An open cluster is a group of up to a few thousand stars that were formed from the same giant molecular cloud and have the same age. More than 1,100 open clusters have been discovered within the Milky Way Galaxy, many more are thought to exist, they are loosely bound by mutual gravitational attraction and become disrupted by close encounters with other clusters and clouds of gas as they orbit the galactic center. This can result in a migration to the main body of the galaxy and a loss of cluster members through internal close encounters. Open clusters survive for a few hundred million years, with the most massive ones surviving for a few billion years. In contrast, the more massive globular clusters of stars exert a stronger gravitational attraction on their members, can survive for longer. Open clusters have been found only in spiral and irregular galaxies, in which active star formation is occurring. Young open clusters may be contained within the molecular cloud from which they formed, illuminating it to create an H II region.
Over time, radiation pressure from the cluster will disperse the molecular cloud. About 10% of the mass of a gas cloud will coalesce into stars before radiation pressure drives the rest of the gas away. Open clusters are key objects in the study of stellar evolution; because the cluster members are of similar age and chemical composition, their properties are more determined than they are for isolated stars. A number of open clusters, such as the Pleiades, Hyades or the Alpha Persei Cluster are visible with the naked eye; some others, such as the Double Cluster, are perceptible without instruments, while many more can be seen using binoculars or telescopes. The Wild Duck Cluster, M11, is an example; the prominent open cluster the Pleiades has been recognized as a group of stars since antiquity, while the Hyades forms part of Taurus, one of the oldest constellations. Other open clusters were noted by early astronomers as unresolved fuzzy patches of light; the Roman astronomer Ptolemy mentions the Praesepe, the Double Cluster in Perseus, the Ptolemy Cluster, while the Persian astronomer Al-Sufi wrote of the Omicron Velorum cluster.
However, it would require the invention of the telescope to resolve these nebulae into their constituent stars. Indeed, in 1603 Johann Bayer gave three of these clusters designations; the first person to use a telescope to observe the night sky and record his observations was the Italian scientist Galileo Galilei in 1609. When he turned the telescope toward some of the nebulous patches recorded by Ptolemy, he found they were not a single star, but groupings of many stars. For Praesepe, he found more than 40 stars. Where observers had noted only 6-7 stars in the Pleiades, he found 50. In his 1610 treatise Sidereus Nuncius, Galileo Galilei wrote, "the galaxy is nothing else but a mass of innumerable stars planted together in clusters." Influenced by Galileo's work, the Sicilian astronomer Giovanni Hodierna became the first astronomer to use a telescope to find undiscovered open clusters. In 1654, he identified the objects now designated Messier 41, Messier 47, NGC 2362 and NGC 2451, it was realised as early as 1767 that the stars in a cluster were physically related, when the English naturalist Reverend John Michell calculated that the probability of just one group of stars like the Pleiades being the result of a chance alignment as seen from Earth was just 1 in 496,000.
Between 1774–1781, French astronomer Charles Messier published a catalogue of celestial objects that had a nebulous appearance similar to comets. This catalogue included 26 open clusters. In the 1790s, English astronomer William Herschel began an extensive study of nebulous celestial objects, he discovered. Herschel conceived the idea that stars were scattered across space, but became clustered together as star systems because of gravitational attraction, he divided the nebulae into eight classes, with classes VI through VIII being used to classify clusters of stars. The number of clusters known continued to increase under the efforts of astronomers. Hundreds of open clusters were listed in the New General Catalogue, first published in 1888 by the Danish-Irish astronomer J. L. E. Dreyer, the two supplemental Index Catalogues, published in 1896 and 1905. Telescopic observations revealed two distinct types of clusters, one of which contained thousands of stars in a regular spherical distribution and was found all across the sky but preferentially towards the centre of the Milky Way.
