The Whale and the Hockey Stick Galaxies are visible through moderate sized apertures (6” to 8”), but are really appealing through larger telescopes. I was introduced to these two by none other Al Nagler at a Riverside Telescope Makers Convention at Big Bear Lake Lake in 1989. The instrument used was a custom 24” equatorially mounted Newtonian mounted on a flatbed trailer using the new Tele Vue prototype Panoptic eyepieces..
NGC 4631 is a SB class barred edge-on spiral galaxy with a slightly distorted wedge shape giving it the appearance of a whale, thus giving the galaxy its nickname.
The Whale Galaxy was discovered in 1787 by William Herschel. Astronomers have estimated that NGC 4631 is only 25 million light-years awayand is of similar size to our Milky Way galaxy. NGC 4631 has a recessional velocity of 605 km/sec that is too small to be a reliable indicator of distance, because of the possibility of significant peculiar (non-Hubble-expansion) velocities. However, its distance based on that recessional velocity (about 27 million light years away) is in reasonable agreement with redshift-independent distance estimates of 18 to 24 million light years. In larger telescopes than an 8”, a small companion E4 elliptical galaxy NGC 4627 can be seen nearby the Whale Galaxy, making this a Cosmic Duet for larger (16”+) telescopes.
NGC 4656 is a large Sb spiral galaxy discovered by William Herschel in 1787.Why the two NGC designations? The bright knot on the East of this galaxy has been assigned the separate NGC number NGC 4657, since William Herschel had cataloged it separately. Some astronomers believe NGC 4657 is a companion to the galaxy.
The Hockey Stick galaxy upward curve is a result of distortion by the interaction with The Whale Galaxy and its small elliptical NGC 4627 companion. A bridge of hydrogen gas is connecting both galaxies.
With March fast approaching, now is a good time to practice Messier object location finding and observational skills. Ursa Major is a perfect constellation to familiarize with deep sky observing, with seven Messier objects within this favorite constellation.
As an somewhat odd start, M40 is NOT a deep sky object, but a double star! Historians have long felt that Charles Messier mistook this double star for a nebula. But it must still be accounted for in a mini- or full Messier Marathon. M40 is easily observed with a four-inch telescope.
M81 and M82 are a cosmic duet pair of galaxies is one of the deep sky showpieces that captures the imagination of every backyard astronomer. Easily seen through a 4-inch refractor on a dark moonless night and a favorite target for 8-inch SCT owners, M81 and M82 are separated by only 38′. M81 and M82 can even be seen through 50-mm or greater binoculars from a dark country site.
Pierre Mechain independently recovered both galaxies in August 1779 and reported their positions to his friend Charles Messier. Messier added both galaxies to his catalog after his position measurements on February 9, 1781.
The pronounced grand-design spiral galaxies M81 and M82 are part of a nearby group called M81. M81 is characterized in the Hubble classification system as a classic Sa-type galaxy, while M82 is an irregular or IO classification. Astronomers believe tens of million years ago, a close encounter occurred between the galaxies M81 and M82. During this near-miss, the larger and more massive M81 has dramatically deformed M82 by gravitational interaction. The encounter has also left traces in the spiral pattern of the brighter and larger galaxy M81, first making it overall more pronounced, and second in the form of the dark linear feature in the nuclear region. The galaxies are still close together, their centers separated by a linear distance of only about 150,000 light years.
This pair of galaxies can be seen with 12×60 or 20×80 binoculars, and occasionally with 7×50 binoculars by sharp-eyed observers in very dark sites. My f/7.8 4-inch refractor with a wide-field 24-mm eyepiece with an AFOV of 68ºyields a magnification of 36x and a true field of 2.24º. This combination easily captures M81 as a bright oval haze and M82 as a slim cigar shape. The 8-inch SCT with the same eyepiece at 83x and a true FOV of 0.98º begins to show a hazy halo of nebulosity around M81, with M82 displaying a nucleus. Higher magnifications will help bring out the detail, and a larger telescope will bring out additional detail.
The Owl Nebula, M97, is a planetary nebula that is noted for features that faintly resembles an owl’s head. The Owl Nebula monicker was attached to M97 following Lord Rosse’s observations of the planetary nebula through his famous 72-inch Leviathan of Parsonstown.
