Can you observe the central white dwarf star in the Ring Nebula, M57?
The Ring Nebula, M57, is a treasured deep-sky object of the summer sky. For many it represents their first view of a planetary nebula. This is in part due to the nebula being reasonably bright – by planetary nebula standards at least – and because it’s relatively easy to find. M57 represents the outer layers ejected from a star; the remaining white dwarf sits at the centre shining at mag. +15.2 (see below). The challenge is to observe M57’s central star by whatever means available.
Before we try to record the central star, let’s familiarise ourselves with how to find M57. This is a mag. +8.8 planetary nebula, set between the two stars at the southern end of the squashed diamond pattern forming the body of Lyra the Lyre. A lyre is a musical instrument not dissimilar to a harp: and Lyra’s diamond shape represents the stringed portion of the instrument.
Your two guide stars are Sheliak
(Beta (β) Lyrae) and Sulafat (Gamma (γ) Lyrae). M57 sits a fraction south of the line joining these stars, 40 per cent of the way along this line starting at Sheliak. Looking for M57 with a low power eyepiece may initially prove tricky because it’s actually quite small and easily overlooked as a star. The ‘trick’ to locating it is to line up with the area using a wide-angle eyepiece, pick the most likely fuzzy star contender and increase the magnification. If you’ve chosen correctly the ‘fuzzy star’ should start to look a bit like a small, dim planet, the reason why these objects are called planetary nebulae. Larger apertures with higher magnifications will reveal M57’s disc to be oval in shape and appear darker in the centre. Overall, this gives the appearance of a ring, explaining why M57 is called the Ring Nebula.
To see the central star visually, you’ll ideally need a large scope, say around 400mm aperture. This is ideal territory if you have access to a large Dobsonian. If not, you might take heart in hearing that it has been reported through 300mm reflectors, 250mm Schmidt-Cassegrains and even a 200mm refractor. Seeing conditions need to be near perfect for this to happen though. Photography is perhaps a more fruitful method of recording it. Here, you’ll need to use a reasonable image scale which shows M57 as a tangible ring. If you do manage to record it and have access to different sizes scopes, experiment to find the smallest instrument you can record it with. Also see how many different cameras you can catch it with – what about using a smartphone camera pointed down the eyepiece of a telescope? If you have success, please don’t forget to send us your results.
1 M6
The Butterfly Cluster, M6, is located west of the Teapot asterism’s spout. Identify the Teapot and extend the line of the spout – Delta (d) to Gamma (g) Sagittarii – about 1.8x. M6 lies 1° below the position you come to. Despite its proximity to Sagittarius, M6 lies within Scorpius. A 150mm scope shows around 40 stars in an area two-thirds the apparent size of the full Moon. The group is elongated northeastsouthwest. A low power view reveals two lobe-like patterns, symmetrically arranged like the wings of a butterfly. One star shines out above the others here, mag. +6.0 BM Scorpii. With a wide-field eyepiece BM appears orange in colour. SEEN IT
2 NGC 6383
Head 1.2° west and 0.2° south from M6 and you’ll arrive at the open cluster NGC 6383. This is dimmer than M6 at mag. +5.5 but a similar size, 20 arcminutes across. There are fewer stars here: a 150mm scope reveals around 20 appearing to spread mostly northwest of a brighter, mag. +5.7 star. In fact, this bright blue-coloured star is good at hiding the rest of the cluster. Look at it using a low-power eyepiece and the star dominates; increase magnification to 100–150x to reveal the other stars. Look out for the small arc of stars to the northwest of the brighter star, visually balanced by a straighter line running east. SEEN IT
3 M7
M7 is easy to find because it’s big and relatively bright. Shining with an integrated magnitude of +3.3, this most southerly Messier occupies an area 90 arcminutes across. It’s located 3.9° southeast of M6 and easy to find from low northern or southern latitudes, standing out well to the naked eye. From mid-northern latitudes, it never gets significantly above the southern horizon and its impact is muted. There are lots of blue stars here, some of which form a
This Deep-Sky Tour has been automated ASCOM-enabled Go-To mounts can now take you to this month’s targets at the touch of a button, with our Deep-Sky Tour file for the EQTOUR app. Find it online.