Capella OnlineApril 2017 Edition
|Pronunciation||/ˈliːoʊ/, genitive /liːˈoʊnᵻs/|
|Area||947 sq. deg. (12th)|
|Main stars||9, 15|
|Stars with planets||13|
|Stars brighter than 3.00m||5|
|Stars within 10.00 pc (32.62 ly)||5|
|Brightest star||Regulus (α Leo) (1.35m)|
|Nearest star||Wolf 359
(7.78 ly, 2.39 pc)
|Visible at latitudes between +90° and −65°.
Best visible at 21:00 (9 p.m.) during the month of April.
Leo /ˈliːoʊ/ is one of the constellations of the zodiac, lying between Cancer the crab to the west and Virgo the maiden to the east. Its name is Latin for lion, and to the ancient Greeks represented the Nemean Lion killed by the mythical Greek hero Heracles (known to the ancient Romans as Hercules) as one of his twelve labors. Its symbol is (Unicode ♌). One of the 48 constellations described by the 2nd century astronomer Ptolemy, Leo remains one of the 88 modern constellations today, and one of the most easily recognizable due to its many bright stars and a distinctive shape that is reminiscent of the crouching lion it depicts. The lion’s mane and shoulders also form an asterism known as “The Sickle,” which to modern observers may resemble a backwards “question mark.”
Leo contains many bright stars, many of which were individually identified by the ancients. There are four stars of first or second magnitude, which render this constellation especially prominent:
- Regulus, designated Alpha Leonis, is a blue-white main-sequence star of magnitude 1.34, 77.5 light-years from Earth. It is a double star divisible in binoculars, with a secondary of magnitude 7.7. Its traditional name (Regulus) means “the little king”.
- Beta Leonis, called Denebola, is at the opposite end of the constellation to Regulus. It is a blue-white star of magnitude 2.23, 36 light-years from Earth. The name Denebola means “the lion’s tail”.
- Algieba, Gamma Leonis, is a binary star with a third optical component; the primary and secondary are divisible in small telescopes and the tertiary is visible in binoculars. The primary is a gold-yellow giant star of magnitude 2.61 and the secondary is similar but at magnitude 3.6; they have a period of 600 years and are 126 light-years from Earth. The unrelated tertiary, 40 Leonis, is a yellow-tinged star of magnitude 4.8. Its traditional name, Algieba, means “the forehead”.
- Delta Leonis, called Zosma, is a blue-white star of magnitude 2.58, 58 light-years from Earth.
- Epsilon Leonis is a yellow giant of magnitude 3.0, 251 light-years from Earth.
- Zeta Leonis, called Adhafera, is an optical triple star. The brightest and only star designated Zeta Leonis, is a white giant star of magnitude 3.65, 260 light-years from Earth. The second brightest, 39 Leonis, is widely spaced to the south and of magnitude 5.8. 35 Leonis is to the north and of magnitude 6.0.
- Iota Leonis is a binary star divisible in medium amateur telescopes; they are divisible in small amateur telescopes at their widest in the years 2053–2063. To the unaided eye, Iota Leonis appears to be a yellow-tinged star of magnitude 4.0. The system, 79 light-years from Earth, has components of magnitude 4.1 and 6.7 with a period of 183 years.
- Tau Leonis is a double star visible in binoculars. The primary is a yellow giant of magnitude 5.0, 621 light-years from Earth. The secondary is a star of magnitude 8. 54 Leonis is a binary star 289 light-years from Earth, divisible in small telescopes. The primary is a blue-white star of magnitude 4.5 and the secondary is a blue-white star of magnitude 6.3.
Leo is also home to one bright variable star, the red giant R Leonis. It is a Mira variable with a minimum magnitude of 10 and normal maximum magnitude of 6; it periodically brightens to magnitude 4.4. R Leonis, 330 light-years from Earth, has a period of 310 days and a diameter of 450 solar diameters.
The star Wolf 359 (CN Leonis), one of the nearest stars to Earth at 7.8 light-years away, is in Leo. Wolf 359 is a red dwarf of magnitude 13.5; it periodically brightens by one magnitude or less because it is a flare star.Gliese 436, a faint star in Leo about 33 light years away from the Sun, is orbited by a transiting Neptune-mass extrasolar planet.
The star SDSS J102915+172927 (Caffau’s star) is a population II star in the galactic halo seen in Leo. It is about 13 billion years old, making it one of the oldest stars in the Galaxy. It has the lowest metallicity of any known star.
