Spring Sp Target Information

Home , M51 Group, Messier 37, NGC 2438, NGC 2800, NGC 3242

SPRING SP TARGET INFORMATION

MESSIER 45 (THE PLEIADES)

BASIC INFORMATION OBJECT TYPE: Open Cluster CONSTELLATION: Taurus BEST VIEW: Late January DISCOVERY: Known in Antiquity DISTANCE: 440 ly DIAMETER: 86 ly APPARENT MAGNITUDE: +1.6 APPARENT DIMENSIONS: 110’ AGE: ~100 million years

DISTANCE DETERMINATION Trigonometric parallax: As Earth orbits the Sun, the position of nearby objects will shift relative to more distant objects. Measuring this shift and applying simple trigonometry can yield the distance to the nearby object.

MS Cluster Fitting: The colors and magnitudes of cluster members are plotted on an H-R diagram. Specific features, such as the location of the main sequence, have known theoretical positions on the plot. Comparison of the observed position of these features to the theoretical position can yield the distance.

AGE DETERMINATION Astronomers plot the colors and magnitudes of cluster stars on an H-R diagram to get an overall picture of the evolutionary states of the cluster stars. This, in turn, allows astronomers to constrain the age of the cluster.

NOTABLE FEATURES/FACTS • The earliest reference to the Pleiades is by Homer in 750 B.C. • M45 is also known as “The Seven Sisters,” referring to the seven daughters of Atlas in Greek mythology. In Japan, the cluster is known as “Subaru.” • The Pleiades contains at least 1000 stars. • Nebulosity is evident in photographs and in views through large telescopes. The nebulosity is due to reflection off dust grains in a cloud through which the cluster is traveling. It is not a remnant of the cloud from which the stars formed, as previously thought. • Charles Messier cataloged this object on the night of 4 March 1769. There is speculation he added this object simply to boost the number of objects in his catalog to exceed that of his contemporary, Nicholas Louis de la Caille. • Many Pleiades stars appear blue, typical of hot, young stars. • M45 serves as one of the first rungs in the cosmic distance ladder. Accurate, direct determination of its distance allows calibration of other distance determination methods for more distant objects. • Astronomers have detected large amounts of dust surrounding one Pleiades member. The dust is thought to be the result of large collisions among bodies in a still forming solar system. SPRING SP TARGET INFORMATION

NGC 1535 (CLEOPATRA’S EYE)

BASIC INFORMATION OBJECT TYPE: Planetary Nebula CONSTELLATION: Eridanus BEST VIEW: February DISCOVERY: William Herschel, 1785 DISTANCE: 3960 – 7520 ly DIAMETER: Approximately 1 ly APPARENT MAGNITUDE: +10.5 APPARENT DIMENSIONS: 0.6’

DISTANCE DETERMINATION The distances to most planetary nebulae are very poorly known. A variety of methods can be used, providing mixed results. The range adopted above represents a variety of recent studies, using methods including:

Trigonometric Parallax – Measure the apparent shift of the central star relative to background stars as Earth orbits the Sun or as a spacecraft orbits Earth. Trigonometry yields the distance.

Statistical Analyses – Correlate measurable physical properties of the nebula with distance. This requires making some big assumptions, like that all planetary nebulae have similar properties.

Expansion Velocity – Measure the rate at which the nebula is expanding in physical units and angular measure. Trigonometry yields the distance.

NOTABLE FEATURES/FACTS • Cleopatra’s Eye is the remnant of a dying star that was about the same size as the Sun. When the Sun exhausts its fuel in about five billion years, it will produce a similar structure. • The central star is transitioning to a white dwarf. The energy from this central star causes the nebular material to glow. • The distinct blue color of the nebula is due to emission from ionized oxygen atoms. • The density of the nebular material indicates it is a relatively young object. The planetary nebula likely began forming just a few thousand years ago. • Upon discovering the star in 1845, J.R. Hind described it as looking “like a drop of blood on a black field.” • R Lep is currently about 500 times the size of the Sun. If placed at the center of our solar system, it would engulf the Earth and extend almost halfway to Jupiter.

SPRING SP TARGET INFORMATION

HIND’S CRIMSON STAR (R LEP)

BASIC INFORMATION OBJECT TYPE: Carbon Star CONSTELLATION : Lepus BEST VIEW: February DISCOVERY: J. R. Hind, 1845 DISTANCE: 1360 ly MASS: 2.5-5 MSOLAR APPARENT MAGNITUDE: +5.5 to +11.7*

*Magnitude estimates are based on the star’s 40-year cycle.

DISTANCE DETERMINATION After measuring the shift in position of the star relative to background stars as Earth orbits the Sun, simple trigonometry can yield the distance. The Gaia satellite was launched in 2013 to create a comprehensive catalog of trigonometric parallax measurements from space. The distance quoted above is from this catalog.

MASS DETERMINATION The mass quoted above is an estimate based on the average masses of this kind of star. A direct mass measurement is unavailable.

NOTABLE FEATURES/FACTS • R Lep is a Mira-type variable star. Its brightness varies by about four magnitudes (approx. +7 to +11) over a period of about 14.5 months. This variation is due to stellar pulsations common at the end of a star’s life. • Typically, R Lep is visible only with optical aid, but it also has a longer period of variation over about 40 years. At its brightest during this cycle, R Lep is just barely visible to the unaided eye. This variation is likely due to ejection of stellar material. • This star is in its final stages of evolution. It is currently expelling its outer layers into space and will ultimately form a planetary nebula. • Convection has dredged up large amounts of carbon from the core to the outer layers of the star. This carbon absorbs blue light, giving the star its distinct crimson color. • The redness of the star varies with its brightness. It looks most red when at its dimmest. • Upon discovering the star in 1845, J.R. Hind described it as looking “like a drop of blood on a black field.” • R Lep is currently about 500 times the size of the Sun. If placed at the center of our solar system, it would engulf the Earth and extend almost halfway to Jupiter. SPRING SP TARGET INFORMATION

MESSIER 79

BASIC INFORMATION OBJECT TYPE: Globular Cluster CONSTELLATION: Lepus BEST VIEW: Late February DISCOVERY: Pierre Mechain, 1780 DISTANCE: 42,000 ly DIAMETER: 115 ly MASS: 200,000 MSUN APPARENT MAGNITUDE: +8.2 APPARENT DIMENSIONS: 9.6’ AGE: 10-12 billion years

DISTANCE DETERMINATION Astronomers measure the variation in brightness of RR Lyrae stars in the cluster. The period of variation is directly related to their luminosity. Comparing the luminosity to the apparent magnitude yields the distance.

