Orwell Astronomical Society (Ipswich)
Variable Nebulae, 08 April 2008 - 01 February 2021
This page presents observations for five variable nebulae visible from the northern hemisphere plus one visible from the southern as follows:
Hind’s Varable Nebula (NGC1555)
Hubble’s Variable Nebula (NGC 2261)
Thomme’s Variable Nebula
North is up in all images below. Fields of view and other details are provided in the full images below (but not in the thumbnails). The telescopes employed are listed at the foot of the page.
The BAA website also has pages on variable nebulae.
Gyulbudaghian's Nebula is a little-observed and poorly understood variable nebula at the heart of which lies the recently-formed pre-main sequence star PV Cephei (typically magnitude 16-18). The nebula is usually small and faint.
My initial observations of the nebula coincided with an observational programme by the Deep Sky Section of the BAA, coordinated by Grant Privett, to monitor the object. Thanks to this programme, observations by BAA member David Boyd were made available for comparison purposes.
Figures 1-4 below show the appearance of the nebula over a period of 16 months, April 2008 - August 2009, and illustrate clearly changes in its appearance. Between April 2008 and October 2008, it appeared to become more extensive and the locus of its peak density moved further from PV Cep. Between October 2008 and August 2009, the nebulosity disappeared completely!
Figures 5-7 span a period of eight months from late March to early December 2012. David Boyd captured figure 5 on 28 March 2012; I took figure 6 using my Newtonian reflector on 16 October 2012; and David took figure 7 on 05 December 2012. (I am grateful to Stewart Moore for providing David's images.) The images show a significant patch of nebulosity becoming visible and brightening over a period of months.
Becoming increasingly frustrated with the weather in the UK shortly before Christmas 2012, I decided to try remote observing. There are many telescopes available via the Internet and I chose to use one controlled by the SSON as colleagues have obtained good results with their equipment. SSON has three telescopes but, as Gyulbudaghian's Nebula is small and usually faint, I chose the largest, the Mount Lemmon 81 cm Cassegrain reflector in Arizona. After some delays caused by a snow storm (36 cm of snow on the dome!), moonlight and Christmas I received my first images on 02 January 2013. I compiled figure 8 from the resulting stack of 5x2 minute exposures after some basic image processing. It is clearly superior to the earlier images with my 34 cm Newtonian.
Figure 9, again taken with the SSON 81 cm Cassegrain reflector (using five 2 minute exposures), shows the nebula on 01 April 2013. Figure 10 compares side-by-side the images of the nebula on 02 January and 01 April 2013. Figure 11, taken with my 34 cm Newtonian (49x30 s exposures), shows the nebula on 07 May 2013. Clearly, there has been little change since the start of 2013.
Throughout summer 2013 I continued to monitor the nebula with the iTelescope.net T11 reflector in New Mexico. It appeared still bright with some very subtle changes from month to month. Maybe some structure was developing on the left hand edge? See figures 12 and 13.
In early September, for the first time since I started using remote telescopes, there were four consecutive days of bad weather in New Mexico and, as a result, I was unable to capture my monthly image of Gyulbudaghian’s nebula. However, I did have good conditions at home during this period and, on the evening of Saturday 07 September, managed to take probably the best image yet (figure 14) with my own equipment. Two factors contributed to the excellent quality of the image: I had the telescope mirror re-coated over the summer (a HiLux coating from Orion optics replacing the original aluminium coating applied 30 years previously) and I spent an hour at the telescope taking very many images.
The image from 07 September appears to show the brightening on the left hand side of the nebula has increased in extent over the preceding month. Clearly better conditions and more signal might reveal more structure, but I think the change is real given that the brightening wasn’t visible previously in images with bigger telescopes from better sites. Figure 15 is a greatly stretched negative image to highlight the "new" appendage. It’s nice to see some change at last!