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 (Berenice’s hair), although there was precedent for that designation among the ancient Greeks and Romans.
The Leo Ring, a cloud of hydrogen and helium gas, is found in orbit of two galaxies found within this constellation.
M66 is a spiral galaxy that is part of the Leo Triplet, whose other two members are M65 and NGC 3628. It is at a distance of 37 million light-years and has a somewhat distorted shape due to gravitational interactions with the other members of the Triplet, which are pulling stars away from M66. Eventually, the outermost stars may form a dwarf galaxy orbiting M66. Both M65 and M66 are visible in large binoculars or small telescopes, but their concentrated nuclei and elongation are only visible in large amateur instruments.
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.
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 and is located 25 million light-years from Earth. 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.
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 (see also NQ2-NQ4 GRB overdensity).
The Leonids occur in November, peaking on November 14–15, and have a radiant close to Gamma Leonis. Its parent body is Comet Tempel-Tuttle, which causes significant outbursts every 35 years. The normal peak rate is approximately 10 meteors per hour.
History and mythology
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”.
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.
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).
As of 2002, the Sun appears in the constellation Leo from August 10 to Sept 10. In tropical astrology, the Sun is considered to be in the sign Leo from July 23 to August 27, and in sidereal astrology, from August 16 to September 17.
Leo is commonly represented as if the sickle-shaped asterism of stars is the back of the Lion’s head. The sickle is marked by six stars: Epsilon Leonis, Mu Leonis, Zeta Leonis, Gamma Leonis, Eta Leonis, and Alpha Leonis. The lion’s tail is marked by Beta Leonis (Denebola) and the rest of his body is delineated by Delta Leonis and Theta Leonis.
H.A. Rey has suggested an alternative way to connect the stars, which graphically shows a lion walking. The stars delta Leonis, gamma Leonis, eta Leonis, and theta Leonis form the body of the lion, with gamma Leonis being of the second magnitude and delta Leonis and theta Leonis being of the third magnitude. The stars gamma Leonis, zeta Leonis, mu Leonis, epsilon Leonis, and eta Leonis form the lion’s neck, with epsilon Leonis being of the third magnitude. The stars mu Leonis, kappa Leonis, lambda Leonis, and epsilon Leonis form the head of the lion. Delta Leonis and beta Leonis form the lion’s tail: beta Leonis, also known as Denebola, is the bright tip of the tail with a magnitude of two. The stars theta Leonis, iota Leonis, and sigma Leonis form the left hind leg of the lion, with sigma Leonis being the foot. The stars theta Leonis and rho Leonis form the right hind leg, with rho Leonis being the foot. The stars eta Leonis and Alpha Leonis mark the lion’s heart, with alpha Leonis, also known as Regulus, being the bright star of magnitude one. The stars eta Leonis and omicron Leonis form the right front foot of the Lion.
- Ridpath & Tirion 2001, pp. 166-168.
- “Leo”. Constellationsofwords.com. Retrieved 2016-01-19.
- “Astronomers discover smallest “exoplanets” yet”. Toronto. Archived from the original on January 16, 2009.
- L. Phil Simpson (Springer 2012) Guidebook to the Constellations: Telescopic Sights, Tales, and Myths, p. 235 (ISBN 9781441969415).
- Wilkins, Jamie; Dunn, Robert (2006). 300 Astronomical Objects: A Visual Reference to the Universe. Buffalo, New York: Firefly Books. ISBN 978-1-55407-175-3.
- Prostak, Sergio (11 January 2013). “Universe’s Largest Structure Discovered”. scinews.com. Retrieved 15 January 2013.
- Ridpath & Tirion 2001, pp. 166-167.
- Jenniskens, Peter (September 2011). “Mapping Meteoroid Orbits: New Meteor Showers Discovered”. Sky & Telescope: 24.
- Pasachoff, Jay M. (2006). Stars and Planets. Boston, Massachusetts: Houghton Mifflin. ISBN 9780395537596.
- Tamra Andrews (Oxford University Press 2000) Dictionary of Nature Myths: Legends of the Earth, Sea, and Sky (ISBN 9780195136777).
- Babylonian Star-lore by Gavin White, Solaria Publications, 2008 page 140, ISBN 978-0955903700
- Janet Parker; et al., eds. (2007). Mythology: Myths, Legends and Fantasies. Struik. pp. 121–122. ISBN 9781770074538.
