Leo is the 12th largest constellation in size, occupying an area of 947 square degrees. It is located in the second quadrant of the northern hemisphere (NQ2) and can be seen at latitudes between +90° and -65°. The neighboring constellations are Cancer, Coma Berenices, Crater, Hydra, Leo Minor, Lynx, Sextans, Ursa Major and Virgo.
[http://www.constellation-guide.com/constellation-list/leo-constellation/]
Leo is also the fifth astrological sign of the zodiac, originating from the constellation of Leo. It comes after Cancer and before Virgo. It spans the 120-150th degree of the Tropical zodiac, between 125.25 and 152.75 degree of celestial longitude. Under the tropical zodiac, the Sun transits this area on average between July 23 and August 22 each year, and under the sidereal zodiac, the Sun currently transits this area from approximately August 16 to September 15. The symbol of the lion is based on the Nemean lion, a lion with an impenetrable hide.
[https://en.wikipedia.org/wiki/Leo_%28astrology%29]
Leo, Urania’s Mirror 1825
[http://www.constellationsofwords.com/Constellations/Leo.html]
In Greek mythology, Leo was identified as the Nemean Lion which was killed by Heracles (Hercules to the Romans) during the first of his twelve labours. The Nemean Lion would take women as hostages to its lair in a cave, luring warriors from nearby towns to save the damsel in distress, to their misfortune. The Lion was impervious to any weaponry; thus, the warriors’ clubs, swords, and spears were rendered useless against it. Realizing that he must defeat the Lion with his bare hands, Hercules slipped into the Lion’s cave and engaged it at close quarters. When the Lion pounced, Hercules caught it in midair, one hand grasping the Lion's forelegs and the other its hind legs, and bent it backwards, breaking its back and freeing the trapped maidens. Zeus commemorated this labor by placing the Lion in the sky.
The Roman poet Ovid called it Herculeus Leo and Violentus Leo. Bacchi Sidus (star of Bacchus) was another of its titles, the god Bacchus always being identified with this animal. However, Manilius called it Jovis et Junonis Sidus (Star of Jupiter and Juno).
Modern astronomers, including Tycho Brahe in 1602, excised a group of stars that once made up the ‘tuft’ of the lion’s tail and used them to form the new constellation Coma Berenices, although there was precedent for that designation among the ancient Greeks and Romans.
Leo was one of the earliest recognized constellations, with archaeological evidence that the Mesopotamians had a similar constellation as early as 4000 BCE.
The Persians called Leo Ser or Shir; the Turks, Artan; the Syrians, Aryo; the Jews, Arye; the Indians, Simha, all meaning ‘lion.’
Some mythologists believe that in Sumeria, Leo represented the monster Humbaba, who was killed by Gilgamesh. In Babylonian astronomy, the constellation was called UR.GU.LA, the ‘Great Lion;’ the bright star Regulus was known as ‘the star that stands at the Lion’s breast.’ Regulus also had distinctly regal associations, as it was known as the King Star.
Also it has been said that the Great Sphinx in Egypt represents the constellation Leo. The Great Sphinx is commonly accepted by Egyptologists to represent King Khafra (about 2500 BCE). Because the limited evidence giving provenance to Khafra is ambiguous and circumstantial, the idea of who built the Sphinx, and when, continues to be the subject of debate. An argument put forward by Robert Bauval and Graham Hancock is that the construction of the Great Sphinx was begun in 10,500 BCE; that the Sphinx’s lion-shape is a definitive reference to the constellation of Leo; and that the layout and orientation of the Sphinx, the Giza pyramid complex and the Nile River are an accurate reflection or ‘map’ of the constellations of Leo, Orion (specifically, Orion’s Belt) and the Milky Way, respectively. The date of 10,500 BCE is chosen because they maintain this is the only time in the precession of the equinoxes when the astrological age was Leo and when that constellation rose directly east of the Sphinx at the vernal equinox.
The theory that the Sphinx is actually far older has received some support from geologists. Most famously, Robert M. Schoch has argued that the effects of water erosion on the Sphinx and its surrounding enclosure mean that parts of the monument must originally have been carved at the latest between 7000- 5000 BCE. Schoch’s analysis has been broadly corroborated by another geologist, David Coxill, who agrees that the Sphinx has been heavily weathered by rainwater and therefore must have been carved in pre-dynastic times. A third geologist, Colin Reader, has suggested a date only several hundred years prior to the commonly accepted date for construction. These views have been almost universally rejected by mainstream Egyptologists who together with a number of geologists stand by the conventional dating for the monument. Their analyses attribute the apparently accelerated wear on the Sphinx variously to modern industrial pollution, qualitative differences between the layers of limestone in the monument itself, scouring by wind-borne sand, or temperature changes causing the stone to crack.
[https://en.wikipedia.org/wiki/Orion_correlation_theory#Leo_and_the_Sphinx]
In traditional Chinese uranography, the modern constellation Leo lies across one of the quadrants symbolized by the The Vermillion Bird of the South (Nán Fāng Zhū Què), and Three Enclosures (Sān Yuán), that divide the sky. The name of the western constellation in modern Chinese is ‘shī zi zuò,’ which means ‘the lion constellation.’
[https://en.wikipedia.org/wiki/Leo_%28Chinese_astronomy%29]
Constellation of Leo
[http://www.davidmalin.com/fujii/source/Leo.html]
[http://www.astronomytrek.com/leo-the-lion/]
Leo is a highly recognizable constellation, as it is one of the few constellations that resemble its namesake. It is fairly easy to find because the ‘pointer stars’ of the Big Dipper point to Leo. The constellation can be found by looking for the ‘sickle’ starting at the Regulus star. Regulus, Al Jabbah (Heta Leonis), and Algieba (Gamma Leonis), together with the fainter stars ζ Leo (Adhafera), μ Leo (Ras Elased Borealis), and ε Leo (Ras Elased Australis), constitute the sickle. A triangle of stars forms the lion’s haunches, with the brightest star of this trio being Denebola, which means ‘tail of the lion.’
[http://www.space.com/16845-leo-constellation.html]
Star map showing the region of the night sky around the constellations Cancer, Leo and Virgo
[http://www.nakedeyeplanets.com/zodiac-constellations/cnc-leo-vir.htm]
Leo contains many bright stars, many of which were individually identified by the ancients:
Regulus through Celestron
Regulus, also designated Alpha Leonis, is the brightest star in the constellation of Leo and one of the brightest stars in the night sky, lying approximately 79 light years from the Sun. The name is Latin for ‘prince’ or ‘little king.’
