9:22 PM 1/15/2023 Aldebaran Web Images News Blogs Scholar α Tau, 87 Tau, HD 29139, SAO 94027, HR 1457 Aldebaran, (α Tau / α Tauri / Alpha Tauri), is the brightest star in the constellation Taurus and one of the brightest stars in the nighttime sky. Because of its location in the head of Taurus, it has historically been called the Bull's Eye.Its name is derived from the Arabic الدبران al-dabarān meaning "the follower", a reference to the way the star follows the Pleiades star cluster in its nightly journey across the sky. Aldebaran has the appearance of being the brightest member of the more scattered Hyades cluster, which is the closest star cluster to Earth. However, it is merely located in the line of sight between the Earth and the Hyades, and is actually an independent star.Aldebaran is a K5 III star, which means it is orangish, large, and has moved off of the main sequence by using all its hydrogen fuel. It has a minor companion (a dim M2 dwarf orbiting at several hundred AU). Now primarily fusing helium, the main star has expanded to a diameter of approximately 5.3 × 107 km, or about 38 times the diameter of the Sun. The Hipparcos satellite has measured it as 65.1 light years away, and it shines with 150 times the Sun's luminosity. Taken together this distance and brightness makes it the 14th brightest star, having an apparent magnitude of 0.87. It is slightly variable, of the irregular variable type, by about 0.2 magnitude.In 1997, a possible large planet (or small brown dwarf) companion was reported, with a mass equalling that of 11 Jupiters and orbiting at a distance of 1.35 AU.Aldebaran is one of the easiest stars to find in the night sky, partly due to its brightness and partly due to its spatial relation to one of the more noticeable asterisms in the sky. If one follows the three stars of Orion's belt from left to right (in the Northern Hemisphere) or right to left (in the Southern), the first bright star found by continuing that line is Aldebaran.The unmanned Pioneer 10 spacecraft was last reported to have been heading toward Aldebaran. Assuming the spacecraft avoids some form of collision, the spacecraft will arrive at Aldebaran in 2 million years. Full Article Text available from Wikipedia under the terms of the GNU Free Documentation License More technical information on Aldebaran available from SIMBAD Location RA: 4h35m55.2s DEC: +16°30m33.0s 6:40 PM 12/7/2023 The star to the left is Aldebaran, a red giant star in the Taurus constellation. Located about 65 light years away, its proximity and the fact that it is 150 times as luminous as the Sun make it one of the brightest stars in the sky. The majority of the visible stars outside of the main sequence are red giants. These stars have exhausted the supply hydrogen in their cores, so they no longer have a source of energy to prevent gravitational collapse. As a result, their cores begin to contract. The energy released during this process ignites hydrogen burning in a shell around the core, causing their outer layers puff out (the source of the giant nomenclature) and cool down (which makes them appear red in optical light). The results of this process can be dramatic. For instance, despite having about 2.5 times the mass of our Sun, Arcturus has a radius nearly 25 times as large. With this greater surface area, the luminosity of the star increases tremendously; Aldebaran emits over 150 times the light of the Sun. When our own Sun enters its red giant phase, its radius will expand to just short of our current distance from the Sun. Our orbit will have taken us about 70% further from the Sun by that point, so the Earth won't be engulfed by the expansion. However, the increase in luminosity will be enough to boil off our oceans and atmosphere. Fortunately, this won't happen for another 4.5 billion years. Nearly all stars will go through some sort of red giant phase. What happens after that, however, depends on the star's mass. The most massive stars will eventually produce a supernova explosion, while those smaller than about twice the Sun's mass will end up as a planetary nebula. 