Wilhelm Tempel discovered NGC 1435, the Merope Nebula, on 19 Oct 1859 from Venice with his personal 4-inch Steinheil refractor using 45x. The following historical summary is from Wolfgang Steinicke's book "Observing and Cataloguing Nebulae and Star Clusters".

The Merope Nebula was the first deep sky object Tempel discovered. He initially thought it was a comet, but the next night (20th) he checked and found no movement. The discovery was published on 23 Dec 1860 (AN 54, 285). Christian August Peters, the editor of Astronomische Nachricten, confirmed the observation using a 7-inch refractor. Auwers first observed it on 14 Jan 1861, but d'Arrest was unsuccessful using the 11-inch Merz refractor at Copenhagen in Aug 1862. Based on his negative results on several attempts, he reported "I have hitherto been able positively to see nothing. ...I therefore, even yet, am of opinion that this nebula is variable, otherwise the original announcement of the discovery ... must be looked upon as been greatly exaggerated. This report began a heated interchange involving many of the world's most prominent visual observers over the next 30 years (see NGC 1555 = Hind's Variable Nebula for a similar situation).

In September 1862, Julius Schmidt supported d'Arrest, claiming if it was not variable he would have noticed it while carefully observing the Pleiades since 1841. He first reported a sighting on 5 Feb 1861, describing it as "very large, very pale and quite shapeless." Auwers responded critically to d'Arrest, claiming neither Tempel's (Merope) nebula nor NGC 1333 were variable but that "large, blurred, faint objects are much more easily visible in small instruments than in large ones" and d'Arrest's failure was due to "a small field of view, completely filled by the 15' large nebula". Charcornac at Paris Observatory also reported the nebula was difficult to see at high power. Sch?nfeld wrote that the nebula "instantly stuck out in the local telescope (6.5-inch refractor in Mannheim, Germany) on Sept 20, 1862 when I pointed it freely towards Merope, without knowing the exact place, looking like a blurred nebula with the shape and size described by Auwers."

d'Arrest responded to the attack on 12 Nov 1862 (AN 1393) stating "after a long effort I actually set eyes on Tempel's Nebula", though it was "the faintest object which I remember ever having seen in the refractor". He was "still convinced that the nebula was variable; otherwise the discovery report ["large, bright nebula"] must be seen as highly exaggerated." In March 1862, Winnecke viewed the nebula with a 4.1-inch refractor at low power and asked Otto Struve to take a look in the 15-inch Merz refractor, convinced that it would be difficult to see in the larger scope. Winnecke noted "Indeed, we were not convinced about its existence until the telescope was moved quickly back and forth". Winnecke concluded there was no reason to invoke variability to explain the observations. In 1863, Tempel wrote a letter to the French magazine Le Monde asserting that nebulae, in general, are unchanging (otherwise their constituent stars would have to be vary simultaneously) and that atmospheric conditions were the source of different observational results.

Reverend Thomas Webb observed the nebula on 6 Oct 1863 with his 5.5-inch Clark refractor, stating "on turning the telescope upon the group at 29x and 64x, though I probably should not have it discovered unknown, I found it with ease, as a very ill-defined, but on the whole egg-shaped haze, encompassing a brilliant star with its smaller but rather brighter end." As far as the variability "he [Sch?nfeld] thinks this and other suspected nebulae, being very feeble, large and diffuse, are influenced in visibility by magnifying power, varying transparency of the air, and practice of the eye, so that aperture is less concerned in their case than in that of minute stars." Although he never observed the nebula, John Herschel catalogued the Merope Nebula as GC 768 and his description stated "VAR" [variable].

The controversy about the variability and GC entry caused Lawrence Parsons (4th Earl of Rosse) to take a look with the 36-inch and 72-inch reflectors at Birr Castle, but he found no nebulosity in five observations from Feb 1871 to Sep 1873! Dreyer, himself, was unsuccessful (on a "misty" night) on 24 Dec 1875. The first (marginal) successful observation at Birr Castle was not made until 10 Dec 1877 and confirmed later that month.

The debate over variability wasn't settled. In 1875 Charles Wolf at Paris Observatory reported he was unable to see the Merope Nebula from Nov 1874 to Feb 1875 and Stephan at Marseille confirmed this. Wolf concluded, "This nebula is truly variable and its period seems to be rather short". But Tempel published another report in Jan 1877 (AN 2139) concluding, "the invisibility of the Merope Nebula in a large telescope is due to the eyepiece and its field of view. If d'Arrest had used an eyepiece of lower power than 95x, giving a field of 20 to 25'; he would have seen the nebula very easily." Tempel also made disparaging remarks about the large reflectors at Birr Castle, claiming the 36-inch and 72-inch didn't show more stars than his 11-inch Amici refractor (Tempel and Dreyer had a bitter dispute in 1878 about the "spiral form of nebulae", which Tempel couldn't see in his 11-inch).