Figure 16, taken on 04 October 2013 using the iTelescope.net T11 reflector, appears to show some further change. The eastern extension of the nebula looks narrower and fainter than in the image taken at the beginning of September (figure 14). Perhaps this section of nebulosity is fading? Figure 17 provides a negative view of the same field.
Figure 18, taken on 01 November 2013, provides the obligatory monthly watch for changes. The image is similar to that of the previous month, although the long eastern extension may now be thinner.
Bad weather in New Mexico in early December meant that I had to do my own imaging using my 30 cm F4.1 astrograph. The images aren't up to the standard of those taken with the much larger instrument in New Mexico, but do maintain monthly monitoring of the nebula. Figure 19 was taken on 04 December 2013. Figure 20 is a rather over-stretched full field view which starts to show the large dust cloud within which the the nebula is embedded. This is a typical environment for all the variable nebulae as they are associated with newly formed stars.
Figure 21, taken on 01 January 2014 with the iTelescope.net T11 reflector, shows that the nebula has changed little in the previous month.
Figure 22, taken on 28 February 2014, shows that remote telescopes don't always deliver excellent results. It was taken with the iTelescope.net T11 telescope and, unfortunately, is degraded by slight trailing and poor focus. This may be a result of the relatively low altitude of the target. Despite the degradation, the image shows that the nebula remains relatively "bright" with a shape that has changed little in the last year.
Figure 23, taken 04 March 2014 with the iTelescope.net T11 instrument, still shows some image degradation. The image is based on ten 2 minute exposures stacked to give increased depth and reveal some of the background interstellar cloud.
Figure 24, taken one month after the previous image, with the iTelescope.net T11 instrument, shows no significant change in the nebula. At least the image isn't trailed.
Figure 25, another month, another image! The figure was captured on 03-04 May 2014 with the iTelescope.net T11 instrument. It comprises a stack of ten 2 minute exposures, which reduces the noise.
Figure 26 was taken on 19 January 2016 with my 30.5 cm astrograph and H16 CCD. It is a stack of 118x30 s exposures taken with a luminance filter.
Figure 27 was taken on 03 May 2017 with the SSON 0.51 m Gemini telescope. Five 180 s exposures. Figure 28 is a highly contrast-stretched negative of the image.
Figure 29 was taken on 20 April 2018 with my 30.5 cm astrograph and H16 CCD. 137x180 s exposures with luminance filter. Figure 30 is a highly contrast-stretched negative of the image. Figures 26-30 show a noticeable change in the shape of the nebula over the 2¼ year period.
Figure 31 was captured on 07 May 2018 with my 30.5 cm astrograph and H16 CCD. 161x30 s exposures with luminance filter.
Figure 32 was captured on 04 October 2018 with my 30.5 cm astrograph and H16 CCD. Astrodon LRGB filters 173:47:47:49x30 s exposures.
Figure 33 was captured on 02 November 2018 with my 30.5 cm astrograph shortly after its upgrade with a new Barlow corrector and the resulting increase in f-ratio to f6.8. H16 CCD. Luminance filter. 195x30 s exposures.
Figure 34 was taken on 04 January 2019 with the SSON 0.51 m Gemini telescope. Single 180 s exposure with luminance filter.
Figure 35 was taken on 11 February 2019 with my 30.5 cm astrograph and H16 CCD. 165x30 s exposures with luminance filter. FoV approx. 15x15 arcmin.
Figure 36 was taken during the period 04 January - 06 May 2019. It shows a slow fade of Gyulbudaghian’s variable nebula. I took the images with the University of Iowa 51 cm telescope in Arizona, using single 3 minute exposures. The images are noisy with some artefacts but show the fade clearly, although the last image was taken in poorer conditions than the first two so may exaggerate the effect.
Figure 37, taken on 01 August 2019 with my 30.5 cm astrograph and H16 CCD, shows the nebula recovering in brightness.
Figure 38 is a stack of all good images from late August and late September 2019, totalling four hours exposure over six nights. The resulting image is not dramatically better than usual, but is less noisy. There is an exceedingly faint "bubble" just below PV Cephei, the star at the point of the main nebula. The object may be an artefact, but there is nothing else like it in the field. Only time will tell if it's real...