MASS DETERMINATION The motion of stars in a cluster is dictated by gravity, which is a function of mass. Astronomers measure the motion of cluster stars, and then calculate the mass using dynamical models.

NOTABLE FEATURES/FACTS • William Herschel was first to resolve M79 into individual stars. He made the observation in 1784. • M79 contains about 100,000 stars. • This cluster may not be native to our galaxy. The Milky Way is currently in the process of “eating” the Canis Major Dwarf Galaxy. M79 may have been captured during this ongoing event. • M79 may contain an intermediate mass black hole. If it exists, the black hole could be up to 3000 times as massive as the Sun. • Charles Messier cataloged this object on 17 December 1780. SPRING SP TARGET INFORMATION

MESSIER 1 (THE CRAB NEBULA)

BASIC INFORMATION OBJECT TYPE: Supernova Remnant CONSTELLATION: Taurus BEST VIEW: Late February DISCOVERY: John Bevis, 1731 DISTANCE: 6500 ly DIAMETER: 11 ly MASS: 4.6 MSUN APPARENT MAGNITUDE: +8.4 APPARENT DIMENSIONS: 6’x4’

DISTANCE DETERMINATION Using spectroscopy, astronomers directly measure the absolute expansion rate of the nebula. Comparing images of the nebula over time provides a measure of the apparent angular expansion. This value directly relates to the distance: for a given absolute expansion, a nearby object will have a higher apparent angular expansion than a distant one.

AGE DETERMINATION The expansion rate of the nebula is measured directly using spectroscopy. From this, astronomers work backward to the time at which the nebula’s extent would have been zero. This yields the age of the nebula, and thus, the date of the supernova.

NOTABLE FEATURES/FACTS • The Crab Nebula is the remnant of a Type II supernova that was first observed on 4 July 1054. According to Chinese records, this “guest star” was visible to the unaided eye for about two years; it was visible in broad daylight for several weeks. • The Crab Nebula is currently expanding at a rate of about 1500 km/s (3.4 million mph). • Three-dimensional models suggest the nebula is a prolate spheroid, or shaped somewhat like a football. • At the center of the nebula is the Crab Pulsar, a neutron star, which is spinning at a rate of about 30 times a second. • The Crab Pulsar is about 30 km (19 mi.) across, and its mass is estimated to be a little greater than the mass of the Sun. • Across all wavelengths, the Crab Pulsar is about 100,000 times more energetic than the Sun. Energy from the pulsar plays a significant role in causing the nebula to glow. • The Crab Pulsar’s progenitor star was at least eight times the mass of the sun. • In the 1840’s, Lord Rosse made a drawing of the nebula that he thought looked like a crab, so he called the object the “Crab Nebula.” • Messier added this object to his catalog on 9/12/1758. SPRING SP TARGET INFORMATION

MESSIER 42 (THE ORION NEBULA)

BASIC INFORMATION OBJECT TYPE: Star Forming Region CONSTELLATION: Orion BEST VIEW: Late February DISCOVERY: Peiresc, 1610 (nebula), Galileo Galilei, 1617 (Trapezium) DISTANCE: 1350 ly DIAMETER: Approximately 24 ly APPARENT MAGNITUDE: +4.0 APPARENT DIMENSIONS: 65’x60’

DISTANCE DETERMINATION Trigonometric parallax: After measuring the shift in position of nebula stars relative to background stars as Earth orbits the Sun, simple trigonometry can yield the distance. Because many of the stars in the Orion Nebula are obscured by dust, this is often performed using radio telescopes.

Luminosity Distance: Using spectroscopy, astronomers determine the temperature and diameter of a star, then calculate the luminosity. This is compared to the apparent magnitude to get the distance.

AGE DETERMINATION The presence of protoplanetary disks and pre-main-sequence stars within the nebula places an upper limit on the age. Astronomers can also plot the colors and magnitudes of nebula stars on an H-R Diagram to get an overall picture of the evolutionary states of the nebula stars and further constrain the age.

NOTABLE FEATURES/FACTS • The Orion Nebula is the closest star-forming region to Earth. • M42 contains the Trapezium star cluster, which contains some of the youngest known stars -- with an estimated age of less than one million years. • The Hubble Space Telescope has detected several thousand stars associated with the nebula, including some T Tauri stars and brown dwarfs. • Infrared observations reveal the presence of nearly 200 planet-sized objects. • Astronomers have observed protoplanetary disks, the precursors of planet formation, associated with at least 150 stars in the nebula. • Three-dimensional models suggest the nebula is bowl shaped, with a large cavity formed by the stellar winds of the Trapezium members. We are looking down this cavity to the Trapezium. • The energy emitted by the Trapezium stars is responsible for the visibility of the nebula. Starlight triggers emission in gaseous regions and reflects off of dust grains, giving the nebula its distinctive glow. • Messier added this object to his catalog on the night of 4 March 1769. SPRING SP TARGET INFORMATION

MESSIER 37

BASIC INFORMATION OBJECT TYPE: Open Cluster CONSTELLATION: Auriga BEST VIEW: Late February DISCOVERY: Giovanni Battista Hodierna, before 1654 DISTANCE: Approximately 4500 ly DIAMETER: 20-25 ly APPARENT MAGNITUDE: +6.2 APPARENT DIMENSIONS: 24’ AGE: ~500 million years

DISTANCE DETERMINATION The colors and magnitudes of cluster members are plotted on an H-R diagram. Specific features, such as the location of the main sequence, have known theoretical positions on the plot. Comparison of the observed position of these features to the theoretical position can yield the distance.