The other type consisted of a sparser population of stars in a more irregular shape. These were found in or near the galactic plane of the Milky Way. Astronomers dubbed the former globular clusters, the latter open clusters; because of their location, open clusters are referred to as galactic clusters, a term, introduced in 1925 by the Swiss-American astronomer Robert Julius Trumpler. Micrometer measurements of the positions of stars in clusters were made as early as 1877 by the German astronomer E. Schönfeld and further pursued by the American astronomer E. E. Barnard prior to his death in 1923. No indication of stellar motion was detected by these efforts. However, in 1918 the Dutch-American astronomer Adriaan van Maanen was able to measure the proper motion of stars in part of the Pleiades cluster by comparing photographic plates taken at different times; as astrometry became more accurate, cluster stars were found to share a common proper motion through space. By comparing the photographic plates of the Pleiades cluster taken in 1918 with images taken in 1943, van
A constellation is a group of stars that forms an imaginary outline or pattern on the celestial sphere representing an animal, mythological person or creature, a god, or an inanimate object. The origins of the earliest constellations go back to prehistory. People used them to relate stories of their beliefs, creation, or mythology. Different cultures and countries adopted their own constellations, some of which lasted into the early 20th century before today's constellations were internationally recognized. Adoption of constellations has changed over time. Many have changed in shape; some became popular. Others were limited to single nations; the 48 traditional Western constellations are Greek. They are given in Aratus' work Phenomena and Ptolemy's Almagest, though their origin predates these works by several centuries. Constellations in the far southern sky were added from the 15th century until the mid-18th century when European explorers began traveling to the Southern Hemisphere. Twelve ancient constellations belong to the zodiac.
The origins of the zodiac remain uncertain. In 1928, the International Astronomical Union formally accepted 88 modern constellations, with contiguous boundaries that together cover the entire celestial sphere. Any given point in a celestial coordinate system lies in one of the modern constellations; some astronomical naming systems include the constellation where a given celestial object is found to convey its approximate location in the sky. The Flamsteed designation of a star, for example, consists of a number and the genitive form of the constellation name. Other star patterns or groups called asterisms are not constellations per se but are used by observers to navigate the night sky. Examples of bright asterisms include the Pleiades and Hyades within the constellation Taurus or Venus' Mirror in the constellation of Orion.. Some asterisms, like the False Cross, are split between two constellations; the word "constellation" comes from the Late Latin term cōnstellātiō, which can be translated as "set of stars".
The Ancient Greek word for constellation is ἄστρον. A more modern astronomical sense of the term "constellation" is as a recognisable pattern of stars whose appearance is associated with mythological characters or creatures, or earthbound animals, or objects, it can specifically denote the recognized 88 named constellations used today. Colloquial usage does not draw a sharp distinction between "constellations" and smaller "asterisms", yet the modern accepted astronomical constellations employ such a distinction. E.g. the Pleiades and the Hyades are both asterisms, each lies within the boundaries of the constellation of Taurus. Another example is the northern asterism known as the Big Dipper or the Plough, composed of the seven brightest stars within the area of the IAU-defined constellation of Ursa Major; the southern False Cross asterism includes portions of the constellations Carina and Vela and the Summer Triangle.. A constellation, viewed from a particular latitude on Earth, that never sets below the horizon is termed circumpolar.
From the North Pole or South Pole, all constellations south or north of the celestial equator are circumpolar. Depending on the definition, equatorial constellations may include those that lie between declinations 45° north and 45° south, or those that pass through the declination range of the ecliptic or zodiac ranging between 23½° north, the celestial equator, 23½° south. Although stars in constellations appear near each other in the sky, they lie at a variety of distances away from the Earth. Since stars have their own independent motions, all constellations will change over time. After tens to hundreds of thousands of years, familiar outlines will become unrecognizable. Astronomers can predict the past or future constellation outlines by measuring individual stars' common proper motions or cpm by accurate astrometry and their radial velocities by astronomical spectroscopy; the earliest evidence for the humankind's identification of constellations comes from Mesopotamian inscribed stones and clay writing tablets that date back to 3000 BC.
It seems that the bulk of the Mesopotamian constellations were created within a short interval from around 1300 to 1000 BC. Mesopotamian constellations appeared in many of the classical Greek constellations; the oldest Babylonian star catalogues of stars and constellations date back to the beginning in the Middle Bronze Age, most notably the Three Stars Each texts and the MUL. APIN, an expanded and revised version based on more accurate observation from around 1000 BC. However, the numerous Sumerian names in these catalogues suggest that they built on older, but otherwise unattested, Sumerian traditions of the Early Bronze Age; the classical Zodiac is a revision of Neo-Babylonian constellations from the 6th century BC. The Greeks adopted the Babylonian constellations in the 4th century BC. Twenty Ptolemaic constellations are from the Ancient Near East. Another ten have the same stars but different names. Biblical scholar, E. W. Bullinger interpreted some of the creatures mentioned in the books of Ezekiel and Revelation as the middle signs of the four quarters of the Zodiac, with the Lion as Leo, the Bull as Taurus, the Man representing Aquarius and the Eagle standing in for Scorpio.