On 6 Mar 1877, Maxwell Hall drew the nebula with his 4-inch refractor at 100x and was amazed it was invisible to Lord Rosse and Robert Newall, who had a 25-inch Cooke refractor. Hall was also critical of Schiaparelli's description of the orientation of the nebula. Hall's article touched off another debate between Wolf, Common, Hough, Tempel, Swift, Barnard and Burnham.

Charles Wolf published his work on the Pleiades and included a sketch made in Nov 1875. He saw nebulosity extending to Electra and Celaeno, by masking Merope with the micrometer bar. A much earlier report by Hermann Goldschmidt to Leverrier in Paris on 21 Sep 1863, claimed he saw not only the Merope nebula but that the Pleiades were completely surrounded by diffuse nebulosity, extending over an area of 5?.

In 1880, Ainslie Common published a drawing of the Pleiades nebulosity using his 36-inch reflector. It showed a large, elongated patch SE of Merope (the wrong direction!) and two additional patches; one north of Merope and another to the NW of Alcyone. This caused some more controversy.

In 1880, Tempel published (MNRAS, 40, 622) an excellent drawing of the nebula using Amici I, with accurate form and brightness levels, along with a large number of nearby faint stars. He mentioned the various astronomers who confirmed the object, including Schmidt, Winnecke Auwers and Sch?nfeld, and also opponents such as d'Arrest, Secchi and the Birr Castle observers. He stated "But all ambiguity has been since cleared up, for on fitting the large telescopes with eyepieces of a low magnifying power the nebula becomes distinctly visible, and is shown by them with image equal in clearness to that given by the smaller instrucments. He also criticized Goldschmidt's observation of the Pleiades surrounded by nebulous clouds and the drawing of Common, saying the sketch must have "evidently been executed with a telescope of insufficient power to show the Merope Nebula." He concluded with satisfaction "It is now ascertained beyond question that the nebula exists...and anyone publishing statements about its non-existence merely uses vain words, and proclaims himself wanting in knowledge of the history and nebulae and the management of telescopes."

Common was offended and responded the "three-foot telescope" mentioned in his report was of three-foot aperture! Hall wrote one more report on 13 Dec 1880, claiming the nebula had changed shape, now "extending as far as Electra, and the parabolic form of the Nebula, as seen 1877, was destroyed." He wondered why Tempel had overlooked the "extension of the nebula in the direction of Electra."

Amazingly, the controversy of the existence of the Merope Nebula wasn't over. At Dearborn Observatory in Chicago, Hough and Burnham had previously been critical of earlier reports, because of their discordant descriptions and their negative results in 1879 and 1880 using the 18.5-inch Clark refractor at 120x and higher. After Tempel's paper, they made a concerted effort from 29 Nov 1880 to 22 Mar 1891 with various eyepieces, stopping down the refractor to 12-inch, even masking Merope. But they came up empty and decided the previous positive observers were misled by the glare from Merope and the neighboring stars! Dreyer immediately responded, criticizing the large exit pupil used and furthermore he didn't see anything unusual about or contradictory about previous published reports of a "large and diffused nebulosity". Also, the theory about the glare from Merope causing an illusion was rejected. Swift also responded on 2 Dec 1881, that he independently ran across the Merope Nebula in 1874 while searching for comets with his 4.5-inch refractor and "strongly suspected it was a new comet." His analysis was that Hough and Burnham used too high of a power as he could see the nebula even stopped down to 2-inch aperture at 25x.

Barnard observed and drew the Merope Nebula and nearby stars with his 5-inch refractor in 1883. He wrote "it is plainly visible in my 5-inch refractory, it has been seen with a 2.5-inch telescope, in the presence of a quarter-full moon." He criticized Common's sketch but felt his sketch agreed with Tempel's (though it extended further west past Electra). Barnard also mentioned that Trouvelot reported that it is variable and had become very faint (he described the nebula as changing to a dim purplish color) and "can now be seen only by those acquainted with its former appearance"!

Paul and Prosper Henry first photographed the Pleiades on 16 Nov 1885 and revealed additional nebulosity around Maia, later catalogued as NGC 1432 (the only photographic discovery in the NGC) as well as faint nebulosity near Electra. In 1886 Charles Wolf published a comparison between the photographic image and the visual observations that showed significant changes in the Merope Nebula. Morever, the separate nebula observed by Goldschmidt and Wolf had disappeared but he concluded that photographic and visual observations can never be reconciled as objects invisible on photographs can exist visually. Surprisingly, the image most closely resembled the ridiculed drawing of Common. Common wrote that his sketch showed the Maia Nebula, however the connection is poor - his placement is closer to Alcyone than Maia.