6:40 PM 12/7/2023 6:44 PM 12/7/2023 Alnath Web Images News Blogs Scholar β Tau, 112 Tau, HD 35497, SAO 77168, HR 1791 Beta Tauri (β Tau / β Tauri) is the second brightest star in the constellation Taurus, with apparent magnitude 1.7. Because it is on the boundary of Taurus with Auriga, it also has the redundant Bayer designation Gamma Aurigae (γ Aur), which is today very rarely used. It also has the traditional name Elnath or El Nath.Relative to our Sun, this star is notable for a high abundance of manganese, but a paucity of calcium and magnesium. This star has begun to evolve away from the main sequence, becoming an orange giant.The traditional name is from the Arabic النطح an-naţħ "the butting" (i.e., with the bull's horns). As in many other (but not all) Arabic star names, the article ال is transliterated literally as el, despite the fact that in Arabic pronunciation it's assimilated to the following n. Full Article Text available from Wikipedia under the terms of the GNU Free Documentation License More technical information on Alnath available from SIMBAD Location RA: 5h26m17.5s DEC: +28°36m27.0s 6:45 PM 12/7/2023 6:59 PM 12/7/2023 ε Tau Web Images News Blogs Scholar 74 Tau, HD 28305, SAO 93954, HR 1409 Epsilon Tauri (ε Tau / ε Tauri) is a star in the constellation Taurus and a member of the Hyades open cluster. It has the traditional names Ain, or Oculus Borealus, both of which mean "eye".ε Tau belongs to the spectral class K0 and has apparent magnitude +3.6. It is 155 light years away from the Sun, has a luminosity of 90 times that of the Sun and a radius of 13 times solar. The surface temperature of this star is measured at 4925 kelvins. It has an 11th magnitude companion 182 arcseconds from the primary.Since ε Tau lies near the plane of the ecliptic, it is sometimes occulted by the Moon and (very rarely) by planets. Full Article Text available from Wikipedia under the terms of the GNU Free Documentation License More technical information on ε Tau available from SIMBAD Location RA: 4h28m37.0s DEC: +19°10m49.0s Distance Spectral Type 160 light-years G9.5IIICN0.5 6:59 PM 12/7/2023 6:46 PM 12/7/2023 ζ Tau Web Images News Blogs Scholar 123 Tau, HD 37202, SAO 77336, HR 1910 Zeta Tauri (ζ Tau / ζ Tauri) is a binary star in the constellation Taurus, the Bull. Known to the ancient Babylonians as Shurnarkabti-sha-shutu, meaning "the star in the bull towards the south," Zeta Tauri is among the most prominent of the stars in well-known constellation figures, representing one of the celestial bull's protruding horns. Defining mid-third magnitude (3.00), Zeta Tauri is a brilliant hot blue-white B-type giant star approximately 417 light years from Earth. It is classified as a Gamma Cassiopeiae type variable star. Its brightness varies from magnitude +2.88 to +3.17 due to both its intrinsic variablility, and also because it is an eclipsing binary. The two components of the binary system are separated by approximately one Astronomical Unit and complete an orbit once every 133 days. Its much lower mass companion star is a yellow G-type star, which has a magnitude of +5.2. A 9 solar mass star around 25 million years old, Zeta Tauri is now evolving, and is close to giving up core hydrogen fusion, if it has not done so already.It radiates the light of approximately 5,700 of our own sun from a surface heated to 22,000 kelvins. Together, temperature and luminosity yield a radius 5.2 times that of the Sun. What makes the star really special, however, is not its high temperature and luminosity, but its rotation and mass loss. The equatorial rotation speed has been measured as high as 330 kilometers per second, which is 115 times that of the Sun, the star spinning around with a period of only one day (as opposed to the 25-day solar rotation period). The rotation, which is still well short of that needed to break up the star, is somehow related to a thick disk of matter that surrounds it. The disk radiates bright emissions from hydrogen in the red and blue parts of the spectrum, making Zeta Tauri