The biblical Book of Job also
Auriga is one of the 88 modern constellations. Located north of the celestial equator, its name is the Latin word for “the charioteer”, associating it with various mythological beings, including Erichthonius and Myrtilus. Auriga is most prominent during winter evenings in the northern Hemisphere, along with the five other constellations that have stars in the Winter Hexagon asterism; because of its northern declination, Auriga is only visible in its entirety as far as 34° south. A large constellation, with an area of 657 square degrees, it is half the size of the largest constellation, Hydra, its brightest star, Capella, is an unusual multiple star system among the brightest stars in the night sky. Beta Aurigae is an interesting variable star in the constellation; because of its position near the winter Milky Way, Auriga has many bright open clusters in its borders, including M36, M37, M38, popular targets for amateur astronomers. In addition, it has one prominent nebula, the Flaming Star Nebula, associated with the variable star AE Aurigae.
In Chinese mythology, Auriga's stars were incorporated into several constellations, including the celestial emperors' chariots, made up of the modern constellation's brightest stars. Auriga is home to the radiant for the Aurigids, Zeta Aurigids, Delta Aurigids, the hypothesized Iota Aurigids; the first record of Auriga's stars was in Mesopotamia as a constellation called GAM, representing a scimitar or crook. However, this may have represented just the modern constellation as a whole. GAM in the MUL. APIN; the crook of Auriga shepherd. It was formed from most of the stars of the modern constellation. Bedouin astronomers created constellations that were groups of animals, where each star represented one animal; the stars of Auriga comprised a herd of goats, an association present in Greek mythology. The association with goats carried into the Greek astronomical tradition, though it became associated with a charioteer along with the shepherd. In Greek mythology, Auriga is identified as the mythological Greek hero Erichthonius of Athens, the chthonic son of Hephaestus, raised by the goddess Athena.
Erichthonius was credited to be the inventor of the quadriga, the four-horse chariot, which he used in the battle against the usurper Amphictyon, the event that made Erichthonius the king of Athens. His chariot was created in the image of the Sun's chariot, the reason Zeus placed him in the heavens; the Athenian hero dedicated himself to Athena and, soon after, Zeus raised him into the night sky in honor of his ingenuity and heroic deeds. Auriga, however, is sometimes described as Myrtilus, Hermes's son and the charioteer of Oenomaus; the association of Auriga and Myrtilus is supported by depictions of the constellation, which show a chariot. Myrtilus's chariot was destroyed in a race intended for suitors to win the heart of Oenomaus's daughter Hippodamia. Myrtilus earned his position in the sky when Hippodamia's successful suitor, killed him, despite his complicity in helping Pelops win her hand. After his death, Myrtilus's father Hermes placed him in the sky, yet another mythological association of Auriga is Theseus's son Hippolytus.
He was ejected from Athens after he refused the romantic advances of his stepmother Phaedra, who committed suicide as a result. He was revived by Asclepius. Regardless of Auriga's specific representation, it is that the constellation was created by the ancient Greeks to commemorate the importance of the chariot in their society. An incidental appearance of Auriga in Greek mythology is as the limbs of Medea's brother. In the myth of Jason and the Argonauts, as they journeyed home, Medea killed her brother and dismembered him, flinging the parts of his body into the sea, represented by the Milky Way; each individual star represents a different limb. Capella is associated with the mythological she-goat Amalthea, it forms an asterism with the stars Epsilon Aurigae, Zeta Aurigae, Eta Aurigae, the latter two of which are known as the Haedi. Though most associated with Amalthea, Capella has sometimes been associated with Amalthea's owner, a nymph; the myth of the nymph says that the goat's hideous appearance, resembling a Gorgon, was responsible for the Titans' defeat, because Zeus skinned the goat and wore it as his aegis.