Regulus is a multiple star system consisting of at least four stars. Regulus A is the dominant star, with a binary companion 177" distant that is thought to be physically related. Regulus D is a 12th magnitude companion at 212", which shares a common motion with the other stars.
Regulus A is a binary star consisting of a blue-white main sequence star of spectral type B7V, which is orbited by a star of at least 0.3 solar masses, which is probably a white dwarf. The two stars take approximately 40 days to complete an orbit around their common center of mass. Regulus A was long thought to be fairly young, only 50 - 100 million years old, calculated by comparing its temperature, luminosity, and mass. The existence of a white dwarf companion would mean that the system is at least a 1,000 million years old, just to account for the formation of the white dwarf. The discrepancy can be accounted for by a history of mass transfer onto a once-smaller Regulus A.
The primary of Regulus A has about 3.5 times the Sun’s mass. It is spinning extremely rapidly, with a rotation period of only 15.9 hours, which causes it to have a highly oblate shape. This results in so-called gravity darkening: the photosphere at Regulus’ poles is considerably hotter, and five times brighter per unit surface area, than its equatorial region. If it were rotating only 15% faster, the star’s gravity would be insufficient to hold it together, and it would spin itself apart.
Regulus BC is 5,000 AU from Regulus A. They share a common proper motion and are thought to orbit each other. Designated Regulus B and Regulus C, the first is a K2V star, while the companion is approximately M4V. The companion pair has an orbital period of about 600 years with a separation of 2.5" in 1942.
The Regulus system as a whole is the twenty-first brightest star in the night sky with an apparent magnitude of +1.35. The light output is dominated by Regulus A. Regulus B, if seen in isolation, would be a binocular object of magnitude +8.1, and its companion, Regulus C, the faintest of the three stars that has been directly observed, would require a substantial telescope to be seen, at magnitude +13.5. Regulus A is itself a spectroscopic binary: the secondary star has not yet been directly observed as it is much fainter than the primary. The BC pair lies at an angular distance of 177 arc-seconds from Regulus A, making them visible in amateur telescopes.
Regulus is 0.46 degree from the ecliptic, the closest of the bright stars, and is regularly occulted by the Moon. Occultations by the planets Mercury and Venus are possible but rare, as are occultations by asteroids.
The last occultation of Regulus by a planet was on July 7, 1959, by Venus. The next will occur on October 1, 2044, also by Venus. Other planets will not occult Regulus over the next few millennia because of their node positions. An occultation of Regulus by the asteroid 166 Rhodope was observed by 12 researchers from Portugal, Spain, Italy, and Greece on October 19, 2005. Differential bending of light was measured to be consistent with general relativity. It was also occulted by the asteroid 163 Erigone in the early morning of March 20, 2014.
Although best seen in the evening in northern hemisphere in late winter and spring, Regulus appears at some time of night throughout the year except for about a month on either side of August 22, when the Sun is too near. Regulus passes through SOHO’s (Solar and Heliospheric Observatory) LASCO (Large Angle and Spectrometric Coronagraph) C3 every August. For most Earth observers, the heliacal rising of Regulus occurs in the first week of September. Every 8 years, Venus passes Regulus around the time of the star’s heliacal rising, as on 5 September 2014.
[https://en.wikipedia.org/wiki/Regulus]
Gamma Leonis is a binary star system in the constellation of Leo. It also bore the traditional name Algieba or Al Gieba, which originated from the Arabic ‘Al-Jabhah,’ meaning ‘the forehead.’ Algieba (gamma), Adhafera (Zeta Leonis), and Al Jabbah (Eta Leonis) have collectively been called ‘the Sickle,’ which is an asterism formed from the head of Leo.
The bright binary system in Leo with orange-red and yellow or greenish-yellow components is visible through a modest telescope under good atmospheric conditions. To the naked eye, the Algieba system shines at mid-second magnitude, but a telescope easily splits the pair. The brighter component has an apparent magnitude of +2.28 and is of spectral class K1-IIIbCN-0.5. The giant K star has a surface temperature of 4,470 K, a luminosity 180 times that of the Sun, and a diameter 23 times that of the Sun. The companion star has an apparent magnitude of +3.51 and belongs to the spectral class G7IIICN-I. The giant G star has a temperature of 4,980 K, a luminosity of 50 times that of the Sun, and a diameter 10 times that of the Sun. With angular separation of just over 4", the two stars are at least 170 AU apart (four times the distance between the Sun and Pluto), and have an orbital period of over 500 years. Because the orbital period is so long, only a fraction of the full path has been observed since discovery.
Both stars are almost certainly true giants, meaning that they have stopped fusing hydrogen to helium in their cores and have expanded to great proportions. Although there has been too little observation of their orbit to calculate their masses, comparison with evolutionary calculations suggests that each are about double the mass of the Sun. Originating from the same interstellar cloud some two billion years ago, the stars have iron contents about a third that of the Sun. It is hard to tell how far along they might be in their life cycle. They both may be fusing helium in their cores, or they could be giants in development, with quiet helium cores that are waiting to fire up. The chemical composition at the surface, which is influenced by age, suggests the former.
On November 6, 2009, the discovery of a planetary companion around primary star Gamma-1 Leonis was announced. The radial velocity measurements suggest two additional periodicities of 8.5 and 1340 days. The former is likely due to stellar pulsation, whereas the latter could be indicative of the presence of an additional planetary companion with 2.14 Jupiter masses, moderate eccentricity (e=0.13) and located at 2.6 Astronomical Units away from the giant star. Nevertheless, the nature of such a signal is still unclear and further investigations are needed to confirm or rule out an additional substellar companion.
[https://en.wikipedia.org/wiki/Gamma_Leonis]
Denebola, also designated Beta Leonis, is the third-brightest star in the zodiac constellation of Leo. The traditional name Denebola is shortened from Deneb Alased, from the Arabic phrase ‘ðanab al-asad,’ ‘tail of the lion.’ It is located at a distance of about 36 light-years (11 parsecs) from the Sun.
Denebola is a relatively young star with an age estimated at less than 400 million years. Interferometric observations give a radius that is about 173% that of the Sun. However, the high rate of rotation results in an oblate shape with an equatorial bulge. It has 75% more mass than the Sun, which results in a much higher overall luminosity and a shorter life span on the main sequence.
