NGC 1740 in Orion

January 2023 - Galaxy of the Month

For this month’s challenge I am going very deep into Orion. I am going to throw this out there and apologise that the challenge may be too extreme. The challenge is the faint galaxy pair NGC 1740 and NGC 1753.

NGC 1740 was discovered in 1830 by John Herschel using an 18.3 speculum metal telescope. NGC 1753 had to wait another 50 years or so for Lewis Swift to find it using a 16” refractor in 1889, I suspect at this date from the Lowe observatory on Echo Mountain. Unfortunately it seems that confusion arose in the area and it appears that there is some conflict between the NGC numbers 1740 and 1742 due to an error in John Herschel’s positions. NGC 1742 is almost certainly just a star. It was found by Ball using Lord Rosse’s 72” at Birr.

NGC 1740 is classified as a lenticular galaxy S0 at a distance of perhaps 59 Mpc. NGC 1753 is classified as a spiral SBa (pec) with a redshift derived distance of 57 Mpc so they may be a physical pair. Perhaps unsurpingly for such non-descript galaxies there is not much written on them. Both galaxies do appear surprisingly bright in the GALEX images which suggests that there is some star formation going on, which would be surprising for a lenticular galaxy as most of the star forming gas is normally stripped out of these.

Holmberg thought NGC 1740 was a double nebula with NGC 1742 and classified it as Holmberg 84 in his catalogue of double and multiple galaxies. Unfortunately, as noted above NGC 1742 does not exist. It is possible that Barrachi using the 40” Great Melbourne telescope found these two galaxies independently.

I have to say both of these are going to be very challenging objects and probably a bit faint really for any spectacular views. The altitude is also not going to help as seen from the UK but they do rise above 30 degrees. The galaxies are relatively close together and will be in the field of view of a modern widefield eye at a power of 265x. I suspect that using a high power to increase the contrast is probably going to be the only way to pick up NGC 1753. Using a medium power eyepiece may also bring the galaxy NGC 1729 into the field. This is also a faint object though.

Steve Gottlieb suggests that even with his old 17.5” both these galaxies were no more than faint smudges. Perhaps unsurprisingly they are not in the Night Sky Observer's Guide (NSOG) Vol. 1.

Owen Brazell - Galaxy Section Director