NOTABLE FEATURES/FACTS • M37 contains several thousand stars. • Charles Messier cataloged this object on the night of 30 August 1764. SPRING SP TARGET INFORMATION

MESSIER 35

BASIC INFORMATION OBJECT TYPE: Open Cluster CONSTELLATION: Gemini BEST VIEW: Early March DISCOVERY: Philippe Loys de Cheseaux, 1745 DISTANCE: 2800 ly DIAMETER: 23 ly APPARENT MAGNITUDE: +5.3 APPARENT DIMENSIONS: 28’ AGE: ~150 million years

NOTABLE FEATURES/FACTS • M35 is dominated by several hundred massive blue stars. • The cluster has at least 2500 confirmed members. Some mass estimates suggest there may be as many as 8000 stars in the cluster. • Charles Messier cataloged this object on the night of 30 August 1764.

SPRING SP TARGET INFORMATION

MESSIER 41

BASIC INFORMATION OBJECT TYPE: Open Cluster BEST VIEW: March CONSTELLATION: Canis Major DISCOVERY: Giovanni Batista Hodierna c. 1654 DISTANCE: 2300 ly DIAMETER: 25 ly APPARENT MAGNITUDE: +4.5 APPARENT DIMENSIONS: 38’ AGE: ~200-250 million years

NOTABLE FEATURES/FACTS • M41 contains at least 100 bright, young stars. • The cluster’s discovery is credited to Hodierna, but it may have been noted as early as 325 B.C. by Aristotle. • Charles Messier cataloged this object on the night of 16 January 1765. SPRING SP TARGET INFORMATION

NGC 2362 (Tau Canis Majoris Cluster)

BASIC INFORMATION OBJECT TYPE: Open Cluster DISCOVERY: Giovanni Batista Hodierna, c. 1654 CONSTELLATION: Canis Major BEST VIEW: March DISTANCE: 4800 ly DIAMETER: 11 ly APPARENT MAGNITUDE: +4.1 APPARENT DIMENSIONS: 8’ AGE: ~5 million years

NOTABLE FEATURES/FACTS • The brightest star in the field of view is t CMa, a multiple star system containing a massive O-type supergiant. It is uncertain if the star is a true member of the cluster. • t CMa is sometimes referred to as the “Mexican Jumping Star” because its marked contrast with the cluster makes it appear to jump around. • The cluster contains at least 250 stars, with some estimates as high as 1200. • The lack of dust in NGC 2362 makes this an ideal location to study the evolution of very young stars. • The stars of NGC 2362 appear to have formed in a single burst of star formation that lasted about three million years. SPRING SP TARGET INFORMATION

NGC 2392 (THE ESKIMO NEBULA)

BASIC INFORMATION OBJECT TYPE: Planetary Nebula CONSTELLATION: Gemini BEST VIEW: March DISCOVERY: William Herschel, 1787 DISTANCE: 3000 - 5000 ly DIAMETER: 0.8 ly (brightest part at 4000 ly) APPARENT MAGNITUDE: +10.1 APPARENT DIMENSIONS: 44”

Trigonometric Parallax – Measure the apparent shift of the central star relative to background stars as Earth orbits the Sun or as a spacecraft orbits Earth. Trigonometry yields the distance.

Statistical Analyses – Correlate measurable physical properties of the nebula with distance. This requires making some big assumptions, like all planetary nebulae have similar properties.

Expansion Velocity – Measure the rate at which the nebula is expanding in physical units and angular measure. Trigonometry yields the distance.

NOTABLE FEATURES/FACTS • This object’s nickname comes from its resemblance to the fur ruff on the hood of a parka. It’s also known as the Clownface Nebula. • The Eskimo is the remnant of a dying star that was once slightly larger than the Sun. When the Sun exhausts its fuel, it will produce a similar structure. • NGC 2392 has two distinct expanding shells of material. The inner shell is expanding more quickly than the outer shell. Unique features of the outer shell may be the result of the faster gas colliding with slower material. • The inner shell is actually bipolar. It consists of two large bubbles of gas expanding above and below a central torus of matter. From our perspective, the bubbles extend toward and away from us, and the nearer bubble is partially obscuring the farther one. This is why the inner shell has a somewhat heart-shaped appearance. • The Chandra X-Ray Telescope detected unusually hot gas near the central star, suggesting the possible presence of a binary companion. • The energy from the central star causes the nebular material to glow. • The nebula is believed to have begun forming about 10,000 years ago. SPRING SP TARGET INFORMATION

WINTER ALBIREO (145 CMa)

BASIC INFORMATION OBJECT TYPE: Double Star CONSTELLATION: Canis Major BEST VIEW: March DISCOVERY: John Herschel, 1847 DISTANCE: 1420 ly ANGULAR SEPARATION: 26.8” APPARENT MAGNITUDE: 4.8

DISTANCE DETERMINATION After measuring the shift in position of the star relative to background stars as Earth orbits the Sun, simple trigonometry can yield the distance. The Hipparcos satellite was launched in 1989 to create a comprehensive catalog of trigonometric parallax measurements from space.

NOTABLE FEATURES/FACTS • These stars are known as “The Winter Albireo” because their contrasting colors are similar to those of Albireo. • The color difference between the stars reveals a difference in temperature. The orange primary star is cooler than the blue companion. • Information on 145 CMa is scarce. Some sources indicate the two stars are a true binary, while others suggest the stars are not related. If they are a true binary, their angular separation would translate to an apparent linear separation of nearly 12,000 AU, or about 0.2 light years.