This is an object that benefits form the use of a large aperture telescope or the use of an UHC nebula filter or OIII nebula filter. The “owl eyes” are clearly obvious with a telescope of apertures larger than 8”, especially with a nebula filter. Dark skies and nebula filter is needed with smaller apertures.
The Owl Nebula is an interesting object to test the effectiveness of light pollution filters and nebula filters. Under suburban skies, even an eleven inch SCT had difficulty seeing M97 without a filter aid. The addition of an LPR filter enabled sighting the Owl with averted vision. However the use of an OIII or UHC filter enabled the direct observation of the Owl Nebula even under light polluted suburban skies.
M101 was initially discovered by Pierre Mechain in 1781. He later that year made a duplicate observation of this galaxy, which was cataloged by Messier as M102. Mechain retracted is
his M102 sighting in 1783, realizing his duplication mistake. Thus, in counting Messier objects captured during a mini- or full Marathon, this galaxy counts as two objects.
M101 in astrophotos is a beautiful face-on Sc spiral galaxy with clearly separated arms filled with blue stars. The arms can be observed in telescopes of double digit apertures, but the spiral shape will not be seen in a four inch refractor. Instead only the central concentration of stars can be seen.
M108 is a Sc spiral galaxy seen from a nearly edge-on perspective. Another Pierre Mechain discovery from his 1781-1782 observations. This rather large object can be seen in dark skies through binoculars, and is easily captured by a four-inch refractors and 120x or higher. It is only 1ºfrom M97. It is visually a series of mottled patches of light. Larger apertures brings a broken patched structure into view.
M109 is an unspectacular barred galaxy that can be seen through binoculars just 1ºfrom the Ursa Major star Phecda at the bottom of the Big Dipper bowl. Seen through a 4-inch refractor the bright central region can be seen. M109 is another Pierre Mechain discovery during his productive 1781-1782 period.
Locating and observing Ursa Major Messier objects is good practice for the March Messier Marathon, or half-marathon if you want to go to sleep at midnight!
The 4” telescope is one of the most popular size telescopes in the world. Every amateur astronomer has owned or currently uses a 4” reflector or refractor.
For many beginning backyard astronomers, a 114 mm (or 4.5”) Newtonian reflector is the entry-level telescope of choice. Whether on a Dobsonian, alt-az, equatorial, or GoTo mount, this telescope is readily available at local shopping malls, warehouse stores, sporting goods stores, mail-order, or on-line stores. Some are well made. Some, not so much. But the 4.5” Newtonian is a very popular telescope, and is a very powerful optical tool in the right hands.
For many advanced amateur astronomers, a 102 mm (or 4”) achromat or apochromat refractor is the workhorse instrument in their collection of telescopes. The versatile 4” refractoris a light, portable, and low maintenance telescope that offers sharp contrasty images of the Moon, planets, bright deep sky objects, and are a favorite for astrophotography. Many notable astronomy writers, such as the late Walter Scott Houston, Stephen James O’Meara, and John H. Mallas, have based their writings on their observations through a 4” refractor. Every telescope manufacturer features a bread-and-butter 4” refractor in their catalogs. With aperture variations ranging from 100 mm to 105 mm, these telescopes represent the elbow of the price curve for refractors, the maximum aperture available for a refractor without busting the budget. Especially when comparing the cost of apochromat refractors, going past the 4” aperture to larger refractors represents an enormous increase in cost for the telescope and the larger mounting required to support such a beast. For example, a typical 102 mm apochromat refractor can cost $2,500 for the optical tube assembly, or OTA. For a typical 130 mm apochromat refractor, the OTA cost doubles to the $5,000 to $6,000 range. A 152 mm apochromat refractor easily exceeds the $10,000 to $12,000 range and anything of larger aperture represents the cost of a new car or SUV. The cost of mounting larger refractors often represents an investment equal to or greater than the OTA!
I have three refractors in this size range: a 102mm doublet apochromat mounted on a modern computerized German mount, a 102mm achromat mounted on a vintage 60 year old weight driven German mount, and a slightly smaller 94mm triplet apochromat on a mid-1970’s/early 1980”s single axis RA driven German mount.
