How to Observe Hubble's Variable Nebula (NGC 2261), an ever changing nebula

When viewing deep-sky objects, most appear static within the timescales of human observers. However, there are exceptions, such as supernovas exploding in distant galaxies, eclipsing binaries and the expanding crab nebula.

Another type of deep-sky object that changes over time is a variable nebula. A variable nebula is a type of reflection nebula, which means the nebula is reflecting light from a nearby star.

As the star lighting, the nebula is variable, its brightness changes over time. This change in brightness changes the brightness and shape of the associated nebula.

While other Variable Nebulae, such as Hind’s Variable Nebula, the easiest and brightest variable nebula to observe in the night sky is Hubble’s Variable Nebula. It is visible in large binoculars or a small telescope. However, as with many astronomical objects, it is best viewed in dark skies.

Click to enlarge the NGC 2261 star chart
So, to find Hubble’s Variable Nebula, or NGC 2261 in the constellation Monoceros. First, find the Orion constellation, then Betelgeuse. From this point, work your way across to the Rosette nebula.

Then work your way north and slightly across to find the cone nebula. The centre of the cone nebula has the brightest star in the area, which helps with identification.

From here, work your way down to Hubble’s Variable Nebula.

Unfortunately, the nebula is not visible through a finderscope well most finderscopes as it is too faint. So, scan the skies with a low powered eyepiece.

When you spot it, you may mistake the nebula for a comet as it is very comet-like in appearance. A nice feature of this variable nebula is that it can alter its appearance down to a minimum of once every two days.

This effect is due to the variability of the star R Monocerotis, which can change in magnitude from +10 to +12, combined with the erratic behaviour of an accretion disk of gas and dust surrounding the star.

Once you have found the nebula, either take a photo or draw the nebula. Then return in a few days and repeat the process you should see a definite change in shape and brightness.

To see the changes in brightness and shape over one week of the variable nebula, please watch the episode below.


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