SPRING SP TARGET INFORMATION

MESSIER 46

BASIC INFORMATION OBJECT TYPE: Open Cluster CONSTELLATION: Puppis BEST VIEW: Late March DISCOVERY: Charles Messier, 1771 DISTANCE: 5400 ly DIAMETER: 30 ly APPARENT MAGNITUDE: +6.0 APPARENT DIMENSIONS: 27’ AGE: ~250 million years

NOTABLE FEATURES/FACTS • M46 contains at least 500 stars. • Planetary nebula NGC 2438 appears superimposed on the cluster. It is estimated to be about 3000 ly away. • The planetary nebula was discovered by William Herschel in 1786. • The cluster is moving away from Earth at a rate of about 40 km/s (89,000 mph). This differs significantly from the radial velocity of the planetary nebula, suggesting the nebula is a foreground object unrelated to the cluster. • Charles Messier cataloged this object on the night of 19 February 1771. SPRING SP TARGET INFORMATION

MESSIER 44 (THE BEEHIVE CLUSTER)

BASIC INFORMATION OBJECT TYPE: Open Cluster CONSTELLATION: Cancer BEST VIEW: Early April DISCOVERY: Known in Antiquity DISTANCE: 577 ly DIAMETER: 39 ly APPARENT MAGNITUDE: +3.7 APPARENT DIMENSIONS: 95’ AGE: ~700 million years

NOTABLE FEATURES/FACTS • This cluster is easily seen with the naked eye as a nebulous patch in the direction of the constellation Cancer. In 260 B.C., the Greek philosopher Aratos identified it as “the little mist.” • M44 is also known as Praesepe, which is Latin for “manger.” The ancient Greeks saw it as a manger from which two donkeys were eating. • M44 was one of the first objects Galileo observed through his telescope in 1609. He counted about 40 stars. • The Beehive contains several hundred stars, with some estimates identifying over 1000 candidate members. • Charles Messier cataloged this object on the night of 4 March 1769. There is speculation he added this object simply to boost the number of objects in his catalog so that it exceeded that of his contemporary, Nicholas Louis de la Caille. • The proper motion, age, and stellar population of the Beehive are very much like that of the Hyades cluster in Taurus, suggesting the two may have a common origin. • Multiple exoplanets have been detected in M44, including the first two explanets to be observed orbiting sun-like stars in a cluster. SPRING SP TARGET INFORMATION

MESSIER 67

BASIC INFORMATION OBJECT TYPE: Open Cluster CONSTELLATION: Cancer BEST VIEW: Early April DISCOVERY: Johann Gottfried Koehler, 1779 DISTANCE: 2700 ly DIAMETER: 160 ly APPARENT MAGNITUDE: +6.1 APPARENT DIMENSIONS: 30’ AGE: ~4 billion years

NOTABLE FEATURES/FACTS • While Koehler is credited with first observing M67, he was unable to resolve the cluster into stars. Charles Messier did so about a year later. • M67 is the oldest open cluster in the Messier catalog and one of the oldest known in the Milky Way. Most open clusters break up within about a billion years. The fact that M67 is still intact indicates it was extremely massive in the distant past. • The cluster contains at least 500 stars, about 100 of which are similar to the Sun. • There are about 30 known “blue stragglers” in M67. These stars appear much younger than their neighbors, due to their blue color. It’s thought that the outer layers of these stars may have been stripped away in close encounters with other cluster members. • Several exoplanets have been discovered in M67. • Messier added this object to his catalog on the evening of 6 April 1780. SPRING SP TARGET INFORMATION

NGC 3242 (THE GHOST OF JUPITER)

BASIC INFORMATION OBJECT TYPE: Planetary Nebula CONSTELLATION: Hydra BEST VIEW: Early April DISCOVERY: William Herschel, 1785 DISTANCE: 1400 – 3600 ly DIAMETER: 0.3 – 0.8 ly APPARENT MAGNITUDE: +8.6 APPARENT DIMENSIONS: Inner Shell = 28” x 20” Outer Shell = 46” x 40”

Statistical Analyses – Correlate measurable physical properties of the nebula with distance. This requires making some big assumptions, like that all planetary nebulae have similar properties.

Expansion Velocity – Measure the rate at which the nebula is expanding in physical units and angular measure. Trigonometry yields the distance.

NOTABLE FEATURES/FACTS • This object’s nickname comes from its apparent size, which is about the same as that of Jupiter. • Another nickname for this object is the “CBS Eye” nebula for its similarity in appearance to the logo of the CBS television network. • The Ghost of Jupiter is the remnant of a dying star that was about the same size as the Sun. When the Sun exhausts its fuel in about five billion years, it will produce a similar structure. • NGC 3242 has two distinct expanding shells of material. The inner shell is expanding more quickly than the outer shell, causing a brighter ring to appear where the two stellar winds collide. • The bright inner shell of matter began to form about 1500 years ago. The outer shell may have begun to expand as long ago as 100 thousand years. • The temperature of the central star is estimated to be between 60,000 and 90,000K (approx. 100,000° – 160,000° F). The energy from the central star causes the nebular material to glow. SPRING SP TARGET INFORMATION

MESSIER 81 & 82

BASIC INFORMATION OBJECT TYPE: Interacting Galaxies CONSTELLATION: Ursa Major BEST VIEW: April DISCOVERY: Johann Elert Bode, 1774 DISTANCE: 11.8 million ly (M81) 11.5 million ly (M82) DIAMETER: ~95,000 ly (M81) ~37,000 ly (M82) APPARENT MAGNITUDE: 6.9 (M81), 8.4 (M82) APPARENT DIMENSIONS: 27’ x 14’ (M81) 11’ x 4’ (M82)

DISTANCE DETERMINATION Astronomers use Cepheid variables to gauge the distance to galaxies. Cepheids are a type of standard candle. The variation in the brightness of the star over time directly relates to its luminosity. Comparing this to the star’s apparent magnitude yields the distance.

NOTABLE FEATURES/FACTS • M81 is also known as Bode’s Galaxy, after its discoverer. M82 is also known as the Cigar Galaxy, due to its apparent shape. • M81 is a spiral galaxy, seen almost face-on. M82 is classified as an irregular or starburst galaxy, although it is likely a distorted spiral, seen edge-on. • M81 and M82 are interacting with one another, with their most recent encounter a few tens of millions of years ago. The interaction has distorted the shape of M82 and sparked intense rounds of star formation. • M81 and M82 are members of the nearby M81 Group, a cluster of galaxies containing at least 30 members. • M81 and M82 are currently separated by a distance of about 150,000 ly. • Charles Messier added these galaxies to his catalog on the night of 9 February 1781.