Figure 39 is the result of a total of 133.5 minutes of imaging taken on 02 October 2019 with my 30.5 cm astrograph and H16 CCD. There is no sign of the "bubble" seen on the previous image: perhaps it was a transient effect or maybe just an artefact.
Figure 40 shows the nebula on 24 December 2019, imaged with the 30.5 cm astrograph and H16 CCD. Little change is evident in the nebula.
Figure 41, taken on 24 March 2020 with the 30.5 cm astrograph and H16 CCD, continues to show little change in the nebula.
Figure 42 is a selection of images taken with the 30.5 cm astrograph and H16 CCD, using an Astrodon luminance filter (400-700 nm). It shows the evolution of Gyulbudaghian's nebula through 2020, starting in March. (January and February were missed due to telescope downtime and, due to twilight in the UK, only a remote telescope image is available for June, omitted from the image.) Letters indicate months starting in March. Each field is 6x6 arcminutes with north up.
The fade of the nebula is clear in the image for August. The images for September and onwards show a dramatic dip in the brightness of PV Cephei and its recovery by the end of the year.
Figure 43 shows the nebula on 12 January 2021, imaged with the 30.5 cm astrograph and H16 CCD. Little change is evident in the nebula.
Figure 44, taken on 01 February 2021 with the 30.5 cm astrograph and H16 CCD, shows that the nebula may be starting to grow again. The small blob to the north-east of PV Cephei wasn't there in early January but has been visible for a few weeks now so may be the start of a revival...
Fig. 42. Evolution of the nebula March - December 2020. 30.5 cm f/3.6 astrograph.
Hind’s Varable Nebula (NGC1555) lies close to the Hyades star cluster in Taurus. It was discovered by John Russell Hind in October 1852 and was found to be variable within years of its discovery. The object next to it in the images below is the very young variable star T Tauri.
I captured figure 1 below from my home in 09 October 2008. Over four years later, on 07 January 2013, I used the SSON 81 cm reflector to capture figure 2. The nebula doesn’t appear to have changed significantly during the intervening period. (Note that, after I submitted the imaging request to the SSON, I realised that Jupiter was in the Hyades, close to the nebula. However the quality of the telescope and sky conditions on Mount Lemmon are such that the planet caused no serious glare in the image.)
I captured figure 3 with my 30 cm F4.1 astrograph on 04 December 2013. Figure 4 is a highly-stretched image taken on the same date which shows the dust cloud enveloping the nebula.
Figure 5 is a comparison of the image taken on 07 January 2013 (figure 2) with one captured in 2018 from the 2.0 m LCO Cassegrain at Siding Springs. The field of view is 5x5 arcminutes. Some change has evidently occurred in the five years between the two images: the single filament to the south-west (below-right of T Tauri) in 2013 is double in 2018.
Figure 6 extends the comparison of figure 5 by adding an image taken on 06 October 2019. The latest image was captured with the 0.51 m Gemini telescope in Arizona. Three 180 s exposures with luminance filter. The images have been scaled and rotated from the originals to provide a matching field of view which 9 x 9 arcminutes for each panel. The three images clearly show some small but significant changes in the nebula.
McNeil’s Nebula lies just south of M78 in Orion. It was discovered on 23 January 2004 by US amateur astronomer Jay McNeil. It is variable and brightened in late 2008.
I captured figure 1 below from my home in January 2009. (In the full image [not the thumbnail], M78 is overexposed to bring out faint detail in the nebula.) Four years later, on 04 January 2013, I used the SSON 81 cm reflector to capture figure 2. The nebula doesn’t appear to have changed significantly during the intervening period.
Almost one year later still, on 28 December 2013, I checked again for change, using the SSON 81 cm reflector. Figure 3 compares the appearance of the nebula on 04 January and 28 December 2013. There appears to have been little change in the intervening period.
