Eta Carinae has a mass of approximately 150 times that of the sun, and is about 4 million times brighter than our local star, making it one of the most massive and most luminous stars known. Eta Carinae is highly unstable, and prone to violent outbursts. The last of these occurred in 1841, when despite its distance (over 10,000 light years away) Eta Carinae briefly became the second brightest star in the sky.

Pre-servicing mission HST observations taken with the WF/PC-I reveled new detail in the rapidly expanding shell of material which was ejected during the last century's outburst. However, the earlier effects of HST's spherical aberration obscured the structure of the material very near Eta Carinae itself.

The clear view of Eta Carinae now provided by WFPC-2 dramatically demonstrates the ability of HST to reliable study faint structure near bright objects. The picture is a combination of three different images taken in red, green, and blue light. The ghostly red outer glow surrounding the star is composed of the very fastest moving of the material which was ejected during the last century's outburst. This material, much of which is moving more than two million miles per hour, is largely composed of nitrogen and other elements formed in the interior of the massive star, and subsequently ejected into interstellar space.

The bright blue-white nebulosity closer in to the star also consists of ejected stellar material. Unlike the outer nebulosity, this material is very dusty and reflects starlight. The new data show that this structure consists of two lobes of material, one of which (lower left) is moving toward us and the other of which (upper right) is moving away. The knots of ejected material have sizes comparable to that of our solar system.

Previous models of such bipolar flows predict a dense disk surrounding the star which funnels the ejected material out of the poles of the system. In Eta Carinae, however, high velocity material is spraying out in the same plane as the hypothetical disk, which is supposed to be channeling the flow. This is quite unexpected. The WFPC-2 observations of Eta Carinae raise as many questions as they answer.

The Cat's Eye Nebula image from Hubble, shows one of the most complex planetary nebulae ever seen, nicknamed what is estimated to be 1,000 years old. It contains surprisingly intricate structures including concentric gas shells, jets of high-speed gas, and unusual shock-induced knots of gas. Estimated to be 1,000 years old, the nebula is a visual "fossil record" of the dynamics and late evolution of a dying star.

A preliminary interpretation of the Cat's Eye Nebula suggests that the object might be a double-star system. The dynamical effects of two stars orbiting one another most easily explains the intricate structures, which are much more complicated than features seen in most planetary nebulae. The two stars are too close together to be individually resolved by Hubble and instead appear as a single point of light at the center of the Cat's Eye Nebula.

According to this model, a fast "stellar wind" of gas blown off the central star of the Cat's Eye nebula, created the elongated shell of dense, glowing gas. This structure is embedded inside two larger lobes of gas blown off the star at an earlier phase. These lobes are "pinched" by a ring of denser gas, presumably ejected along the orbital plane of the binary companion.

The suspected companion star also might be responsible for a pair of high-speed jets of gas that lie at right angles to this equatorial ring. If the companion were pulling in material from a neighboring star, jets escaping along the companion's rotation axis could be produced.

These jets would explain several puzzling features of the Cat's Eye nebula along the periphery of the gas lobes. Like a stream of water hitting a sand pile, the jets compress gas ahead of them, creating the "curlicue" features and bright arcs near the outer edge of the lobes. The twin jets are now pointing in different directions than these features. This suggests the jets are wobbling, or processing, and turning on and off episodically.

The image of the cat's eye nebula was taken with the Wide Field Planetary Camera-2 on September 18, 1994. NGC 6543 is 3,000 light-years away in the northern constellation Draco. The term planetary nebula is a misnomer; dying stars create these cocoons when they lose outer layers of gas. The process has nothing to do with planet formation, which is predicted to happen early in a star's life.

This nebula was discovered by Charles Messier in 1764. The Dumbbell (Helix) Nebula M27 was the first planetary nebula ever discovered. On July 12, 1764, Charles Messier discovered this new and fascinating class of objects, and describes this one as an oval nebula without stars. The name "Dumbbell" goes back to the description by John Herschel, who also compared it to a "double-headed shot".

We happen to see this one approximately from its equatorial plane (approx. left-to-right in our image); this is similar to our view of another, fainter Messier planetary nebula, M76, which is called the Little Dumbbell. From near one pole, it would probably have the shape of a ring, and perhaps look like we view the Ring Nebula M57.

