Category: Guide to Space

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The mass of a star defines its lifespan. The least massive stars will live the longest, while the most massive stars in the Universe will use their fuel up in a few million years and end in a spectacular supernova explosion. So, how long do stars last?

There are factors that will define how long a star will survive; how quickly they burn through the hydrogen fuel in their cores, and whether they have any way to keep the fuel in their core mixed up. Our own Sun has three distinct layers, the core, where nuclear fusion takes place, the radiative zone, where photons are emitted and then absorbed by atoms in the star. The final zone is the convective zone. In this region, hot gas from the edge of the radiative zone is carried upwards to the surface of the star in columns of hot plasma.

Let’s star with the largest stars. The largest possible stars probably have 150 times the mass of the Sun; for example, the monster Eta Carinae located about 8,000 light years from here. Eta Carinae was probably formed less than 3 million years ago. It consumes fuel so fast in its core that it gives off 4 million times the energy of the Sun. Astronomers think that Eta Carinae has less than 100,000 years to live. In fact, it could detonate as a supernova any day now…

As stars get smaller, they live longer. Our own Sun has been around for 4.5 billion years, slowly turning hydrogen into helium at its core. The Sun will run out of this hydrogen fuel in another 5 billion year or so, and it will turn into a red giant. It will expand to many times its original size and then eject its outer layers and shrink down to a tiny white dwarf star, a dense object the size of the Earth. So the total lifespan of a star with the mass of the Sun is about 10 billion years.

The smallest stars are the red dwarfs, these start at 50% the mass of the Sun, and can be as small as 7.5% the mass of the Sun. A red dwarf with only 10% the mass of the Sun will emit 1/10,000th the amount of energy given off by the Sun. Furthermore, red dwarfs lack radiative zones around their cores. Instead, the convective zone of the star comes right down to the cure. This means that the core of the star is continuously mixed up, and the helium ash is carried away to prevent it from building up. Red dwarf stars use up all their hydrogen, not just the stuff in the core. It’s believed that the smaller red dwarf stars will live for 10 trillion years or more.

How long do stars last? The biggest stars last only millions, the medium-sized stars last billions, and the smallest stars can last trillions of years.

We have written many articles about stars here on Universe Today. Here’s an article about the biggest star in the Universe. And here’s an article about how the Earth won’t survive when the Sun becomes a red giant.

If you’d like more information on stars, check out Hubblesite’s News Releases about Stars, and here’s the stars and galaxies homepage.

We have recorded several episodes of Astronomy Cast about stars. Here are two that you might find helpful: Episode 12: Where Do Baby Stars Come From, and Episode 13: Where Do Stars Go When they Die?

References:
SEDS.org
University of California – Berkeley
NASA

Think you know everything there is to know about stars? Think again! Here’s a list of 10 interesting facts about stars; some you might already know, and few that are going to be new.

1. The Sun is the closest star

Okay, this one you should know, but it’s pretty amazing to think that our own Sun, located a mere 150 million km away is average example of all the stars in the Universe. Our own Sun is classified as a G2 yellow dwarf star in the main sequence phase of its life. The Sun has been happily converting hydrogen into helium at its core for 4.5 billion years, and will likely continue doing so for another 7+ billion years. When the Sun runs out of fuel, it will become a red giant, bloating up many times its current size. As it expands, the Sun will consume Mercury, Venus and probably even Earth. Here are 10 facts about the Sun.

2. Stars are made of the same stuff

All stars begin from clouds of cold molecular hydrogen that gravitationally collapse. As they cloud collapses, it fragments into many pieces that will go on to form individual stars. The material collects into a ball that continues to collapse under its own gravity until it can ignite nuclear fusion at its core. This initial gas was formed during the Big Bang, and is always about 74% hydrogen and 25% helium. Over time, stars convert some of their hydrogen into helium. That’s why our Sun’s ratio is more like 70% hydrogen and 29% helium. But all stars start out with 3/4 hydrogen and 1/4 helium, with other trace elements.

3. Stars are in perfect balance

You might not realize but stars are in constant conflict with themselves. The collective gravity of all the mass of a star is pulling it inward. If there was nothing to stop it, the star would just continue collapsing for millions of years until it became its smallest possible size; maybe as a neutron star. But there is a pressure pushing back against the gravitational collapse of the star: light. The nuclear fusion at the core of a star generates a tremendous amount of energy. The photons push outward as they make their journey from inside the star to reach the surface; a journey that can take 100,000 years. When stars become more luminous, they expand outward becoming red giants. And when they run out of light pressure, they collapse down into white dwarfs.

4. Most stars are red dwarfs

If you could collect all the stars together and put them in piles, the biggest pile, by far, would be the red dwarfs. These are stars with less than 50% the mass of the Sun. Red dwarfs can even be as small as 7.5% the mass of the Sun. Below that point, the star doesn’t have the gravitational pressure to raise the temperature inside its core to begin nuclear fusion. Those are called brown dwarfs, or failed stars. Red dwarfs burn with less than 1/10,000th the energy of the Sun, and can sip away at their fuel for 10 trillion years before running out of hydrogen.

