What is the Local Group?

Our universe contains at least hundreds of billions of galaxies, maybe trillions, in all shapes and sizes. Most are very far away from our home galaxy, the Milky Way. At billions of light-years away, most are too far to see without binoculars or a telescope. But our Local Group of galaxies is different. It consists of our neighboring galaxies within the vast universe. The Local Group galaxies are all located within roughly 5 million light-years of space around us. The Local Group’s diameter is about 10 million light-years.

Our Milky Way is just one of three large galaxies in the Local Group. But it’s not the biggest of the Local Group galaxies. That would be the Andromeda galaxy. And the third galaxy, called the Triangulum galaxy, is the smallest of the three large ones. There are also 50 or so dwarf galaxies in the Local Group. So is the Local Group considered a large structure in our universe? Yes and no. Keep reading to learn more.

It’s all relative

On the vast astronomical distance scale, the Local Group galaxies are relatively close to us. They’re only millions of light-years away, instead of billions. As a result, some Local Group galaxies are visible to the unaided eye from a dark site.

The illustration above suggests our Milky Way galaxy lies at the center of the Local Group. It doesn’t, of course, but the image is organized that way, honoring our human perspective. On the other hand, the Local Group does have a gravitational center. It’s somewhere between the Milky Way and the Andromeda galaxy.

Also, astronomers have also discovered that our Local Group is on the outskirts of a giant supercluster of galaxies, known as the Virgo Supercluster.

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Want to get to know the neighbors?

Read more about the Milky Way

Andromeda galaxy: All you need to know

Triangulum galaxy: 2nd-closest large spiral galaxy

The Large and Small Magellanic Clouds

What’s bigger than the Local Group?

The Local Group is a collection of galaxies. It spans some 10 million light-years of space. But, although gravity is the weakest of the four fundamental forces of nature, gravity has an infinite range. So it’s no wonder that – as astronomers look out into space – they see groups of galaxies on both small and large scales. They see groups like the Local Group belonging to even more gigantic structures.

At least 100 galaxy groups and clusters – including our Local Group – are located within the Virgo Supercluster. Astronomers believe the diameter of this great supercluster – sometimes called our “local” supercluster – is about 110 million light-years.

And, in 2014, astronomers announced that the Virgo Supercluster itself might be part of an even-larger structure, which astronomers call the Laniakea Supercluster. They described that greater supercluster as consisting of perhaps 100,000 galaxies stretched out over some 520 million light-years. At that time, astronomers pointed to this vast supercluster as one of many such structures known in space.

But, a few years later, another group of astronomers showed that the galaxies in the Laniakea Supercluster aren’t gravitationally bound. So, they said then, this cluster will disperse over time, rather than maintain itself as a bound object.

Will it? We don’t know for sure yet. What we do know is that gravity works across our universe to form collections of galaxies in space. Our Local Group is just one example – albeit an interesting one to us – of how galaxies like to congregate.

Big, bigger, biggest?

Bottom line: The Local Group of galaxies consists of three large galaxies – the Andromeda galaxy (biggest), our Milky Way (2nd-biggest) and the Triangulum galaxy (3rd biggest) – along with 50 or so much-smaller dwarf galaxies.

The post The Local Group is our galactic neighborhood first appeared on EarthSky.

The Triangulum galaxy, also known as Messier 33 (M33), is theoretically the farthest object visible with the unaided eye. But, in practice, you’ll need perfect dark sky conditions – and good eyesight – to see it with the eye alone. Even with binoculars and a telescope, this pinwheel-shaped spiral galaxy is a challenge to spot. It’s relatively nearby. But it’s turned face-on to us, so it has a low surface brightness in our sky.

The Triangulum galaxy, named for its location in the constellation Triangulum, is the 2nd-nearest spiral galaxy to our Milky Way, after the Andromeda galaxy (M31). If you do manage to glimpse it, you’re looking across a distance of 2.7 million light-years.

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How to find the Triangulum Galaxy

Have you ever seen the Andromeda galaxy (Messier 31), closest spiral galaxy to our Milky Way? It’s about 2.2 million light-years away, and appears edge-on to us. It’s much easier to see. Try finding the Andromeda galaxy before you take on the Triangulum galaxy. Here are two ways to find the Andromeda galaxy:

Use constellation Cassiopeia to find Andromeda galaxy

Use Great Square of Pegasus to find Andromeda galaxy

The Andromeda galaxy shines eight times more brightly in our sky than the Triangulum galaxy. The Triangulum and Andromeda galaxies are relatively close together in our sky, only 15 degrees apart. For reference, a fist-width at arm’s length approximates 10 degrees.

Seeing M33

Star-hop to the Andromeda galaxy to orient yourself to the Triangulum galaxy. As seen on the sky chart, the star Mirach stands about midway between the two galaxies. Once you find Mirach and the Andromeda galaxy, you can draw a line between them to point in the general direction of the Triangulum galaxy.