This planetary nebula is certainly the most impressive object of its kind in the sky, as the angular diameter of the luminous body is nearly 6 arc minutes, with a faint halo extensing out to over 15', half the apparent diameter of the Moon (Millikan 1974). It is also among the brightest, being at most little less luminous with its estimated apparent visual magnitude 7.4 than the brightest, the Helix Nebula NGC 7293 in Aquarius, with 7.3, which however has a much lower surface brightness because of its larger extension (estimates from Stephen Hynes); it is a bit unusual that this planetary is only little fainter photographically (mag 7.6). The present author (hf) was surprized how fine this object was seen in his 10x50 binoculars under moderately good conditions!

As measured by Soviet astronomer O.N. Chudowitchera from Pulkowo, the bright portion of the nebula is apparently expanding at a rate of 6.8 arc seconds per century, leading to an estimated age of 3,000 to 4,000 years, i.e. the shell ejection probably would have been observable this time ago (it actually happened earlier as the light had to travel all the distance of perhaps about 1000 light years). She estimated the distance somewhat short at only about 490 ly. Another estimate, given by Burnham, has obtained a rate 1.0 arc seconds per century, and an estimated age of 48,000 years.

The central star of M27 is quite bright at mag 13.5, and an extremely hot blueish subdwarf dwarf at about 85,000 K (so the spectral type is given as O7 in the Sky Catalog 2000). K.M. Cudworth of the Yerkes Observatory found that it probably has a faint (mag 17) yellow companion at 6.5" in position angle 214°.

As for most planetary nebulae, the distance of M27 (and thus true dimension and intrinsic luminosity) is not very well known. Hynes gives about 800, Kenneth Glyn Jones 975, Mallas/Kreimer 1250 light years, while other existing estimates reach from 490 to 3500 light years. Currently, investigations with the Hubble Space Telescope are under work to determine a more reliable and acurate value for the distance of the Dumbbell Nebula.

Adopting our value of 1200 light years, the intrinsic luminosity of the gaseous nebula is about 100 times that of the Sun (about -0.5 Mag absolute) while the star is at about +6 (1/3 of the Sun) and the companion at +9..9.5 (nearly 100 times fainter than the Sun), all in the visual light part of the electromagnetic spectrum. That the nebula is so much brighter than the star shows that the star emits primarily highly energetic radiation of the non-visible part of the electro-magnetic spectrum, which is absorbed by exciting the nebula's gas, and re-emitted by the nebula, at last to a good part in the visible light. Actually, as for almost all planetary nebulae, most of the visible light is even emitted in one spectral line only, in the green light at 5007 Angstrom (see our planetary nebula description)!

By comparing images of the Dumbbell Nebula M27, Leos Ondra has discovered a variable star situated in the very outskirts of the nebula which he called Goldilocks' Variable. This variable can be found in some of our images, namely those of Jack Newton, Peter Sütterlin and (faintly) David Malin's INT photo, as well as one of the images by John Sefick. Other images such as the one in this page don't show this star, proving its variability.

About 2° to the West of M27 is inconspicuous open cluster NGC 6830, containing about 20-30 widely scattered stars; this cluster is about 5500 light-years distant.

A shimmering hourglass 8,000 light-years away, the planetary nebula MyCn 18, is striking in its beauty and complexity. However, the only time this hourglass can keep is the death knell of a star, and it is so odd that astronomers say it is forcing them to rethink the physics that shapes it.

Not only does MyCn 18 display a second, smaller hourglass of gas inside the larger one, but neither hourglass is position symmetrically around the central star. The central star is a white dwarf, a very hot, compact, spent star that wouldn't have enough gas remaining to generate such an extraordinary nebula.

"What we thought we understood of planetary nebulae we no longer do," says Raghvendra Sahai, an astronomer at the Jet Propulsion Laboratory in Pasadena, California. Something different and dramatic is going on.

The asymmetrical hourglass architecture and revealing images obtained by the Hubble Space Telescope are spawning a renaissance, he says in the study of planetaries. They form when an aging ordinary-mass star, having exhausted most of its nuclear fuel, starts to expand into a red giant. Escaping gas and dust accumulate first as a belt around the equator of the star. As the volume of escaping gas increases, the belt constricts the star's midsection and forces the increasingly fast moving gas into an hourglass shape. The escaping gas, heated and ionized by the dying star, shines. However, MnCy 18 may very well be a highly unusual planetary.

Sahai and others reported in the July issue of The Astronomical Journal that MyCn 18 must result from a binary-star system. They argue that the nebula needs a source of a lot of gas, one that a white dwarf alone would lack. Gas escaping what might be a nearby red giant (or alternatively a smaller, dim, Jupiter-sized star) could be sucked onto the dwarf where it could accumulate and eventually fuel a nova explosion, the gas of which would spread outward to form the hourglass.