5. Mass = temperature = color

The color of stars can range from red to white to blue. Red is the coolest color; that’s a star with less than 3,500 Kelvin. Stars like our Sun are yellowish white and average around 6,000 Kelvin. The hottest stars are blue, which corresponds to surface temperatures above 12,000 Kelvin. So the temperature and color of a star are connected. Mass defines the temperature of a star. The more mass you have, the larger the star’s core is going to be, and the more nuclear fusion can be done at its core. This means that more energy reaches the surface of the star and increases its temperature. There’s a tricky exception to this: red giants. A typical red giant star can have the mass of our Sun, and would have been a white star all of its life. But as it nears the end of its life it increases in luminosity by a factor of 1000, and so it seems abnormally bright. But a blue giant star is just big, massive and hot.

6. Most stars come in multiples

It might look like all the stars are out there, all by themselves, but many come in pairs. These are binary stars, where two stars orbit a common center of gravity. And there are other systems out there with 3, 4 and even more stars. Just think of the beautiful sunrises you’d experience waking up on a world with 4 stars around it.

7. The biggest stars would engulf Saturn

Speaking of red giants, or in this case, red supergiants, there are some monster stars out there that really make our Sun look small. A familiar red supergiant is the star Betelgeuse in the constellation Orion. It has about 20 times the mass of the Sun, but it’s 1,000 times larger. But that’s nothing. The largest known star is the monster VY Canis Majoris. This star is thought to be 1,800 times the size of the Sun; it would engulf the orbit of Saturn!

8. The most massive stars are the shortest lived

I mentioned above that the low mass red dwarf stars can sip away at their fuel for 10 trillion years before finally running out. Well, the opposite is true for the most massive stars that we know about. These giants can have as much as 150 times the mass of the Sun, and put out a ferocious amount of energy. For example, one of the most massive stars we know of is Eta Carinae, located about 8,000 light-years away. This star is thought to have 150 solar masses, and puts out 4 million times as much energy. While our own Sun has been quietly burning away for billions of years, and will keep going for billions more, Eta Carinae has probably only been around for a few million years. And astronomers are expecting Eta Carinae to detonate as a supernovae any time now. When it does go off, it would become the brightest object in the sky after the Sun the Moon. It would be so bright you could see it during the day, and read from it at night.

9. There are many, many stars

Quick, how many stars are there in the Milky Way. You might be surprised to know that there are 200-400 billion stars in our galaxy. Each one is a separate island in space, perhaps with planets, and some may even have life. But then, there could be as many as 500 billion galaxies in the Universe, and each of which could have as many or more stars as the Milky Way. Multiply those two numbers together and you’ll see that there could be as many as 2 x 10²³ stars in the Universe. That’s 200,000,000,000,000,000,000,000.

10. And they’re very far

With so many stars out there, it’s amazing to consider the vast distances involved. The closest star to Earth is Proxima Centauri, located 4.2 light-years away. In other words, it takes light itself more than 4 years to complete the journey from Earth. If you tried to hitch a ride on the fastest spacecraft ever launched from Earth, it would still take you more than 70,000 years to get there from here. Traveling between the stars just isn’t feasible right now.

If you’d like more information on stars, check out Hubblesite’s News Releases about Stars, and here’s the stars and galaxies homepage.

We have recorded several episodes of Astronomy Cast about stars. Here are two that you might find helpful: Episode 12: Where Do Baby Stars Come From, and Episode 13: Where Do Stars Go When they Die?

References:
NASA: How Do Stars Form and Evolve?
NASA: Stars

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The color of a star comes from the temperature of its surface. The hottest stars are blue, cooler stars are white and yellow, and the coolest stars of all are red. Red stars come in one color, but many different shapes and sizes. Let’s take a look at the different kids of red stars that are out there in the Universe.

First, let’s talk about temperature. As I mentioned above, the color of a star comes from its surface temperature. A star that emits mostly red light will have a surface temperature of about 3,500 Kelvin. Just for comparison, the Sun’s surface temperature is about 6,000 Kelvin and emits yellow/white light.

Red Dwarf Stars
The first kind of red stars are red dwarfs. These are actually the most common stars in the Universe. The smallest red dwarf stars can be 7.5% the mass of our Sun, and be as large as about half the mass of the Sun. Even a star with this little mass has enough temperature and pressure at its core to carry out nuclear fusion. This is where atoms of hydrogen are fused into atoms of helium; this process releases lots and lots of heat.

Red dwarfs generate much less energy than a larger star like our Sun. In fact, a red dwarf emits 1/10,000th the energy. Even the largest red dwarf only has about 10% of the Sun’s luminosity. Red dwarfs use their hydrogen fuel slowly and so they last a very long time. It’s believed that a red dwarf star could survive for 10 trillion years.

Red Giant Stars
Stars like our Sun spend most of their lives as main sequence stars with a surface temperature that’s much hotter than a red star. But at the end of their lives, when they have used up all their hydrogen fuel, these medium-sized stars will puff out much bigger than their original size – these are red giants. When our Sun becomes a red giant, it will expand out to encompass the orbit of the Earth. After a few hundred million years, it will puff its outer layers and become a white dwarf star.

They start out as regular stars, but they grow to such an enormous size that their heat is spread out across a much larger surface area. This is why they appear very bright, but still have a red color.

Red Supergiant
The biggest stars in the Universe are the red supergiants. They’re not the most massive; Betelgeuse, for example, only has about 20 times the mass of the Sun. But the largest red supergiants can expand out to be more than 1500 times the size of the Sun. Imagine a star that engulfed the orbit of Saturn! Just like the red giants, red supergiants occur when a star has used up the hydrogen fuel in its core, and then expand out during their helium-burning phase. Red supergiants will have the mass to continue fusing elements in their cores, all the way up to iron.