Now for a word of warning: even if you’re staring right at the Triangulum galaxy, it’s still possible to miss it. You won’t see the galaxy’s stars at all. Sometimes, this galaxy looks almost transparent, like a water spot on a window. The small blob in your binocular field might resemble an unwashed spot on an otherwise clean window.

Science of the Triangulum galaxy

The Triangulum galaxy – at 2.7 million light-years from our Milky Way – is a spiral galaxy. Its face-on orientation has given it the nickname the Pinwheel (another face-on spiral, Messier 101, also has this nickname).

The Triangulum galaxy is the 3rd-largest member of our Local Group of galaxies. Our Local Group consists of several dozen galaxies. Our Milky Way, the Andromeda galaxy and the Triangulum galaxy are the largest members.

The Triangulum galaxy’s diameter is about 60,000 light-years, or about 60% that of our Milky Way. It’s thought to contain some 40 billion stars. In contrast, there are 100-400 billion stars in the Milky Way and a trillion (1,000 billion) stars in the Andromeda galaxy.

In 2004, astronomers found evidence for a clumpy stream of hydrogen gas linking the Triangulum galaxy with the nearby Andromeda galaxy. A year later, astronomers were able to estimate the proper motion – or sideways motion on our sky’s dome – of the Triangulum Galaxy for the first time. They found that this galaxy is moving towards the Andromeda galaxy. Afterwards, some astronomers suggested the Triangulum galaxy might be a satellite of the Andromeda galaxy. In other words, over a timescale so vast we haven’t yet comprehended it, the Triangulum galaxy might orbit around the Andromeda galaxy.

The fate of the Triangulum galaxy

It’s well known that the Andromeda galaxy is moving toward our Milky Way and that a collision between the two galaxies will occur some 4 billion years from now.

Meanwhile, the fate of the Triangulum galaxy isn’t known for certain. It might someday be torn apart and absorbed by the Andromeda galaxy. It might participate in the collision between the Milky Way and Andromeda galaxies. Two other possibilities are a collision with the Milky Way before Andromeda arrives or an ejection from the Local Group.

It’s safe to say that the fate of these great galaxies is beyond human knowledge at this time!

Bottom line: The Triangulum Galaxy, aka M33, is the farthest object you can see with the unaided eye, if in fact you can see it. But seeing it is a challenge.

The post Triangulum galaxy is 2nd-closest to Milky Way first appeared on EarthSky.

Double Cluster in Perseus

The Double Cluster in Perseus consists of two open star clusters near each other on the sky’s dome. Amateur astronomers know them as h and Chi Persei. The two clusters reside in the northern part of the constellation Perseus, quite close to the constellation Cassiopeia the Queen. If you have a dark sky and find Cassiopeia – which is easy, because the constellation has a distinctive M or W shape – be sure to look for Perseus, too. Then just scan between the two constellations with your binoculars for two glittering groups of stars. The Double Cluster – a breathtaking pair of open clusters, each containing supergiant suns – will be there.

These two star clusters are located about 7,640 (Chi) and 7,460 (h) light-years away. So, they’re separated from one another by a few hundred light-years. It’s amazing that we can see these stars at all across this great span of space. Plus, we know they must be bright stars, intrinsically, or we wouldn’t be able to see them. Each cluster contains a few hundred stars, and, indeed, these stars are young, hot supergiant suns that are many thousands of times more luminous than our sun.

Astronomers tell us that the Double Cluster lies within the Perseus arm of the Milky Way galaxy. However, our solar system resides in the inner part of the Orion arm. Therefore, looking at the Double Cluster, we are looking through our local spiral arm and all the way to the next spiral arm outward from the galactic center.

How to find the Double Cluster

To locate the Double Cluster, find the W- or M-shaped constellation Cassiopeia the Queen. If your sky is dark enough, you will be able to see the graceful pattern of Perseus the Hero nearby. Then scan between them with binoculars to find the Double Cluster.

At mid- and far-northern latitudes, the Double Cluster is circumpolar – above the horizon every night of the year at any hour of the night. If you are farther south (but still in the Northern Hemisphere), try looking for the Double Cluster in the evening in autumn or winter.

Just remember … the Double Cluster is harder to see when it’s close to the horizon. If you can’t spot it between Cassiopeia and Perseus, wait until later at night. Or look later in the year, when it’s higher in the sky.

For general reference, the Double Cluster is high in the sky when the Big Dipper is low, and vice versa. Because the Big Dipper is lowest in the northern sky on late autumn and early winter evenings, the Double Cluster is highest in the northern sky at these times. As a matter of fact, the Double Cluster is pretty much always visible in the evening except in late spring and summer.

