility list is provided here by the software publisher, Simulation Curriculum, as the StarSense Explorer app is a special version of their popular SkySafari mobile app.

The first step is to adjust the X and Y motions of the dock (left) so the camera is positioned properly over the mirror (right) for an unobstructed view (center). Credit: Alan Dyer

While no individual star alignments are needed, there are two forms of alignment required to get your phone pointing accurately. First, after clamping the phone into the dock, you use its geared X and Y adjustments to position the phone’s camera so it sees as much of the dock’s mirror as possible. The little mirror allows the phone to look up at the sky while keeping the phone’s screen more or less horizontal so you can see it. Unless you change phones, that alignment is a one-time adjustment.

In-app videos step you through aligning the phone’s image to a distant target centered in the main scope. This alignment might need to be re-done from time to time. Credit: Alan Dyer

Next, like aligning a finder scope, you have to aim the scope at a distant target (this can be done during the day), then tap on that same object in the phone’s field of view to electronically align its view with the telescope’s. In-app tutorial pages with videos step you through the process; there is no written instruction manual for the software.

That last adjustment is also usually set-and-forget. I found when removing and replacing my phone each night, it went back to the same place, and no re-alignment was needed.

But when you start up the StarSense function, you are asked if a re-alignment is needed or not. If it is (perhaps because you’ve found the pointing is always off), it can be done at night, by using the Night Mode setting on the alignment screen, which brightens the camera image.

The first night out with the scope I was amazed at how fast — in just seconds — the app saw and correctly identified the stars overhead and was ready to guide me to the first object. And that was in twilight with only the brightest stars visible.

In previous tests of the first StarSense scopes, I found the plate solving worked well in moonlight and even with some haze in the sky. It should work under city skies, but it does need to see quite a lot of the sky. Sites hemmed in by tall trees and buildings might prove problematic. To that end, a StarSense scope likely won’t be a good choice for apartment dwellers doing balcony stargazing.

Unlike traditional GoTo telescopes, the StarSense technology works only at night when it can see stars. It can’t be used to find stars or planets by day, as the warnings state. Credit: Alan Dyer

I found in previous tests that the StarSense dock’s mirror, despite being exposed to the sky, stays surprisingly clear of dew and frost. But in humid climates, having the mirror fog up will prevent the phone camera from seeing the sky, something it has to continue to do throughout a session for the pointing to work.

I did find that now and then after the scope and app had been idling unused for an hour or more, while the phone did not go to sleep the pointing arrows disappeared and the StarSense button had to be pressed again, bringing up the Alignment message screen.

Each object has extensive information and images, and audio narration. Tonight’s Sky tour is a mix of deep-sky objects, bright stars and double stars. Objects can also be selected from lists, such as Brightest Stars (which, oddly, includes the Sun) and the new “More Deep Sky Objects” list. Credit: Alan Dyer

StarSense Catalogs

While getting the StarSense going is easy, I think beginners might still be a bit lost if they don’t know much about what the sky has to offer. It’s helpful to understand the kinds of objects that are up there and what catalogs, such as the Messier and Caldwell lists, have to offer.

However, the app does boot up with its curated pick of “Tonight’s Best Objects” indicated with blue circles on the sky chart. It’s a good selection for novices to begin their celestial explorations. In the tabular listing, objects are labeled as “City Viewable” vs. “Dark Sky Viewable.”

Tapping on any object and hitting the “i” button next to its name brings up a text description and image of the target. The Data panel provides all the stats like magnitude, distance, size, etc. Many targets also have an associated audio narration, great for beginners and for public outreach.

The app version I reviewed (v1.1.6.1) was released just prior to the official launch of the StarSense Dobs in May 2022. Like earlier versions of the StarSense Explorer app, the new one has a catalog of some 140 double stars, plus the 110 objects in each of the Messier and Caldwell lists. You can also use it to point to the Moon, the seven major planets, about 100 bright stars, each of the constellations, and a couple of dozen popular asterisms. Asteroids and comets can be found by searching for the object name in the Search bar. That also applies to Pluto.

The new app version adds a list called “More Deep Sky Objects,” an eclectic collection of targets from the NGC, IC, PGC, UGC and Sharpless catalogs, all fainter objects suited for the larger aperture of the two Dobs. However, the curated list contains only 160 objects and, oddly, 30 of them are Messier objects, needlessly repeating entries from that catalog.

However, deep sky fans will not be left wanting. The tens of thousands of objects from the Abell, Arp, Barnard, Cederblad, Hickson, NGC, IC, PK, PGC, UGC, and Sharpless catalogs (phew!) are all in the database and can be called up and displayed on the chart using the app’s Search function by entering a specific object.

Or, if you want to see the complete listing of NGC objects, search for just “NGC” to bring up a scrollable list of 7,987 objects. Pick the one you want, hit Center, and it’ll be displayed on the chart so StarSense arrows can lead you to it. The app’s database set is now similar to what’s included in the SkySafari Plus mobile app. However, how to access and find objects from the new extended databases is not obvious. The StarSense Explorer app could use some on-line instructions.

Assembling the mount from flat-pack to finished product is similar to most Dobsonian telescopes. The printed instructions were clear and no parts were missing. Credit: Alan Dyer

The Mount

As with all Dobsonians, the wood mount comes in an IKEA-style flat-pack box and requires full assembly by screwing parts together using the included wood screws into the pre-drilled holes. Assembly took about an hour, with the printed instructions providing a clear guide to the steps in words and pictures.

