Celestron StarSense Explorer™ 130mm Smartphone App-Enabled Tabletop Dobsonian Telescope

StarSense Explorer: Your Phone Finds the Way

Celestron says it has reinvented the tabletop Dobsonian with StarSense Explorer, the first tabletop Dobsonian that uses your smartphone to analyze the night sky and calculate its position in real time, and calls it ideal for beginners thanks to the app's user-friendly interface and detailed tutorials. StarSense Explorer uses patented sky recognition technology and your smartphone to work out where the telescope is pointed: a Lost in Space Algorithm (LISA), like the ones satellites use to orient themselves in orbit, matches the star patterns the phone detects overhead to the app's internal database.

Place your phone in the StarSense dock and launch the app. After you align the phone to the telescope's optics, a quick and easy procedure, Celestron says, the app lists the celestial objects currently visible. Pick one from the planetarium view or the Tonight's Best list and arrows appear on screen to guide you; the bullseye turns yellow when the telescope has detected stars but is not yet on target, and green when the object is ready to view in the low-power eyepiece. Celestron's app guide suggests stopping for a few seconds as you get close, so the telescope can sense the stars in its new position. As you observe, Celestron says you can listen to hundreds of audio descriptions and read detailed information about thousands of objects in the app's database; press the bar with the object's name at the bottom of the screen.

130mm f/5 Newtonian Optics

The 130mm parabolic primary mirror and 650mm focal length give 345x the light gathering power of the eye, a limiting stellar magnitude of 13.1 and a resolution of 1.06 arc seconds (Rayleigh) or 0.89 arc seconds (Dawes). Both mirrors are standard optical glass coated with aluminum and an SiO2 overcoat, and the secondary mirror's minor axis is 38mm (1.50").

The steel tube is 615.95mm (24.25") long and 165.1mm (6.5") in diameter and weighs 8.2 lbs (3.72 kg). Celestron says you can expect sharp, bright views of Jupiter's four Galilean moons, its cloud bands and Great Red Spot, the rings of Saturn, the Trapezium in the Orion Nebula and the Pleiades. Celestron says that even from a light-polluted city, the 130mm Tabletop Dobsonian can pick out Jupiter, Saturn, open clusters like the Pleiades, double stars like Albireo, the Orion Nebula, the Andromeda Galaxy and more of the brightest objects, and that from even slightly darker skies more objects become visible.

The Tabletop Dobsonian Base

The tabletop Dobsonian base is an altazimuth mount: it moves the telescope up and down (altitude) and left to right (azimuth). Celestron describes it as compact, lightweight and easy to transport, with bearings that give smooth motion in both axes and an integrated altitude brake. The altitude tensioning knob sets enough tension for a smooth up-and-down motion; under most circumstances you won't need much, but a heavy eyepiece may need more so the telescope stays still when you let go. If it still does not hold, or becomes hard to move, rebalance the tube. The base measures 482.6mm x 482.6mm x 419.1mm (19" x 19" x 16.5") and weighs 11 lbs (4.99 kg); it is particle board with melamine surfaces, CARB compliant.

The base's low profile makes the eyepiece easier to reach for some observers, especially children, Celestron says. You can set it on a sturdy table or even the hood of a car to bring the eyepiece to a comfortable height, or on the ground, where you will likely sit on the ground too, which the manual calls an excellent way for younger astronomers to use it. Celestron also offers an optional adjustable-height tripod, sold separately: the base sits on the tripod head, and the securing knobs on the head connect directly to the tripod adapters under the base.

The tube rides in tube rings on a dovetail bar: loosen the knob on the dovetail holder on the side panel, insert the dovetail and retighten until it is secure. For the best performance, balance the tube front to back: slightly loosen the clamping knob(s) on the tube rings, slide the telescope forward or back until it balances, and retighten. Loosening the same knobs lets you rotate the tube so the focuser sits in a more comfortable position.

Focuser, Eyepieces and Magnification

The 1.25" rack-and-pinion focuser takes 1.25" eyepieces: place one in the focuser, tighten the thumbscrews and turn the focus knobs until the view is sharp. Like all Newtonian reflectors, the telescope shows images upside down compared to the naked eye, which Celestron says has little impact on astronomy but can be confusing on land objects.

Magnification is the telescope's focal length divided by the eyepiece's: with the 650mm focal length, the 25mm eyepiece gives 26x and the 10mm 65x. Use low power to find objects and for wide deep-sky objects, higher power for the Moon and planets. The manual gives the maximum magnification of any telescope as about 60 times per inch of aperture, 307x for this telescope, but notes that in many locations air turbulence makes sharp images much over 100x difficult: if the stars twinkle heavily, stay at low power, and if they shine steadily, try a higher-power eyepiece. The eyepiece rack on the base keeps spare eyepieces at hand. Celestron lists the lowest useful magnification as 19x.

You won't need the StarPointer red-dot finder when using the app, but it helps you align the app with the telescope and finds objects during the day, since the app only works under the stars at night. Align it on an object at least a quarter mile away, ideally in daylight (a distant tree, sign or building; at night a streetlight, the Moon or a bright star or planet): center the object in the eyepiece, turn the StarPointer on with its LED dial, and without moving the telescope use its altitude and azimuth knobs to put the red dot on the same object. Turn it off after use; it takes a CR2032 3V lithium button cell.