Stars probably only exist as red supergiants for a few hundred thousand years; a million at most. At the end of this period, the star will have used up all the fuel it can in its core; most will detonate as Type II supernovae.

We have written many articles about stars here on Universe Today. Here’s an article about a planet surviving when its star became a red giant, and here’s a deathwatch on a red giant star.

Want more information on stars? Here’s Hubblesite’s News Releases about Stars, and more information from NASA’s imagine the Universe.

We have recorded several episodes of Astronomy Cast about stars. Here are two that you might find helpful: Episode 12: Where Do Baby Stars Come From, and Episode 13: Where Do Stars Go When they Die?

References:
http://www.telescope.org/pparc/res8.html
http://en.wikipedia.org/wiki/Red_giant
http://en.wikipedia.org/wiki/Red_dwarf

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White dwarf stars are the corpses of stars; what happens once they’ve used up all their fuel and lack the temperature and pressure to continue fusion in their core. A white dwarf will be the end for all the small and medium mass stars out there – 97% of the stars in the Universe will become white dwarfs. The most massive stars in the Universe will suffer far more violent ends as supernovae or neutron stars. Let’s take a look at white dwarf stars.

For the majority of its lifetime, a star is in the main sequence phase of life; it’s converting hydrogen into helium at its core, and producing a tremendous amount of energy. Eventually a star runs out of hydrogen fuel in its core and its fusion stops. The star starts to collapse, but then a new shell of hydrogen fuel gets going. This causes the outer envelope of the star to puff out into a red giant. If a star is large enough, it will even be able to begin helium burning in its core creating carbon.

Once this fuel runs out, though, that’s it. The star is completely out of fuel it can use, and so it puffs out its outer layers, revealing the hot carbon core; the leftover material from this last fusion reaction. The star is now a white dwarf. It starts out hot, the temperature that the star’s core was, but then it starts to cool down over time. Eventually, after billions and even trillions of years time, the white dwarf will cool down to the background temperature of the Universe.

A white dwarf star is roughly the same size as the Earth, but it’s extremely dense, compacting the core of the former star into a region only 10,000 km across. Their average density is about 1,000,000 times denser than the density of the Sun. A single sugar cube sized amount of white dwarf would weigh about 1 tonne.

White dwarfs can only be up to 1.4 solar masses. Beyond this point, the pressure exerted by the individual atoms can’t hold back the gravitational pressure pulling it together. The white dwarf would collapse down to a more compact object, like a neutron star or a black hole.

We have written many articles about stars on Universe Today. Here’s an article about a new type of white dwarf star detected. And here’s an article about a missing white dwarf.

Want more information on stars? Here’s Hubblesite’s News Releases about Stars, and more information from NASA’s imagine the Universe.

We have recorded several episodes of Astronomy Cast about stars. Here are two that you might find helpful: Episode 12: Where Do Baby Stars Come From, and Episode 13: Where Do Stars Go When they Die?

References:
NASA
Wikipedia
Windows to Universe

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Our Sun is such a familiar sight in the sky that you might think stars like our Sun are common across the Universe. But the most common stars in the Universe are actually much smaller and less massive than the Sun. The Universe is filled with red dwarf stars.

Astronomers categorize a red dwarf as any star less than half the mass of the Sun, down to about 7.5% the mass of the Sun. Red dwarfs can’t get less massive than 0.075 times the mass of the Sun because then they’d be too small to sustain nuclear fusion in their cores.

Red dwarfs do everything at a slower rate. Since they’re a fraction of the mass of the Sun, red dwarfs generate as little as 1/10,000th the energy of the Sun. This means they consume their stores of hydrogen fuel at a fraction of the rate that a star like the Sun goes through. The largest known red dwarf has only 10% the luminosity of the Sun.

And red dwarfs have another advantage. Larger stars, like the Sun, have a core, surrounded by a radiative zone, surrounded by a convective zone. Energy can only pass from the core through the radiative zone by emission and absorption by particles in the zone. A single photon can take more than 100,000 years to make this journey. Outside the radiative zone is a star’s convective zone. In this region, columns of hot plasma carry the heat from the radiative zone up to the surface of the star.

Red dwarfs have no radiative zone, which means that the convective zone comes right down to the star’s core and carries away heat. It also mixes up the hydrogen fuel and carries away the helium by-product. Regular stars die when they use up just the hydrogen in their cores, while red dwarfs keep all their hydrogen mixed up and will only die when they’ve used up every last drop.

With such an efficient use of hydrogen, red dwarf stars with 10% the mass of the Sun are through to live 10 trillion years. Our own Sun will only last about 12 billion or so.

You might be interested to know that the closest star to Earth, Proxima Centauri, is a red dwarf star. Unfortunately, these stars are so small and dim that they can’t be seen without a telescope.

We have written many articles about stars on Universe Today. Here’s an article about how red dwarf stars might have tiny habitable zones. And here’s an article about how they destroy their dust disks.

Want more information on stars? Here’s Hubblesite’s News Releases about Stars, and more information from NASA’s imagine the Universe.

We have recorded several episodes of Astronomy Cast about stars. Here are two that you might find helpful: Episode 12: Where Do Baby Stars Come From, and Episode 13: Where Do Stars Go When they Die?