"The second hourglass is more difficult to explain. It's very hard to see how you get it," says Sahai. "You just don't have enough material."

Astronomers say that perhaps the explosion itself was asymmetrical. Arizona State University astronomer Paul Scowen theorizes that the interstellar medium around the star system itself may have been inhomogeneous, allowing the expanding nebula to form asymmetrically.

The intrigue continues. Astronomers used Hubble to capture two other rings at the neck of the hourglass-possibly a belt of dense gas escaping the unseen star and a second ring perpendicular to it. "What forces are responsible for the rings? We have no idea," says Sahai. We have to make a fresh start to understand the physics of planetary nebulae.

"This nebula has caused a lot of speculation," says Scowen, "and for now it is just speculation." Meanwhile, he is fascinated by the intricate pattern of rills and ripples setup in the gas at the upper reaches of the nebula, created by turbulence. Planned computer simulations that test various theories might give a clearer explanation of just how the puzzling, stunning nebula was sculpted.

NGC 2440 is another planetary nebula ejected by a dying star, but it has a much more chaotic structure than NGC 2346. The central star of NGC 2440 is one of the hottest known, with a surface temperature near 200,000 degrees Celsius.

The complex structure of the surrounding nebula suggests to some astronomers that there have been periodic oppositely directed outflows from the central star, somewhat similar to that in NGC 2346, but in the case of NGC 2440 these outflows have been episodic, and in different directions during each episode. The nebula is also rich in clouds of dust, some of which form long, dark streaks pointing away from the central star.

In addition to the bright nebula, which glows because of fluorescence due to ultraviolet radiation from the hot star, NGC 2440 is surrounded by a much larger cloud of cooler gas which is invisible in ordinary light but can be detected with infrared telescopes. NGC 2440 lies about 4,000 light-years from Earth in the direction of the constellation Puppis.

The Hubble Heritage team made this image from observations of NGC 2440 acquired by Howard Bond (STScI) and Robin Ciardullo (Penn State).

A constellation, which is the head of a constellation family, located in the equatorial region of the sky and belongs certainly to the most famous constellations. It extends from RA= 4h 40m to RA= 6h 20m and DECL= +23° to DECL= +8°.

In some ways the central part of this constellation reminds on a oblique sand-glass. In wintertime Orion is a magnificent constellation which can easily be found by the the three stars forming a line building the belt of the Hunter (these stars are sometimes called Jacob's Ladder or Jacob's Stick). The belt stars point towards Sirius, the brightest star in the constellation of the Larger Dog, Canis Maioris, situated SE of Orion.

From his belt there hangs a well defined dagger (known as "Sword of Orion"), which is known for one of the most famous nebulas in the sky: The Large Orion Nebula (M42).

Orion lies close enough to the Milky Way to be interesting enough to be swept even with low-power telescopes or binoculars. Additionally to the data given above there is a skychart to locate the stars and objects.

The shoulder star Alpha Ori, Betelgeuse, is a variable red giant; its brightness varies from 0.4 mag to 1.3 mag with no set period. It belong to the 20 brightest stars in the sky. During it pulsations the diameter of the star varies from 300 to 400 times the diameter of the sun.

The leg of the hunter, Beta Ori, Rigel (arab.: the foot), is a blue-white giant of 0.08 mag. This makes it the sixth brightest star in the sky and the brightest in the constellation Orion. With medium sized telescopes it is possible to distinguish the companion of Rigel, a 7th mag star (smaller telescopes may fail to reveal the companion because of the glare of Rigel).

This constellation offers a great number of binaries and multiple stars. For binoculars and smaller telescopes the following stars are of interest:

• Delta Ori, Mintaka (arab.: upper end of the girdle), a blue-white star of 2.2 mag with a 7th mag companion.
• Iota Ori, a 3rd mag and a 7th mag star forming an unequal double; in the same field the wider double
• Struve 747 can be found - a pair of a 5th mag and a 6th mag star.
• Lambda Ori, a tight pair of 4th and 6th mag stars. Sigma Ori is a terrific multiple star; in binoculars this blue-white star of 4 mag and a 7th mag companion can be resolved; using a small telescope two closer companions of 7th mag and 10th mag are revealed. These stars are grouped in a way that they look like a planet with moons.

If the resolution is not too high in the same telescopic field as Sigma Ori the triple star Struve 761 can be seen. It consists of a triangle of 8th mag and 9th mag stars. Together with Sigma Ori this triple star gives a delightfully rich grouping. NGC 1981, a little cluster of 10 stars including the binary Struve 750, a pair of a 6th mag and a 8th mag star.