Based upon the star’s spectrum, it has a stellar classification of A3 V, with the luminosity class ‘V’ indicating this is a normal main sequence star that is generating energy through the nuclear fusion of hydrogen at its core. The effective temperature of Denebola’s outer envelope is about 8,500 K, which results in the white hue typical of A-type stars. Denebola has a high projected rotational velocity of 128 km/s, which is of the same order of magnitude as for the very rapidly rotating star Achernar. Compare this to the Sun’s more leisurely equatorial rotation velocity of 2 km/s. This star is believed to be a Delta Scuti variable star that exhibits fluctuations in luminosity of 0.025 magnitudes roughly ten times per day.
Denebola shows a strong infrared excess, which most likely means there is a circumstellar debris disk of cool dust in orbit around it. As the solar system is believed to have formed out of such a disk, Denebola and similar stars such as Vega and Beta Pictoris may be candidate locations for extrasolar planets. The dust surrounding Denebola has a temperature of about 120 K (−153 °C). Observations with the Herschel Space Observatory have provided resolved images, which show the disk to be located at a radius of 39 astronomical units from the star, or 39 times the distance from the Earth to the Sun.
Kinematic studies have shown that Denebola is part of a stellar association dubbed the IC 2391 supercluster. All the stars of this group share a roughly common motion through space, although they are not gravitationally bound. This suggests that they were born in the same location, and perhaps initially formed an open cluster. Other stars in this association include Alpha Pictoris, Beta Canis Minoris and the open cluster IC 2391. In total more than sixty probable members of the group have been identified.
[https://en.wikipedia.org/wiki/Denebola]
Zosma (Delta Leonis) (Apr 14, 2004)
[http://www.nikomi.net/english/art/photo/astro/stars/zosma.htm]
Delta Leonis is also named Zosma, which means ‘girdle’ in ancient Greek, referring to the star’s location in its constellation, on the hip of the lion. It lies at a distance of about 58.4 light-years (17.9 parsecs) from the Sun.
It is a relatively ordinary main sequence star with a stellar classification of A4 V, making it is somewhat larger and hotter than the Sun. It is a fairly well-studied star, allowing relatively accurate measurements of its age and size. The radius of the star, as measured directly using an interferometer, is about 214% of the Sun’s radius and it is emitting more than 15 times as much luminosity as the Sun. The energy is being emitted from the outer envelope with an effective temperature 8,296 K, giving it the white hue characteristic of an A-type star. Having a larger mass than the Sun it will have a shorter lifespan, and in another 600 million years or so will swell into an orange or red giant star before decaying quietly into a white dwarf.
This star is rotating rapidly, with a projected rotational velocity of 180 km s−1. The inclination of the axis of rotation to the line of sight from the Earth is estimated at 38.1°, which would mean the azimuthal velocity along the equator is about 280 km s−1. This rotation is producing an equatorial bulge, giving the star a pronounced oblate spheroidal shape. The polar radius is about 84% of the radius along the equator.
Based upon the location and trajectory of this star through space, it may be a member of the Ursa Major Moving Group, a type of stellar kinematics group that share a common origin and motion through space. The age of this group is about 500 million years.
[https://en.wikipedia.org/wiki/Delta_Leonis]
Epsilon Leonis is the fifth-brightest star in the constellation Leo, consistent with its Bayer designation Epsilon. The star has the traditional names Ras Elased (Australis), Asad Australis and Algenubi, all of which derive from the Arabic ‘rās al-’asad al-janūbī,’ which means ‘the southern (star) of the lion’s head;’ ‘australis’ is Latin for ‘southern.’
Epsilon Leonis has a stellar classification of G1 II, with the luminosity class of II indicating that, at an age of 162 million years, it has evolved into a bright giant. It is much larger and brighter than the Sun with a luminosity 288 times and a radius 21 times solar. Consequently, its absolute magnitude is actually –1.49, making it one of the more luminous stars in the constellation, significantly more than its alpha star, Regulus. Algenubi’s apparent brightness, though, is only 2.98. Given its distance of about 247 light-years (76 parsecs), the star is more than three times the distance from the Sun than Regulus. At this distance, the visual magnitude of Epsilon Leonis is reduced by 0.03 as a result of extinction caused by intervening gas and dust.
Algenubi exhibits the characteristics of a Cepheid-like variable, changing by an amplitude of 0.3 magnitude every few days. It has around four times the mass of the Sun and a projected rotational velocity of 8.1 km s−1. Based upon its iron abundance, the metallicity of this star’s outer atmosphere is only around 52% of the Sun’s. That is, the abundance of elements other than hydrogen and helium is about half that in the Sun.
[https://en.wikipedia.org/wiki/Epsilon_Leonis]
Adhafera- Zeta Leonis
[http://www.astrosurf.com/carreira/comentario_tak_sky90_eng.html]
Zeta Leonis, also named Adhafera, is a third-magnitude star. It forms the second star (after Gamma Leonis) in the blade of ‘the Sickle,’ which is an asterism formed from the head of Leo. The traditional name (Aldhafera, Adhafara) comes from the Arabic ‘al-ðafīrah,’ ‘the braid/curl,’ a reference to its position in the lion’s mane.
Adhafera is a giant star with a stellar classification of F0 III. Since 1943, the spectrum of this star has served as one of the stable anchor points by which other stars are classified. Its apparent magnitude is +3.44, making it relatively faint for a star that is visible to the naked eye. Nevertheless, it shines with 85 times the luminosity of the Sun. Adhafera has about three times the Sun’s mass and six times the radius of the Sun. Parallax measurements from the Hipparcos satellite yield an estimated distance to Adhafera of 274 light-years (84 parsecs) from the Sun.
Adhafera forms a double star with an optical companion that has an apparent magnitude of 5.90. Known as 35 Leo, this star is separated from Adhafera by 325.9 arcseconds along a position angle of 340°. The two stars do not form a binary star system as 35 Leo is only 100 light years from Earth, thus separating the two stars by approximately 174 light-years (53 parsecs).
[https://en.wikipedia.org/wiki/Zeta_Leonis]
This is a N.A.S.A. impression of what the solar system of Mu Leonis might look like. If the star is not on display, its because its so small compared to the orbits of the outer planets. The green area denotes the habital zone which if the planet is within that area, life could exist. The habital zone might not appear on the picture because its outside the area for the picture. Our planets show the orbit of the planet if its was in our solar system. For more information about the planet and other exoplanetary stuff, visit N.A.S.A.
[https://www.universeguide.com/star/rasalas]
Mu Leonis is also named Rasalas (Ras Elased Borealis) and Alshemali, both abbreviations of the Arabic ‘Ras al Asad al Shamaliyy,’ ‘the northern (star) of the lion’s head.’ It is located 124 light-years (38.1 parsecs) from the Sun.