References:
http://en.wikipedia.org/wiki/Red_dwarf
http://adsabs.harvard.edu/full/1953ApJ…118..529O

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Look up into the sky and you’ll see the stars twinkling in different colors. Some are dull and red, while others are white and others look bright blue. So how do you get so many different star colors?

The color of a star depends on its surface temperature. Our Sun’s surface temperature is about 6,000 Kelvin. Although it looks yellow from here on Earth, the light of the Sun would actually look very white from space. This white light coming off of the Sun is because its temperature is 6,000 Kelvin. If the Sun were cooler, it would give off light more on the red end of the spectrum, and if the Sun were hotter, it would look more blue.

And that’s just what we see with other stars. The coolest stars in the Universe are the red dwarf stars. These are stars with just a fraction of the mass of our Sun (as low as 7.5% the mass of the Sun). They don’t burn as hot in their cores, and their surface temperature is about 3,500 Kelvin. The light released from their surface looks mostly red to our eyes (although there are different colors mixed up in there too, red is the majority).

This is also the color you see with red giant stars; solar-mass stars that ran out of hydrogen fuel and bloated up many times their original size. The luminosity of the star is spread out over the much larger surface area of the red giant and so they’re cooler,

On the opposite side of the spectrum are blue stars. These are stars with many times the mass of the Sun and so their surface temperatures are much hotter. Blue stars start out above 10,000 Kelvin but they can reach 40,000 Kelvin with the largest hypergiant stars.

We have written many articles about stars on Universe Today. Here’s an article about the biggest stars in the Universe.

Want more information on stars? Here’s Hubblesite’s News Releases about Stars, and more information from NASA’s imagine the Universe.

We have recorded several episodes of Astronomy Cast about stars. Here are two that you might find helpful: Episode 12: Where Do Baby Stars Come From, and Episode 13: Where Do Stars Go When they Die?

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Stars can range in temperature, from the relatively cool red dwarfs to superhot blue stars. So what is the hottest star in the Universe?

First, let’s talk a bit about temperature. The color of a star is a function of its temperature. If a star looks red, that means its surface temperature is approximately 2,500 Kelvin. Just for comparison, our Sun, which actually looks white from space, measures about 6,000 Kelvin. The hotter the star, the further up the spectrum you go. The hottest stars are the blue stars. A star appears blue once its surface temperature gets above 10,000 Kelvin, or so, a star will appear blue to our eyes.

So the hottest stars in the Universe are going to be a blue star, and we know they’re going to be massive. So the question is, how massive can stars get? One example is the star Rigel, in the constellation Orion. Rigel is thought to have 17 times the mass of the Sun, and puts out 40,000 times the luminosity of the Sun. It’s surface temperature is a mere 11,000 Kelvin. Another star in Orion, Bellatrix, has a temperature of 21,500 Kelvin. That’s even hotter.

But the hottest known stars in the Universe are the blue hypergiant stars. These are stars with more than 100 times the mass of the Sun. One of the best known examples is Eta Carinae, located about 7,500 light-years from the Sun. Eta Carinae could be as large as 180 times the radius of the Sun, and its surface temperature is 36,000-40,000 Kelvin.

Just for comparison, 40,000 Kelvin is about 72,000 degrees F.

So it’s the blue hypergiants, like Eta Carinae, which are probably the hottest stars in the Universe.

We have written many articles about stars on Universe Today. Here’s an article about how Eta Carinae is almost ready to explode as a supernova. And here’s a link to a nice photo of the nebula around Eta Carinae.

Want more information on stars? Here’s Hubblesite’s News Releases about Stars, and more information from NASA’s imagine the Universe.

We have recorded several episodes of Astronomy Cast about stars. Here are two that you might find helpful: Episode 12: Where Do Baby Stars Come From, and Episode 13: Where Do Stars Go When they Die?

References:
NASA: Eta Carinae
University of Illinois

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The constellation of Vulpecula is unusual, because it did not belong originally to those created by Ptolemy – but to the works of Johannes Hevelius. Vulpecula was included in Firmamentum Sobiescianum, a 56 page atlas created by Hevelius, which outlined seven new constellations which survived time – and many which did not. Positioned north of the ecliptic plane, it spans 268 square degrees of sky, ranking 55th in constellation size. It has 5 main stars in its asterism and 33 Bayer Flamsteed designated stars within its confines. Vulpecula is bordered by the constellations of Cygnus, Lyra, Hercules, Sagitta, Delphinus and Pegasus. It is best seen at culmination during the month of September.

Since Vulpecula is considered a “modern” constellation, there is no mythology associated with it – although the stellar pattern was very visible to the ancient Greeks and Romans. Late in 17th century, astronomer Johannes Hevelius created the constellation of Vulpecula when he was preparing his own set of star charts known as Firmamentum Sobiescianum At the time, he named it “Vulpecula Cum Ansere” which literally translated to the little fox with the goose – and he illustrated it as a fox with a goose caught in its jaws. At the time, Hevelius did not consider it to be two separate constellations – yet it was later divided into two halves – Vulpecula and Anser “The Goose”. When star charts were once again consolidated, the constellations merged again to be known under to modern named assigned to it by the International Astronomical Union as Vulpecula, yet the primary star retains a reminder be being properly named Anser.