A further five years later, on 05 November 2018, I captured an image with the University of Iowa 0.51 m Gemini telescope. This revealed a dramatic fade, the nebula being almost invisible. See figure 4. I contacted Nick Hewitt of the BAA who confirmed the disappearance in an image taken with iTelescope T24 on 06 November. Nick subsequently issued a BAA alert announcing the disappearance and asking for recent images of the region to check for visibility of the object. Nick had an image of the region from October 2017 which showed the nebula and I found an image on the LCO web site taken in March 2018 which also showed the nebula (but already fading?) Then Nick received an image from Richard Berry taken on 12 October 2018 which showed that the nebula had virtually disappeared. Unfortunately, Orion is too close to the Sun between April and September each year for images to be taken so the details of the fade over the summer may never be known.
Figure 5 compares four images spanning the period when the nebula disappeared:
Figure 6 shows the appearance of McNeil's Nebula on 04 January 2013 (taken from figure 3, above) and an inverted, annotated version marking the features discussed below. A paper in the Astrophysical Journal  discusses the outburst of the nebula in 2004 which led to its discovery. The authors identify S1 and S2 as young T Tauri type stars but it is star A that illuminates the nebula and holds the key to its behaviour. The star can increase in brightness by ~100 times over a period of a few months as it did in late 2003 to early 2004 and make the nebulosity B and C visible in amateur-sized telescopes. The paper explains why B and C exhibit contrasting colours; the contrast is shown well in an image of M78 together with the nebula in Sky at Night magazine . Recent observations show that star A can fade to its 'quiescent' state in similar timescales to those in which it can increase; when this happens it is simply too faint to illuminate the nebula, which disappears. Star A is now designated as variable star V1647 Orionis.
Historical images were examined when McNeil first discovered the nebula and it appears that, for most of the time from the early 1950s to the early 2000s, the nebula was invisible. Just one image from 1966  shows the nebula yet it was visible continuously from 2004 to 2018. So, its behaviour is far from regular and there is no way to predict how it will behave.
The fade of the nebula in summer 2018 was the first to be observed. Star A faded by about five magnitudes and is no longer bright enough to make the nebulosity visible in typical amateur sized telescopes (although very faint remnants of regions B and C are still visible in deep CCD images). It is not possible to predict when the nebula will become visible again.
Fig. 6. McNeil's Nebula on 04 January 2013 and an inverted, annotated version.
C. Briceno et. al., "McNeil's Nebula in Orion: The Outburst History”, The Astrophysical Journal 606: L123-L126 2004 May 10. http://iopscience.iop.org/article/10.1086/421395/fulltext/18263.text.html
Sky at Night magazine, December 2016, p. 6. Image with ESO VISTA telescope taken on 05 October 2016.
Image by Evered Kreimer, 20 October 1966, in The Messier Album, CUP 1979.
Hubble’s Variable Nebula is the most famous of the five variable nebulae visible in the northern hemisphere. It is located approximately 4° north-east of the Rosette Nebula in Monoceros and has a striking comet-like shape. Although it was discovered by William Herschel in 1783, it wasn't until 1916 that Edwin Hubble noticed changes in its structure when comparing photographs taken on different times.
I captured figure 1 from my home on 03 January 2009. Four years later, on 07 January 2013, I used the SSON 81 cm reflector to capture figure 2. The shape of the nebula appears to have changed slightly during the intervening period.
One year later still, on 28 December 2013, I decided to check again for change, using the SSON 81 cm reflector. Figure 3 compares the appearance of the nebula on 07 January and 28 December 2013. Change is apparent in structure close to the star at the base of the nebula but structure further out appears relatively unchanged.
On 21 February 2014, with the Moon not rising until after midnight, it was a good time to take another look at the nebula. I used the iTelescope.net T11 instrument to capture figure 4, based on five 3 minute exposures through a luminance filter. There are subtle changes in structure since my last image on 28 December 2013, showing that the nebula is well worth monitoring on a regular basis.