one the sky's best-known "B-emission" stars. The star and disk are both large enough to have had their angular diameters actually measured. The disk is some 64 solar diameters across. Full Article Text available from Wikipedia under the terms of the GNU Free Documentation License More technical information on ζ Tau available from SIMBAD Location RA: 5h37m38.7s DEC: +21°8m33.0s 6:46 PM 12/7/2023 7:54 PM 12/7/2023 Crab Nebula Web Images News Blogs Scholar Messier 1, NGC 1952 The Crab Nebula (catalogue designations M1, NGC 1952) is a supernova remnant in the constellation of Taurus. The nebula was first observed in 1731 by John Bevis. It is the remnant of a supernova that was recorded by Chinese and Arab astronomers in 1054. Located at a distance of about 6,300 light years (1.93 kpc) from Earth, the nebula has a diameter of 11 ly (1.84 pc) and is expanding at a rate of about 1,500 kilometres per second.The nebula contains a pulsar in its centre which rotates thirty times per second, emitting pulses of radiation from gamma rays to radio waves. Its discovery provided the first conclusive evidence that supernova explosions produce pulsars.The nebula acts as a source of radiation for studying celestial bodies that occult it. In the 1950s and 1960s, the Sun's corona was mapped from observations of the Crab's radio waves passing through it, and more recently, the thickness of the atmosphere of Saturn's moon Titan was measured as it blocked out X-rays from the nebula. Full Article Text available from Wikipedia under the terms of the GNU Free Documentation License More technical information on Crab Nebula available from the NASA/IPAC Extragalactic Database and SIMBAD Location RA: 5h34m32.0s DEC: +22°0m52.1s 7:54 PM 12/7/2023 6:57 PM 12/7/2023 θ1 Tau Web Images News Blogs Scholar 77 Tau, HD 28307, SAO 93955, HR 1411 Theta Tauri (θ Tau / θ Tauri) is a star system in the constellation Taurus and a member of the Hyades open cluster. It is approximately 155 light years from Earth.The system is dominated by two 3rd magnitude stars, θ¹ Tauri and θ² Tauri, which are separated by 5.62 arcminutes on the sky. θ¹ Tauri is the dimmer component, an orange K-type giant with an apparent magnitude of +3.84. θ² Tauri is a white A-type giant with a mean apparent magnitude of +3.40. θ² Tauri is classified as a Delta Scuti type variable star and its brightness varies from magnitude +3.35 to +3.42 with a period of 1.82 hours. Both bright stars are spectroscopic binaries and have at least one closer companion. θ¹ Tauri has a 7th magnitude companion 0.082 arcseconds, or at least 4 Astronomical Units (AU), away from the primary. θ² has a 6th magnitude companion 0.005 arcseconds, or at least 2 AU, distant. It completes an orbit once ever 141 days. Full Article Text available from Wikipedia under the terms of the GNU Free Documentation License More technical information on θ1 Tau available from SIMBAD Location RA: 4h28m34.5s DEC: +15°57m44.0s Distance Spectral Type 86 light-years K0IIIbFe-0.5 6:57 PM 12/7/2023 6:55 PM 12/7/2023 θ2 Tau Web Images News Blogs Scholar 78 Tau, HD 28319, SAO 93957, HR 1412 Theta Tauri (θ Tau / θ Tauri) is a star system in the constellation Taurus and a member of the Hyades open cluster. It is approximately 155 light years from Earth.The system is dominated by two 3rd magnitude stars, θ¹ Tauri and θ² Tauri, which are separated by 5.62 arcminutes on the sky. θ¹ Tauri is the dimmer component, an orange K-type giant with an apparent magnitude of +3.84. θ² Tauri is a white A-type giant with a mean apparent magnitude of +3.40. θ² Tauri is classified as a Delta Scuti type variable star and its brightness varies from magnitude +3.35 to +3.42 with a period of 1.82 hours. Both bright stars are spectroscopic binaries and have at least one closer companion. θ¹ Tauri has a 7th magnitude companion 0.082 arcseconds, or at least 4 Astronomical Units (AU), away from the primary. θ² has a 6th magnitude companion 0.005 arcseconds, or at least 2 AU, distant. It completes an orbit once ever 141 days. Full Article Text available from Wikipedia