The 102mm apochromat and the 94mm apochromat are unequivocally the most used telescopes in my collection., with 75% of my viewing and observing done with these two telescopes. The 94mm is my favorite telescope for public outreach. They are both easily carried out from my living room to my deck, easy to set up, and easy to use. The optics never need re-alignment. Both show exquisite planetary views. Deep sky views are comparable to reflectors 6” or more. Because they are refractors, there is no secondary mirror present in the optical system to block and scatter incoming light and affect contrast. As a result of the higher contrast, the background space is darker and allowing the fainter light of DSO’s to be seen.
When people ask me what telescope they should buy, I give them two pieces of advice. The first is to buy their second telescope first. Never buy a “beginner” telescope. It is false economy to buy a cheap telescope with the false the interest in astronomy will build from there. A cheap telescope just ends up in a closet or a yard sale. A quality telescope provides quality images that truly builds interest and knowledge in astronomy.
The second piece of advice is to buy a telescope that will be used often, rather than a larger telescope that is difficult to move, setup, and use. The smaller will “see” more because of its frequency of use. A 102mm refractor is the perfect size that will maximize frequency of use.. The 102mm telescope never disappoints and will always be used, even if larger aperture telescopes are acquired in the future. A 102mm refractor can always take the role of a grab-and-go scope, easy to transport, easy to setup, and easy to use!
The time has come where the warm sweaty humidity of summer observing gives way to the cooling dry air of autumn. Slowly, my observing wardrobe changes from shorts and t-shirts to layers of long pants and long sleeves, light jackets and heavier coats.
The Milky Way objects of summer also gives way to clusters, nebulae, and galaxies of the fall. The Earth’s position in its orbit around the Sun also changes the perspective of the sky. No longer are astronomers stargazing into the heart of the Milky Way, but more towards deep sky of far off galaxies.
As the backyard astronomer experiences the cooling weather, I have learned lessons of being prepared for the cooler autumn nights that eventually trasnsitions to the freezing winter.
Never underestimate the cooling temperatures. Observing through a telescope means sitting quietly with eye to eyepiece, the lower temperatures during an autumn night can have a chilling effect. I have learned to dress in layers and to dress like its 20°colder. Coats, sweaters, sock hats, gloves or mittens, and blankets are the dress code.
I take my telescope and eyepiece case outside from my warm house to the cool night to acclimate to the ambient temperature. Going from a warm home or car to a cool outdoor environment will require at least 30 minutes to adjust to the cooler air.
Dewing can be a problem. As the temperature drops, optics can attract a layer of dew. There are several ways of combating dewing: dew caps for the front of the telescope, and dew heater devices to gently maintain the temperature of the optics a few degrees above the dew point. Avoid observing objects directly overhead. Once infected with dew, a brief exposure to the warm air of a hairdryer may help, but then the optics will have to acclimate to the ambient temperature all over again.
Beware of fogging, and condensation. It is easy to fog over eyepieces and finderscopes by inadvertently breathing on them. Don’t!
In early autumn, the bugs and insects that bite and sting may still be a problem. As the weather gets colder, some remaining insects may seek a warmer environment in eyepiece cases, telescope cases, and telescopes and mounts. Check all equipment before packing it in for a night.
In the process of selecting a suitable observing site for the Shenandoah Astronomical Society’s members-only star party, I had the opportunity to visit some candidate state parks. Many could have worked, but ultimately I placed a priority on a dark site as being more appealing than accessibility to club members.
Ironically, I choose my own backyard! I discovered that the criteria I used for my search for a site for the star party was similar to the criteria that I originally used for my search for a new home in the Winchester VA area eight years ago: namely little or no trees and a dark sky.
The tree criteria is easily understandable. But the definition of a dark sky is not.
The darkest sky I’ve ever experienced was on a drive from Las Vegas NV to the San Bernadino Mountains to attend the now-defunct Riverside Telescope Makers Convention (RTMC), formerly held at a Boys and Girls campground just outside Big Bear Lake, CA. After crossing the state line and entering California, there is a long stretch of highway through the desert before reaching the base of the mountains. While driving in the middle of the night, my friend and I stopped to view the night sky. Incredible! The night sky was extraordinarily dark. There were so many stars that it was hard to pick out the constellations. M31 the Andromeda Galaxy, M33 the Triangulum Galaxy, and NGC 7000 the North America Nebula were clearly visible with the naked eye.
