PLEIDES

On cold winter nights one of the most noticeable star groups is the Pleides, an open star cluster.  The Pleides group is sometimes mistaken for the little dipper, while in fact it is much smaller and nowhere near the North celestial pole.  The unaided eye can see 6 stars, which are all brighter than magnitude 6.  It is alleged that in ancient times 7 stars were easily seen, implying that one star has dimmed since then.  It is more likely that clearer skies, and better eyesight, account for this legend.

Figure 1.  The Pleides open star cluster is in the middle of this constellation-scale picture.  Constellation lines show Taurus on the left, the southern end of Perseus at the top, and the eastern end of Aries on the right.  The faintest stars shown are magnitude 10.  Saturn is inside the oval in Taurus.  Approximately 10,000 stars are present in this image.  The sky area is 27 x 18 degrees.  [Nikon F3, 75 mm FL, f/4; 2002.01.03/04; average of four 4-minute exposures; Santa Barbara ressidence.]

The original of the Fig. 1 image shows far more detail than this web page version.  For example, a tiny region north of the Pleides is shown blown-up 7 times in the next image.

In this deatil from the first image, notice the different star colors and distinct star widths.  The dim stars are "unsaturated" and have widths of 110 "arc (1.8 'arc).  The faintest stars are magnitude 11.

Figure 2. This image brings us closer to the Pleides than in Fig. 1, by factor 3.  The two-star "handle" is attached to the 5-star "cup" at a location marked by the brightest star in the group, Alcyone.  The "cup" part of the open cluster covers a sky area comparable to the full moon.  Sky area is 6.9 x 4.6 degrees. [Nikon F3, 300 mmFL, f/5.6, mounted to Meade LX-200 for tracking; avg of four 4-minute exposures, Fujifilm Superia X-tra 400; Santa Barbara residence; 2002.01.03/04.]

Figure 3. Closer by factor 2.4.  Detail of previoous image, covering sky area of 2.8 x 3.3 degrees.  Bluish nebulosity is faintly visible around two stars.  Faintest stars visible are magnitude 13.5.

Figure 4.  Same scale, but using different telephoto lens onsame camera.  The area shown is 4.0 degrees wide.  North is at the top.  [Average of two 5 -minute exposures with a 35-mm Nikon F3 film camera, with a Megrez 80 telescope lens (480 mm FL, f/6, semi-APO), attached to a Meade LX-200 telescope for tracking, using Fujifilm Superia X-tra 800 film; Santa Barbara residence, 200-foot altitude, 2001.10.14, 0720Z].

Figure 5.  Detail from previous picture, showing faint stars behind a blue nebulosity.  Faintest stars are magnitude 12.7, and appear as 24 arc second wide Gaussian distributions.

Figure 6.  Same scale approximately, but this and the following images were taken with an astronomy black-and-white CCD imager.  Mosaic of 9 images, each an average of two 20-second CCD exposures.  The 7 brightest stars are easily visible to the naked eye, with the brightest being 2.9 magnitude Alcyone, seen here in the middle of the image.  Alcyone is at the center of a circular nebulosity.  The star below and to the right is Merope, a 4th magnitude star, embedded in a different nebulosity (shown more clearly in the next image).

Figure 7.  Close-up of Alcyone and Merope, showing nebulosity around both stars.  Alcyone has a circular shell with a well-defined boundary with some radial structure inside, whereas Merope has lineaments with slight curvatures having no discernible distortion near Merope. [Average of eight 40-second exposures (equivalent to a well guided 5.3 minute single exposure), using the Meade Pictor 416XTE CCD imager with a Meade LX-200 10-inch Schmidt-Cassegrain telescope, taken 2000.10.30/31.]
 

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This site opened:  October 31, 2000.  Last Update:  January 9, 2002