under the terms of the GNU Free Documentation License More technical information on θ2 Tau available from SIMBAD Location RA: 4h28m39.7s DEC: +15°52m15.0s Distance Spectral Type 110 light-years A7III 6:49 PM 12/7/2023 λ Tau Web Images News Blogs Scholar 35 Tau, HD 25204, SAO 93719, HR 1239 Lambda Tauri (λ Tau / λ Tauri) is a triple star system in the constellation Taurus. It is approximately 370 light years from Earth.The primary component, Lambda Tauri A, is a blue-white B-type main sequence dwarf with a mean apparent magnitude of +3.41. It has a luminosity of about 4,000 times that of the Sun and a radius of 6.6 times solar. The companion is a white A-type subgiant of 5.5 solar radii and 95 solar luminosities. They orbit around a common centre of gravity once every 3.95 days. The spatial separation between these two stars is measured at 0.1 astronomical unit.Because the system is an eclipsing binary its brightness varies from magnitude +3.37 to +3.91 as first one star and then the other pass in front of its companion. The system has a third, dimmer star with an orbital period of 33 days. Full Article Text available from Wikipedia under the terms of the GNU Free Documentation License More technical information on λ Tau available from SIMBAD Location RA: 4h0m40.8s DEC: +12°29m25.0s Distance Spectral Type 1630 light-years B3V+A4IV 6:50 PM 12/7/2023 6:52 PM 12/7/2023 ο Tau Web Images News Blogs Scholar 1 Tau, HD 21120, SAO 111172, HR 1030 Omicron Tauri (ο Tau / ο Tauri) is a star in the constellation Taurus.Omicron Tauri is a yellow G-type giant with an apparent magnitude of +3.61. It is approximately 212 light years from Earth. Full Article Text available from Wikipedia under the terms of the GNU Free Documentation License More technical information on ο Tau available from SIMBAD Location RA: 3h24m48.8s DEC: +9°1m44.0s Distance Spectral Type 200 light-years G6IIIFe-1 6:52 PM 12/7/2023 7:02 PM 12/7/2023 ψ Tau Web Images News Blogs Scholar 42 Tau, HD 25867, SAO 76461, HR 1269 Psi Tauri (ψ Tau / ψ Tauri) is a star in the constellation Taurus.Psi Tauri is a yellow-white F-type main sequence dwarf with an apparent magnitude of +5.21. It is approximately 90.0 light years from Earth. Full Article Text available from Wikipedia under the terms of the GNU Free Documentation License More technical information on ψ Tau available from SIMBAD Location RA: 4h7m0.5s DEC: +29°0m5.0s Spectral Type F1V 7:03 PM 12/7/2023 6:51 PM 12/7/2023 ξ Tau Web Images News Blogs Scholar 2 Tau, HD 21364, SAO 111195, HR 1038 Xi Tauri (ξ Tau / ξ Tauri) is a triple star system in the constellation Taurus. It is approximately 222 light years from Earth.Xi Tauri a spectroscopic and eclipsing triple star. It consists of three blue-white B-type main sequence dwarfs. Two of the stars are in a close orbit and revolve around each other once every 7.15 days. These in turn orbit the third star once every 145 days. The mean combined apparent magnitude of the system is +3.73 but, because the stars eclipse one another during their orbits, it is classified as a variable star, and its brightness varies from magnitude +3.70 to +3.79. Full Article Text available from Wikipedia under the terms of the GNU Free Documentation License More technical information on ξ Tau available from SIMBAD Location RA: 3h27m10.2s DEC: +9°43m58.0s Spectral Type B9Vn 6:51 PM 12/7/2023 7:01 PM 12/7/2023 φ Tau Web Images News Blogs Scholar 52 Tau, HD 27382, SAO 76558, HR 1348 Phi Tauri (φ Tau / φ Tauri) is a binary star in the constellation Taurus. It is approximately 342 light years from Earth.The primary component, Phi Tauri A, is an orange K-type giant with an apparent magnitude of +4.97. The companion star has a magnitude of +8.5 and is 52 arcseconds from the primary. Full Article Text available from Wikipedia under the terms of the GNU Free Documentation License More technical information on φ Tau available from SIMBAD Location RA: 4h20m21.3s DEC: +27°21m3.0s Spectral Type K1III 7:01 PM 12/7/2023 Pleiades Web Images News Blogs Scholar Messier 45 The Pleiades - also known as M45 or