2 Attachment(s)
Object of the Week - December 13th, 2020 M76
M76
NGC 650-51, Little Dumbbell, PN G130.9-10.5, PK 130-10.1, ARO 2, H I-193
R.A. 01h42m19.7s
Dec. +51°34'35" (2000)
Magnitude: 10.10
Size: 2.7'
Mag CS 15.9
Attachment 4129
It has been a bit of a surprise that M76 has not yet been covered as an OOTW. Although it is bright
it does offer a range of features for small to large telescopes. As it is a fine object from almost all
types of observing site, particularly with the use of a nebula filter, I thought it was time to rectify
this omission. M76 was first discovered as a hazy patch by Pierre Mechain in 1780 and, after receiving
Mechain’s note, by Messier himself who thought that he could resolve it into stars before adding it
into his catalogue. William Herschel on observing it with his 18.7” 20ft telescope in 1787 saw two
nebulae almost touching, hence the fact that it has two NGC numbers in NGC 650 and 651 for the
northern and southern lobes. It was Heber Curtis who recognised it to be a planetary nebula in 1918,
although this maybe controversial as Isaac Roberts was inclined to think it may have been one after
his photographs of it in 1891 when he thought it might be similar to the Ring Nebula. Classically M76
is thought to be a typical butterfly type planetary nebula with a main ring and broad bipolar extensions.
The central star is amongst the hottest known with a suggested temperature of around 204000K,
although this appears to have a significant range depending on how it is calculated. Deep images
show an extended halo which is probably the shells of material thrown off by the star as it went
through the AGB stage, http://www.elcielodecanarias.com/wp-...z-1024x576.jpg.
This halo is also starting to show signs of interactions with the local ISM as there seems to be a
bow shock in the direction of travel of the central star. The distance to M76 is somewhat uncertain
but is thought to be about 2500 light years. If so the nebula is about 1.2 light years across. The
central star is about 16th magnitude.
Attachment 4130
M76 - HST
Visually M76 has often been thought of as one of the more difficult Messier objects to find, although
I am sure that there will be observations with binoculars, although these will be difficult on account
of its small size. Through a small telescope what is mostly seen is the main bar as seen by Messier.
Larger telescopes will show both the two sperate sections of the main bar but also with the addition
of a nebula filter the outer lobes as well, which is why the nebula makes an interesting challenge for
all sizes of optical equipment. My favourite observations of it were with a 55cm (22”) telescope u
sing the new TeleVue Bandmate 2 Nebustar (UHC) filter which showed the external lobes well, even
though the object was not that high at the time and the observation was made from close to sea level
under the usual 80% humidity skies of the UK. It appears however that the handles are not equally bright.
As always,
“Give it a go and let us know! Goodluck and great viewing!”
