Celestron Cosmos 90GT Review – Celestron’s Cosmos 90GT is a beginners’ telescope with a twist – there is no handset. That’s because this system is specifically designed with smartphone and tablet users in mind. The scope is supplied with 25mm and 10mm eyepieces, a star diagonal (all 1.25-inch fit), StarPointer red-dot finder, a battery pack for eight AA batteries, which we found lasted for the entire review period, and a Cosmic Calendar poster.
This instrument was produced in association with Cosmos: a Spacetime Odyssey, the TV successor to Carl Sagan’s original Cosmos: a Personal Journey in the 1980s. The logo of new series, which was fronted by Neil DeGrasse Tyson and broadcast earlier this year, appears on the telescope tube; the single arm mount, meanwhile, is based on the show’s fictional ‘Spaceship of the Imagination’. Its red lights come on when the scope’s Wi-Fi is active.
Assembly was very easy, requiring no tools, and within a few minutes the telescope was ready for use. The primary 3.5-inch lens is fully coated, and gave lovely views of both bright deep-sky objects and the Moon. The scope has a focal length of 910mm and a focal ratio of f/10.1, which give magnifications of 36x with the 25mm eyepiece and 91x with the 10mm. The lack of a handset makes this instrument appear a little strange, as there is no way to manually move the scope in either axis – but that is the point of this system. The Cosmos 90GT takes full advantage of smart technology using purposebuilt apps. However, there is an aux port on the mount that allows you to connect a NexStar handset (sold separately), which provides an alternative method of control if you don’t own a smart device.
Note that without either there is no way to operate this scope. Getting online We found it easy to connect to the built-in SkyQLink Wi-Fi network and download the recommended Cosmos Navigator app (free; available for iOS and Android) The app acts like a planetarium program and is a ‘lite’ version of Celestron’s SkyPortal app, which can also be used with this telescope. Once aligned on three stars, selecting a celestial object and pressing ‘Go-To’ causes the Cosmos 90GT to slew to it. If your alignment is very accurate then the chosen target does end up reasonably close to the centre of the 25mm eyepiece, which has a 1° field of view. Bear in mind that the view is the right way up, but left and right are swapped. A clever little feature is that you can’t select an object near to the zenith or directly above, preventing the telescope from catching on the tripod, and a warning pops up telling you as much. It’s a nice touch. We enjoyed good views of prominent open clusters, including the Pleiades in Taurus and the Double Cluster in Perseus.
The lovely Ring Nebula in Lyra was small in the 25mm eyepiece, but a nice smoke ring in the 10mm. The Dumbbell Nebula in Vulpecula was a fine sight in both eyepieces; back in Taurus, the Crab Nebula was fainter but still viewable as a hazy patch. The Andromeda Galaxy, meanwhile, appeared as a glowing oval patch with a hint of the surrounding disc. Searching nearby, we could pick out its two companions, M32 and M110. We also enjoyed a good range of double stars. Colourful Albireo in Cygnus was a treat, especially in the 10mm eyepiece, and by adding a 2x Barlow lens of our own we were able to split the triple star Iota Cassiopeiae. Finally, we took a tour of the Moon’s terminator and were rewarded with enough detail to keep us happy for a long time indeed. We even managed to capture a picture of it with our iPhone adaptor.
Celestron have done a good job in bringing a basic beginners’ telescope into the 21st Century. If you are keen on getting the most out of your tablet or smartphone, you’ll certainly enjoy using it to take a tour of the heavens.
Celestron Cosmos 90GT Specifications
- Price £399
- Optics Refractor
- Aperture 90mm (3 inches)
- Focal length 910 mm (f/10.1)
- Mount Computerised single fork arm (altaz) with integrated Wi-Fi network.
- App Celestron Cosmos Navigator or SkyPortal (£free, available for iOS and Android, must be downloaded separately)
- Extras 25mm and 10mm eyepieces, star diagonal, StarPointer red-dot finderscope, accessories tray with smartphone / tablet holder.
- Weight 7kg
- Supplier David Hinds http://www.celestron.uk.com
- Tel 01525 852696