The asterism containing the three goats had been a separate constellation. Before that, Capella was sometimes seen as its own constellation—by Pliny the Elder and Manilius—called Capra, Caper, or Hircus, all of which relate to its status as the "goat star". Zeta Aurigae and Eta Aurigae were first called the "Kids" by Cleostratus, an ancient Greek astronomer. Traditionally, illustrations of Auriga represent it as its driver; the charioteer has two kids under his left arm. However, depictions of Auriga have been inconsistent over the years; the reins in his right hand have been drawn as a whip, though Capella is always over his left shoulder and the Kids under his left arm. The 1488 atlas Hyginus deviated from this typical depiction by showing a four-wheeled cart driven by Auriga
Right ascension is the angular distance of a particular point measured eastward along the celestial equator from the Sun at the March equinox to the point above the earth in question. When paired with declination, these astronomical coordinates specify the direction of a point on the celestial sphere in the equatorial coordinate system. An old term, right ascension refers to the ascension, or the point on the celestial equator that rises with any celestial object as seen from Earth's equator, where the celestial equator intersects the horizon at a right angle, it contrasts with oblique ascension, the point on the celestial equator that rises with any celestial object as seen from most latitudes on Earth, where the celestial equator intersects the horizon at an oblique angle. Right ascension is the celestial equivalent of terrestrial longitude. Both right ascension and longitude measure an angle from a primary direction on an equator. Right ascension is measured from the Sun at the March equinox i.e. the First Point of Aries, the place on the celestial sphere where the Sun crosses the celestial equator from south to north at the March equinox and is located in the constellation Pisces.
Right ascension is measured continuously in a full circle from that alignment of Earth and Sun in space, that equinox, the measurement increasing towards the east. As seen from Earth, objects noted to have 12h RA are longest visible at the March equinox. On those dates at midnight, such objects will reach their highest point. How high depends on their declination. Any units of angular measure could have been chosen for right ascension, but it is customarily measured in hours and seconds, with 24h being equivalent to a full circle. Astronomers have chosen this unit to measure right ascension because they measure a star's location by timing its passage through the highest point in the sky as the Earth rotates; the line which passes through the highest point in the sky, called the meridian, is the projection of a longitude line onto the celestial sphere. Since a complete circle contains 24h of right ascension or 360°, 1/24 of a circle is measured as 1h of right ascension, or 15°. A full circle, measured in right-ascension units, contains 24 × 60 × 60 = 86400s, or 24 × 60 = 1440m, or 24h.
Because right ascensions are measured in hours, they can be used to time the positions of objects in the sky. For example, if a star with RA = 1h 30m 00s is at its meridian a star with RA = 20h 00m 00s will be on the/at its meridian 18.5 sidereal hours later. Sidereal hour angle, used in celestial navigation, is similar to right ascension, but increases westward rather than eastward. Measured in degrees, it is the complement of right ascension with respect to 24h, it is important not to confuse sidereal hour angle with the astronomical concept of hour angle, which measures angular distance of an object westward from the local meridian. The Earth's axis rotates westward about the poles of the ecliptic, completing one cycle in about 26,000 years; this movement, known as precession, causes the coordinates of stationary celestial objects to change continuously, if rather slowly. Therefore, equatorial coordinates are inherently relative to the year of their observation, astronomers specify them with reference to a particular year, known as an epoch.
Coordinates from different epochs must be mathematically rotated to match each other, or to match a standard epoch. Right ascension for "fixed stars" near the ecliptic and equator increases by about 3.05 seconds per year on average, or 5.1 minutes per century, but for fixed stars further from the ecliptic the rate of change can be anything from negative infinity to positive infinity. The right ascension of Polaris is increasing quickly; the North Ecliptic Pole in Draco and the South Ecliptic Pole in Dorado are always at right ascension 18h and 6h respectively. The used standard epoch is J2000.0, January 1, 2000 at 12:00 TT. The prefix "J" indicates. Prior to J2000.0, astronomers used the successive Besselian epochs B1875.0, B1900.0, B1950.0. The concept of right ascension has been known at least as far back as Hipparchus who measured stars in equatorial coordinates in the 2nd century BC, but Hipparchus and his successors made their star catalogs in ecliptic coordinates, the use of RA was limited to special cases.