SPRING SP TARGET INFORMATION

NGC 2903

BASIC INFORMATION OBJECT TYPE: Galaxy CONSTELLATION: Leo BEST VIEW: April DISCOVERY: William Herschel, 1784 DISTANCE: ~31 million ly DIAMETER: ~115,000 ly* APPARENT MAGNITUDE: +9.7 APPARENT DIMENSIONS: 12.6’ x 6.0’

*Value based on estimated distance and apparent dimensions.

DISTANCE DETERMINATION The rotational characteristics of spiral galaxies are directly related to their luminosities. So, by measuring the rotation of a galaxy and using this relationship, astronomers can calculate the galaxy’s intrinsic brightness. This method is known as the Tully-Fisher Relation.

NOTABLE FEATURES/FACTS • NGC 2903 is a barred spiral galaxy with a stellar mass of about 60 billion MSOLAR, slightly less than the Milky Way. • When Herschel first observed this object, he thought he was seeing two distinct nebulae. He gave each a designation in his catalog. This led John Dreyer to assign two numbers to the object in the New General Catalog: NGC 2903 and NGC 2905. Today, NGC 2905 generally refers to a bright knot in one of the spiral arms. • Lord Rosse was first to report spiral structure in this object, using his 72” reflector at Birr Castle, Ireland in 1848. • Although NGC 2903 does not appear in the Messier catalog, there is some indication that Messier only just missed discovering it. Several comets he discovered were in the vicinity of this object. SPRING SP TARGET INFORMATION

ALGIEBA (g LEO)

BASIC INFORMATION OBJECT TYPE: Binary Star CONSTELLATION: Leo BEST VIEW: Late April DISCOVERY: Known to Ancients DISTANCE: 131 ly BINARY SEPARATION: 4” (170 AU) ORBITAL PERIOD: ~500 yr. APPARENT MAGNITUDE: 1.98

NOTABLE FEATURES/FACTS • William Herschel discovered Algieba’s binary nature in 1782. • Both components of Algieba have evolved beyond the main sequence. They began their lives as B-type stars, and they will end their lives as white dwarfs. • In 2010, a team including former UT astronomer Arte Hatzes discovered a planet orbiting Algieba A. The planet is nine times the mass of Jupiter and orbits the star in 1.2 years at an average distance of 1.2 AU. SPRING SP TARGET INFORMATION

MESSIER 97 (THE OWL NEBULA)

BASIC INFORMATION OBJECT TYPE: Planetary Nebula CONSTELLATION: Ursa Major BEST VIEW: Early May DISCOVERY: Pierre Mechain, 1781 DISTANCE: ~2000 ly DIAMETER: 1.8 ly APPARENT MAGNITUDE: +9.9 APPARENT DIMENSIONS: 3.3’

DISTANCE DETERMINATION The distances to most planetary nebulae are very poorly known. A variety of methods can be used, providing mixed results.

In many cases, astronomers resort to statistical methods to estimate the distances to planetary nebulae. Although we don’t have accurate distances for most of the planetary nebulae in the Milky Way, we do know exactly how far away the Large Magellanic Cloud is. There are lots of planetary nebulae in the LMC, and we know their distances because we know the distance to the LMC. So, astronomers measure physical properties (such as mass, temperature) of lots of planetary nebulae in the LMC. Using this information, astronomers can create a mathematical relationship between certain observed properties and the distance. This method is based on assumptions that are still up for debate, and thus is subject to errors of as much as a factor of two or three.

NOTABLE FEATURES/FACTS • M97 is known as the “Owl Nebula” because an early drawing by Lord Rosse in 1848 resembles the face of an owl.

Figure 1: Drawing by Lord Rosse, 1848 • Analysis of the expansion rate of the nebula suggests the progenitor star died out 6000 to 8000 years ago. • The central star is a white dwarf estimated to have slightly more than half the mass of the Sun. It shines at an apparent magnitude of +15.8, but is at least 50 times as luminous as the Sun. • Messier added this object to his catalog in 1781, shortly after its discovery by his friend Pierre Mechain. SPRING SP TARGET INFORMATION

THE LEO TRIPLET (M65, M66, NGC 3628)

BASIC INFORMATION OBJECT TYPE: Galaxy Group CONSTELLATION: Leo BEST VIEW: Early May DISCOVERY: Charles Messier, 1780 (M65 & M66) William Herschel, 1784 (NGC 3628) DISTANCE: 41.1 million ly (M65) 33.6 million ly (M66) 37.8 million ly (NGC 3628) DIAMETER: ~117,000 ly (M65), ~89,000 ly (M66), ~163,000 ly (NGC 3628) APPARENT MAGNITUDE: 10.3 (M65), 9.7 (M66), 9.5 (NGC 3628)

DISTANCE DETERMINATION Cepheid Variables: Cepheids are a type of standard candle. The variation in the brightness of the star over time directly relates to its luminosity. Comparing this to the star’s apparent magnitude yields the distance. This method was used to determine the distance to M66.

Tully-Fisher Relation: The rotational characteristics of spiral galaxies are directly related to their luminosities. So, by measuring the rotation of a galaxy and using this relationship, astronomers can calculate the galaxy’s intrinsic brightness. This method was used to determine the distances to M65 and NGC 3628.