Let’s begin our binocular tour of Vulpecula with a look at the Alpha (“a”) star – Anser. Its name literally translates to “goose”, but this class M giant star is anything but flighty. Residing 297 light years from Earth, Anser puts out 390 times more light energy than our Sun from a size about 45 times larger. It may have a dead helium core about to begin hydrogen fusion – and it may have a dead carbon-oxygen core awaiting a second brightening before turning K class. If you’ve notice another nearby star – good for you! Although it’s only a line of sight companion, 8 Vulpeculae makes checking out Anser a real treat!

Now head on to Collinder 399. This wonderful asterism is often called “Brocchi’s Cluster” or the “Coathanger” and it’s a splendid object in binoculars or a rich field telescope. This unique collection of stars was known as far back as 964 AD when astronomer Al Sufi recorded it, and it was independently rediscovered by Giovanni Hodierna in the seventeenth century. In the 1920s, D. F. Brocchi, an amateur astronomer and chart maker for the American Association of Variable Star Observers, created a map of this object for use in calibrating photometers. Thanks to its expansive size of more than 60 arc minutes, it escaped the catalogues of both Messier and Herschel. Only around a half dozen stars share the same proper motion, which may make it a cluster much like the Pleiades, but studies suggest it is merely an asterism…but one with two binary stars at its heart.

Our next target is the magnificent Messier 27 (RA 19 : 59.6 Dec +22 : 43). This incredible planetary nebula appears like a pale green apple core and is unquestionably the brightest study of its kind. Easily located around a finger-width north of Gamma Sagittae, it’s not the largest of all planetaries but is the largest of its kind on the Messier list. M27’s expanse and luminosity suggest that it is quite close to our own system. Some think it difficult to find, but there is a very simple trick. Look for the primary stars of Sagitta just to the west of bright Albireo. Make note of the distance between the two brightest and look exactly that distance north of the “tip of the arrow” and you’ll find M27.

Discovered in 1764 by Messier in a 3.5 foot focal length telescope, I discovered this 48,000 year old planetary nebula for the first time in a 4″ telescope. I was hooked immediately. Here before my eager eyes was a glowing green “apple core” which had a quality about it that I did not understand. It somehow moved… It pulsated. It appeared “living.” For many years I quested to understand the 850 light-year distant M27, but no one could answer my questions. I researched and learned it was made up of doubly ionized oxygen. I had hoped that perhaps there was a spectral reason to what I viewed year after year – but still no answer. Like all amateurs, I became the victim of “aperture fever” and I continued to study M27 with a 12″ telescope, never realizing the answer was right there – I just hadn’t powered up enough.

Several years later while studying at the Observatory, I was viewing through a friend’s identical 12″ telescope and, as chance would have it, he was using about twice the magnification that I normally used on the “Dumbbell.” Imagine my total astonishment as I realized for the very first time that the faint central star had an even fainter companion that made it seem to wink! At smaller apertures or low power, this was not revealed. Still, the eye could “see” a movement within the nebula – the central, radiating star and its companion. Do not sell the Dumbbell short. It can be seen as a small, unresolved area in common binoculars, easily picked out with larger binoculars as an irregular planetary nebula, and turns astounding with even the smallest of telescopes. In the words of Burnham, “The observer who spends a few moments in quiet contemplation of this nebula will be made aware of direct contact with cosmic things; even the radiation reaching us from the celestial depths is of a type unknown on Earth…”

Ready for a galactic star cluster for both binoculars and a small telescope? The return to Alpha and begin about two fingerwidths southeast and right on the galactic equator you’ll find NGC 6823 (RA 19 : 43.1 Dec +23 : 18). The first thing you will note is a fairly large, somewhat concentrated magnitude 7 open cluster. Resolved in larger telescopes, the viewer may note these stars are the hot, blue/white variety. For good reason. NGC 6823 only formed about 2 billion years ago. Although it is some 6000 light-years away and occupies around 50 light-years of space, it’s sharing the field with something more – a very large emission/reflection nebula, NGC 6820. In the outer reaches of the star cluster, new stars are being formed in masses of gas and dust as hot radiation is shed from the brightest of the stellar members of this pair. Fueled by emission, NGC 6820 isn’t always an easy visual object – it is faint and covers almost four times as much area as the cluster. But trace the edges very carefully, since the borders are much more illuminated than the region of the central cluster. Take the time to really observe this one! Its processes are very much like those of the “Trapezium” area in the Orion nebula. Be sure to mark your observing notes. NGC 6823 is Herschel VII.18 and NGC 6820 is also known as Marth 401!

If you’d like to try something new, return to M27 and head 2 degrees west-northwest to find NGC 6830 (RA 19 : 51.0 Dec +23 : 04). This rich 7.9 magnitude, cross-shaped open cluster is a real treat. Continue another 2 degrees in the same direction to pick up 7.1 magnitude cluster NGC 6823. Those with large telescopes should look for a faint sheen of nebulosity associated with this youthful open cluster!

Now let’s work on a pair of open star clusters for both binoculars and small telescopes, starting with NGC 6885 (RA 20 : 12.0 Dec +26 : 29). This little 6th magnitude sparkle of stars includes that bright O class star you can see visually and is also known as Caldwell 37. In binoculars you’ll see another compression nearby listed as NGC 6882 (RA 20 : 11.7 Dec +26 : 33). While it doesn’t contain a bright and splashy star like its neighbor, NGC 6882 is a nice ring shaped collection!