The multiple star Theta1 Ori, the northern star of the dagger of the Hunter is also called the Trapezium; it is located in the heart of the Orion nebula. This group of stars has been formed from the gas of the nebula, which now glows in their light. Small telecopes (about 2-inch and higher) show four stars, ranging from 5th mag to 8th mag, which form a rectangular figure. Scopes with an aperture of about 100 mm show two more stars of 11th mag in this group.

Next to it lies Theta2 Ori, a duo of a 5th and a 6th mag star. For resolving the tight double of Zeta Ori (Alnitak) in its consisting parts, a bright star of 2.02 mag and a 4th mag companion, scopes with an aperture of at least 75mm and a high resolution are required. Further more there is a wider companion of 10th mag.

Eta Ori is a difficult pair. Scopes with an aperture of 100 mm and higher are necessary to split it into its 4th mag and 5th mag stars.

The constellation Orion became most famous for its nebula. The Messier database has detailed information about The Large Orion Nebula M 42 and M 43, the DeMairan nebula, which is a part of the Orion Nebula.

Around October 21 each year the famous Orionid meteor shower reaches its peak. Coming from the the border to the constellation gemini as much as 20 meteors per hour can be seen. More information about this meteor shower and the Chi Orionids, which are active around the beginning of december can be found in the meteor shower calendar by Gary Kronk. (Readers in the US might use the original site of Gary Kronk).

According to greek mythology Orion died being stung by a scorpion. He is set such in the sky that he sets in the west while his slayer, the Scorpius raises in the east. Followed by his two dogs he is now fighting the bull Taurus. According to Secrets of the Night Sky (Bob Berman, William Morrow &Co, 1995) the ancient Sumerians saw in this star pattern a sheep. The name Betelgeuse literally means "the armpit"; in case of the Sumerians it meant "the armpit of the sheep."

The famous Ring Nebula (M57) is often regarded as the prototype of a planetary nebula, and a showpiece in the northern hemisphere summer sky. Recent research has confirmed that it is, most probably, actually a ring (torus) of bright light-emitting material surrounding its central star, and not a spherical (or ellipsoidal) shell, thus coinciding with an early assumption by John Herschel. Viewed from this equatorial plane, it would thus more resemble the Dumbbell Nebula M27 or the Little Dumbbell Nebula M76 than its appearance we know from here: We happen to view it from near one pole.

This is contrary to the belief expressed in Kenneth Glyn Jones' book. There are even indications from investigations of deep observations such as George Jacoby's deep photos obtained at Kitt Peak National Observatory that the overall shape might be more that of a cylinder viewed along the direction of the axis than that of a ring, that is, we are looking down a tunnel of gas ejected by a star at the end of its nuclear-burning life. Eventually, these observations have given evidence that the equatorial ring or cylinder has lobe-shaped extensions in polar directions, similar to those found in deep images of M76, but even more resembling other planetaries like NGC 6302, see e.g. the review by Sun Kwok (2000).

The deep observations also show an extended halo of material extending off to over 3.5 arc minutes (Hynes gives 216 arc seconds, quoting Moreno & Lopez, 1987), remainders of the star's earlier stellar winds. The halo was discovered in 1935 by J.C. Duncan (Duncan, 1935).

Our color photo (taken with the 200-inch Hale telescope at Mt. Palomar) shows that the material of the Ring is exposing a decreasing ionization level with increasing distance from the 100,000 to 120,000 K hot central star. The innermost region appears dark as it emits merely UV radiation, while in the inner visible ring, greenish forbidden light of ionized oxygene and nitrogene dominates the color, and in the outer region, only the red light of hydrogene can be excited.

The central star was discovered in 1800 by the German astronomer Friedrich von Hahn (1742-1805), with a 20-foot FL reflector. This object is a planet-sized white dwarf star, which shines at about 15th magnitude. It is the remainder of a sunlike star, probably once of more mass than our sun, which has blown away its outer envelopes at the end of its Mira-like phase of evolution. Now over 100,000 K hot, it will soon start to cool down, shine as a white dwarf star for a while of several billions of years, and then eventually end as a cold Black Dwarf.