Mu Leonis is an evolved K-type giant star with a stellar classification of K2 IIIb CN1 Ca1. The trailing notation indicates that, for a star of its type, it has stronger than normal absorption lines of cyanogen and calcium in its spectrum. It has around 1.5 times the Sun’s mass, but has expanded to around 14 times the Sun’s radius. With an apparent visual magnitude of 3.88, Mu Leonis shines with 63 times the luminosity of the Sun from an outer atmosphere that has an effective temperature of 4,436 K. It is around 3.35 billion years old.
In 2014 it was announced that Mu Leonis has a planetary companion that is at least 2.4 times as massive as Jupiter and orbits with a period of 358 days. This planet was detected by measuring radial velocity variations caused by gravitational displacement from the orbiting body.
[https://en.wikipedia.org/wiki/Mu_Leonis]
Wolf 359 is the orange-hued star located just above the center of this 2009 astrophotograph
Wolf 359 is a red dwarf that is located in the constellation Leo, near the ecliptic. At a distance of approximately 7.8 light years from Earth, it has an apparent magnitude of 13.5 and can only be seen with a large telescope. Wolf 359 is one of the nearest stars to the Sun; only the Alpha Centauri system (including Proxima Centauri), Barnard’s Star and the brown dwarfs Luhman 16 and WISE 0855−0714 are known to be closer.
Wolf 359 first came to the attention of astronomers because of the relatively high rate of transverse motion against the background, known as the proper motion. A high rate of proper motion can indicate that a star is located nearby, as more distant stars must move at higher velocities in order to achieve the same rate of angular travel across the celestial sphere. The proper motion of Wolf 359 was first measured in 1917 by German astronomer Max Wolf, with the aid of astrophotography. In 1919 he published a catalog of over one thousand stars with high proper motions, including this one, that are still identified by his name. He listed this star as entry number 359, and the star has since been referred to as Wolf 359 in reference to Max Wolf’s catalogue.
Wolf 359 is one of the faintest and lowest-mass stars known. At the light-emitting layer called the photosphere, it has a temperature of about 2,800 K, which is low enough for chemical compounds to form and survive. The absorption lines of compounds such as water and titanium(II) oxide have been observed in the spectrum. The surface has a magnetic field that is stronger than the average magnetic field on the Sun. As a result of magnetic activity caused by convection, Wolf 359 is a flare star that can undergo sudden increases in luminosity for several minutes. These flares emit strong bursts of X-ray and gamma ray radiation that have been observed by space telescopes. Wolf 359 is a relatively young star with an age of less than a billion years. No companions or disks of debris have been detected in orbit around it.
Wolf 359 has a stellar classification of M6.5, although various sources list a spectral class of M5.5, M6 or M8. An M-type star is known as a red dwarf: it is called red because the energy emission of the star reaches a peak in the red and infrared parts of the spectrum. Wolf 359 has a very low luminosity, emitting about 0.1% of the Sun’s energy. If it were moved to the location of the Sun, it would appear ten times as bright as the full Moon.
At an estimated 9% of the Sun’s mass, Wolf 359 is just above the lowest limit at which a star can perform hydrogen fusion through the proton–proton chain reaction: 8% of the Sun’s mass. (Substellar objects below this limit are known as brown dwarfs.) The radius of Wolf 359 is an estimated 16% of the Sun's radius, or about 110,000 km. For comparison, the equatorial radius of the planet Jupiter is 71,492 km, which is 65% as large as Wolf 359’s.
The entire star is undergoing convection, whereby the energy generated at the core is being transported toward the surface by the convective motion of plasma, rather than by transmission through radiation. This circulation redistributes any accumulation of helium that is generated through stellar nucleosynthesis at the core throughout the star. This process will allow the star to remain on the main sequence as a hydrogen fusing star proportionately longer than a star such as the Sun where helium steadily accumulates at the core. In combination with a lower rate of hydrogen consumption due to its low mass, the convection will allow Wolf 359 to remain a main-sequence star for about eight trillion years.
A search of this star by the Hubble Space Telescope revealed no stellar companions, although this does not preclude the presence of smaller companions that are below the telescope’s detection limit, such as a planet orbiting within one astronomical unit of the star. No excess infrared emission has been detected, which may indicate the lack of a debris disk in orbit around it. Radial velocity measurements of this star using the Near Infrared Spectrometer (NIRSPEC) instrument at the Keck II observatory have not revealed any variations that might otherwise indicate the presence of an orbiting companion. This instrumentation is sensitive enough to detect the gravitational perturbations massive, short period companions with the mass of Neptune or greater.
The outer, light-emitting layer of a star is known as the photosphere. Temperature estimates of the photosphere of Wolf 359 range from 2,500 K to 2,900 K, which is sufficiently cool for equilibrium chemistry to occur. The resulting chemical compounds survive long enough to be observed through their spectral lines. Numerous molecular bands appear in the spectrum of Wolf 359, including those of carbon monoxide (CO), iron hydride (FeH), chromium hydride (CrH), water (H2O), magnesium hydride (MgH), vanadium(II) oxide (VO), titanium(II) oxide (TiO) and possibly the molecule CaOH. Since there are no lines of lithium in the spectrum, this element must have already been consumed by fusion at the core. This indicates the star must be at least 100 million years old.
Beyond the photosphere lies a nebulous, high temperature region known as the corona. In 2001, Wolf 359 became the first star other than the Sun to have the spectrum of its corona observed from a ground-based telescope. The spectrum showed emission lines of Fe XIII, which is heavily ionized iron that has been stripped of twelve of its electrons. The strength of this line can vary over a time period of several hours, which may be evidence of microflare heating.
Wolf 359 is classified as a UV Ceti-type flare star, which is a star that undergoes brief, energetic increases in luminosity because of magnetic activity in the photosphere. Its variable star designation is CN Leonis. Wolf 359 has a relatively high flare rate. Observations with the Hubble Space Telescope detected 32 flare events within a two-hour period, with energies of 1027 ergs (1020 joules) and higher. The mean magnetic field at the surface of Wolf 359 has a strength of about 2.2 kG (0.22 teslas), but this varies significantly on time scales as short as six hours. By comparison, the magnetic field of the Sun averages 1 gauss (100 µT), although it can rise as high as 3 kG (0.3 T) in active sunspot regions. During flare activity, Wolf 359 has been observed emitting X-rays and gamma rays.