Setting Up the App and Phone

Download the StarSense Explorer app before your first night out, then unlock it with the code printed on the card that comes with the telescope; each code enables up to five devices. With the phone in the dock, press the StarSense icon at the bottom of the planetarium screen, choose NEEDS ALIGNMENT and follow the on-screen prompts to align the phone's camera with the telescope.

The StarSense dock's bayonet mount goes into the port on the side panel of the base: line up the arrow on the dock with the alignment mark, press in and turn counterclockwise until the orange release button snaps into place. To remove it, press the orange button and turn the dock clockwise. Celestron says the app works with most modern smartphones and keeps a compatibility list on its site; on older phones the app can still be used, but it cannot be reinstalled once uninstalled. Most phones fit the dock with the case on, but a bulky or folio-style case may need to come off.

To align the phone, which Celestron recommends practicing during the day, insert the low-power eyepiece, place the phone in the dock and turn the knobs at the bottom of the bracket until the camera view is centered, unobstructed, in the dock's mirror. Point the telescope at a very distant object, at least a quarter mile away, such as a streetlight, a license plate, a stop sign or a treetop, center it in the eyepiece, then slide the camera view until the same object sits in the crosshairs. If you have removed the phone from the dock since the last alignment, the app suggests aligning again.

The app keeps the phone's camera looking at the sky and its processor working out where the telescope points, so it uses significant power. Celestron says a fully charged phone should last several hours, and recommends bringing a charger for an all-night session. It names its PowerTank Glow 5000, sold separately, a USB power bank with a red flashlight that straps to the base handle with its own bands.

Pointing, Cool-Down and Dark Skies

Pointing is simply a matter of moving the tube up and down and left to right until the object appears in the eyepiece. The SSE Tabletop Dobs are not motorized, so objects drift out of the field within a minute or two depending on the magnification, faster with high-power eyepieces; nudge the telescope slightly up, down, left or right to keep them centered.

The best views come once the telescope reaches thermal equilibrium with the outside air: while a warm mirror acclimates, its figure changes and the image is less sharp. Celestron says to allow around one hour when moving the telescope from a heated house, and recommends storing it in a dry but unheated place such as a garage or shed, or taking it outside an hour before sunset.

It takes at least half an hour for your eyes to dark-adapt, so the manual suggests avoiding bright lights while observing and using a red flashlight. Local light pollution greatly reduces the contrast of faint deep-sky objects, while the Moon, planets, double stars and bright open clusters are much less affected; schedule deep-sky observing near New Moon.

Collimation

Collimation aligns the parabolic primary and the flat secondary mirror, and Celestron recommends checking it periodically with the included collimation cap; the primary mirror is center-marked with an adhesive ring label. With the eyepiece removed and the cap in the focuser, you should see the whole primary mirror centered in the secondary, and the reflection of the secondary centered in the primary. Celestron suggests collimating during the day with the telescope pointed at a blank wall, adjusting the secondary first with the tube horizontal so nothing can fall onto the primary. At night, a bright star centered at high power and slightly defocused should look like a circle with the secondary's shadow centered in it.

The secondary's tilt is set with three socket-head set screws and the supplied 2mm hex key. For the primary, remove the mirror cell's rear cover (three screws), then adjust its three pairs of push-pull screws with the supplied 2.5mm hex key and Phillips screwdriver, loosening one screw of a pair and tightening the other.

What to Expect, Filters, Transport and Care

The manual sets realistic expectations: the Moon shows craters, maria, valleys and mountains, and is bright enough that an optional Moon filter helps; Saturn's rings, Jupiter's surface detail and moons and the phases of Venus are within reach; stars stay points of light at any magnification, but higher power splits double stars. Open clusters are best at low power, and brighter globular clusters resolve into stars in good conditions. Nebulae generally need dark skies, and while the brightest galaxies can be detected from somewhat light-polluted skies, many galaxies appear only as faint smudges.

Optional 1.25" filters thread onto the bottom of the eyepiece barrel. The manual names Moon filters and variable polarizers to dim bright views, colour filters for planetary contrast, and light pollution filters, which help most on nebulae.

In most cases you won't need to take the telescope apart to move it: grasp the base by its integrated handle with one hand and support the bottom with the other. The dock comes off by pressing its orange lock button and turning it clockwise, and the eyepiece rack lifts out. To remove the tube, unthread the knob on the dovetail clamp and lift the tube out with its rings and dovetail attached.

Store the telescope indoors in a dry place; a garage is ideal, since it keeps the optics near the outdoor temperature. Keep the dust cover and the focuser cap on when it is not in use, and dry any dew off the tube and base with a towel before storing it: the wooden base has sealed melamine surfaces, but water can seep into cracks if it is left wet. Some dust on the primary mirror is normal and has no effect on performance. If it gets excessively dirty, remove the mirror cell (the screws just above it, with the Phillips screwdriver), blow off dust with a blower bulb and brush, then wipe with lens cleaning fluid on lens tissue in radial strokes from the center out, a new tissue for every wipe, leaving the mirror in its cell.