The mount moves very smoothly on slick plastic pads, with the tension adjustable in azimuth by turning the nuts on either side of the central bolt. That requires removing the scope and getting at the top and bottom of the mount’s ground boards. Inconvenient, but it likely needs to be done only occasionally.

The tension in altitude, which needs to be adjusted more frequently as the eyepiece weight changes, is easy to do by turning the knob on the altitude bearing on the eyepiece side. I found no balance problems when using relatively heavy eyepieces. The mount is quite solid; vibrations damped down in about a second.

A handle and grip holes on the mount make it easy to carry around. A metal eyepiece rack holds three 1.25-inch eyepieces and one 2-inch eyepiece.

The Crayford focuser proved smooth and precise, handling the heaviest 2-inch eyepieces with no slippage. Removing the 2-inch extension tube allows a DSLR camera (with a 2-inch camera adapter) to reach focus, for shots of the Moon. Credit: Alan Dyer

A mid-tube handle aids carrying the telescope tube and inserting it into the mount’s sideboards. The left knob serves as a tension adjustment for the altitude motion. Credit: Alan Dyer

The Fittings

A well-placed knob at the front of the tube below the focuser is handy when nudging the scope to follow objects. A handle on the top of the aluminum tube is also well-placed at the balance point for carrying the tube. All Dobs should be so equipped.

With the two side bolts attached, the tube can be dropped into the slots on the mount’s two sideboards and removed easily. There are no tensioning springs that need be attached and detached. The aluminum tube is solid, so takes up some four feet of storage space, unlike more costly truss-tube or collapsible Dobs that are more compact for storage and transport.

The optical tube comes with a smoothly operating two-inch Crayford focuser, with an extension tube (needed for most eyepieces to reach focus) and a step-down adapter for 1.25-inch eyepieces. The included eyepiece is a 25mm Plössl from Celestron’s Omni series. It’s a fine eyepiece to get started with. In testing the scope with my box-load of 1.25- and 2-inch eyepieces, I found all reached focus.

While the focuser’s drawtube can intrude into the light path, with most eyepieces the drawtube is racked out far enough so as not to block light or cause diffraction.

he included red-dot finder is on the “wrong” side of the tube for right-eyed use, and is physically difficult to look through from the eyepiece side of the tube. Credit: Alan Dyer

The tube is also supplied with a standard red-dot finder. As long as the StarSense app (and your phone) is working well, the finder isn’t really needed. That’s just as well, as its placement on the far side of the tube (the only spot available as the StarSense dock takes up the prime position) makes it very tortuous to look through. Using the red-dot finder for quick sessions without the StarSense app will be physically difficult for all but the most agile.

The spider has thin vanes for minimizing diffraction, and has collimation adjustments for the 1.83-inch secondary mirror, while the 8-inch f/6 primary has a center dot for collimation. Credit: Alan Dyer

The Optics

The primary and secondary mirrors have collimation adjustments. A peep-hole collimation cap is provided. However, despite its long journey from China to California, then by UPS to me in Canada, the optics arrived in almost perfect collimation. I didn’t need to adjust the mirrors.

The primary mirror’s collimation adjustments are recessed and require a hex wrench and Philips head screwdriver to adjust. The mirror back is exposed to help in cooling. Credit: Alan Dyer

The optical quality was also excellent. In high-power star tests, I could see little in the way of aberrations, zonal errors, or pinched optics distorting the images. This is a telescope that will provide pleasing views not only of deep-sky objects at low power, but also high power views of the Moon, planets, and double stars.

Who Is It For?

Yes, the StarSense Explorer Dobsonians will be great for beginners looking for a more serious first scope than a small refractor or reflector. An 8-inch Dobsonian has long been my top recommendation for anyone looking for the most scope for the least money. It offers a good balance of portability, generous aperture, and affordable price.

However, I think even more experienced observers will enjoy one of the StarSense Dobs. If you’ve paid your dues star-hopping, the StarSense tech gives you the ease of computerized finding without the fuss, expense, and power requirements of a traditional GoTo scope. You can have the scope set up and be finding things in moments, with no dreaded “Alignment Failed” messages that can plague GoTo scopes.

The main point of failure would be if the cold of a winter night kills your phone battery. On cool spring nights I found my iPhone still had plenty of power left even after several hours of running the StarSense app.

The 8-inch StarSense Dob’s tube is 44 inches (1.12 meters) long. The mount and optical tube each weigh 20 lbs (9 kg). The tube is finished in the StarSense metallic grey livery. Credit: Alan Dyer

The StarSense Dobs provide enough aperture for pleasing views of much of what the sky has to offer, and an app with huge databases to find thousands of objects. I think veteran observers will find that the scopes put the fun back into observing. I enjoyed using all the StarSense telescopes I’ve tested. I soon forgot the test procedures and just enjoyed finding and viewing favorite objects with ease, with no need to bend over to peer through finder scopes (great for aging backs!).

Celestron’s StarSense Dobsonians stand out as prime choices for anyone considering a Dob. While there are many competing Dobsonians to pick from, why not have one with computerized pointing? I think the added cost (about $150 to $200) over a basic Dob, such as one of the Sky-Watcher Classic models, is well worth it for the convenience and fun that StarSense technology provides.

 

Plus: Accurate and easy computerized finding; excellent optics and mount
Minus: Partly inaccessible red-dot finder; solid tube takes up storage space

 

Retail: $799.95 (8-inch); $1099.95 (10-inch)
Website: www.celestron.com