Fast forward to 2013 when my wife and I had decided to move from Bowie, Maryland and its light polluted skies and were searching for country home with dark skies. We eventually settled on our current home. No trees around the house that would block my view of the horizon. And save for a slight light dome from Winchester, dark skies from my backyard allow me to see the Milky Way across the summer sky.
In the magazine Sky and Telescope February 2001 issue, the Bortle scale was introduced as a rating system for the night sky brightness of a particular observing location. John E. Bortle created the scale that quantifies the observability of astronomical objects and the interference of light pollution.
The Bortle scale ranges from Class 1 representing the darkest skies on Earth to Class 9 representing inner-city skies. The following are the definitions of each class:
Class 1 – An excellent dark sky site, representing the almost mythical descriptions of the night sky described by veterans returning from desert wars and my own experience in the desert of California. The naked eye limiting magnitude is 7.6 to 8.0! Phenomena such as the zodiacal light, gegenschein and the zodiacal band are clearly visible. Light domes of distant cities can be seen. The Milky Way in the regions of Sagittarius and Scorpio clearly display the dark cloud shadows. Constellations are barely recognizable due to the abundance of stars. Many Messier globular clusters, open clusters, and bright galaxies are naked eye objects! M33 the Triangulum Galaxy is a direct eye visibility object. The night is so srak that a bright Venus and Jupiter can affect your night vision!
Class 2 – A typical dark sky site. Magnitude limit from 7.1 to 7.5. A yellowish zodiacal light is visible. Some sky domes are visible. Fainter constellations are barely recognizable amid the the abundance of stars. Clouds and structural surroundings are visible as dark holes and silhouettes in the sky. The summer Milky Way appears highly structured. Many Messier objects and globular clusters are visible, with M33 still visible with the naked eye.
Class 3 – Rural sky, with a limiting magnitude of 6.6-7.0. The zodiacal light is visible in the spring and autumn. Some light pollution is weakly detected near the horizon. Clouds are dark overhead but illuminated near the horizon.Surrounding trees and buildings are vaguely visible. Although the Milky Way still appears complex, only the brightest globulars, such as M13, M22, M15, M4, and M5 are naked eye visible, with M33 an averted eye object.
Class 4 -Rural/suburban sky. Limiting magnitude 6.1-6,5. The zodiacal light is visible but does not extend halfway to the zenith. Light pollution is clearly visible is several directions. Clouds are illuminated by light sources but dark overhead. Near and distant surrounding are visible. The Milky Way is visible but lacks detail. M33 is a difficult avert vision object.
Class 5 – Suburban sky. Limiting magnitude 5.6 -6.0. The zodiacal light is just hunted during the autumn and spring. Light pollution is visible in all directions. Clouds are noticeably brighter in the sky. The Milky Way is not detectable in the horizon and is washed out overhead. The night sky is more dark blue than it is black.
Class 6 – Bright Suburban sky. Limiting magnitude of 5.1-5.5. No zodiacal light . Light pollution extends to 35°from the horizon. Clouds are brightly lit. Binoculars and telescopes are needed to see Messier objectsThe sky appears blue.
Class 7 – Suburban/Urban transition. 4.6-5.0 limiting magnitude. Light pollution makes the night sky appear grey. Strong lights source are visible in all directions.The Milky Way, forget it, invisible. A telescope is needed to view anything, with any detail being washed out.
Class 8 – City Sky. Limiting magnitude 4.1-4.5. The sky is a light grey or orange. Many constellations are invisible. Even a telescope is unable to detect some of the dimmer Messier objects.
Class 9 – Inner city. <4.0 magnitude visible. For example, in Las Vegas, only the Moon can be seen. In Las Vegas, the only stars visible are Celine Dion, Penn & Teller, and Elvis impersonators. Most inner cities, the astronomer is limited to viewing the Moon, Jupiter, Saturn, Venus and the Pleiades.
So with the Bortle scale, how do you rate your own back yard? I rate my backyard somewhere between a Class 3/Class 4, mostly due to the light and proximity from Winchester VA and locally the community of Lake Holiday. My front yard is a solid Class 3 view. Completely acceptable for an amateur astronomer.