Figure 5 is an image taken on 18 September 2018 with the LCO 2.0 meter instrument on Haleakala. The field of view is 4x4 arcmins.
Thommes' Nebula is relatively recent addition to the group. It was discovered by a Californian amateur astronomer in November 2009 - see http://www.ifa.hawaii.edu/users/reipurth/PREPRINTS/ms_V900Mon.pdf for details. Although the nebula is not visually impressive, it does illustrate the fact that there are still things out there waiting to be discovered! The star V900 Mon and its associated nebula are in the centre of figure 1 below.
Figure 1 was captured on 11 January 2013 with the SSON 81 cm telescope. Five 120 s exposures. FoV is 11x11 arcmin.
Variable nebulae NGC6729, lying in the constellation Corona Australis at declination -37°, cannot be observed from the UK so I used remote telescopes to image it. It lies close to the irregular nebulae NGC6726 and NGC6727 and the globular cluster NGC6729, which appear in several of the images below.
Figure 1 is an all-sky image taken on 20 March 2013, one day before my first image of NGC6729. The position of the nebula is marked with a red arrow. Note the unexpected light pollution from the zodiacal light at top left!
Figure 2, taken on 21 March 2013, is the full field view from T30, showing NGC6729 at bottom left together with irregular nebulae NGC6726-7 and globular cluster NGC6723 at top right. (I deliberately offset the field to capture the latter.)
Figure 3, also taken on 21 March 2013, is an enlarged view showing detail in the variable nebula.
Figure 4, taken on 04 October 2013, was inspired by a presentation by Jeremy Shears, at the "The Astronomer" 2013 AGM, on Harold Knox-Shaw and the Helwan Observatory (see www.theastronomer.org/). In the presentation, Jeremy showed an image of NGC6729 taken by Knox-Shaw in Egypt early in the 20th Century. The image prompted me to make another observation of the object with T30 (figure 4,) and to compare it with the earlier image in figure 3. There appear to be some subtle changes between the two figures; however, note that figure 4 represents a first pass at a new image and I need to do further careful processing to confirm that the apparent changes are real. Unfortunately there are confounding factors: exposure times of the two images are slightly different (I didn’t book enough time to take all five exposures first time round!) and the orientation of the CCD on the telescope has been rotated through 90°.
Figure 5 was taken on 06 May 2014 with T30. Figure 6 is a composite image, comparing the nebula on three dates from early 2013 to early 2014 (specifically 21 March 2013, 04 October 2013 and 06 May 2014). There are clearly changes going on in the nebula, or at least in its illumination.
Figure 7, taken on 02 June 2014, is my first image with T27 (a 0.7 m astrograph). The telescope has a 3056 x 3056 pixel CCD which gives superb resolution throughout a 27x27 arcminute FoV. The image below is at half the original size. Figure 8 is a full resolution 5x5 arcminute view of the variable nebula itself.
Figure 9 was taken on 21 September 2018 with the LCO 2.0m Cassegrain at Siding Spring. It is a stack of four 30 second exposures. The Moon was just 35° away at the time.
I captured images with the following telescopes.
The latter five instruments are, in fact, evolutions of the same base telescope. The 30 cm, f4.3 mirror was the original one, but I also used a 34 cm, f4.3 mirror at around the same time. The latter never produced really good images, so I eventually abandoned it and used exclusively the former. I later purchased a prime focus corrector by Wynne which reduced the focal ratio from f/4.3 to f/4.1 and produced a wide, flat field, leading me to term the instrument an astrograph. Later, I upgraded the main mirror to 30.5 cm (actually 12.0"), f/3.8 which, with the corrector, gives f/3.6. In late 2018, I obtained a Barlow corrector which I used sometimes in place of the Wynne corrector; this almost doubled the focal length, giving a focal ratio f/6.8. (The Barlow corrector required a lens heater to keep the front lens free of dew.)