Our last official target in Vulpecula is superb galactic star cluster NGC 6940 (RA 20 : 34.6 Dec +28 : 18). This 6th magnitude, 31 arc minute cloud of stars is sure to please anyone with any size binoculars or telescope. The more aperture you have – the more stars you resolve! Discovered by Sir William Herschel in 1784 and logged as H VIII.23, this intermediate-aged galactic cluster will blow your mind in large aperture. Although visible in binoculars, as aperture increases the field explodes into about 100 stars in a highly compressed, rich cloud. Although not visited often, NGC 6940 is on many observing challenge lists. Use low power to get the full effect of this stunning starfield!

While NGC 6834 (RA 19 : 52.2 Dec +29 : 25) is officially listed as Cygnus, why not visit anyway? You’re in the neighborhood! It’s a very rich and compact small star cluster that’s a worthy challenge to pick out of the Milky Way star field in a telescope!

Sources:
Wikipedia
SEDS
Chart Courtesy of Your Sky.

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The southern circumpolar constellation of Volans was first introduced in 1589 by Petrus Plancius on a celestial globe which was later added to Johann Bayer’s atlas – Uranometria – in 1603. Volans spans 141 square degrees of sky, ranking 76th in size. It has 6 mains stars in its asterism and 12 Bayer Flamsteed designated stars within its confines. Volans is bordered by the constellation of Carina, Pictor, Dorado, Mensa and Chamaeleon and is best seen at culmination during the month of March.

Since Volans is considered a “new” constellation, it has no mythology associated with it – only what the constellation is meant to represent. The constellation of Volans was originally created by Petrus Plancius from the stellar observations of Dutch sea navigators Pieter Dirkszoon Keyser and Frederick de Houtman when exploring the southern hemisphere. Volans’ stellar patterns became known when it appeared on a celestial globe in 1597 and was considered a constellation when it was added to Johann Bayer’s Uranometria catalog in 1603 and it was then called Piscis Volans – the “Flying Fish”. When it was later adopted as a permanent constellation by the International Astronomical Union, the name was simplified and shortened to just Volans.

Let’s begin our binocular tour of Volans with its Alpha star – the “a” symbol on our chart. Alpha Volantis is located approximately 124 light years from Earth and it is a white class A (A2.5) subgiant star. While it is not anything particularly special, it is about twice the size of our Sun and shines about 30 times brighter. Somehow it got the Alpha designation, even though Beta (the “B” symbol) is physically brighter and 16 light years closer! Want a real trip? Then have a look at Delta – the “8” symbol. Even though it appears almost as bright as the rest of the stars, Delta is an F-type bright giant star that’s 660 light years from our solar system!

Now, get out your telescope for Epsilon Volantis – the backwards “3”. Epsilon is a triple star system! Located approximately 642 light years from Earth, the primary component, Epsilon Volantis A, is a spectroscopic binary star all of its own. It’s a blue-white B-type subgiant star with a companion that orbits so close we can only see it spectroscopically and know that it causes changes about every two weeks. But take a close look and you’ll discover a third, 8th magnitude star there, too. Epsilon Volantis B is 6.05 arcseconds away and an easy capture for a small telescope and large binoculars.

How about Gamma Volantis? It’s the “Y” symbol. This wide double star was just meant for binoculars! The two members are brighter, western Gamma-1 Volantis (magnitude 5.67) and dimmer, eastern Gamma-2 (magnitude 3.78). Set apart by 14.1 seconds of arc, you won’t have any trouble cutting these two stars apart and their color contrast make them a real winner in a telescope. Gamma-2 is a standard orange class K (K0) giant star and Gamma-1 is a a white class F (F2) dwarf star. While you might think this is an optical double star, it isn’t. The pair is physically bound to each other and both stars are about 142 light years away.

For those wishing a challenge, take on about the only deep sky study to be found in Volans – NGC 2442 (RA 7 : 36.4 Dec -69 : 32). At 11th magnitude and 6 arc minutes in size, this low surface brightness barred spiral galaxy is a nice study for a large telescope. Located about 50 million light years away from our Milky Way Galaxy, NGC 2442 was first was discovered by Sir John Herschel and contains a very unusual dark cloud of gas – one devoid of any stars. How did this come to be? Astronomers believe the cloud was torn loose from NGC 2442 by a companion during a galaxy interaction. Why not? After all, NGC is surrounded! If you have large aperture, you’ll see PGC 21457, PGC 21406, NGC 2434, PGC 21212, PGC 21323, PGC 21369 and PGC 21426 are nearby, too. Several of these satellite galaxies are physically related to NGC 2442. Be sure to look for two spiral arms extending from a pronounced central bar, giving the whole galaxy a hook-shaped appearance.

Sources:
Wikipedia
University of Wisconsin
Chart Courtesy of Your Sky.

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As one of the zodiacal signs, Virgo resides directly on the ecliptic plane and was one of the original 48 constellations charted by Ptolemy. It spans 1294 degrees and is the second largest constellation in the sky. Virgo also contains the point where the celestial equator crosses the ecliptic plane – the the autumn equinox. Between 9 and 15 stars make up its asterism and it contains 96 Bayer Flamsteed designated stars within its confines. Virgo is bordered by the constellations of Bootes, Coma Berenices, Leo, Crater, Corvus, Hydra, Libra and Serpens Caput. It is visible to all observers located at latitudes between +80° and ?80° and is best seen at culmination during the month of May.