The Double Cluster is visible to the unaided eye

The Double Cluster rates among the most magnificent deep-sky objects not to be included in the famous Messier catalog. Of course, Charles Messier (1730-1817) was looking for deep-sky objects that could be mistaken for comets. Maybe he thought nobody would see this pair of glittery clusters as a comet in the sky.

Although considered a deep-sky jewel, the Double Cluster is visible to the unaided eye in a dark country sky.

If you zoom in on them with binoculars or a wide view telescope, you’ll see them as two glorious star clusters. Also they’re an easy target through a telescope and will wow your friends!

The position of h Persei is Right Ascension: 2h 19m; Declination: 57^o 9′ north

The position of Chi Persei is Right Ascension: 2h 22.4m; Declination: 57^o 7′ north

Bottom line: On an autumn or winter evening, scan between Cassiopeia and Perseus for the magnificent Double Cluster in Perseus. The stars in these two clusters are young, hot supergiant suns that are many thousands of times more luminous than our sun.

The post Double Cluster in Perseus on October evenings first appeared on EarthSky.

Rename the Magellanic Clouds?

The controversy about renaming the Magellanic Clouds is heating up again. It’s been brewing for at least a couple of years. On September 12, 2023, astronomer Mia de los Reyes of Amherst College wrote in an opinion piece in the American Physical Society’s online magazine Physics:

The Milky Way is surrounded by a host of smaller satellite galaxies. The two brightest are known as the Large and Small Magellanic Clouds. Both galaxies are visible to the unaided eye, and both have been known for centuries by viewers of the Southern Hemisphere sky.

But the beauty of these starry objects is clouded by their names, which honor a man who was a colonizer, a slaver, and a murderer. Now I and a coalition of astronomers are calling for the scientific community to rename these galaxies …

These two famous Milky Way satellites are named for the Portuguese explorer Ferdinand Magellan, who led the first expedition to circumnavigate the globe.

Why rename the galaxies?

According to Mia de los Reyes and her colleagues, on Magellan’s travels, he killed and enslaved the native peoples he met. De los Reyes wrote:

… Magellan was no astronomer, and he was not the first to document these galaxies. Indigenous peoples across the Southern Hemisphere have names and legends for these systems that predate Magellan by thousands of years.

Some of the previous names and descriptions for the satellite galaxies are beautiful and descriptive. De los Reyes wrote:

… the Mapuche of modern-day Chile and Argentina call them Rvganko, or water ponds, which they think are in the process of drying out. The Kamilaroi of modern-day Australia regard the galaxies as places where people go after death. And the Arimi of modern-day Tanzania see the clouds as a man and a woman who help the Pleiades bring heavy rains during the rainy season.

Read the September 12, 2023, opinion piece by Mia de los Reyes here.

What do you think? Share your opinion in the comments below.

More from Mia de los Reyes

Furthermore, she wrote:

… Magellan committed horrific acts. A first-hand account of Magellan’s expedition describes how, in what is now known as Argentina, Magellan enslaved the native Tehuelche people. He placed iron manacles on the ‘youngest and best proportioned’ men, telling them that the manacles were gifts. In what became Guam and the Philippines, Magellan and his men burned villages and killed their inhabitants.

Despite his actions, Magellan has been – and continues to be – widely honored by the field of astronomy. Magellan’s name currently appears in over 17,000 peer-reviewed academic articles. His name is attached to astronomical objects such as a lunar crater and a Martian crater, both of which are named Magalhaens; the NASA Magellan spacecraft; the twin 6.5-m Magellan telescopes; and most recently, an under construction, next-generation extremely large telescope called the Giant Magellan Telescope. The Magellan telescopes are all located in Chile, a country with a history of violent Spanish conquest. Indeed, Magellan’s ‘discovery’ of the Strait of Magellan allowed Spanish conquistadors to explore Chile’s coast and led to genocidal campaigns against the native Mapuche people.

I and many other astronomers believe that astronomical objects and facilities should not be named after Magellan, or after anyone else with a violent colonialist legacy. We would like the International Astronomical Union – the body in charge of naming astronomical objects – to rename the Magellanic Clouds. We hope other astronomical institutions, particularly the consortia that manage the 6.5-m Magellan telescopes and the upcoming Giant Magellan Telescope, will also revisit the use of Magellan’s name.

Read the September 12, 2023, opinion piece by Mia de los Reyes here.

What do you think? Share your opinion in the comments below.

What would we call them?

Writing in Science News on September 26, 2023, senior physics writer Emily Conover explained:

The galaxies have been known scientifically by Magellan’s name since only the end of the 19th century, well after Magellan’s voyage. That’s just a blip in the history of astronomy, the researchers argue.