With the invention of the telescope, it became possible for astronomers to observe celestial objects in greater detail, provided that the telescope could be kept pointed at the object for a period of time. The easiest way to do, to use an equatorial mount, which allows the telescope to be aligned with one of its two pivots parallel to the Earth's axis. A motorized clock drive is used with an equatorial mount to cancel out the Earth's rotation; as the equatorial mount became adopted for observation, the equatorial coordinate system, which includes right ascension, was adopted at the same time for simplicity. Equatorial mounts could be pointed at objects with known right ascension and declination by the use of setting circles; the first star catalog to use right ascen
Sloan Digital Sky Survey
The Sloan Digital Sky Survey or SDSS is a major multi-spectral imaging and spectroscopic redshift survey using a dedicated 2.5-m wide-angle optical telescope at Apache Point Observatory in New Mexico, United States. The project was named after the Alfred P. Sloan Foundation. Data collection began in 2000; the main galaxy sample has a median redshift of z = 0.1. Data release 8, released in January 2011, includes all photometric observations taken with the SDSS imaging camera, covering 14,555 square degrees on the sky. Data release 9, released to the public on 31 July 2012, includes the first results from the Baryon Oscillation Spectroscopic Survey spectrograph, including over 800,000 new spectra. Over 500,000 of the new spectra are of objects in the Universe 7 billion years ago. Data release 10, released to the public on 31 July 2013, includes all data from previous releases, plus the first results from the APO Galactic Evolution Experiment spectrograph, including over 57,000 high-resolution infrared spectra of stars in the Milky Way.
DR10 includes over 670,000 new BOSS spectra of galaxies and quasars in the distant universe. The publicly available images from the survey were made between 1998 and 2009. SDSS uses a dedicated 2.5 m wide-angle optical telescope. The imaging camera was retired in late 2009, since the telescope has observed in spectroscopic mode. Images were taken using a photometric system of five filters; these images are processed to produce lists of objects observed and various parameters, such as whether they seem pointlike or extended and how the brightness on the CCDs relates to various kinds of astronomical magnitude. For imaging observations, the SDSS telescope used the drift scanning technique, which tracks the telescope along a great circle on the sky and continuously records small strips of the sky; the image of the stars in the focal plane drifts along the CCD chip, the charge is electronically shifted along the detectors at the same rate, instead of staying fixed as in tracked telescopes.. This method allows consistent astrometry over the widest possible field, minimises overheads from reading out the detectors.
The disadvantage is minor distortion effects. The telescope's imaging camera is made up of 30 CCD chips, each with a resolution of 2048×2048 pixels, totaling 120 megapixels; the chips are arranged in 5 rows of 6 chips. Each row has a different optical filter with average wavelengths of 355.1, 468.6, 616.5, 748.1 and 893.1 nm, with 95% completeness in typical seeing to magnitudes of 22.0, 22.2, 22.2, 21.3, 20.5, for u, g, r, i, z respectively. The filters are placed on the camera in the order r, i, u, z, g. To reduce noise, the camera is cooled to 190 kelvins by liquid nitrogen. Using these photometric data, stars and quasars are selected for spectroscopy; the spectrograph operates by feeding an individual optical fibre for each target through a hole drilled in an aluminum plate. Each hole is positioned for a selected target, so every field in which spectra are to be acquired requires a unique plate; the original spectrograph attached to the telescope was capable of recording 640 spectra while the updated spectrograph for SDSS III can record 1000 spectra at once.
Over the course of each night, between six and nine plates are used for recording spectra. In spectroscopic mode, the telescope tracks the sky in the standard way, keeping the objects focused on their corresponding fibre tips; every night the telescope produces about 200 GB of data. During its first phase of operations, 2000–2005, the SDSS imaged more than 8,000 square degrees of the sky in five optical bandpasses, it obtained spectra of galaxies and quasars selected from 5,700 square degrees of that imaging, it obtained repeated imaging of a 300 square degree stripe in the southern Galactic cap. In 2005 the survey entered a new phase, the SDSS-II, by extending the observations to explore the structure and stellar makeup of the Milky Way, the SEGUE and the Sloan Supernova Survey, which watches after supernova Ia events to measure the distances to far objects; the survey covers over 7,500 square degrees of the Northern Galactic Cap with data from nearly 2 million objects and spectra from over 800,000 galaxies and 100,000 quasars.
The information on the position and distance of the objects has allowed the large-scale structure of the Universe, with its voids and filaments, to be investigated for the first time. All of these data were obtained in SDSS-I, but a small part of the footprint was finished in SDSS-II; the Sloan Extension for Galactic Understanding and Exploration obtained spectra of 240,000 stars in order to create a detailed three-dimensional map of the Milky Way. SEGUE data provide evidence for the age and phase space distribution of stars within the various Galactic components, providing crucial clues for understanding the structure, formation a
Frederick William Herschel, was a German-born British astronomer and brother of fellow astronomer Caroline Herschel, with whom he worked. Born in the Electorate of Hanover, Herschel followed his father into the Military Band of Hanover, before migrating to Great Britain in 1757 at the age of nineteen. Herschel constructed his first large telescope in 1774, after which he spent nine years carrying out sky surveys to investigate double stars. Herschel published catalogues of nebulae in 1802 and in 1820; the resolving power of the Herschel telescopes revealed that many objects called nebulae in the Messier catalogue were clusters of stars. On 13 March 1781 while making observations he made note of a new object in the constellation of Gemini; this would, after several weeks of verification and consultation with other astronomers, be confirmed to be a new planet given the name of Uranus. This was the first planet to be discovered since antiquity and Herschel became famous overnight; as a result of this discovery, George III appointed him Court Astronomer.