As for most planetary nebulae, the distance to the Ring Nebula M57 is not very wellknown. In case of this nebula, however, an attempt was made to relate its angular expansion rate of roughly 1 arc second per century with its radial expansion velocity. These results, however, were based on wrong assumptions of the geometry of this nebula, presuming a spherical shape. Therefore, until recently, only rough estimates could be made, based on various theoretical assumptions and models. The following distance values have been given: 4,100 ly (K.M. Cudworth 1974; Mallas/Kreimer), 1,410 ly (Kenneth Glyn Jones), 2,000 to 2,500 ly (Vehrenberg), 2,000 ly (Sky Catalogue 2000.0), "more than 2,000 ly" (Murdin/Allen's Catalogue of the Universe), 5,000 ly (Chartand/Wimmer's Skyguide), 3,000 ly (WIYN), and 1,000 to 2,000 ly (Sun Kwok, 2000). A good value for the distance still needs to be determined (e.g., parallax by Hubble Space Telescope), but recently improved CCD technics was used at the US Naval Observatory (USNO) to determine a trigonometric parallax for the central star of M57, yielding 2,300 ly (Harris et.al. 1997, see also STScI/Nasa, Jan 1999).

As most planetary nebulae, the Ring is much brighter visually at magnitude 8.8 than photographically at only 9.7 mag; a consequence of the fact that most light is emitted in very few particular spectral lines (see the discussion in our planetary nebulae page). Assuming a distance of 2,300 lightyears, this corresponds to an absolute magnitude of -0.3 visually (+0.5 photographically), or an intrinsic brightness of about 50 to 100 times that of our Sun. Even the 14.7-mag central star, of the size of a terrestrial planet, is only little fainter than our Sun with an absolute magnitude of about +5 or 6. Its apparent dimension of 1.4 arc minutes corresponds to a linear diameter of 0.9 lightyears (5.5 trillion miles or 8.8 trillion km, or 60,000 Astronomical Units), the halo extending out to a diameter of 2.4 lightyears.

The mass of the nebular matter has been estimated at about 0.2 solar masses, the density at about 10,000 ions per ccm (cm^3). Its chemical composition has been determined as follows: On each Fluor (Fl) atom, the Ring Nebula contains 4.25 million atoms of Hydrogene (H), 337,500 Helium (He), 2,500 Oxygene (O), 1,250 Nitrogene (N), 375 Neon (Ne), 225 Sulfur (S), 30 Argon (Ar) and 9 Chlorine (Cl) atoms. It is expanding at 20 to 30 km/s, and approaching us at 21 km/s.

M57 images by Finnish astronomers have shown a star which is superimposed (before or behind) over the ring. For amateurs, it is always a challenge to identify the faint central star of the Ring. Note Tom Polakis' photometric data of stars around M57 and the Photometry of M57 Field Stars, by Brian Skiff.

M57 was the second planetary nebula to be discovered (in January 1779), 15 years after the first one, M27. Antoine Darquier de Pellepoix (Darquier), who discovered the Ring Nebula only a few days before Charles Messier found and cataloged it, described it as "a dull nebula, but perfectly outlined; as large as Jupiter and looks like a fading planet." This comparison to a planet may have influenced William Herschel, who found the objects of this type resembling the planet newly discovered by him, Uranus, and introduced the name "Planetary Nebulae". Herschel described M57 as "a perforated nebula, or ring of stars;" this was the first mention of the ring shape. Oddly, the inventor of the name "Planetary Nebula" did not count this most prominent representative in this object class, but described it as a "curiosity of the heavens", a peculiar object. Herschel also identified some of the superimposed stars, and correctly assumed that "none [of them] seems to belong to it."

M57 is very easy to locate as it is situated between Beta and Gamma Lyrae, at about one-third the distance from Beta to Gamma. It can be seen with binoculars as an almost stellar object, difficult to identify just because of its small apparent diameter. In smaller amateur telescopes, the ring becomes apparent at about 100 magnification, with a darker middle; a 12th-mag star is east of the planetary nebula, about 1' of the center. If ever color is notable, the Ring Nebula appears slightly greenish, not unexpected because most of its light is emitted in few green spectral lines. Even in small scopes, a slight ellipticity can be noted, with major axis in a position angle of about 60 deg. With increasing aperture and under good condition, more and more detail becomes visible, but even in large instruments, the central star will be apparent only under exceptionally good conditions, or with the help of filters. In large instruments, several very faint foreground or background stars can be glimpsed within the nebula's extension under very good conditions.

Of the neighboring stars, Beta Lyrae (Sheliak) is a notable eclipsing binary, with components of spectral type B7 and A8, varying between mag 3.4 and 4.4 with a period of 12.91 days. Gamma Lyrae (Sulaphat, Arabic for "Tortoise") is a giant of spectral type B9 III and mag 3.2 with a mag 12 companion at 13.8" distance in position angle 300°. The 0.4' small and 14.4-mag faint galaxy IC 1296 is situated just 4' NW of M57 and can be found with large instruments.