More than 100 astronomers have expressed interest in the campaign, anchored by a core group of about 50, de los Reyes says. The group aims to bring the proposal to the International Astronomical Union, in hopes of eventually holding a vote on the name change …

The astronomers are now trying out new names. One popular suggestion is to call them the ‘Milky Clouds.’ That would maintain the commonly used acronyms, LMC and SMC.

And, Conover wrote, it would reflect the galaxies’ connection to something much bigger than any one person: our home galaxy, the Milky Way.

Read the September 26, 2023, reporting by Emily Conover in Science News, here.

What do you think? Share your opinion in the comments below.

The Magellanic Clouds from the Southern Hemisphere

If you want to see the Magellanic Clouds, you have to head south. They’re not visible north of about 17 degrees north latitude. If you’re in the Southern Hemisphere, you can see these satellite galaxies any night of the year because they’re south circumpolar. In other words, they’re close enough to the South Celestial Pole that they never set.

The Large Magellanic Cloud is one of the closest galaxies to us at about 160,000 light-years away. It’s about 40,000 light-years closer than the Small Magellanic Cloud. As some of the closest galaxies to our home galaxy, they stand out as big, misty blobs of light under dark skies.

Scientists estimate the Small Magellanic Cloud contains around 3 billion stars, while the Large Magellanic Cloud houses some 30 billion stars.

The Clouds in myth

In the Southern Hemisphere, Australian Aborigines, the Maori people of New Zealand and the Polynesian people of the South Pacific were familiar with both the Large and Small Clouds. They used them as navigational markers during their oceanic expeditions. They considered these hazy star-clouds predictors of the winds. The website OzSky.org explains:

Many tribes of Australian Aboriginals have ‘dreamtime stories,’ which they have passed down from generation to generation, to explain the universe as they perceive it. One such legend describes the Clouds as the campfires of an old couple, the Jukara. The Jukara relied on other star people to supply them with fish and lily bulbs caught in the Milky Way to survive. The old couple cooked the food over their campfire, which was the star Achernar. The Large Cloud represented the old man while the Small Cloud was the old woman.

Another myth comes from South Africa. The nearby constellation Mensa the Table got its name from South Africa’s Table Mountain. One story says that the Large Magellanic Cloud is a puff of smoke from a pipe-smoking contest held on the mountain.

In history, Abd al-Rahman al-Sufi, a Persian astronomer, described the Large Magellanic Cloud in his Book of Fixed Stars in 964 CE. He called it Al Bakr, describing it as the White Ox of southern Arabia.

Science of the Magellanic Clouds

Henrietta Swan Leavitt – famous for her work on the Cepheid variable stars – studied the Large and Small Magellanic Clouds from Harvard College Observatory in Southern Peru. In the early 1900s, she published her work on variable stars in the Small Magellanic Cloud, famously showing the relationship between the periods (cycles) of the stars’ variability and their luminosities. Her study was titled 1777 variables in the Magellanic Clouds. The period-luminosity relationship later became a reliable gauge for astronomers trying to parse the riddle of star and galaxy distances.

Astronomers believe that the Large and Small Clouds formed around the same time as our Milky Way, some 12 to 13 billion years ago. Due to their repeated interaction with our larger Milky Way galaxy, it’s thought that great galactic tides might have caused their irregular shape.

The ongoing Dark Energy Survey found a dark stream of interacting matter between the Large and Small Magellanic Clouds. Simulations performed by a team of scientists at the University of Arizona suggested that the two galaxies might be interacting with each other and might eventually merge.

Bottom line: The Large and Small Magellanic Clouds are two of the closest galaxies to the Milky Way. They can be seen without optical aid from southern skies. In September 2023, astronomers again began calling for the clouds to be renamed.

The post Do the Large and Small Magellanic Clouds need new names? first appeared on EarthSky.

The large spiral galaxy next door

Although several dozen minor galaxies lie closer to our Milky Way, the Andromeda galaxy is the closest large spiral galaxy to ours. Excluding the Large and Small Magellanic Clouds, visible from Earth’s Southern Hemisphere, the Andromeda galaxy is the brightest external galaxy visible in our night sky. And, at 2.5 million light-years, it’s the most distant thing we humans can see with the unaided eye.

Note: The large spiral Triangulum galaxy is slightly more distant at 2.7 million light-years. Like the Andromeda galaxy, it’s a member of our Local Group of galaxies. And it’s sometimes said to be visible to the eye also. But it’s turned face-on to us, and so has a low surface brightness. Unlike the Andromeda galaxy, it’s very hard to see.

Astronomers sometimes call the Andromeda galaxy by the name Messier 31, or M31. It was the 31st on a famous list of fuzzy sky objects compiled by the French astronomer Charles Messier (1730-1817). His catalog listed “objects to avoid” when comet-hunting. Nowadays, amateur astronomers seek out these objects with their telescopes and binoculars. They’re some of most beautiful deep-sky objects known.