He was elected as a Fellow of the Royal Society and grants were provided for the construction of new telescopes. Herschel pioneered the use of astronomical spectrophotometry, using prisms and temperature measuring equipment to measure the wavelength distribution of stellar spectra. In addition, Herschel discovered infrared radiation. Other work included an improved determination of the rotation period of Mars, the discovery that the Martian polar caps vary seasonally, the discovery of Titania and Oberon and Enceladus and Mimas. Herschel was made a Knight of the Royal Guelphic Order in 1816, he was the first President of the Royal Astronomical Society when it was founded in 1820. He died in August 1822, his work was continued by his only son, John Herschel. Herschel was born in the Electorate of Hanover in Germany part of the Holy Roman Empire, one of ten children of Isaac Herschel by his marriage to Anna Ilse Moritzen, of German Lutheran ancestry, it has been proposed by Hershel's biographer Holden that his father's family traced its roots back to Jews from Moravia who converted to Christianity in the seventeenth century, they themselves were Lutheran Christians.
Herschel's father was an oboist in the Hanover Military Band. In 1755 the Hanoverian Guards regiment, in whose band Wilhelm and his brother Jakob were engaged as oboists, was ordered to England. At the time the crowns of Great Britain and Hanover were united under King George II; as the threat of war with France loomed, the Hanoverian Guards were recalled from England to defend Hanover. After they were defeated at the Battle of Hastenbeck, Herschel's father Isaak sent his two sons to seek refuge in England in late 1757. Although his older brother Jakob had received his dismissal from the Hanoverian Guards, Wilhelm was accused of desertion. Wilhelm, nineteen years old at this time, was a quick student of the English language. In England he went by the English rendition of Frederick William Herschel. In addition to the oboe, he played the violin and harpsichord and the organ, he composed numerous musical works, including 24 symphonies and many concertos, as well as some church music. Six of his symphonies were recorded in April 2002 by the London Mozart Players, conducted by Matthias Bamert.
Herschel moved to Sunderland in 1761 when Charles Avison engaged him as first violin and soloist for his Newcastle orchestra, where he played for one season. In "Sunderland in the County of Durh: apprill 20th 1761" he wrote his Symphony No. 8 in C Minor. He was head of the Durham Militia band from 1760 to 1761, he visited the home of Sir Ralph Milbanke at Halnaby Hall near Darlington in 1760, where he wrote two symphonies, as well as giving performances himself. After Newcastle, he moved to Leeds and Halifax where he was the first organist at St John the Baptist church. In 1766, Herschel became organist of the Octagon Chapel, Bath, a fashionable chapel in a well-known spa, in which city he was Director of Public Concerts, he was appointed as the organist in 1766 and gave his introductory concert on 1 January 1767. As the organ was still incomplete, he showed off his versatility by performing his own compositions including a violin concerto, an oboe concerto and a harpsichord sonata. On 4 October 1767, he performed on the organ for the official opening of the Octagon Chapel.
His sister Caroline arrived in England on 24 August 1772 to live with William in New King Street, Bath. The house they shared is now the location of the Herschel Museum of Astronomy. Herschel's brothers Dietrich and Jakob appeared as musicians of Bath. In 1780, Herschel was appointed director of the Bath orchestra, with his sister appearing as soprano soloist. Herschel's reading in natural philosophy during the 1770s indicates his personal interests but suggests an intention to be upwardly mobile and professionally, he was well-positioned to engage with eighteenth-century "philosophical Gentleman" or philomaths, of wide-ranging logical and practical tastes. Herschel's intellectual curiosity and interest in music led him to astronomy. After reading Robert Smith's Harmonics, or the Philosophy of Musical Sounds, he took up Smith's A Compleat System of Opticks, which described techniques of telescope construction, he read James Ferguson's Astronomy explained upon Sir Isaac Newton's principles and made easy to those who have not studied mathematics and William Emerson's The elements of trigonometry, The elements of optics a