Messier 13, M13, is one of the showcase deep sky objects in the Northern Hemisphere night time sky. For many who can’t see Omega Centauri, M13 is the most spectacular globular, although M22 in Sagittarius is considered by many its equal.
Discovered by Edmond Halley in 1714, this globular cluster was catalogued by Charles Messier on June 1, 1764 in his famous list of fuzzy objects that were not comets.
As shown in the image, there are dark lanes of globular cluster M13 known as “the propeller” (above and to the left of center in the image of M13)l. This image also shows the distant galaxy IC 4617 to the upper right of the cluster, which lies at a distance of 500 million light-years compared to M13’s distance of about 25,000 light years. A Cosmic Duet!
The question is how many of you have visually or photographically seen the propeller? Or better yet, how many of you knew of its existence?
This little-known feature of M13 is a challenge to view visually. I had seen it through my old C-11 Celestron before I sold it. It’s visible in my new 9.25” Celestron SCT through a 10mm eyepiece at 250x. I have heard of observers visually seeing the propeller through telescopes with apertures as small as 6”. A clear, low humidity, transparent night helps. Averted vision is needed to spot this feature, especially through single digit (in inches) aperture optics. High power in the range of 250x to 300x is the order of the day.
Astro-imagers should have success imaging the M13 propeller, but I have not seen any images using an 80mm aperture or smaller. That doesn’t mean it can’t be done with an 80mm, it just that I haven’t seen a published example.
NGC 663 is a large open cluster compared with NGC 654 and 659. NGC 654 and 659 are small and NGC 659 is significantly dimmer than the three clusters. All are visible using a 10×50 binoculars in dark skies, although NGC 659 will pop in-and-out with averted vision. Even in a 12×60 binocular, NGC 659 needs good dark skies, since it has no stars brighter than mag 10.4. NGC 654 is barely seen as non- stellar and 663 is large and fairly bright with a handful of stars resolvable. In a 15×70 binocular, NGC 659 is seen but just very faintly. NGC 654 has one bright star to the south with a faint glow to the northwest and NGC 663 has several pairs resolved with a faint glow all around them.
NGC 654 was discovered by William Herschel in 1787.It is 7,830 light-years away. It is a very young cluster, with an age between 14 to 15 million years. The cluster has approx. 80 members.
NGC 659 was discovered by Caroline Herschel in 1783.
NGC 663, also known as Caldwell 10, is a young cluster of about 400 stars. The largest cluster of CD-B-14, it spans about a quarter of a degree across the sky. Backyard astronomers with dark skies reportedly have detected NGC 663 with naked eye observing, although 10×50 or 12×60 binoculars bring out more detail. The brightest members of the cluster can be viewed with binoculars. It is located about 6,850 light-years distant with an estimated age of 20–25 million years.
Author Stephen James O’Meara, in his book The Caldwell Objects,wrote he was able to spot NGC 654 and NGC 659 with 7×35 binoculars, but with some difficulty. This author was not able to duplicate this observation primarily due the lack of a suitable pair of 7×35 binoculars. The reader is invited to attempt this challenge.
All three open clusters are members of the Perseus Arm of the Milky Way. I was never able to obtain an astrophoto of this pair could not be obtained during the preparation of my ill-fated Cosmic Duets book in Spring, 2017 due to bad weather.
Alternative Nomenclature: NGC 6995, NGC 6974, IC 1340, Cygnus Loop, Cirrus Nebula, Filamentary Nebula, Witch’s Broom Nebula (NGC 6960), Caldwell 33, Caldwell 34, Pickering’s Triangle
Right Ascension: 20h 45m 8.23s
Declination: +30deg 42min 30s
News flash: The Veil Nebula is a cosmic duet! It can be seen with 15×70 binoculars under a dark sky.
Yes, the Veil Nebula is the remnant of a supernova, but parts of the Veil Nebula have been assigned different NGC catalog numbers. Therefore, in my book it qualifies as a cosmic duet!
The nebula was discovered on September 5, 1784, by William Herschel. He described in his observational notes the western end of the nebula as:“Extended; passes thro’ 52 Cygni… near 2 degree in length.”