There are two annual meteor showers associated with constellation Virgo. The Virginids peak on or about April 10th of each year and will appear to come from a point in the sky near Gamma. This is a relatively active and predictable meteor shower and you can expect to see about 10 meteors per hour on the average during a dark night from a dark location. The second is the Mu Virginids, which peak on or about April 25th. This is also a fairly reliable meteor shower and you can expect to see 7 to 10 meteors per hour on the average coming from an area near the Virgo/Leo border.

In mythology, Virgo is meant to represent the “Virgin”, but who exactly this woman is has never been established – only that she plays an important cultural role. Virgo is often portrayed carrying two sheaves of wheat, one of which is marked by the bright star Alpha – Spica – and it is the only astrological sign represented by a female. Perhaps she is Astraea, the virgin daughter of Zeus who was known as the goddess of justice. After all, Libra, the scales of justice is nearby!

Let’s begin our tour of Virgo with its brightest star – Alpha – the “a” symbol on our map. Alpha Viriginis is best known as Spica. Located 262 light-years away from Earth, 1.0 magnitude Spica glows with the combined light of four unresolved stars and has a visual luminosity 2100 times that of the Sun. As a rotating ellipsoidal variable, the four stars cause complex changes in luminosity by distorting the shape of the brightest components. The dominant star – Spica A – has a mass 11 times that of the Sun and fluctuates in physical size as it varies in brightness. The primary star is at maximum when smallest, giving it the highest photospheric surface temperature. Spica B has a mass of 7 suns. As a spectral type B, these two components produce more light in ultraviolet due to exceedingly high surface temperatures. Spica has two distant telescopic companions – magnitude 12 to the north-northeast, and magnitude 10.5 to the east-northeast.

Now head towards Beta – the “B”. Named Zavijava (sounds like something you’d get at Starbuck’s doesn’t it?) and located about 36 light years away from our solar system, this star holds a very special place in history because of its position in the sky. Since it is so near the ecliptic plane, it can frequently be occulted by the Moon, occasionally a planet, and even the Sun. In Zavijava’s case, it had the honor of being the star Einstein used during the solar eclipse of September 21, 1922 to determine the speed of light in space! What’s more, according to studies, Beta Virginis could host two or three Jupiter-sized planets – either brown dwarf stars in wide orbits or true planetary objects.

Ready for Gamma Virginis? That’s the “Y” symbol. Best known as Porrima, this binary star of nearly matched magnitudes was an easy object for amateur astronomers, but now the smaller apparent distance between the stars requires a larger telescope. Because of its relatively quick orbital period of 168.93 years, you’ll sometimes hear Porrima referred to as the “Shrinking Star”. At the time of this writing (early 2009), the pair is only separated by about .04″ and it will be another 11 years before they have moved apart enough again to be easily split with a small telescope!

Because there are massive amounts of deep sky objects in Virgo, annotating a map would be so cluttered it would be difficult to read. Let us begin first with the chart we have above which highlights the brighter objects in Virgo – ones easily seen with binoculars and small telescopes. Ready to dance?

Our first target will be Messier 104 (RA 12 : 40.0 Dec -11 : 37). Now, shake your fist at Spica… Because that’s all it takes to find the awesome M104, eleven degrees due west. (If you still have trouble finding M104, don’t worry. Try this trick! Look for the upper left hand star in the rectangle of Corvus – Delta. Between Spica and Delta is a diamond-shaped pattern of 5th magnitude stars. Aim your scope or binoculars just above the one furthest south.) Also known as the “Sombrero Galaxy” this gorgeous 8th magnitude spiral galaxy was discovered by Pierre Mechain in 1781, added by hand to Messier’s catalog and observed independently by William Herschel as H I.43 – who was probably the first to note its dark inclusion. The Sombrero’s rich central bulge is comprised of several hundred globular clusters and can be hinted at in just large binoculars and small telescopes. Large aperture telescopes will revel in this galaxy’s “see through” qualities and bold, dark dustlane – making it a seasonal favorite!

Now, let’s take a look at one of the brightest members of the Virgo Cluster – Messier 49. Located about eight degrees northwest of Delta Virginis almost directly between a pair of 6th magnitude stars (RA 12 29 46 Dec +07 59 59), the giant elliptical galaxy M49 holds the distinction of being the first galaxy in the Virgo cluster to be discovered – and only the second beyond our local group. At magnitude 8.5, this type E4 galaxy will appear as an evenly illuminated egg shape in almost all scopes, and as a faint patch in binoculars. While a possible supernova event occurred in 1969, don’t confuse the foreground star noted by Herschel with something new! Although most telescopes won’t be able to pick this region apart, there are also many fainter companions near M49, including NGC 4470. But a sharp-eyed observer named Halton Arp noticed them and listed them as Peculiar Galaxy 134 – one with “fragments!”

Next up, Messier 87 (RA 12 : 30.8 Dec +12 : 24). It’s a radio-source galaxy so bright it can be seen in binoculars – 8.6 magnitude M87, about two fingerwidths northwest of Rho Virginis. This giant elliptical galaxy was discovered by Charles Messier in 1781 and cataloged as M87. Spanning 120,000 light-years, it’s an incredibly luminous galaxy containing far more mass and stars than the Milky Way Galaxy – gravitationally distorting its four dwarf satellites galaxies. M87 is known to contain in excess of several thousand globular clusters – up to 150,000 – and far more than our own 200.