the Seven Sisters - Alcyone Eta Tau (25) Atlas (Father) 27 Tau Electra 17 Tau Maia 20 Tau Merope 23 Tau Taygeta 19 Tau Pleione (Mother) 28 Tau Celeano 16 Tau Asterope (Sterope I and II) 21 Tau is the name of an open cluster in the constellation of Taurus. It is among the nearest to the Earth of all open clusters, probably the best known and certainly the most striking to the naked eye. This asterism is sometimes referred to as the Maia Nebula, perhaps erroneously considering that the reflection nebulosity surrounding Maia is extrinsic (see below). More technical information on Pleiades available from the NASA/IPAC Extragalactic Database and SIMBAD Location RA: 3h47m10s DEC: +24°7m32s Merope Nebula Web Images News Blogs Scholar NGC 1435 NGC 1435 is a reflection nebula in the Pleiades open cluster in the constellation of Taurus. It was discovered by Wilhelm Tempel in October 19, 1859. The nebula consists of dust left over from the formation of the cluster, which reflects the blue starlight of the hot young stars. It shows up clearly on long-exposure photographs, and may be visible to the naked eye from the darkest observing sites. Full Article Text available from Wikipedia under the terms of the GNU Free Documentation License More technical information on Merope Nebula available from the NASA/IPAC Extragalactic Database and SIMBAD Location RA: 3h46m10.0s DEC: +23°45m54.0s 7:04 PM 12/7/2023 η Tau Web Images News Blogs Scholar 25 Tau, HD 23630, SAO 76199, HR 1165 Alcyone (η Tau / η Tauri / Eta Tauri) is a star system in the constellation Taurus. It is the brightest star in the Pleiades open cluster. Alcyone is approximately 440 light years from Earth. Full Article Text available from Wikipedia under the terms of the GNU Free Documentation License More technical information on η Tau available from SIMBAD Location RA: 3h47m29.1s DEC: +24°6m18.0s Distance Spectral Type 410 light-years B7IIIe 7:04 PM 12/7/2023 6:32 PM 12/7/2023 Known pre-historically. Mentioned by Homer about 750 B.C., by biblical Amos about 750 B.C., and by Hesiod about 700 B.C. The Pleiades, also known as Messier 45 (M45), are among those objects which are known since the earliest times. At least 6 member stars are visible to the naked eye, while under moderate conditions this number increases to 9, and under clear dark skies jumps up to more than a dozen (Vehrenberg, in his Atlas of Deep Sky Splendors, mentions that in 1579, well before the invention of the telescope, astronomer Moestlin has correctly drawn 11 Pleiades stars, while Kepler quotes observations of up to 14). Modern observing methods have revealed that at least about 500 mostly faint stars belong to the Pleiades star cluster, spread over a 2 degree (four times the diameter of the Moon) field. Their density is pretty low, compared to other open clusters. This is one reason why the life expectation of the Pleiades cluster is also pretty low (see below). According to Kenneth Glyn Jones, the earliest known references to this cluster are mentionings by Homer in his Ilias (about 750 B.C.) and his Odyssey (about 720 B.C.), and by Hesiod, about 700 B.C.. According to Burnham, they were seen in connection to the agricultural seasons of that time. Also, and the Bible has three references to the Pleiades (the Hebrew "Kiymah"): Job 9:7-9, Job 38:31-33, and Amos 5:8; the prophet Amos is believed to have given his message in 750 B.C. or 749 B.C., while there is no consent on the dating of the book of Job: Some believe it was written about 1,000 B.C. (the regency of Kings David and Solomon in old Israel) or earlier (Moses, about 13th to 16th century B.C.), others give reasons that it may have been created as late as the 3rd to 5th century B.C.. The present author [hf] does not know if the cluster is mentioned in one of the earlier Assyrian or Sumerian sources. The Pleiades also carry the name "Seven Sisters"; according to Greek mythology, seven daughters and their parents. Their Japanese name is "Subaru", which was taken to christen the car of same name. The Persian name is "Soraya", after which the