The image encouraged others to search for addition nebulae in the Pleiades. On 26 Feb 1886, Spitaler and Palisa in Vienna reported the Maia nebula appeared as a "small flaky nebulosity, completely separated from Maia" and on 3 Mar, the former was "only the brightest knot of an extended nebulosity, completely covering Maia." Spitaler wrote "one can hardly refrain from thinking that at least the whole Pleiades region west and north of Alcyone is covered by an extended nebulosity, of which all previously perceived, apparently isolated nebulae, are merely bright knots of light."

On 23 Oct 1886 Isaac Roberts took a 3 hour exposure which revealed "not only are the stars [Alcyone, Maia, Electra, Merope] surrounded by nebulae, but the nebulosity extends in streamers and fleecy masses, till it seems almost to fill the spaces between the stars, and to extend far beyond them." Common again felt vindicated and repeated his treatment by Tempel, "who thought I had not used a sufficiently large telescope" (a misunderstanding by Tempel).

Another image was taken by the Henry brothers in 1888 showing extensive nebulosity. At an RAS meeting on 8 Jun 1888, Common says "I immediately compared my sketches with it and found that every star I had seen, except one, was there, and, of course, in their proper places." Robert Newall, who also attended the meeting, stated he was certain that his observations differed from Common with Merope appearing as an oval comet with Merope at the focus and he had not seen the additional patches claimed by Common.

In an 1888 issue of Knowledge, English astronomer Arthur Ranyard wrote an article titled "Great Nebula in the Pleiades" and stated "The observations are worth examining, as they throw some light on the differences which are always likely to exist when observations are pushed into the border-land of vision, where by reason of the extreme faintness or minuteness of the objects examined, the eye begins to fail, and the imagination begins to play a larger and larger part in filling up the gaps where the senses of the eye-straining observer fail him."

Maxwell Hall made a late interesting set of observations in 1889 in Jamaica. He compared the view of the Merope Nebula using a 9-inch reflector with a glass mirror and his 4-inch Cook refractor. He reported "a glance through the refractor showed the well-known nebula projected against the dark background or field of view; but in the reflector there was so much light scattered around the field of view that the nebula was invisible." He concluded this explained the positive sightings in smaller refractors and vice versa, the failure with larger reflectors (especially Lord Rosse's initial failures). In 1891, Spitaler reviewed the major observations of the Pleiades nebulae in a 20-page paper and created a remarkable map of the region, showing extensive nebulosity surrounding the Pleiades. He argues his map shows the main structures were correctly drawn and generally only the boundaries vary.

IC 349 is a knot of nebulosity just 0.6' SSE of Merope discovered and sketched by Barnard in 1890 using the 36-inch refractor at Lick. The discovery was published in AN 3018. See WSQJ July 1992. In terms of distance, Steinicke notes this is the closest NGC object.

200/250mm - 8" (10/4/80): very large, faint, very elongated tear-drop shaped nebulosity extending SW away from Merope. Has a sharper edge along the eastern side. Best view using the Rich Field Adapter at 37x-50x.

400/500mm - 17.5" (3/2/02): at 100x, the Merope Nebula is the brightest of the reflection nebulae that encase the Pleiades. It appears as a moderately bright, very large, fan-shaped cone of light extended in a wedge SW to SE from Merope. The boundary of the nebulosity is straighter and better defined along the SE edge where it follows a string of mag 10-11 stars. The SW border is not as well defined but extends beyond a trio of mag 13 stars. The fan is broadest at its southern extremity which is roughly 15' from Merope.

16x80 (12/22/84): the Merope nebula was faint but definite in the 16x80 finder using a Deep Sky filter. Also, nebulosity surrounding other stars were confirmed with confidence at full aperture in the 13.1" at 62x.

600/800mm - 24" (12/28/16): at 124x (unfiltered): the huge Merope Nebula was easily visible, roughly spanning 20' in a wedge or triangular shape with mag 4.2 Merope close to the northeast vertex. The most well defined edge is clearly the eastern side as it extends N-S. The edge passes close to a string of 7 stars oriented NNW-SSE, including two mag 10 stars and nearly reaches mag 8.1 HD 23512, which is 20' SSE of Merope. Just before reaching this star the nebulosity clearly curves to the west and extends ~20' generally northwest, passing north of mag 9.0 HD 23326, though the border is slightly less defined. At this point the edges of the nebulosity can be traced back east or ENE back to Merope, though the edge here is the least defined. The surface brightness of the interior is irregular with some slightly brighter patches and weaker areas.

Notes by Steve Gottlieb