NOTABLE FEATURES/FACTS • All three galaxies in the triplet are spirals. M65 and M66 are seen at oblique angles (M65 is the upper one in the image). NGC 3628 is seen almost edge on. • These three galaxies appear to have interacted hundreds of millions of years ago. NGC 3628 and M66 display the most significant signs of past interaction. • M65 contains a generally older stellar population than its neighbors but may be undergoing a new round of star formation. • M66 displays an unusual spiral arm pattern that may be a result of its encounter with NGC 3628. • NGC 3628 displays a dense dust band that is likely the result of its interaction with M66. • In 2014, astronomers detected a star-forming clump in the trio that may be a Tidal Dwarf Galaxy. This type of galaxy forms from the tidal debris of a galactic interaction. • In 2015, astronomers discovered a dense star cluster in NGC 3628 that may be similar to our own Omega Centauri. The cluster appears to have formed from the debris of a disrupted dwarf galaxy, lending credence to the hypothesis that some of the Milky Way’s globular clusters were formed or captured during galactic interactions. • Charles Messier added M65 and M66 to his catalog on the night of 1 March 1780. SPRING SP TARGET INFORMATION

NGC 4565

BASIC INFORMATION OBJECT TYPE: Galaxy CONSTELLATION: Coma Berenices BEST VIEW: May DISCOVERY: William Herschel, 1785 DISTANCE: 41 million ly DIAMETER: ~190,000 ly APPARENT MAGNITUDE: +10.4 APPARENT DIMENSIONS: 16’ x 3’

DISTANCE DETERMINATION One way to determine the distance to a galaxy is to figure out its intrinsic brightness. Once astronomers know this, they can observe how bright the galaxy appears, and then use the inverse square law of light to calculate the distance. The Tully-Fisher Relation quantifies the connection between the rotational characteristics of spiral galaxies and their luminosities. By measuring the rotation of a galaxy and using this relationship, astronomers can calculate the galaxy’s intrinsic brightness, and thus, its distance.

NOTABLE FEATURES/FACTS • NGC 4565 is also known as “The Needle Galaxy.” • This galaxy is an edge-on spiral. Infrared observations confirm it also has a central bar structure. • NGC 4565 is similar in size and structure to the Milky Way. This galaxy is a nice example of what the Milky Way would look like if seen edge-on from about 40 million miles away. • NGC 4565 hosts a supermassive black hole at its center. The black hole is estimated to be about three million times the mass of the Sun. • This galaxy is moving away from the Milky Way at a speed of 2.8 million miles per hour. SPRING SP TARGET INFORMATION

MESSIER 104 (THE SOMBRERO GALAXY)

BASIC INFORMATION OBJECT TYPE: Galaxy CONSTELLATION: Virgo BEST VIEW: Late May DISCOVERY: Pierre Mechain, 1781 DISTANCE: ~31 million ly DIAMETER: ~80,000 ly (based on 31 Mly distance) APPARENT MAGNITUDE: +8.0 APPARENT DIMENSIONS: 9’ x 4’

DISTANCE DETERMINATION The most commonly used method to obtain a distance to M104 is by measuring fluctuations in the surface brightness of the galaxy. Galaxies are made up of individual stars. The stars cannot be resolved at very great distances, but sensitive instruments can detect graininess in the galaxy’s texture. The more distant the galaxy, the less grainy its texture appears. Astronomers are able to quantify these surface brightness fluctuations and their relationship to distance. The above value is an average of recent measurements using the surface brightness fluctuation method.

NOTABLE FEATURES/FACTS • M104 is classified as a spiral galaxy, but it also has some characteristics of an elliptical galaxy. For example, it is “bulge dominated,” meaning it has an unusually large galactic bulge relative to the size of its disk. • We are viewing M104 just six degrees from perfectly edge-on. • A prominent dust ring encircles the galaxy. This ring and the dominant galactic bulge give the galaxy the appearance of a large hat. • The dust ring is the primary location of new star formation in M104. • The Sombrero Galaxy contains at least 1900 globular clusters… the most of any known galaxy. • M104 has a supermassive black hole at its center. Astronomers at the University of Texas have measured its mass at 660 million times the mass of the Sun. • The Sombrero Galaxy is moving away from us at a speed of about 1000 km/s (about 2.2 million mph). • Charles Messier never officially added this object to his catalog. A hand- written note in his personal catalog mentions that he observed the galaxy on 5/11/1781; the same day Mechain discovered it. The galaxy was added to the catalog as entry number 104 in 1921. SPRING SP TARGET INFORMATION

MESSIER 64 (THE BLACK EYE GALAXY)

BASIC INFORMATION OBJECT TYPE: Galaxy CONSTELLATION: Coma Berenices BEST VIEW: Late May DISCOVERY: Edward Pigott, 1779 DISTANCE: ~17 million ly DIAMETER: ~50,000 ly APPARENT MAGNITUDE: +8.5 APPARENT DIMENSIONS: Approx. 10’ x 5’

DISTANCE DETERMINATION Two methods are commonly used to determine the distance to M64. Both are actually methods to determine the intrinsic brightness of the galaxy (or stars within it). Comparing this absolute magnitude to the observed brightness of the galaxy (or stars) yields the distance.

Tip of the Red Giant Branch: Stars at the “tip of the red giant branch” have evolved to a point where they are just beginning to fuse helium in their cores. These stars have a known intrinsic brightness.

The distance value adopted above is based on the mean value of distances obtained using these two methods.

NOTABLE FEATURES/FACTS • M64 gets its nickname due to the appearance of a prominent dark dust band. It is also sometimes called the Sleeping Beauty or the Evil Eye galaxy. • The galaxy contains two counter-rotating disks of gaseous material. The inner disk extends about 3000 ly from the galaxy’s core. The outer disk extends from there to the outskirts of the galaxy. • A new wave of star formation is underway as a result of friction between the counter-rotating gas disks. • Messier added this object to his catalog on the night of 1 March 1780. SPRING SP TARGET INFORMATION

MIZAR & ALCOR

BASIC INFORMATION OBJECT TYPE: Multiple Star System CONSTELLATION: Ursa Major BEST VIEW: Early June DISCOVERY: Known to Ancients DISTANCE: 83 ly BINARY SEPARATION: ALCOR & MIZAR: 11.8’ (0.3 ly) MIZAR A & B: 14.4” (367 AU), ALCOR A & B: 1.1” (28 AU) ORBITAL PERIOD: ALCOR & MIZAR: 750,000 yr MIZAR A & B: 5000 yr +, ALCOR A & B: 90 yr + APPARENT MAGNITUDE: MIZAR: 2.2, ALCOR: 4.0