former Iranian empress was named. Old European (e.g., English and German) names indicate they were once compared to a "Hen with Chicks". Other cultures tell more and other lore of this naked-eye star cluster. Ancient Greek astronomers Eudoxus of Knidos (c. 403-350 BC) and Aratos of Soloi (c. 310-245 BC), in his Phainomaina (c. 270 BC), listed them as an own constellation: The Clusterers. This is also referred to by Admiral Smyth in his Bedford Catalog. Burnham points out that the name "Pleiades" may be derived from either the Greek word for "to sail", or the word "pleios" meaning "full" or "many". The present author prefers the view that the name may be derived from the mythological mother, Pleione, which is also the name of one of the brighter stars. According to Greek mythology, the main, visible stars are named for the seven daughters of "father" Atlas and "mother" Pleione: Alcyone, Asterope (a double star, also sometimes called Sterope), Electra, Maia, Merope, Taygeta and Celaeno. Bill Arnett has created a map of the Pleiades with the main star names. These stars are also labeled in a labeled copy of the UKS image which appears in this page. Also note our Pleiades map. In 1767, Reverend John Michell used the Pleiades to calculate the probability to find such a group of stars in any place in the sky by chance alignment, and found the chance to be about 1/496,000. Therefore, and because there are more similar clusters, he concluded correctly that clusters should be physical groups (Michell 1767). On March 4, 1769, Charles Messier included the Pleiades as No. 45 in his first list of nebulae and star clusters, published 1771. About 1846, German astronomer Mädler (1794-1874), working at Dorpat, noticed that the stars of the Pleiades had no measurable proper motion relative to each other; from this he boldly concluded that they form a motionless center of a larger stellar system, with star Alcyone in the center. This conclusion was to be, and was, rejected by other astronomers, in particular Friedrich Georg Wilhelm Struve (1793-1864). Nevertheless, the common proper motion of the Pleiades was a proof that they move as a group in space, and a further hint that they form a physical cluster. Longer exposure photographs (and also short focal ratio, i.e. short focal length compared to their aperture, "rich field" telescopes of considerably good quality, especially good binoculars) have revealed that the Pleiades are apparently imbedded in nebulous material, obvious in our image, which was taken by David Malin with the UK Schmidt Telescope, and is copyrighted by the Royal Observatory Edinburgh and the Australian Astronomical Observatory. More information on this image is available. The Pleiades nebulae are blue-colored, which indicates that they are reflection nebulae, reflecting the light of the bright stars situated near (or within) them. The brightest of these nebulae, that around Merope, was discovered on October 19, 1859 by Ernst Wilhelm Leberecht (Wilhelm) Tempel at Venice (Italy) with a 4-inch refractor; it is included in the NGC as NGC 1435. Leos Ondra has made the biography of Wilhelm Tempel available online together with a drawing of the Merope Nebula, and has agreed to include it in this database. The extension to Maia was discovered by the brothers Paul and Prosper Henry in Paris on a photographic plate taken on November 16, 1885; this is NGC 1432 or the Maia Nebula. The nebulae around Alcyone, Electra, Celaeno and Taygeta were found on photographs in the later 1880s. The full complexity of the Pleiades nebulae was revealed by the first astro cameras, e.g. by that of the brothers Henry in Paris and Isaac Roberts in England, between 1885 and 1888. In 1890, E.E. Barnard discovered a starlike concentration of nebulous matter very close to Merope, which found its way into the IC as IC 349. The analysis of the spectra of the Pleiades nebulae by Vesto M. Slipher in 1912 reveiled their nature as reflection nebulae, as their spectra are exact copies of the spectra of the stars illuminating them. More information can