The rotation of a star causes a Doppler shift to the spectrum. On average, this results in a broadening of the absorption lines in its spectrum, with the lines increasing in width with higher rates of rotation. However, only the rotational motion in the direction of the observer can be measured by this means, so the resulting data provides a lower limit on the star's rotation. This projected rotational velocity of Wolf 359’s equator is less than 3 km/s, which is below the threshold of detection through spectral line broadening. This low rate of rotation may have been caused by loss of angular momentum through a stellar wind. Typically, the time scale for the spin down of a star at spectral class M6 is roughly 10 billion years, because fully convective stars like this lose their rotation more slowly than other stars. However, evolutionary models suggest that Wolf 359 is a relatively young star with an age of less than a billion years.
Distances of the nearest stars from 20,000 years ago until 80,000 years in the future
The proper motion Wolf 359 against the background is 4.696 arcseconds per year, and it is moving away from the Sun at a velocity of 19 km/s. When translated into the galactic coordinate system, this motion corresponds to a space velocity of (U, V, W) = (−26, −44, −18) km/s. The space velocity of Wolf 359 implies that it belongs to the population of old-disk stars. It follows an orbit through the Milky Way that will bring it as close as 20.5 kly (6.3 kpc) and as distant as 28 kly (8.6 kpc) from the Galactic Center. The galactic orbit has an eccentricity of 0.156, and the star can travel as far as 444 light-years (136 pc) away from the galactic plane. The closest stellar neighbor to Wolf 359 is the red dwarf Ross 128 at 3.79 ly (1.16 pc) away. Approximately 13,850 years ago, Wolf 359 was at its minimal distance of about 7.35 ly (2.25 pc) from the Sun.
[https://en.wikipedia.org/wiki/Wolf_359]
Rendering of R Leonis’s putative evaporating planetary companion
R Leonis is a red giant Mira-type variable star in the constellation Leo. The apparent magnitude of R Leonis varies between 4.31 and 11.65 with a period of 312 days. At maximum it can be seen with the naked eye, while at minimum a telescope of at least 7 cm is needed. The star’s effective temperature is estimated between 2,930 and 3,080 kelvins and radius spans between 320 and 350 solar radii (as large as 1.36–1.5 astronomical units, roughly Mars’s orbital zone).
In 2009 researchers proposed that quasi-periodic fluctuations observed for the star R Leonis may be due to the presence of an evaporating substellar companion, probably an extrasolar planet. They have inferred a putative mass for the orbiting body of twice the mass of Jupiter, orbital period of 5.2 years and likely orbital separation of 2.7–3 astronomical units. If confirmed such a planetary object could likely be an evaporating planet, with long comet-like trail as hinted by intense SiO maser emissions. Planetary temperature would exceed 1,500 kelvins, accounting a stellar luminosity of more than 8,000 times that of the Sun.
[https://en.wikipedia.org/wiki/R_Leonis]
Artist’s illustration of Gliese 436
[http://www.solstation.com/stars2/gl436.htm]
Gliese 436 is a red dwarf approximately 33 light-years (10 parsecs) away in the zodiac constellation of Leo. It has an apparent visual magnitude of 10.67, which is much too faint to be seen with the naked eye. However, it can be viewed with even a modest telescope of 2.4 in (6 cm) aperture.
This is a M2.5V star, which means it is a red dwarf. Stellar models give an estimated size of about 42% of the Sun’s radius. The same model predicts that the outer atmosphere has an effective temperature of 3,318 K, giving it the orange-red hue of an M-type star. Small stars such as this generate energy at a low rate, giving it only 2.5% of the Sun’s luminosity.
Gliese 436 is older than the Sun by several billion years and it has an abundance of heavy elements (with masses greater than helium-4) equal to 48% that of the Sun. The projected rotation velocity is 1.0 km/s, and the chromosphere has a low level of magnetic activity. Gliese 436 is a member of the ‘old-disk population’ with velocity components in the galactic coordinate system of U=+44, V=−20 and W=+20 km/s.
Size comparison of Gliese 436 b with Neptune
[https://en.wikipedia.org/wiki/Gliese_436_b]
The star is orbited by one known planet, designated Gliese 436 b. The planet has an orbital period of 2.6 Earth days and transits the star as viewed from Earth. It has a mass of 22.2 Earth masses and is roughly 55,000 km in diameter, giving it a mass and radius similar to the ice giant planets Uranus and Neptune in the Solar System. The planet is thought to be largely composed of hot ices with an outer envelope of hydrogen and helium, and is termed a ‘hot Neptune.’
In 2008, a second planet, designated ‘Gliese 436 c’ was claimed to have been discovered, but the discovery was eventually retracted. Despite the retraction, in July 2012, NASA announced that astronomers strongly believe they have observed a second planet. This strong candidate planet was given the preliminary designation UCF-1.01, after the University of Central Florida. It was measured to have a radius of around two thirds that of Earth and, assuming an Earth-like density of 5.5 g/cm^3, was estimated to have a mass of 0.3 times that of Earth and a surface gravity of around two thirds that of Earth. It orbits at 0.0185 AU from the star, every 1.3659 days. The astronomers also believe they have found some evidence for an additional planet candidate, UCF-1.02, which is of a similar size, though with only one detected transit its orbital period is unknown. If these planets are confirmed in the future, they may be given the designations ‘Gliese 436 c’ and ‘Gliese 436 d.’
[https://en.wikipedia.org/wiki/Gliese_436]
A rotating spiral structure around IRC+10216
[http://www.icmm.csic.es/nanocosmos/]
IRC +10216 or CW Leonis is a well-studied carbon star that is embedded in a thick dust envelope. It was first discovered in 1969 by a group of astronomers led by Eric Becklin, based upon infrared observations made with the 62 inches (1.6 m) Caltech Infrared Telescope at Mount Wilson Observatory. Its energy is emitted mostly at infrared wavelengths. At a wavelength of 5 μm, it was found to have the highest flux of any object outside the Solar System.
CW Leonis is believed to be in a late stage of its life, blowing off its own sooty atmosphere to form a white dwarf in a distant future. Based upon isotope ratios of magnesium, the initial mass of this star has been constrained to lie between 3–5 solar masses. The mass of the star’s core, and the final mass of the star once it becomes a white dwarf, is about 0.7–0.9 solar masses. It has a nominal luminosity of 11,300 times the Sun. This varies over the course of a 649-day pulsation cycle, ranging from a minimum of about 6,250 times the Sun’s luminosity up to a peak of around 15,800 times.
The carbon-rich gaseous envelope surrounding this star is at least 69,000 years old and the star is losing about (1–4) × 10^−5 solar masses per year. The extended envelope contains at least 1.4 solar masses of material. Speckle observations from 1999 show a complex structure to this dust envelope, including partial arcs and unfinished shells. This clumpiness may be caused by a magnetic cycle in the star that is comparable to the solar cycle in the Sun and results in periodic increases in mass loss. Various chemical elements and about 50 molecules have been detected in the outflows from CW Leonis, among others nitrogen, oxygen and water, silicon and iron.