NOTABLE FEATURES/FACTS • Mizar and Alcor were known as the “horse and rider” in Arabic astronomy. The pair is thought to symbolize marriage in Indian astronomy. • Historically, Mizar and Alcor are said to have been used as tests of vision. • Mizar and Alcor form a naked-eye double, but it wasn’t until 2009 that astronomers determined the pair are likely gravitationally bound. • In 1617, Benedetto Castelli observed Mizar in his telescope and believed he detected a companion. He wrote to Galileo, asking him to confirm the discovery. Mizar thus became the first telescopic binary to be discovered. • Mizar A was the first spectroscopic binary discovered (Edward Charles Pickering, 1889). The stars that make up Mizar A orbit one another in about 20.5 days. • Mizar B is also a spectroscopic binary. The stars that make it up orbit one another in about six months. • In 2009, astronomers looking for planets orbiting Alcor found an M-dwarf star orbiting the star instead. This brought the total number of known stars in the system to six. • All of the stars in the group except for Alcor’s companion are main-sequence A-type stars. They are on average about 20 times brighter than the Sun and have surface temperatures ranging from 13,000° F to 16,000° F.

SPRING SP TARGET INFORMATION

NGC 5139 (w CENTAURI)

BASIC INFORMATION OBJECT TYPE: Globular Cluster CONSTELLATION: Centaurus BEST VIEW: Early June DISCOVERY: Ptolemy, 150 A.D. DISTANCE: 15,800 ly DIAMETER: 175 ly APPARENT MAGNITUDE: +3.9 APPARENT DIMENSIONS: 36’

DISTANCE DETERMINATION Astronomers measure the proper motion and radial velocity of cluster stars, then use trigonometry to arrive at the distance.

NOTABLE FEATURES/FACTS • Omega Centauri contains at least one million stars. • Pinpointing the age of Omega Centauri is difficult because it appears to contain at least two distinct stellar populations. Estimates range from 11 to 13 billion years old. • The presence of multiple populations of stars in Omega Centauri suggests the cluster may be a remnant core of a dwarf galaxy that was destroyed by the Milky Way billions of years ago. • Omega Centauri is the most massive globular star cluster in the Milky Way. Mass estimates range from about 2.5 million to 5 million times the mass of the Sun. • The average separation between stars in Omega Centauri is about 0.1 ly. • This object was originally misidentified as a faint star, hence its stellar designation. • Omega Centauri may contain an intermediate mass black hole. Measurement of stellar motions near the cluster center suggest the black hole could have a mass of up to 40,000 times the mass of the Sun. • Edmond Halley was the first astronomer of the modern era to describe Omega Centauri. He observed it in 1677. • Charles Messier never added this catalog to his catalog. Although it was certainly the type of object he would have noted, it was just too far south for him to see from Paris. SPRING SP TARGET INFORMATION

MESSIER 3

BASIC INFORMATION OBJECT TYPE: Globular Cluster CONSTELLATION: Canes Venatici BEST VIEW: June DISCOVERY: Charles Messier, 1764 DISTANCE: 33,900 ly DIAMETER: 180 ly MASS: 450,000 MSUN APPARENT MAGNITUDE: +6.2 APPARENT DIMENSIONS: 18’

DISTANCE DETERMINATION Globular clusters contain many RR Lyrae stars, which are a type of standard candle. These stars vary in brightness, and the period of variation relates to the star’s luminosity. Astronomers can measure the period of variability and then calculate the luminosity. Comparison of luminosity to apparent magnitude yields the distance.

NOTABLE FEATURES/FACTS • M3 contains approximately 500,000 stars. Of these, about 275 are known to be variable stars; this is the most found in any globular cluster. • The combined energy of all of the cluster stars is about 300,000 times the energy of the Sun. • Half of the cluster’s mass is concentrated within 11 light years of the center. • The cluster is estimated to be approximately 12 billion years old, making it one of the oldest structures in our Galaxy. • M3 is moving toward Earth at a speed of about 140 km/s (310,000 mph). • Recent analyses suggest M3 likely contains two distinct populations of stars. The cluster probably underwent at least two rounds of star formation. • Many “blue straggler” stars have been observed in M3. These are stars that appear much younger than the other stars in the cluster, largely due to their blue color. The outer layers of these stars may have been stripped away during interactions with other cluster stars, resulting in their blue color. • William Herschel was first to resolve the cluster into individual stars (1784). • Messier added this object to his catalog on 5/3/1764. SPRING SP TARGET INFORMATION

MESSIER 51

BASIC INFORMATION OBJECT TYPE: Galaxy CONSTELLATION: Canes Venatici BEST VIEW: June DISCOVERY: Charles Messier, 1773 DISTANCE: ~25 million ly DIAMETER: ~80,000 ly (visible disk @ 25 Mly) APPARENT MAGNITUDE: +8.4 APPARENT DIMENSIONS: 11’ x 7’

DISTANCE DETERMINATION Redshift: Using spectroscopy, astronomers measure the speed at which a galaxy is receding from us. This rate of recession is directly proportional to the distance (Hubble’s Law).

More current estimates are obtained by measuring the characteristics of several recent supernovae in M51.

Expanding Photosphere: Astronomers can determine the apparent angular expansion and speed of an exploding star’s photosphere. The two values can then be compared to obtain the distance.

Standard Candle: A relatively new method relies on standard characteristics of Type II-P supernovae. These core-collapse supernovae exhibit a characteristic plateau in their light curves. Astronomers have recently been able to calibrate the luminosity of this plateau. Measuring the apparent magnitude of the plateau yields a distance.