- H. A. Rey, The Stars — A New Way To See Them. Enlarged World-Wide Edition. Houghton Mifflin, Boston, 1997. ISBN 0-395-24830-2.
- Star Names: Their Lore and Meaning, by Richard Allen Hinckley, Dover. ISBN 0-486-21079-0
- Ridpath, Ian; Tirion, Wil (2001), Stars and Planets Guide, Princeton University Press, ISBN 0-691-08913-2
- Ian Ridpath and Wil Tirion (2007). Stars and Planets Guide, Collins, London. ISBN 978-0-00-725120-9. Princeton University Press, Princeton. ISBN 978-0-691-13556-4.
- Dictionary of Symbols, by Carl G. Liungman, W. W. Norton & Company. ISBN 0-393-31236-4
Sky Calendar — April 2017
|1||Moon near Aldebaran (evening sky) at 9h UT. Occultation visible from southern Asia, Japan, and Korea.
• Occultation of Aldebaran (IOTA)
|1||Mercury at greatest elongation east (19° from Sun, evening sky) at 10h UT. Mag. 0.0.|
|3||First Quarter Moon at 18:40 UT.|
|5||Moon near Beehive cluster (evening sky) at 12h UT.
• Beehive Cluster (Wikipedia)
• M44: The Beehive Cluster (APOD)
|7||Moon near Regulus (evening sky) at 4h UT. Occultation visible from southern South America.
• Occultation of Regulus (IOTA)
|7||Jupiter at opposition at 21h UT. Best time to observe the largest planet in the solar system. Mag. −2.5.
• Opposition (Wikipedia)
|10||Moon near Jupiter (midnight sky) at 23h UT. Mag. −2.5.|
|11||Full Moon at 6:08 UT.|
|11||Moon near Spica (midnight sky) at 10h UT.|
|15||Moon near Antares (morning sky) at 7h UT.|
|15||Moon at apogee (farthest from Earth) at 10h UT (distance 405,475 km; angular size 29.5′).|
|16||Moon near Saturn (morning sky) at 19h UT. Mag. 0.3.|
|19||Last Quarter Moon at 9:59 UT.|
|20||Mercury at inferior conjunction with the Sun at 6h UT. Mercury passes into the morning sky.|
|21||Mars 3.5° SSE of the Pleiades (28° from Sun, evening sky) at 20h UT. Mag. 1.6.
• The Pleiades (Wikipedia)
|22||Lyrid meteor shower peaks at 12h UT. Active April 16-25. Radiant is between Hercules and Lyra. Expect 10 to 20 bright, fast meteors per hour at its peak.
• Observing the Lyrids (Gary Kronk)
• Meteor Shower Calendar 2017 (IMO)
|23||Moon near Venus (morning sky) at 21h UT. Mag. −4.5.|
|26||New Moon at 12:17 UT. Start of lunation 1167.
• Lunation Number (Wikipedia)
|26||Venus at its brightest at 19h UT. Mag. −4.5.|
|27||Moon at perigee (closest to Earth) at 16:14 UT (359,327 km; angular size 33.3′).|
|28||Moon near the Pleiades (23° from Sun, evening sky) at 2h UT.
• The Pleiades (Wikipedia)
|28||Moon near Mars (27° from Sun, evening sky) at 9h UT. Mag. 1.6.|
|28||Moon near Aldebaran (32° from Sun, evening sky) at 18h UT. Occultation visible from eastern Europe and north central Africa.
• Occultation of Aldebaran (IOTA)
|All times Universal Time (UT).|
Welcome to the April edition of this newsletter.
Thanks to everyone who came up to Keele last week for the three nights of Stargazing Live. Pity about the weather but in all Keele had 200 members of the public up there over the three nights and we had a bit of interest in our display too. Hopefully some of them will come along to our meetings too now.
This month’s observing evening has not been decided yet. It is getting lighter and lighter in the evenings now so it may not be practical to hold another one this season. That said, maybe we could go for the 7/8th and have a look at the moon for a change. Let me know your thoughts and I’ll post on the website.
The next practical workshop is scheduled for Wednesday 19th April. This and any other events are listed on the NSAS Events page.
This month we have the Annual General Meeting. Also it’s subscription time. Please bring your membership forms with you on the night to save time. The subscriptions will be discussed during the AGM with detail of any changes on this page at some point.