Herschel described the eastern end of the Veil Nebula as: “Branching nebulosity… The following part divides into several streams uniting again towards the south.”
The Veil Nebula is a supernova remnant of heated and ionized gas and dust located some 1,470 light years from Earth. The progenitor star exploded somewhere between 5,000 to 8,000 years ago, and the remnants have since expanded to cover an area in the visual range of roughly 3 degrees in diameter. The Veil Nebula is visually about 6 times the diameter, or 36 times the area, of the full Moon.
To view the Veil Nebula, a combination of a dark, moonless night away from city lights and the technology of an O-III filter will be needed. Remember, the Veil Nebula is large, and is made up of several parts. As can be seen in the many names and nomenclatures for the Veil, the observer will be observing all the separate components that make up the Veil when using binoculars.
There are three main visual components, plus faint patches:
The Western Veil (Caldwell 34), consisting of NGC 6960 (the “Witch’s Broom” or Filamentary Nebula
The Eastern Veil (Caldwell 33), whose brightest area is NGC 6992, trailing off farther south into NGC 6995 and IC 1340
Pickering’s Triangle, brightest at the north central edge of the loop, but visible in photographs continuing toward the central area of the loop.
NGC 6974 and NGC 6979 are faint patches of nebulosity on the northern rim between NGC 6992 and Pickering’s Triangle.
The Veil Nebula is a favorite target among amateur astronomers, for the beauty and delicacy of its components. A very dark night at a dark site is needed. With a wide-angle 10×50 or 12×60 binoculars and the help of O-III filters, all the nebula elements will be visible. The O-III filter works the best, since virtually all the visible light from the Veil Nebula is due to doubly ionized oxygen. Remember, binoculars requires two eyes, thus two OIII filters. It can get expensive.
The size of the Veil Nebula is impressively huge, measuring 3.5 degrees by 2.7 degrees.
As an alternative, a modern 102-mm short focus (f/5 – f/7) refractor and a low power ultra wide field eyepiece can encompass a large portion of the Veil at one time. A 2” wide field, 82° or wider, focal length 30mm to 40mm eyepiece is applicable here. In this case, you can get away with one 2” OIII filter.
As previously mentioned, the Veil Nebula is the remains of a star that went supernova and exploded approximately 5,000 to 8,000 years ago.The star that left these scattered remains was once much larger than our own Sun. Instead of dying out to a white dwarf, as do stars the size the Sun, large stars die the violent death of a supernova. The explosion swept out a huge bubble in its surroundings, heating up gas and dust, and the remnants are visible in telescopes.
It’s likely that the progenitor star that exploded creating the Veil Nebula was a spectacular sight to humans on Earth 10,000 years ago. Unfortunately, no archeological evidence has been found documenting the human reaction to this supernova.
In 1888, E.E. Barnard, seen by many as the greatest American observational astronomer, began his work at Lick Observatory in California. Using refining his expertise in astro-photography, Bernard conducted a photographic study of the Milky Way.
The dark nebulas B142 and B143 are a product of E.E. Barnard’s study of photographs of dark nebulae. Barnard 142 and 143 are a pair of gas and dust clouds that block out the background stars and nebulae in the Aquila constellation. They form a dark nebula complex known as Barnard’s “E” Nebula. This pair of dark nebula forms a well-defined dark area on a background of Milky Way consisting of countless stars of all magnitudes. Its size is about that of the full moon, roughly 0.5 degrees, and its distance from earth is estimated at about 2,000 light-years.
Visible (or is it invisible?) through any binocular on dark nights, the reader is reminded to look for where there isn’t any starlight. Such is the nature of observing dark nebulas.
Alternate: NGC 6618, The Swan Nebula, The Omega Nebula, The Checkmark Nebula, Lobster Nebula
RA 18h 20 m 26 s
Dec -16º 10′ 36′
Alternate: NGC 6613
RA 18h 19.9 m
Dec -17º 08′
Alternate: IC 4715, The Sagittarius Star Cloud
RA 18h 17 m
Dec -18º 29′ 00′
The Messier object rich region of Sagittarius (although M16 is really in Serpens) yields this Cosmic Duet, or in this case multiple. This is a bountiful collection of clusters and nebulae, where M16, M17, and M18 can all be seen within a 4° field-of-view. 7×50 or 10×50 binoculars are all that is required to view this Cosmic multiple.