NOTABLE FEATURES/FACTS • M51 was the first galaxy in which spiral structure was detected. Lord Rosse made the observation in 1845 using his 72-inch “Leviathan” telescope at Birr Castle, Ireland. • Pierre Mechain discovered M51’s companion galaxy, NGC 5195, in 1781. • M51 and NGC 5195 are currently in the process of merging. This interaction has enhanced the spiral structure of M51 and triggered new star formation. • Dynamic models suggest M51 and NGC 5195 had their first close encounter about 500 million years ago. Some recent models suggest they had a second close encounter 50-100 million years ago. • M51’s mass is estimated at about 160 billion times the mass of the Sun. This translates to at least 250 billion stars. • The center of M51 contains a supermassive black hole. The upper limit of its mass is about two million times the mass of the Sun. • M51 is the brightest member of the M51 Group. • The Whirlpool Galaxy is moving away from us at a speed of about 460 km/s (about one million mph). • Messier added this object to his catalog on the night of 13 October 1773. SPRING SP TARGET INFORMATION

IZAR (e BOO)

BASIC INFORMATION OBJECT TYPE: Binary Star CONSTELLATION: Aquarius BEST VIEW: Early July DISCOVERY: Known to Ancients DISTANCE: 203 ly BINARY SEPARATION: 2.8” (185 AU) ORBITAL PERIOD: 1000 yr. APPARENT MAGNITUDE: 2.3

NOTABLE FEATURES/FACTS • The name Izar means “girdle” in Arabic. It is also sometimes translated as “veil.” • F.G.W. Struve gave Izar an alternate name in the 1800’s: Pulcherrima, which means “the loveliest” in Latin. • The orange star in the pair is an evolved orange giant star approximately 500 times as luminous as the Sun. • The blue-white star is on the main sequence and is about twice the size of the Sun and 27 times brighter.

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MESSIER 5

BASIC INFORMATION OBJECT TYPE: Globular Cluster CONSTELLATION: Serpens BEST VIEW: Early July DISCOVERY: Gottfried Kirch, 1702 DISTANCE: 24,500 ly DIAMETER: 165 ly MASS: 834,000 MSUN APPARENT MAGNITUDE: +5.6 APPARENT DIMENSIONS: 23’ AGE: 12-13 billion years

DISTANCE DETERMINATION Astronomers measure the proper motion and radial velocity of cluster stars, then use trigonometry to arrive at the distance. Another method involves measuring the variation in brightness of RR Lyrae stars in the cluster. The period of variation is directly related to their luminosity. Comparing the luminosity to the apparent magnitude yields the distance.

NOTABLE FEATURES/FACTS • William Herschel was first to resolve M5 into individual stars. He made the observation in 1791, and he counted about 200 stars. • M5 contains at least 100,000 stars. Some estimates go as high as 500,000 stars. • Charles Messier cataloged this object on 23 May 1764. • Using the Hubble Space Telescope, astronomers have observed many blue stragglers in M5. These stars appear bluer than other stars of the same type and age, suggesting their structures have been altered by close interactions with neighbors in the cluster. • Recent observations with the ESO’s Very Large Telescope in Chile have shown that M5 is rotating, making it just one of a few globular clusters in which evidence of systemic rotation has been observed.

SPRING SP TARGET INFORMATION

MESSIER 4

BASIC INFORMATION OBJECT TYPE: Globular Cluster CONSTELLATION: Scorpius BEST VIEW: July DISCOVERY: Philippe Loys de Chéseaux, 1746 DISTANCE: 5600 – 7200 ly DIAMETER: 75 ly MASS: 450,000 MSUN APPARENT MAGNITUDE: +5.6 APPARENT DIMENSIONS: 36’ AGE: 12-13 billion years

AGE DETERMINATION White dwarf stars in the cluster cool at a predictable rate, related to their age. Using an H-R diagram and stellar evolution models to analyze the evolutionary states of other cluster stars further constrains the age.

NOTABLE FEATURES/FACTS • M4 was the first globular cluster to be resolved into individual stars. Charles Messier made the observation and added the cluster to his catalog on 8 May 1764. • Extinction due to interstellar dust makes a distance to M4 difficult to determine, but at less than 7200 ly, it’s one of the nearest globulars to Earth. • M4 appears to have a “bar” structure made up of 11th magnitude stars across its center. • There appear to be two distinct populations of stars within the cluster. • In 1987, astronomers discovered a millisecond pulsar in M4. It rotates over 300 times per second. • In 1995, the Hubble Space Telescope observed white dwarf stars in M4. These stars are 12.7 billion years old, making them some of the oldest stars in the Milky Way. • In 2003, astronomers identified a possible planet orbiting a white dwarf star in M4. The planet is 2.5 times the mass of Jupiter. SPRING SP TARGET INFORMATION

MESSIER 13

BASIC INFORMATION OBJECT TYPE: Globular Cluster CONSTELLATION: Hercules BEST VIEW: Late July DISCOVERY: Edmond Halley, 1714 DISTANCE: 25,100 ly DIAMETER: 145 ly APPARENT MAGNITUDE: +5.8 APPARENT DIMENSIONS: 20’

DISTANCE DETERMINATION Globular clusters contain many RR Lyrae stars, which are a type of standard candle. These stars vary in brightness, and the period of variation relates to the star’s luminosity. Comparison of luminosity to apparent magnitude yields the distance.

NOTABLE FEATURES/FACTS • M13 contains several hundred thousand stars. Some estimates even go as high as one million. • The cluster is estimated to be 12 to 13 billion years old, making it one of the oldest structures in our Galaxy. • M13 contains at least two distinct populations of stars, indicating that the stars formed during multiple episodes. • Many “blue straggler” stars have been observed in M13. These are stars that appear much younger than the other stars in the cluster, largely due to their blue color. The outer layers of these stars may have been stripped away during interactions with other cluster stars, resulting in their blue color. • In 1974, the Arecibo radio telescope was used to send a signal to M13. The signal contained information including descriptions of DNA, human physiology, and our Solar System. If anyone is in M13 to receive it, we can expect a reply in about 50,000 years. • Messier added this object to his catalog on 1 June 1764.