If the distance to this star is assumed to be at the lower end of the estimate range, 120 pc, then the astrosphere surrounding the star spans a radius of about 84,000 AU. The star and its surrounding envelope are advancing at a velocity of more than 91 km/s through the surrounding interstellar medium. It is moving with a space velocity of [U, V, W] = [21.6 ± 3.9, 12.6 ± 3.5, 1.8 ± 3.3] km s−1.
[https://en.wikipedia.org/wiki/CW_Leonis]
AD Leonis
[https://jumk.de/astronomie/near-stars/ad-leonis.shtml]
AD Leonis (Gliese 388) is a red dwarf star located relatively near the Sun, at a distance of about 16 light years, in the constellation Leo. AD Leonis is a main sequence star with a spectral classification of M3.5V. It is a flare star that undergoes random increases in luminosity.
This is an M-type star with a spectral type M3.5eV, indicating it is a main sequence star that displays emission lines in its spectrum. At a trigonometric distance of 15.9 ly (4.9 pc), it has an apparent visual magnitude of 9.43. It has about 39–42% of the Sun’s mass- above the mass at which a star is fully convective- and 39% of the Sun’s radius. The projected rotation of this star is only 3 km/s, but it completes a rotation once every 2.24 days. It is a relatively young star with an estimated age of 25–300 million years, and is considered a member of the young disk population.
AD Leonis is one of the most active flare stars known, and the emissions from the flares have been detected across the electromagnetic spectrum as high as the X-ray band. Besides star spots, about 73% of the surface is covered by magnetically active regions. Examination of the corona in X-ray shows compact loop structures that span up to 30% of the size of the star. The average temperature of the corona is around 6.39 MK.
[https://en.wikipedia.org/wiki/AD_Leonis]
SDSS J102915+172927 or Caffau’s star is a population II star in the galactic halo, seen in the constellation Leo. It is about 13 billion years old, making it one of the oldest stars in the Galaxy. At the time of its discovery, it had the lowest metallicity of any known star. It is small (less than 0.8 solar masses), deficient in carbon, nitrogen, oxygen, and completely devoid of lithium. Because carbon and oxygen provide a fine structure cooling mechanism that is critical in the formation of low-mass stars, the origins of Caffau’s star are somewhat mysterious:
[https://en.wikipedia.org/wiki/SDSS_J102915%2B172927]
The star that should not exist
A team of European astronomers has used ESO’s Very Large Telescope (VLT) to track down a star in the Milky Way that many thought was impossible. They discovered that this star is composed almost entirely of hydrogen and helium, with only remarkably small amounts of other chemical elements in it. This intriguing composition places it in the ‘forbidden zone’ of a widely accepted theory of star formation, meaning that it should never have come into existence in the first place.
A faint star in the constellation of Leo (The Lion), called SDSS J102915+172927, has been found to have the lowest amount of elements heavier than helium (what astronomers call ‘metals’) of all stars yet studied. It has a mass smaller than that of the Sun and is probably more than 13 billion years old.
“A widely accepted theory predicts that stars like this, with low mass and extremely low quantities of metals, shouldn’t exist because the clouds of material from which they formed could never have condensed,” said Elisabetta Caffau, lead author of the paper. “It was surprising to find, for the first time, a star in this ‘forbidden zone’, and it means we may have to revisit some of the star formation models.”
The team analyzed the properties of the star using the X-shooter and UVES instruments on the VLT. This allowed them to measure how abundant the various chemical elements were in the star. They found that the proportion of metals in SDSS J102915+172927 is more than 20 000 times smaller than that of the Sun .
“The star is faint, and so metal-poor that we could only detect the signature of one element heavier than helium- calcium- in our first observations,” said Piercarlo Bonifacio, who supervised the project. “We had to ask for additional telescope time from ESO’s Director General to study the star’s light in even more detail, and with a long exposure time, to try to find other metals.”
Cosmologists believe that the lightest chemical elements- hydrogen and helium- were created shortly after the Big Bang, together with some lithium, while almost all other elements were formed later in stars. Supernova explosions spread the stellar material into the interstellar medium, making it richer in metals. New stars form from this enriched medium so they have higher amounts of metals in their composition than the older stars. Therefore, the proportion of metals in a star tells us how old it is.
“The star we have studied is extremely metal-poor, meaning it is very primitive. It could be one of the oldest stars ever found,” adds Lorenzo Monaco, also involved in the study.
Also very surprising was the lack of lithium in SDSS J102915+172927. Such an old star should have a composition similar to that of the Universe shortly after the Big Bang, with a few more metals in it. But the team found that the proportion of lithium in the star was at least fifty times less than expected in the material produced by the Big Bang.
“It is a mystery how the lithium that formed just after the beginning of the Universe was destroyed in this star.” Bonifacio added.
The researchers also point out that this freakish star is probably not unique. “We have identified several more candidate stars that might have metal levels similar to, or even lower than, those in SDSS J102915+172927. We are now planning to observe them with the VLT to see if this is the case,” concludes Caffau.
[https://www.eso.org/public/news/eso1132/]
Leo contains many bright galaxies. One of the closest, Leo A, is an irregular galaxy that is part of the Local Group. It lies 2.6 million light-years from Earth, and was discovered by Fritz Zwicky in 1942. The estimated mass of this galaxy is (8.0 ± 2.7) × 10^7 solar masses, with at least 80% consisting of an unknown dark matter. It is one of the most isolated galaxies in the Local Group and shows no indications of an interaction or merger for several billion years. However, Leo A is nearly unique among irregular galaxies in that more than 90% of its stars formed more recently than 8 billion years ago, suggesting a rather unusual evolutionary history. The presence of RR Lyrae variables shows that the galaxy has an old stellar population that is up to 10 billion years in age:
[https://en.wikipedia.org/wiki/Leo_A]
Hubble Peers into the Mouth of Leo A
At first glance, this NASA/ESA Hubble Space Telescope image seems to show an array of different cosmic objects, but the speckling of stars shown here actually forms a single body- a nearby dwarf galaxy known as Leo A. Its few million stars are so sparsely distributed that some distant background galaxies are visible through it. Leo A itself is at a distance of about 2.5 million light-years from Earth and a member of the Local Group of galaxies; a group that includes the Milky Way and the well-known Andromeda galaxy.