Most Messier objects are star clusters or gas clouds in our Milky Way galaxy. But the Andromeda galaxy is a whole separate galaxy, even bigger than our Milky Way. In a dark sky, you can see that it’s big on the sky as well, a smudge of distant light larger than a full moon.

Some images of M31 from our EarthSky community

When to look for it

From mid-northern latitudes, you can see Andromeda – M31 – for at least part of every night, all year long. But most people see the galaxy first around August or September, when it’s high enough in the sky to be seen from evening until daybreak.

In early September, begin looking for the galaxy in mid-evening, about midway between your local nightfall and midnight.

In late September and early October, the Andromeda galaxy shines in your eastern sky at nightfall, swings high overhead in the middle of the night, and stands rather high in the west at the onset of morning dawn.

Winter evenings are also good for viewing the Andromeda galaxy.

If you are far from city lights, and you’re stargazing during a moonless night during the late summer, or on any autumn or winter evening, it’s possible that you’ll simply notice the galaxy there in your night sky. But if you don’t manage to easily see it, you can star-hop to find the galaxy in one of two ways. The easiest way is to use the constellation Cassiopeia the Queen. You can also use the Great Square of Pegasus.

Use Cassiopeia to find the Andromeda galaxy

The constellation Cassiopeia is easy to find. Look generally northward on the sky’s dome for a pattern of stars shaped like the letter M or W. If you can recognize the North Star, Polaris – and if you know how to find the Big Dipper – be aware that the Big Dipper and Cassiopeia move around Polaris like the hands of a clock, always opposite each other.

Once you’ve found Cassiopeia, look for its star Schedar. In the illustration above, see how Schedar points to the Andromeda galaxy?

Or use the Great Square to find M31

You can also star-hop to the Andromeda galaxy, using the Great Square of Pegasus. It’s a longer route. But, in many ways, it’s more beautiful.

You’ll be hopping to the Andromeda galaxy from the Great Square of Pegasus. In autumn, the Great Square of Pegasus looks like a great big baseball diamond in the eastern sky. Envision the bottom star of the Square’s four stars as home plate, then draw an imaginary line from the “1st base” star though the “3rd base” star to locate two streamers of stars flying away from the Great Square. These stars belong to the constellation Andromeda the Princess.

On each streamer, go two stars north (left) of the third base star, locating the stars Mirach and Mu Andromedae. Draw a line from Mirach through Mu Andromedae, going twice the Mirach/Mu Andromedae distance. You’ve just landed on the Andromeda galaxy, which looks like a smudge of light to the unaided eye.

If you can’t see the Andromeda galaxy with the eye alone, by all means use binoculars.

History of our knowledge of the Andromeda galaxy

At one time, the Andromeda galaxy was called the Great Andromeda Nebula. Astronomers thought this patch of light was composed of glowing gases, or was perhaps a solar system in the process of formation.

It wasn’t until the 20th century that astronomers were able to resolve the Andromeda spiral nebula into individual stars. This discovery lead to a controversy about whether the Andromeda spiral nebula and other spiral nebulae lie within or outside the Milky Way.

In the 1920s Edwin Hubble finally put the matter to rest, when he used Cepheid variable stars within the Andromeda galaxy to determine that it is indeed an “island universe” residing beyond the bounds of our Milky Way galaxy.

Andromeda and Milky Way in context

The Andromeda and Milky Way galaxies reign as the two most massive and dominant galaxies within the Local Group of galaxies. The Andromeda galaxy is the largest galaxy of the Local Group, which, in addition to the Milky Way, also contains the Triangulum galaxy and about 30 other smaller galaxies.

Both the Milky Way and the Andromeda galaxies lay claim to about a dozen satellite galaxies. Both are some 100,000 light-years across, containing enough mass to make billions of stars.

Astronomers have discovered that our Local Group is on the outskirts of a giant cluster of several thousand galaxies, which astronomers call the Virgo Cluster.

We also know of an irregular supercluster of galaxies, which contains the Virgo Cluster, which in turn contains our Local Group, which in turn contains our Milky Way galaxy and the nearby Andromeda galaxy. At least 100 galaxy groups and clusters are located within this Virgo Supercluster. Its diameter is thought to be about 110 million light-years.

And the Virgo Supercluster is thought to be one of millions of superclusters in the observable universe.

Will the Andromeda galaxy collide with the Milky Way?

One of our readers wrote:

I’ve heard that the Andromeda galaxy will someday collide with our galaxy! Is that still a definite possibility?

A definite possibility describes much of what we know – or think we know – about the universe. As for the Andromeda galaxy and its future collision with our Milky Way: the first attempt to measure the radial velocity of this galaxy (its motion forward or back, along our line of sight) was made in 1912. After that, astronomers believed for some decades that the galaxy was approaching at nearly 200 miles per second (321 km/s), but later astronomers disagreed.

