The Pleiades, from Bill Gray's Project Pluto "Guide"... magnitudes of fainter stars shown
The Pleiades Star Cluster, known as Messier 45, often called the "Seven Sisters", is the most famous galactic star cluster in the heavens, revered from antiquity.
According to Richard Allen's "Star-Names and their Meanings", the Pleiades seem to be the among the first star mentioned in astronomical literature, appearing in Chinese annals of 2357 B.C. Job is thought to refer to them twice in his word Kimah. The Egyptians called them Chu and said that they represent the goddess Nit. Burnham's Celestial Handbook, Vol III relates an interesting American Indian legend connecting the Pleiades to Devil's Tower. The Kiowa say that the Tower was raised by the Great Spirit to protect seven Indian maidens pursued by giant bears, the maidens afterwards being placed in the heavens for protection, and the bears' claw marks seen today in the vertical striations on the Tower's sides. There are many wonderful references to the Pleiades in tradition and literature, I recommend reading the two books that I have cited.
The Pleiades is an open cluster drifting through space at a distance of 410 lightyears, in a SSE direction at an apparent rate of 6 arcseconds per century, or about 25 miles per second. In 30,000 years, the cluster will show an apparent drift the width of the Moon. The Pleiades are embedded in an interloper cloud of gas, not their birth gas. For more on this, see these articles, compiled by Sue French from the AmAstro mailing list:
"A Model for the Filamentary Structure in the Pleiades
Reflection Nebulosity", Thomas Arny, ApJ 217: 83-89, 1977
"An HI Cloud in the Pleiades: A Cloud-Cluster Collision", Kurtiis J. Gordon and Thomas T. Arny, AJ 89 #5, May 1984
"The Pleiades Cluster. IV. The Visit of a Molecular CO Cloud". Michel Breger, ApJ 319: 754-759, 1987 August 15
"Interstellar Matter Near the Pleiades. IV. The Wake of the Pleiades through the Interstellar Medium in Taurus". Richard E. White and John Bally, ApJ 409: 234-247, 1993 May 20
As with any challenging observing project, be prepared to spend many hours over weeks, months and years. Each time you come back, you will be a bit more familiar and see a tiny bit more. For instance, it was years before I succeeded in seeing the Cone Nebula in a 24". Most of the time, when observing at, or just beyond, the limits of what's observable, you will fail. But every so often, you succeed. Perhaps Skinner's chickens, pecking furiously at random reinforcement, at last have their revenge!
You must absolutely get to the darkest most transparent skies at highest altitude you possibly can. Wait until the Pleiades transits. Get a lawn chair and blanket and commit an hour or two each observing session.
Learn the positions of the Pleiades by studying star atlases. Just like you find the Andromeda Galaxy by finding the great square, then two over, then two up, know where to look in the Pleiades. Most star atlases that I have seen draw a fairly tight circle, about 1.5 degrees, around the Pleiades. Any star inside is countable.
Burnhams, in Volume III, page 1874, is correct when he states that,
"There are at least 20 star in the group which might be glimpsed under the finest conditions, having a brightness just below usual unaided-eye range;" This is true, but the next clause is not true, where he goes on to say,
"the crowded massing of the stars, however, makes this impossible." Actually, the star separations are far greater than the unaided-eye resolution of 1-2 arc minutes. You can test your own unaided-eye resolution by looking at Epsilon Lyra. You should see two adjoining specks of light. If you see clear black inbetween, your resolution limit is closer to 1 arc minute, if you see the specs as an elongated star, you resolution limit is closer to 3 arc minutes. The average resolution is supposed to be 2 arc minutes, but I have found when asking people at star parties to tell me what they see, most of them do not see clear black inbetween, indeed many do not see an elongation.
Break apart the Pleiades into regions. Start with the brightest four stars of the square: Alcyone, Merope, Maia, and Electra. Next find Taygeta, Celaeno, and Atlas. Right on top of Atlas is BU Tauri, a variable star that ranges from 4.8 to 5.5 magnitude.
Probably the biggest problem in going for faint stars in the Pleiades is the nebulosity. In good dark skies, you should see the Pleiades enveloped in a fairly bright solid glow. This is similar to the problem of the central star in the Ring Nebula, where it too is embedded in a faint glow of the ring's interior. The central star in the ring is supposedly at 15.5 to 16 magnitude, but it is more difficult than a stand alone 15.5 star to see. You can see faint stars in nebulosity, but it takes more effort and time.
Now, you are at 8 stars and ready for the next level. Just above Maia are two stars close together, 21 and 22 Tauri, at 5.8 and 6.4 magnitude. A little to the east is an unnamed 6.7 magnitude star, easier to see because it is by itself. The most extreme north star is 18 Tauri, a 5.6 magnitude star just on the edge of our circle.
Between Maia and Alcyone is a star of 7.1 magnitude. Just to the north of Alcyone is a line extending to the east of three stars, magnitudes 7.4, 7.3, and 6.2. South of Alcyone are two stars, magnitude 7.0 and 7.3. Much further to the south, right at the edge of our circle, is a 5.5 magnitude star. Between this star and 27 Tauri to the northeast are 3 stars of 6.1, 6.7, and 7.2 magnitude.
You are now over 20 stars in the count!
We have 11 stars brighter than 6.0,
14 stars brighter than 6.5,
16 stars brighter than 7.0,
and 22 stars brighter than 7.5.
In dark skies, you should catch 13-14 stars, in very dark skies, up to 17 stars, and in exception skies over the years, more than 20 stars.
My personal standard is to record three observations before I count it as real. An observation may only consist of a several second 'popping into view' in the most extreme cases.
Also, as time goes by, one gains a certain ability to guess how an observation might go. One can look at a field, and almost instantly tell if the observation is a possibility. There are many objects that Barbara Wilson, Stephen O'Meara, and the other gifted deep sky observers have seen, that I am still trying my darndest to see!