Astronomers study dwarf galaxies because they are very numerous and are simpler in structure than their giant cousins. However, their small size makes them difficult to study at great distances. As a result, the dwarf galaxies of the Local Group are of particular interest, as they are close enough to study in detail.
As it turns out, Leo A is a rather unusual galaxy. It is one of the most isolated galaxies in the Local Group, has no obvious structural features beyond being a roughly spherical mass of stars, and shows no evidence for recent interactions with any of its few neighbors. However, the galaxy’s contents are overwhelmingly dominated by relatively young stars, something that would normally be the result of a recent interaction with another galaxy. Around 90% of the stars in Leo A are less than eight billion years old- young in cosmic terms! This raises a number of intriguing questions about why star formation in Leo A did not take place on the ‘usual’ timescale, but instead waited until it was good and ready.
[https://www.nasa.gov/image-feature/goddard/2016/hubble-peers-into-the-mouth-of-leo-a]
NGC 2903 is a barred spiral galaxy discovered by William Herschel in 1784. It is very similar in size and shape to the Milky Way. In its core, NGC 2903 has many ‘hotspots,’ which have been found to be near regions of star formation. The star formation in this region is thought to be due to the presence of the dusty bar, which sends shock waves through its rotation to an area with a diameter of 2,000 light-years. The outskirts of the galaxy have many young open clusters:
NGC 2903: A Missing Jewel in Leo
Barred spiral galaxy NGC 2903 is only some 20 million light-years distant. Popular among amateur astronomers, it shines in the northern spring constellation Leo, near the top of the lion’s head. That part of the constellation is sometimes seen as a reversed question mark or sickle. One of the brighter galaxies visible from the northern hemisphere, NGC 2903 is surprisingly missing from Charles Messier’s catalog of lustrous celestial sights. This colorful image from a small ground-based telescope shows off the galaxy’s gorgeous spiral arms traced by young, blue star clusters and pinkish star forming regions. Included are intriguing details of NGC 2903’s bright core, a remarkable mix of old and young clusters with immense dust and gas clouds. In fact, NGC 2903 exhibits an exceptional rate of star formation activity near its center, also bright in radio, infrared, ultraviolet, and x-ray bands. Just a little smaller than our own Milky Way, NGC 2903 is about 80,000 light-years across.
[http://apod.nasa.gov/apod/ap150410.html]
The Leo Triplet (also known as the M66 Group) is a small group of galaxies about 35 million light-years away. This galaxy group consists of the spiral galaxies M65, M66, and NGC 3628:
[https://en.wikipedia.org/wiki/Leo_(constellation)]
The Leo Triplet Galaxies
This popular group is famous as the Leo Triplet- a gathering of three magnificent galaxies in one field of view. Crowd pleasers when imaged with even modest telescopes, these galaxies can be introduced individually as NGC 3628 (left), M66 (bottom right), and M65 (top right). All three are large spiral galaxies. They tend to look dissimilar because their galactic disks are tilted at different angles to our line of sight. NGC 3628 is seen edge-on, with obscuring dust lanes cutting across the plane of the galaxy, while the disks of M66 and M65 are both inclined enough to show off their spiral structure. Gravitational interactions between galaxies in the group have also left telltale signs, including the warped and inflated disk of NGC 3628 and the drawn out spiral arms of M66. This gorgeous deep view of the region was taken by the new VLT Survey Telescope (VST) and spans about one degree (two full moons) on the sky. The field covers over 500 thousand light-years at the trio’s estimated distance of 30 million light-years.
[http://apod.nasa.gov/apod/ap110803.html]
M95 and M96 are both spiral galaxies 20 million light-years from Earth. Though they are visible as fuzzy objects in small telescopes, their structure is only visible in larger instruments. M95 is a barred spiral galaxy. M105 is about a degree away from the M95/M96 pair; it is an elliptical galaxy of the 9th magnitude, also about 20 million light-years from Earth:
M96 Group: M95 (left) and M96 (right)
The M96 Group is located physically near the Leo Triplet. This group contains between 8 and 24 galaxies, including three Messier objects (M95, M96 and M105). The group is one of many groups that lies within the Virgo Supercluster (i.e. the Local Supercluster). These two groups (the M96 Group and the Leo Triplet) may actually be separate parts of a much larger group, and some calculations actually identify the Leo Triplet as part of the M96 Group.
[https://en.wikipedia.org/wiki/M96_Group]
In the center of the Leo Group of galaxies (M96) is located the Leo Ring, an immense intergalactic cloud of hydrogen and helium gas. Radio astronomers discovered the cloud in 1983. They had theorized that the ring was primordial gas in the process of forming a galaxy. In 2010 it was found that the gas was not primordial, but the result of a galactic collision between the two galaxies the ring is closely associated with.
A billion years ago, NGC 3384 collided with M96, at the heart of the Leo Group, expelling a galaxy’s worth of gas into intergalactic space. This gas gathered into a vast set of clouds, the Leo Ring. The two galaxies have now drifted to being 38 Mly (12 Mpc) apart, and the ring is now 650 kilolight-years (200 kpc) wide. The ring is composed of a collection of H I regions. A bridge of gas connects the ring to M96:
[https://en.wikipedia.org/wiki/Leo_Ring]
The Leo ring: deep image in the optical domain with the distribution of the gas in HI in yellow-orange. The thumbnails on the right are a three of the dense areas of the ring with their optical counterparts.
In the current theories on galaxy formation, the accretion of cold primordial gas is a key-process in the early steps of galaxy growth. This primordial gas is characterized by two main features: it has never sojourned in any galaxy and it does not satisfy the conditions required to form stars. Is such an accretion process still ongoing in nearby galaxies? To answer the question, large sky surveys are undertaken attempting to detect the primordial gas.
The Leo ring, a giant ring of cold gas 650,000 light-years wide surrounding the galaxies of the Leo group, is one of the most dramatic and mysterious clouds of intergalactic gas. Since its discovery in the 80s, its origin and its nature were debated. Last year, studies of the metal abundances in the gas led to the belief that the ring was made of this famous primordial gas.
Thanks to the sensitivity of the Canada-France-Hawaii Telescope MegaCam camera, the international team observed for the first time the optical counterpart of the densest regions of the ring, in visible light instead of radio waves. Emitted by massive young stars, this light points to the fact that the ring gas is able to form stars.
A ring of gas and stars surrounding a galaxy immediately suggests another kind of ring: a so-called collisional ring, formed when two galaxies collide. Such a ring is seen in the famous Cartwheel galaxy. Would the Leo ring be a collisional ring too?