Then in May 2012, NASA astronomers announced they can now predict the time of this collision of titanic galaxies with certainty. Remember, though, that the Andromeda galaxy is 2.2 million light-years away, with a single light-year being almost 6 trillion miles (10 trillion kilometers). So although it does appear that this galaxy is approaching our Milky Way galaxy … it’s nothing to lose sleep over. When will they collide? According to NASA astronomers in 2012, it’ll be four billion years from now.

However, in March 2022, the peer-reviewed Astrophysical Journal published new research revealing that the collision between our galaxies is already underway. Or at least our galactic halos – which consist of gas, dust and stray stars – may already be touching.

Read more: Andromeda galaxy and the Milky Way are merging

When galaxies collide …

What happens when galaxies collide? They don’t exactly crash into each other. Because there’s so much more space than stars even in a galaxy, colliding galaxies pass through each other, like ghosts.

But, colliding galaxies do interact via gravity, which will cause them to change shape and even merge into a larger galaxy. Check out this cool video: Night sky as Milky Way and Andromeda galaxies merge.

The Andromeda galaxy (M31) is located at the coordinates RA: 0h 42.7m; Dec: 41^o 16′ north.

Bottom line: At 2.5 million light-years, the great Andromeda galaxy (Messier 31) rates as the most distant object you can see with the unaided eye.

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The post Andromeda galaxy: All you need to know first appeared on EarthSky.

The Great Rift, or Dark Rift, is a long swath of gaseous clouds darkening a stretch of the Milky Way. And yes, it blocks the light from stars behind it. This dark cloudy strip – where stars are forming – is visible in a dark sky.

The Great Rift: How to see it

Summertime is the best time to look for the Great Rift. That’s because the Milky Way is prominent in our evening sky. Pick a night when the moon is out of the way. Under a dark sky, far from city lights, the Milky Way is easy to see at this time of year. It’s a whitish band stretching across the sky. If you want to see the Dark Rift, that’s easy, too, as long as you realize you aren’t looking for a bright object. You’re looking instead for dark lanes of dust running the length of the starlit Milky Way band.

You can see the Milky Way most easily in the evening from around June or July through about October. From a Northern Hemisphere location, you’ll see the thickest part of the Milky Way above the southern horizon. From the Southern Hemisphere, the thickest part of the Milky Way appears more overhead. Notice that the Milky Way band looks milky white, thus its name. The skies aren’t really black like ink between stars in the Milky Way. You’ll know when you see the Dark Rift. That’s because it looks as if someone took a marker and colored parts of the Milky Way darker.

Constellations along the Great Rift

The Dark Rift begins just above the constellation Sagittarius the Archer. Follow the Milky Way up until you see a black area in the Milky Way just before you get to the constellation Cygnus. Cygnus is shaped like a cross. Deneb is the brightest star in Cygnus and part of the famous Summer Triangle asterism. You can see the Dark Rift inside the Summer Triangle.

Be sure to keep your binoculars handy for any Milky Way viewing session. There are many interesting star-forming regions, star clusters and millions of stars that will capture your attention.

The Great Rift is dark due to dust

Stars are formed from great clouds of gas and dust in our Milky Way galaxy and other galaxies. When we look up at the starry band of the Milky Way and see the Dark Rift, we are looking into our galaxy’s star-forming regions. Imagine the vast number of new stars that will emerge, in time, from these clouds of dust.

Ancient cultures focused on dark areas, not light areas

You know those paintings where if you look at the light areas you see one thing, but in the dark areas you see something else?

The Great Rift is a bit like that. A few ancient cultures in Central and South America saw the dark areas of the Milky Way as constellations. These dark constellations had a variety of myths associated with them. For example, one important dark constellation was Yacana the Llama. It rises above Cuzco, the ancient city of the Incas, every year in November.

By the way, the other famous area of the sky that is obscured by molecular dust is visible from the Southern Hemisphere. It’s the famous Coalsack Nebula near the Southern Cross, also known as the constellation Crux. The Coalsack is another region of star-forming activity in our night sky, much like the Dark Rift.

Bottom line: The Great Rift or Dark Rift is a darkened swath of the Milky Way where new stars are forming. It’s best seen from a rural location away from light pollution.

The post The Great Rift is a dark swath in the Milky Way first appeared on EarthSky.

Ordinary binoculars under a dark sky can bring the Lagoon Nebula to you from 5,000 light-years away. Look for it a few degrees above and to the right of the Teapot asterism in the constellation Sagittarius. Messier 8 (M8) is the formal designation for this nebula. It’s a large gas cloud within our Milky Way galaxy, barely visible to the human eye under good conditions, but glorious with a dark sky and a bit of optical aid.

