It’s often a challenge for city-bound stargazers to see much of the deep sky through their telescopes. Light pollution obscures all but the brightest sights, and the time and energy needed to drive to dark-sky locations is hard to find. That’s why many backyard astronomers turn to Electronically-Assisted Astronomy (EAA).
Essentially a form of simple astrophotography, EAA involves capturing and stacking (or averaging) images from a camera to create a pleasing ‘snapshot’ in just a few seconds or minutes. Instead of seeing a few dozen bright deep-sky sights through an eyepiece, you can ‘see’ hundreds or thousands of nebulae, galaxies, and star clusters, even from urban skies, and in nearly real time.
Essential tools for EAA
To get started with EAA, you need a few tools and accessories: a camera, a motorized mount, a small telescope, and a computer or controller to capture and stack the images and control the camera.
Plenty of cameras from vendors such as ZWO or QHYCCD work for EAA. For beginners, a colour camera with a small sensor and two-megapixel resolution such as the ZWO ASI385MC or ASI662MC is a good place to start. Bigger cameras like the ZWO ASI533MC or QHY533C cameras feature a 9-megapixel resolution and larger sensors that give a wider field of view. Large, expensive cameras with APS-C or full-frame sensors are overkill for EAA. And you don’t need cooling, because exposure times are short.
Many telescopes with a focal length of about 400mm to 800mm and a focal ratio faster than f/7 work for EAA. This includes small ED refractors with apertures around 80mm, or small Newtonians of aperture of 125mm to 150mm. For longer focal lengths (and therefore larger images), an f/10 150mm Schmidt-Cassegrain telescope (SCT) works well.
A focal reducer makes for a useful accessory, and it’s all but essential with an SCT. Faster focal ratios make brighter images and enable faster image capture. You can get a small GSO 0.5× focal reducer that threads into the camera nosepiece for about CA $50. You won’t get superb image quality, but these work well enough with small-sensor cameras.
An inexpensive UV/IR blocking filter, which threads into the camera nosepiece, also helps with image quality by passing only visible light to the camera.
A small but powerful set-up for EAA includes an 80mm f/7 refractor and ASI385MC camera with a sensor 7.3mm × 4.1mm. This delivers a field of view of 0.75 degrees × 0.42 degrees. Thread in a 0.5× focal reducer and you get a focal ratio of f/3.5, an image four times as bright, and a field of view of 1.5 degrees × 0.8 degrees.
A tracking mount for your scope is all but essential. Equatorial mounts enable longer exposures, but tracked alt-azimuth mounts work well, especially for exposures less than about 30 seconds. Go-to functionality is useful to help find and centre each object.
Finally, to control and power the camera, and capture and display images, you need a computer or controller. Many EAA enthusiasts use a PC running the popular SharpCap application. The compact ASIAIR Pro or Plus controllers from ZWO offer an alternative to a PC and include software with a basic ‘Live’ stacking capability and go-to functionality with ZWO cameras.
Getting your first images
Once you get everything connected, it’s time to take your first snapshot! Not of a galaxy, but something closer — a tree or house — so you can see if everything is working and connected. Aim your scope, get focused, and try capturing a single image. For your daylight testing, adjust the camera to low gain and set the exposure time to 0.1 seconds or less to start.
Once you’re confident everything’s working, it’s time for a night session. Set your camera to high gain, about 300 to 350 for a ZWO ASI camera, align your mount, then aim your scope at a bright star. Be patient, and take the necessary time to learn how to focus, capture, and stack images with Sharpcap or other controller software.
As with all things, practice makes perfect. If you capture an image of a star and a single so-so image of a galaxy or nebula on your first night, you have done well.
Deep-sky target selection
Then, it’s time to go deep. Spring nights mean galaxies, and you can get snapshots of hundreds of galaxies even with a small 80mm refractor. Start with a big and bright one — the Whirlpool galaxy (M51), for example. Set your exposure to between 10 seconds and 30 seconds and the gain to 300-400. Then capture a single sample image.
Once you centre the object, stack five to 10 frames and watch the image get less noisy as they average out (the noise reduces by the square root of the number of images you stack). Adjust the histogram on your software to improve contrast and reduce the brightness of the background sky.
Other promising spring galaxies include M81/M82 and NGC 4631, as well as edge-on spirals NGC 5907, NGC 4244, and the dazzling NGC 4565. Globular clusters M3, M53, M13, M5, are also great spring EAA targets. While colourful nebulae are sparse in spring, the Owl Nebula (M97) in Ursa Major makes a good target.
During the summer big and colourful nebulae arrive, such as the M27, M8, M20, M16, and M17, as well as lots of globular and open star clusters. Fall offers the Helix Nebula (NGC 7293), the Pacman Nebula (NGC 281), and many star clusters in Cassiopeia, Cepheus, and Perseus. And winter (if it’s not too cold for your electronics) offers plenty more, including perhaps the finest (and easiest) EAA target of all — the Orion Nebula.
A few more tips
Once you stack each image, save it to your computer and adjust it to taste with a simple photo-editing app. Even simple Windows or Mac OS apps do a good job of bringing out a bit of detail.
As you gain more experience with EAA, you can explore more advanced techniques to capture better images. This includes applying calibration frames (flats, darks, and bias) and dithering to even out noise — all basic techniques known to astrophotographers.
Once you get a few bright deep-sky objects under your belt and perfect your EAA techniques, you’ll have a nearly inexhaustible supply of targets that will keep you out under the stars for many years to come.