In 1918, H. D. Curtis of Lick Observatory discovered something else – M87 has a jet of gaseous material extending from its core and pushing out several thousand light-years into space. This highly perturbed jet exhibits the same polarization as synchrotron radiation – a property of neutron stars. Containing a series of small knots and clouds as observed by Halton Arp at Palomar in 1977, he also discovered a second galaxy jet in 1966 erupting in the opposite direction. Thanks to these two properties, M87 made Arp’s “Catalog of Peculiar Galaxies” as number 152. In 1954 Walter Baade and R. Minkowski identified M87 with radio source Virgo A, discovering a weaker galactic halo in 1956. Its position over an x-ray cloud extending through the Virgo cluster make M87 a source of an incredible amount of x-rays. Because of its many strange properties, M87 remains a target of scientific investigation. The Hubble Space Telescope has shown a violent nucleus surrounded by a fast rotating accretion disc, whose gaseous make-up may be part of a huge system of interstellar matter. As of today, only one supernova event has been recorded – yet M87 remains one of the most active and highly prized study galaxies of all. Capture it tonight!

Now we’re heading for our more detailed map and the galaxy fields of Virgo about four fingerwidths east-southeast of Beta Leonis. As part of Markarian’s Chain, this set of galaxies can all be fitted within the same field of view with a 32mm eyepiece and a 12.5″ scope, but not everyone has the same equipment. Set your sights toward M84 and M86 and let’s discover!

Good binoculars and small telescopes reveal this pair with ease as a matched set of elliptical galaxies. Mid-sized telescopes will note the western member of the pair – M84 – is seen as slightly brighter and visibly smaller. To the east and slightly north is larger M86 – whose nucleus is broader, and less intensely brilliant. In a larger scope, we see the galaxies literally “leap” out of the eyepiece at even the most modest magnifications. Strangely though, additional structure fails to be seen. As aperture increases, one of the most fascinating features of this area becomes apparent. While studying the bright galactic forms of M84/86 with direct vision, aversion begins to welcome many other mysterious strangers into view. Forming an easy triangle with the two Messiers and located about 20 arc-minutes south lies NGC 4388. At magnitude 11.0, this edge-on spiral galaxy has a dim star-like core to mid-sized scopes, but a classic edge-on structure in larger ones.

At magnitude 12, NGC 4387 is located in the center of a triangle formed by the two Messiers and NGC 4388. NGC 4387 is a dim galaxy – hinting at a stellar nucleus to smaller telescopes, while the larger ones will see a very small face-on spiral galaxy with a brighter nucleus. Just a breath north of M86 is an even dimmer patch of nebulosity – NGC 4402 – which needs higher magnifications to be detected in smaller scopes. Large apertures at high power reveal a noticeable dust lane. The central structure forms a curved “bar” of light. Luminosity appears evenly distributed end to end, while the dust lane cleanly separates the central bulge of the core. East of M86 are two brighter NGC galaxies – 4435 and 4438. Through average scopes, NGC 4435 is easily picked out at low power with a simple star-like core and wispy round body structure. NGC 4438 is dim, but even large apertures make elliptical galaxies a bit boring. The beauty of NGC 4435 and NGC 4438 is simply their proximity to each other. 4435 shows true elliptical structure, evenly illuminated, with a sense of fading toward the edges… But 4438 is quite a different story! This elliptical galaxy is much more elongated. A highly conspicuous wisp of galactic material can be seen stretching back toward the brighter, nearby galaxy pair M84/86.

Ready for bright galaxy Messier 58 (RA 12 : 37.7 Dec +11 : 49)? It’s a spiral galaxy actually discovered by Messier in 1779! As one of the brightest galaxies in the Virgo cluster, M58 is one of only four that have barred structure. It was cataloged by Lord Rosse as a spiral in 1850. In binoculars, it will look much like our previously studied ellipticals, but a small telescope under good conditions will pick up the bright nucleus and a faint halo of spiral galaxy structure – while larger ones will see the central concentration of the bar across the core. Chalk up another Messier study for both binoculars and telescopes and let’s get on to something really cool!

Around a half degree southwest are NGC 4567 and NGC 4569. L. S. Copeland dubbed them the “Siamese Twins,” but this galaxy pair is also considered part of the Virgo cluster. While seen from our viewpoint as touching galaxies, no evidence exists of tidal filaments or distortions in structure, making them a line of sight phenomenon and not interacting members. While that might take little of the excitement away from the “Twins,” a supernova event has been spotted in NGC 4569 as recently as 2004. While the duo is visible in smaller scopes as two, with soft twin nuclei, intermediate and large telescopes will see an almost V-shaped or heart-shaped pattern where the structures overlap. If you’re doing double galaxy studies, this is a fine, bright one! If you see a faint galaxy in the field as well, be sure to add NGC 4564 to your notes. Moving about a degree north will call up face-on spiral galaxy M89, which will show a nice core region in most telescopes. One half degree northeast is where you will find the delightful 9.5 magnitude M90 – whose dark dust lanes will show to larger telescopes.

Virgo contains many, many more fine objects – so be sure to get a detailed star chart and spend some time with this great constellation!

Sources:
Wikipedia
SEDS
Chandra Observatory
Charts Courtesy of Your Sky.