How to find the Lagoon Nebula

To be sure, you can enjoy great views of M8, but first you have to find it. Let’s start with when to look. In the Northern Hemisphere, mid-summer to mid-fall is ideal. If you’re in the Southern Hemisphere, you’ll want to look in mid-winter to mid-spring. Later, by early July each year, this object is crossing the meridian – appearing highest in the sky – at midnight. And by early September, it’s crossing the meridian as darkness falls, making it prime for early evening observations.

Next, pick a night close to new moon and an observing spot that is far from interfering lights. Visit EarthSky’s Best Places to Stargaze page to find a dark sky location near you.

Then, look for the constellation Sagittarius, which marks the direction of the Milky Way’s center. You’ll be looking southward in the evening from Earth’s Northern Hemisphere. If you’re in the Southern Hemisphere, look northward, closer to overhead, and turn the chart below upside-down. Want a more exact location for Sagittarius? Try using Stellarium, which will let you set a date and time from your exact location on the globe.

What you’ll see

The Lagoon Nebula spans an area of sky about three times the size of the full moon. As the largest and brightest of a number of nebulosities around Sagittarius, it’s widely visible throughout the Northern Hemisphere. Due to its location in the sky (-24 degrees declination), observers farther south see it even higher, which is better for observing.

The nebula is just a very faint patch to the unaided eye, but it takes on an oblong shape in binoculars. A brighter nucleus (the so-called “hourglass”) is visible on one side, separated by a dark rift from an open star cluster on the other side. While you may have seen images of the nebula with stunning color, these are attained via highly technical long-exposure photography. To the unaided eye, the faint nebulosity appears grayish, with little (if any) hint of color.

The science of the Lagoon Nebula

M8 is about 5,000 light-years away, and roughly 130 light-years in length. The Lagoon Nebula is an emission nebula, composed primarily of hydrogen. Much of it is ionized (heated or energized) by radiation from the nearby young and massive star Herschel 36. It’s also a stellar nursery: a place where new stars are born. And an open star cluster – NGC 6530 – made of hot, blue stars just a few million years old lies in this region. In addition to these young stars, there are also many dark Bok globules (dark nebulae) of condensing gas and dust. These are on their way to becoming protostars, and ultimately fully-fledged stars like those already formed nearby.

Early observations of the Lagoon

While the name Lagoon might conjure up a sense of fantasy, there is no known mythology associated with this interstellar cloud. The name apparently refers to the nebula’s appearance, with the dark lane running through the cloud evoking a sandbar between two lagoons. While visible to the unaided eye and therefore certainly seen throughout history, there is no known mention of this nebula until 1654, when Sicilian astronomer Giovanni Battista Hodierna recorded his observations of the star cluster within the nebula.

The area was then observed by several other astronomers, including Charles Messier in 1764, after which it also became known as Messier 8, or M8: the eighth object in Messier’s catalog.

If you’re looking to make some observations yourself, you may want to know that the Lagoon Nebula’s approximate center position is RA: 18h 04m, declination: -24° 22′.

Bottom line: The Lagoon Nebula, or Messier 8, is a large emission nebula in the constellation Sagittarius. You can explore it with binoculars.

The post Explore the Lagoon Nebula, M8, in Sagittarius first appeared on EarthSky.

The Wild Duck Cluster, also known as Messier 11 or M11, is a distant open star cluster. The cluster lies in the direction of the constellation Scutum the Shield. Its distance of 6,120 light-years means it’s quite faint. You’ll need binoculars or a telescope to see it. The Wild Duck Cluster consists of sibling stars born from a cloud of gas and dust in space.

How to find the Wild Duck Cluster

To find M11, first locate the bright star Altair in the sky. It is the brightest star in the constellation Aquila the Eagle, and the second brightest star in the Summer Triangle. Altair is flanked on each side by the two moderately bright stars Tarazed and Alshain.

From Altair, following the chart below, you can star-hop toward the Wild Duck Cluster. Delta Aquilae is your first hop, about 8 degrees from Altair. (For reference, the width of four fingers held at arm’s length approximates 8 degrees of sky.)

Using binoculars, keep going downward a bit more than twice the Altair-Delta Aquilae distance, until you see a semicircle of stars that pretty much fills your binocular field. The Wild Duck Cluster pops out as a hazy star-like object just beneath this semicircle star pattern.

When to look

If you have a telescope, the Wild Duck Cluster appears best when it’s relatively high in the southern sky. That’s in the wee hours before sunrise in spring, late night in early summer, and mid-evening in late summer and early fall.

The science of M11

Like the Pleiades and the Hyades, M11 is an open star cluster, but it’s much farther away than the others. The Pleiades Cluster lies 444 light-years away, and the Hyades Cluster is just 153 light-years away. Compare those to the Wild Duck Cluster, which sits about 6,120 light-years away.