May I remind everyone that the society solar scope is available to loan. It is on a monthly basis and there is just a £25 returnable deposit required. Contact me at the email below or see me at the meeting. More details here.
If anyone has any ideas for new features on the website or on any improvements you’d like to see to existing ones then please drop me an email or text.
Also keep an eye on our Facebook page as any breaking news will more than likely appear there first as I can update that from my phone.
Our new members Facebook group is here
The sky maps can be downloaded from here
The next regular meeting is on May 2nd which is 21st Century Observatory with John from Peak2Valley.
If anyone has anything they want to include on the website/newsletter/etc then please email me email@example.com
Wishing you clear skies, Duncan
Members Area access for this month (see email)
Why Do We Only See One Side of the Moon?
You may have heard references made to the “dark side” of the Moon. This popular term refers to the fact that the same physical half of the Moon, the “near side”, is always facing Earth, which in turn means that there is a far side or so-called “dark side” that is never facing Earth and can only be seen from space.
This phenomenon has nothing to do with illumination or the periodic light and dark we see as the phases of the moon change. Sometimes people refer to a New Moon as a “dark moon” because the moon is fully in shadow as viewed from Earth and we can’t see it, but that’s not the same thing as the dark side of the moon. The side of the moon facing us during a New Moon is the same as any other moon phase, such as a Full Moon when we can see the entire face.
So why can we only see one side of the moon from Earth? We all know that the Earth rotates on its own axis, so theoretically, the Moon should also do the same, allowing us to get a full picture of the planetoid. Why are we limited to seeing only 50 percent? It turns out that the speed at which the Moon rotates has led to this particular phenomenon. Millions of years ago, the Moon spun at a much faster pace than it does now. However, the gravitational influence of the Earth has gradually acted upon the Moon to slow its rotation down, in the same way that the much smaller gravitational influence of the Moon acts upon the Earth to create tides. This influence slowed the rotational period of the Moon to match that of its orbit – about 27.3 days – and it is now “locked in” to this period. (Note that to observers on earth a full moon cycle takes 29.5 days. See Understanding the moon phases).
If the Moon didn’t spin at all, then eventually it would show its far side to the Earth while moving around our planet in orbit. However, since the rotational period is exactly the same as the orbital period, the same portion of the Moon’s sphere is always facing the Earth.
Another interesting fact is that actually a little bit more than half of the Moon’s surface is observable from Earth. Since the Moon’s orbit is elliptical, and not circular, the speed of its orbital travel increases and decreases depending on how close it is to our planet. The rotational speed of the Moon is constant however – and this difference between orbital speed and rotational speed means that when the Moon is farthest from the Earth, its orbital speed slows down just enough to allow its rotational speed to overtake it, giving observers a small glimpse of the usually hidden area. The term for this “rocking” motion of the Moon is called libration and it allows for 59 percent of the Moon to be seen in total (over time).
Finally, one reason that the far side of the Moon is frequently referred to as the “dark side” is because many people mistakenly think that it never sees any light from the Sun. In that sense the term “dark side” is wrong and misleading. In fact, since the Moon is constantly rotating on its own axis, there is no area of the planetoid which is in permanent darkness, and the far side of the Moon is only completely devoid of sunlight during a Full Moon – when the Sun is facing the Moon with the Earth in between.
The Moon generally has one hemisphere facing the Earth, due to tidal locking. Therefore, humans’ first view of the far side of the Moon resulted from lunar exploration on October 7, 1959. However, this simple picture is only approximately true: over time, slightly more than half (about 59%) of the Moon’s surface is seen from Earth due to libration.
Libration is manifested as a slow rocking back and forth of the Moon as viewed from Earth, permitting an observer to see slightly different halves of the surface at different times.
There are three types of lunar libration:
- Libration in longitude results from the eccentricity of the Moon’s orbit around Earth; the Moon’s rotation sometimes leads and sometimes lags its orbital position.
- Libration in latitude results from a slight inclination (about 5 degrees) between the Moon’s axis of rotation and the normal to the plane of its orbit around Earth. Its origin is analogous to how the seasons arise from Earth’s revolution about the Sun.
- Diurnal libration is a small daily oscillation due to the Earth’s rotation, which carries an observer first to one side and then to the other side of the straight line joining Earth’s and the Moon’s centers, allowing the observer to look first around one side of the Moon and then around the other—because the observer is on the surface of the Earth, not at its center.
- Theoretical extent of visible lunar surface (green line) due to libration in Winkel tripel projection.