be found in our table of the main Pleiades stars and the corresponding nebulosity with the catalog numbers. Physically, the reflection nebula is probably part of the dust in a molecular cloud, unrelated to the Pleiades cluster, which happens to cross the cluster's way. It is not a remainder of the nebula from which the cluster once formed, as can be seen from the fact that the nebula and cluster have different radial velocities, crossing each other with a relative velocity of 6.8 mps, or 11 km/sec. According to new calculations published by a team from Geneva (Meynet et.al. 1993), the age of the Pleiades star cluster amounts 100 million years. This is considerably more than the previously published "canonical" age of 60--80 million years (e.g., the Sky Catalog 2000's 78 million). It has been calculated that the Pleiades have an expected future lifetime as a cluster of only about another 250 million years (Kenneth Glyn Jones); after that time, they will have been spread as individual (or multiple) stars along their orbital path. The distance of the Pleiades cluster has been newly determined by direct parallax measures by ESA's astrometric satellite Hipparcos; according to these measurement, the Pleiades are at a distance of 380 light years (previously, a value of 408 light years had been assumed). This value would have required an explanation for the comparatively faint apparent magnitudes of the Pleiades stars. However, subsequent investigations with the Hubble Space Telescope and the Mount Palomar and Mount Wilson Observatories have finally shown that the Hipparcos distance is probably too small: By acurate parallaxes of Pleiades stars, this cluster is at a distance of 440 +/-6 light-years. The Trumpler classification is given for the Pleiades as II,3,r (Trumpler, according to Kenneth Glyn Jones) or I,3,r,n (Götz and Sky Catalog 2000), meaning that this cluster appears detached and strong or moderately concentrated toward its center, its stars are spread in a large range of brightness, and it is rich (has more than 100 members). Some of the Pleiades stars are rapidly rotating, at velocities of 150 to 300 km/sec at their surfaces, which is common among main sequence stars of a certain spectral type (A-B). Due to this rotation, they must be (oblate) spheroids rather than spherical bodies. The rotation can be detected because it leades to broadened and diffuse spectral absorption lines, as parts of the stellar surface approach us on the one side, while those on the opposite side recede from us, relative to the star's mean radial velocity. The most prominent example for a rapidly rotating star in this cluster is Pleione, which is also variable in brightness between mag 4.77 and 5.50 (Kenneth Glyn Jones). It was spectroscopically observed that between the years 1938 and 1952, Pleione has ejected a gas shell because of this rotation, as had been predicted by O. Struve. Cecilia Payne-Gaposhkin mentions that the Pleiades contain some white dwarf (WD) stars. These stars give rise to a specific problem of stellar evolution: How can white dwarfs exist in such a young star cluster ? As it is not only one, it is most certain that these stars are original cluster members and not all field stars which have been captured (a procedure which does not work effectively in the rather loose open clusters anyway). From the theory of stellar evolution, it follows that white dwarfs cannot have masses above a limit of about 1.4 solar masses (the Chandrasekhar limit), as they would collapse due to their own gravitation if they were more massive. But stars with such a low mass evolve so slow that it takes them billions of years to evolve into that final state, not only the 100 million year age of the Pleiades cluster. The only possible explanation seems to be that these WD stars were once massive so that they evolved fast, but due to some reason (such as strong stellar winds, mass loss to close neighbors, or fast rotation) have lost the greastest part of their mass. Possibly they have, in consequence, lost another considerable percentage