In order to secure this hypothesis, the team used numerical simulations (performed on supercomputers at CEA) to demonstrate that the ring was indeed the result of a giant collision between two galaxies more than 38 million light-years apart: at the time of the collision, the disk of gas of one of the galaxies is blown away and will eventually form a ring outside of the galaxy. The simulations allowed the identification of the two galaxies which collided: NGC 3384, one of the galaxies at the center of the Leo group, and M96, a massive spiral galaxy at the periphery of the group. They also gave the date of the collision: more than a billion years ago!
The gas in the Leo ring is definitely not primordial. The hunt for primordial gas is still open!
[http://www.cfht.hawaii.edu/en/news/LeoRing/]
The Cosmic Horseshoe is the nickname given to a gravitationally lensed system of two galaxies in the constellation Leo.
The foreground galaxy lies directly in front in our line of sight to a more distant galaxy. Due to the passage of the light from the background galaxy through the gravity field of the foreground galaxy, the background galaxy’s light is lensed by the warped spacetime environment of the foreground galaxy. Thus giving the background galaxy a warped appearance. Unlike most lensed galaxies, the shape of the lensed light of this background galaxy appears shaped like a horseshoe.
The foreground galaxy, LRG 3-757, is found to be extremely massive, with a mass a hundred times that of our galaxy. It is notable because it belongs to a rare class of galaxies called luminous red galaxies, which has an extremely luminous infrared emission:
[https://en.wikipedia.org/wiki/Cosmic_Horseshoe]
Hubble captures a ‘lucky’ galaxy alignment
An interesting galaxy has been circled in this NASA/ESA Hubble Space Telescope image. The galaxy- one of a group of galaxies called Luminous Red Galaxies- has an unusually large mass, containing about ten times the mass of the Milky Way. However, it’s actually the blue horseshoe shape that circumscribes the red galaxy that is the real prize in this image.
This blue horseshoe is a distant galaxy that has been magnified and warped into a nearly complete ring by the strong gravitational pull of the massive foreground Luminous Red Galaxy. To see such a so-called Einstein Ring required the fortunate alignment of the foreground and background galaxies, making this object’s nickname ‘the Cosmic Horseshoe’ particularly apt.
The Cosmic Horseshoe is one of the best examples of an Einstein Ring. It also gives us a tantalizing view of the early Universe: the blue galaxy’s redshift- a measure of how the wavelength of its light has been stretched by the expansion of the cosmos- is approximately 2.4. This means we see it as it was about 3 billion years after the Big Bang. The Universe is now 13.7 billion years old.
Astronomers first discovered the Cosmic Horseshoe in 2007 using data from the Sloan Digital Sky Survey. But this Hubble image, taken with the Wide Field Camera 3, offers a much more detailed view of this fascinating object.
This picture was created from images taken in visible and infrared light on Hubble’s Wide Field Camera 3. The field of view is approximately 2.6 arcminutes wide.
[https://www.spacetelescope.org/images/potw1151a/]
Leo is also home to some of the largest structures in the observable universe. Some of the structures found in the constellation are the Clowes–Campusano LQG, U1.11, U1.54, and the Huge-LQG, which are all large quasar groups; the latter being the second largest structure known:
Above: Map of the Huge-LQG noted by black circles, adjacent to the Clowes-Campusano LQG in red crosses. Bottom: Image of the bright quasar 3C 273. Each black circle and red cross on the map is a quasar similar to this one.
The Huge Large Quasar Group, (Huge-LQG, also called U1.27) is a possible structure or pseudo-structure of 73 quasars, referred to as a large quasar group, that measures about 4 billion light-years across. At its discovery by Roger Clowes, it was identified as the largest and the most massive known structure in the observable universe, though it has been superseded by the Hercules-Corona Borealis Great Wall at 10 billion light-years.
Quasars are very luminous active galactic nuclei, thought to be supermassive black holes feeding on matter. Since they are only found in dense regions of the universe, quasars can be used to find overdensities of matter within the universe. It has the approximate binding mass of 6.1×10^18 (6.1 trillion (long scale) or 6.1 quintillion (short scale)) M☉. The Huge-LQG was initially named U1.27 due to its average redshift of 1.27, placing its distance at about 9 billion light-years from Earth.
The Huge-LQG is 615Mpc from the Clowes–Campusano LQG (U1.28), a group of 34 quasars also discovered by Clowes in 1991.
[https://en.wikipedia.org/wiki/Huge-LQG]
The Leonids are a prolific meteor shower associated with the comet Tempel–Tuttle. The Leonids get their name from the location of their radiant in the constellation Leo: the meteors appear to radiate from that point in the sky. They peak in the month of November.
Earth moves through the meteoroid stream of particles left from the passages of a comet. The stream comprises solid particles, known as meteoroids, ejected by the comet as its frozen gases evaporate under the heat of the Sun when it is close enough- typically closer than Jupiter’s orbit. The Leonids are a fast moving stream which encounter the path of Earth and impact at 72 km/s. Larger Leonids which are about 10 mm across have a mass of half a gram and are known for generating bright (apparent magnitude -1.5) meteors. An annual Leonid shower may deposit 12 or 13 tons of particles across the entire planet.
The meteoroids left by the comet are organized in trails in orbits similar to though different from that of the comet. They are differentially disturbed by the planets, in particular Jupiter and to a lesser extent by radiation pressure from the sun. These trails of meteoroids cause meteor showers when Earth encounters them. Old trails are spatially not dense and compose the meteor shower with a few meteors per minute. In the case of the Leonids, that tends to peak around November 18, but some are spread through several days on either side and the specific peak changes every year. Conversely, young trails are spatially very dense and the cause of meteor outbursts when the Earth enters one. Meteor storms (large outbursts) exceed 1000 meteors per hour, to be compared to the sporadic background (5 to 8 meteors per hour) and the shower background (several per hour):
[https://en.wikipedia.org/wiki/Leonids]
Leonids Over Monument Valley
What’s happening in the sky over Monument Valley? A meteor shower. Over the past weekend the Leonid meteor shower has been peaking. The image actually a composite of six exposures of about 30 seconds each- was taken in (November 19) 2012, a year when there was a much more active Leonids shower. At that time, Earth was moving through a particularly dense swarm of sand-sized debris from Comet Tempel-Tuttle, so that meteor rates approached one visible streak per second. The meteors appear parallel because they all fall to Earth from the meteor shower radiant- a point on the sky towards the constellation of the Lion (Leo). Although the predicted peak of this year’s Leonid meteor shower is over, another peak may be visible early tomorrow morning.
[http://apod.nasa.gov/apod/ap121119.html]
[https://en.wikipedia.org/wiki/Leo_%28constellation%29]
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