One of solely 4 planetary nebulae to be included in Charles Messier’s well-known catalogue, fabulous Messier 76 (NGC 650/651) in Perseus rewards observers and imagers alike with its dramatic two-loop or -lobe look, which sufficiently resembles that of summer season’s well-known Dumbbell Nebula (Messier 27) in Vulpecula for it to go by the nickname the ‘Little Dumbbell’.
While M76 is a good bit fainter and smaller than M27, and has an unwelcome however well-deserved popularity as one of many hardest objects in Messier’s checklist to watch, a small telescope will determine it and telescopes within the 200–250mm (eight- to ten-inch) class can begin to outline and element its distinctive form and nebulosity.
Messier 76 is an attractive and dramatic trying planetary nebula residing within the magnificent, far-northern constellation of Perseus. Planetary nebulae are the short-lived end-point within the lives of Sun-like stars, their outer layers expelled with the recent core uncovered as an ever-cooling white dwarf remnant, its robust ultraviolet radiation ionising the tenuous surrounding envelope and producing an unimaginable number of stunning nebulae.
M76’s hourglass determine
Messier 76 reveals a outstanding bi-polar construction in deep pictures, a central, brighter space that has been variously coined a ‘box’, a ‘cork’ or an ‘hourglass’, with two nebulous loops or lobes. One might liken it to a barred spiral galaxy with a whopping central bar with the spiral arms wrapping round it from both finish; no signal right here of a M57-like ring construction.
In many respects that is the enjoyment of planetary nebulae, the distinctiveness of every of those objects, with their inherent intricate constructions carved out by the interactions of the expelled outer layers of the dying star throughout its purple large phase with faster-moving, extra lately ejected materials ploughing into it, producing a collection of shock waves.
M76’s look is one thing of an phantasm attributable to its orientation to Earth; the galaxy analogy is related once more, as we see some galaxies face-on, some inclined to our line-of-sight, to these spectacularly showing edge-on.
We see the Little Dumbbell from the aspect, its equator (the angle is 75 levels); if we might look proper down the centre of one of many lobes, it will appear like a hoop, as is the case with Messier 57. Astronomers have decided that the north-western lobe is pointing our manner and the central ‘cork’ is increasing at round 45 km/s.
How distant?
It unsure how distant M76 is and subsequently how large it’s. Distances starting from 2,500 to 12,000 gentle years are quoted within the literature, however a price of 4,000 gentle years is probably going, with the nebula spanning about three gentle years.
The central star, a white dwarf remnant, may very well be as sizzling as 140,000 levels Celsius and in 1973 is was found to have a companion star a mere 1.4 arcseconds away, equating to between 16,000 to twenty,000 gentle years. The companion was itself found to be double in 1995 following Hubble observations, however its now unsure whether or not the pair are bodily associated to the white dwarf.
M76 was found by Pierre Mechain in 1780 and 7 years later William Herschel noticed it along with his a lot bigger telescope. Herschel noticed the 2 lobes and mistook them for 2 separate objects, which accounts for the double NGC numbers 650 and 651 assigned to the Little Dumbbell.
In 1891 Isaac Roberts was the primary to supply photographic proof of the nebula’s true nature. Like all planetaries, M76 is transient, its destiny being to regularly disperse into the interstellar medium over the following a number of thousand years.
How to watch
Messier 76 lies within the excellent late-autumn/early-winter constellation of Perseus, which has the winter Milky Way flowing by way of it and comprises a handful of excellent open clusters and nebulae, together with the magnificent Double Cluster.
M76 might be present in Perseus’ excessive north-western reaches, near its boundaries with Andromeda and Cassiopeia. It lies roughly halfway between the magnitude +2.1 stars gamma (γ) Cassiopeiae and gamma Andromedae, the latter being a marvellous colour-contrast double star.
Zooming in a bit, magnitude +4 phi (φ) Persei lies just below a level to the south-south-east. M76 is circumpolar (by no means setting) from the UK and peaks proper on the zenith at about 11pm GMT on the finish of October/begin of November (British Summer Times (BST) ends at 2am BST on 30 October).
Although catalogued as magnitude +10.4, and spanning 163” x 107” in obvious diameter, many observers discover M76 to be a better goal to seek out and observe than its magnitude suggests. If you’re searching for it on a really clear and moonless evening at a darkish countryside website, attempt sweeping with a pair of 10 x 50 binoculars; in any other case an 80mm (~three inches) telescope ought to bag it.
If you don’t see it at first, attempt the neat trick of utilizing averted imaginative and prescient and enhance the magnification (which will increase distinction too). Neil Bone, our much-missed colleague, reported that M76 was seen at 40x however not at 20x by way of his 80mm telescope and that it appeared to ‘blink’ when he switched between regular and averted imaginative and prescient.
M76 responds effectively to narrowband filters – good outcomes shall be had with both an Ultra High Contrast (UHC) or an Oxygen III (O-III) filter, which passes solely the sunshine of doubly ionised oxygen, M76’s dominant emission.
A moderate- to large-aperture telescope, say from 200mm to 300mm (12-inches) in dimension, can reveal M76’s interior hourglass or dumbbell form, with most observers ranking the south-western lobe, seen maybe within the type of a semicircular arc, which ace American visible observer Stephen James O’Meara describes as a butterfly wing, as brighter and higher outlined than its north-eastern counterpart. How do you see it?
Both lobes are embedded in a fainter, enveloping halo and the nebula’s general form may be very pleasing and photogenic, significantly in deep novice pictures.