of their mass in a planetary nebula. Anyway, the final remaining stars (which was previously the star's core) must have come below the Chandrasekhar limit, so that they could go into the stable white dwarf end state, in which they are now observed. New observations of the Pleiades since 1995 have revealed several candidates of an exotic type of stars, or starlike bodies, the so-called Brown Dwarfs. These hitherto hypothetical objects are thought to have a mass intermediate between that of giant planets (like Jupiter) and small stars (the theory of stellar structure indicates that the smallest stars, i.e. bodies that produce energy by fusion somewhen in their lifetime, must have at least about 6..7 percent of one solar mass, i.e. 60 to 70 Jupiter masses). So brown dwarfs should have 10 to about 60 times the mass of Jupiter. They are assumed to be visible in the infrared light, have a diameter of about or less that of Jupiter (143,000 km), and a density 10 to 100 times that of Jupiter, as their much stronger gravity presses them tougher together. Even with the naked eye and under modest conditions, the Pleiades are rather easily found, roughly 10 degrees north-west of the bright red-giant star Aldebaran (87 Alpha Tauri, mag 0.9, spectral type K5 III). Apparently surrounding Aldebaran is another, equally famous open cluster, the Hyades; Aldebaran is known to be a non-member foreground star (at 68 light years distance, compared to 150 ly for the Hyades). The cluster is a great object in binoculars and rich-field telescopes, showing more than 100 stars in a field about 1 1/5 degrees in diameter. In telescopes, it is frequently even too large to be seen in one lowest magnification field of view. A number of double and multiple stars are contained in the cluster. The Merope Nebula NGC 1435 requires a dark sky and is best visible in a rich-field telescope (Tempel had discovered it with a 4-inch telescope). As the Pleiades are situated close to the ecliptic (4 degrees off), occultations of the cluster by the Moon occur quite frequently: This is a very appealing spectacle, especially for amateurs with less expensive equipment (actually, you can observe it with the naked eye, but even the smallest binoculars or telescopes will increase observing pleasure -- the March 1972 Pleiad occultation was one of the first amateur astronomical experiences of the present author). Such events demonstrate the relations of the apparent sizes of the Moon and the cluster: Burnham points out that the Moon may be "inserted into the quadrangle formed by" Alcyone, Electra, Merope and Taygeta (Maia, and possibly Asterope, is occulted in this situation). Also, planets come close to the Pleiades cluster (Venus, Mars, and Mercury even occasionally pass through) to give a conspicuous spectacle. As mentioned in the description for the Orion Nebula M42, it is a bit unusual that Messier added the Pleiades (together with the Orion Nebula M42/M43 and the Praesepe cluster M44) to his catalog, and will perhaps stay subject to speculation. Historical Observations and Descriptions of M45 More images of M45 Amateur images of M45 X-ray image of M45 by Rosat Bill Arnett's M45 photo page, info page. Multispectral Image Collection of M45, SIRTF Multiwavelength Messier Museum Steven Gibson's Pleiades webpage, focussing on Pleiades mythology WEBDA cluster page for the Pleiades, M45 SIMBAD Data of M45 NED Data of M45 Publications on M45 (NASA ADS) Observing Reports for M45 (IAAC Netastrocatalog) NGC Online data for M45 References G. Meynet, J.-C. Mermilliod, and A. Maeder, 1993. New dating of galactic open clusters. Astronomy and Astrophysics Supplement Series, Vol. 98, pp. 477-504 [ADS: 1993A&AS...98..477M] John Michell, 1767. An Inquiry into the probable Parallax, and Magnitude, of the Fixed Stars, from the Quantity of Light which they afford us, and the particular Circumstances of their Situation. Philosophical Transactions of the Royal Society of London, Vol. 57, pp. 234-264 [ADS: 1767RSPT...57..234M] Hartmut Frommert Christine Kronberg SEDS.ORG 6:34 PM 12/7/2023