The Eagle Nebula M16 is a conspicuous region of active star formation, situated in Serpens Cauda. The star forming nebula, a giant cloud of interstellar gas and dust, has already created a considerable cluster of young stars. M16 is most notably famous for being the home of the “the Pillars of Creation”, a feature within the nebula imaged by Hubble Space Telescope. The cluster is also referred to as NGC 6611, the nebula as IC 4703.
The Eagle Nebula was initially discovered by Jean-Philippe Loys de Cheseaux during the period of 1745 to 1746.
M16’s description by Jean-Philippe Loys de Chéseaux in 1745-46 was cataloged as De Chéseaux: No. 4, he wrote: “A star cluster between the constellations of Ophiuchus, Sagittarius, and Antinous [now Scutum], of which RA is 271d 3′ 10″ and southern declination is 13d 47′ 20″.”
Charles Messier rediscovered it on June 3, 1764, describing it as “enmeshed in a faint glow,” suggesting the presence of the nebula. Interestingly, observations by William, John, and Caroline Herschel noted the star cluster but not the nebula.
Located in the Sagittarius arm of our Milky Way Galaxy in a region of star formation, the open star cluster M16 formed. The diffuse Eagle Nebula IC 4703 shines by emission light caused by the high-energy radiation of its massive hot, young stars.
M17 was discovered by Jean-Philippe Loys de Chéseaux during the same period of discovery of M16 in 1745-46. The Omega was one of only six identified by Chéseaux as a nebula in his catalog. As with M16, his discovery was lost and forgotten, until Charles Messier rediscovered it on June 3, 1764.
Jean-Philippe Loys de Chéseaux wrote:
Finally, another nebula, which has never been observed. It is of a completely different shape than the others: It has perfectly the form of a ray, or of the tail of a comet, of 7′ length and 2′ broadth; its sides are exactly parallel and rather well terminated, as are its two ends. Its middle is whiter than the borders; I have found its RA for this year as 271d 32′ 35″ and its southern declination as 16d 15′ 6″. It has an angle [PA] of 50 deg with the meridian.
The Omega Nebula (M17), also called the Swan Nebula, the Horseshoe Nebula, or in the southern hemisphere it is interestingly known as the Lobster Nebula, is a region of star formation and shines by excited emission, caused by the higher energy radiation of young stars. Unlike in many other emission nebulae, however, these stars are hidden within the nebula and cannot be seen in optical images. Star formation may be either still active in this nebula, or may have ceased very recently. A small cluster of about 35 bright but obscured stars seems to be imbedded in the nebulosity.
M18 was discovered by Charles Messier in 1764.
Open cluster M18 is about 0.2 degrees in diameter. M18 appears loose and not dense. Its distance is somewhat in dispute. According to Kenneth Glyn Jones and Robert Burnham, it lies about 4,900 light years distant. But the sources disagree. John Mallas lists the distance as 6,000 light years, and the Sky Catalog 2000 lists the figure as 3,900 light years.
M24 was discovered in 1764 by Charles Messier. M24 is one of the few particular objects, or curiosities, in Messier’s catalog. Messier’s notes list M24 as a large object of 1 1/2 deg in extension, which he included on June 20, 1764, and describes it as “a large nebulosity in which there are many stars of different magnitudes.”
Messier object number 24 is not a “true” deep sky object, but a huge star cloud in our Milky Way. It is a concentration of stars spread thousands of light years along the line of sight, perceived through a chance tunnel in the interstellar dust. They form a portion of a spiral arm of our galaxy.
M16 can be spotted with 7×50 binoculars because of the embedded cluster. On M17, the nebula is obvious in 20×80 or larger binoculars, as an up-side-down swan. The nebulosity is visible with 12×60 binoculars in dark sky conditions. In 7×50 or 10×50 binoculars, M17 appears smaller with much less prominence. When observing the area of M16 and M17, just below the pair is the open cluster M18, appearing like a small glow. Just south of all these is M24 the vast Sagittarius Star Cloud.
Using the ultra-wide field of 2.1×42 binoculars, by lining up at the south end of the star cloud, the observer can look 4° E for M25 and 5° W for M23.