An open star cluster is a group of stars that formed from the same giant cloud of mostly molecular hydrogen. These gas and dust clouds are nebulae that contain stellar nurseries. Initially, the young stars are loosely bound together by gravity. Some still sit within the cocoon of the nebula they were born in. Eventually the clusters disperse over time.

M11, one of the most massive open star clusters known, has about 3,000 stars. The hot blue stars congregate at the center. Scientists think the cluster formed between 250 to 316 million years ago. Astronomers refer to it as a metal-rich cluster because a nearby supernova likely seeded its molecular cloud complex with heavier elements.

The history of the Wild Duck Cluster

In 1733, English naturalist William Derham was able to resolve the Wild Duck Cluster as individual stars through a telescope. Not long after, in 1764, French astronomer Charles Messier added it to his famous catalog. M11 got its unusual name of the Wild Duck Cluster from Admiral William Henry Smyth. While observing the cluster through a telescope in 1835, Smyth noted a V-shaped pattern of its brightest stars that reminded him of the flight formation of wild ducks.

The Wild Duck Cluster is positioned at RA: 18h 51m 5s; Dec: -6° 16′ 12″

Bottom line: The Wild Duck Cluster, also known as M11, is an open star cluster in the constellation Scutum that appears best through binoculars or a telescope.

The post The Wild Duck Cluster, M11, a lovely open cluster in Scutum first appeared on EarthSky.

Bright red Antares is easy to find in the prominent zodiacal constellation Scorpius the Scorpion. And if you look just slightly west of it through binoculars, you’ll see a small faint diffuse ball of light. Through a moderate-sized telescope, that fuzzy ball resolves into a tight collection of faint stars suspended in the darkness. That’s Messier 4, called M4 for short. It’s a globular star cluster, an ancient member of our Milky Way galaxy. M4 shines at magnitude +5.9, so it may be visible as a smudge on the sky under very dark skies.

Find M4 in binoculars first

If you’ve never found a deep-sky object on your own before, M4 is a grand place to start. Northern Hemisphere summer evenings – or Southern Hemisphere winter evenings – are probably your best bet for catching M4. The M4 globular star cluster is easy to find, because it’s right next to the first-magnitude star Antares, the brightest star in the constellation Scorpius the Scorpion.

In early June, Antares is highest in the sky around midnight your local time (1 a.m. daylight saving time). That means it’s high in the south for Northern Hemisphere viewers, and overhead for Southern Hemisphere viewers. The stars return to the same place in the sky some two hours earlier every month. So, Antares is highest up around 10 p.m. (11 p.m. daylight saving time) in early July, and 8 p.m. (9 p.m. daylight saving time) in early August.

Antares and M4 fit inside the same binocular field of view, with M4 appearing a bit more than 1 degree to the west of Antares. For reference, a typical binocular field has a diameter of 5 to 6 degrees. M4 looks like a rather dim, hazy star in binoculars.

Once you spot it, you might begin longing for a telescope to be able to resolve this fuzzy cluster into a clump of starry pinpoints.

History of Messier 4

Swiss astronomer Jean-Philippe Loys de Chéseaux discovered M4 in 1746. However, it’s named after comet hunter Charles Messier (1730-1817). He listed M4 as object #4 in his famous Messier catalog. The catalog listed over 100 deep-sky objects that look like comets but really aren’t. Charles Messier wanted to steer comet hunters away from these faint fuzzies that masquerade as comets.

Science of M4

Today, we know that M4 is a globular star cluster, a globe-shape stellar city packed with perhaps a hundred thousand stars. At about 6,000 light-years from Earth, M4 is the closest globular cluster to us. In comparison, most globulars in our galaxy reside tens of thousands of light-years away. The farthest globular cluster, M54, is about 87,000 light-years in distance.

Unlike open star clusters – such as the Pleiades and the Hyades – the Milky Way galaxy’s 150 or so known globular star clusters are not part of the galactic disk. Instead, globular clusters populate the galactic halo, the sphere-shaped region of the Milky Way circling above and below the galactic disk. There are likely more globular clusters hidden from view by the Milky Way’s central bulge and by clouds of dust and gas.

Difference between globular and open clusters

Globular clusters are tightly packed with tens to hundreds of thousands of stars, whereas open clusters are loosely-bound stellar groups with only a few hundred to a thousand stars. Globular clusters contain primitive stars that are billions of years old and almost as old as the universe itself. On the other hand, open clusters consist of young, hot stars that tend to disperse after hundreds of millions of years.

If you had a telescope like Hubble, it would allow you to see these ancient stars as shown in this animation.

M4’s position is at Right Ascension: 16h 23m 35s; Declination: -26° 31′ 33″

Bottom line: Find M4, one of the easiest globular star clusters for beginners to spot, located just next to reddish Antares, the brightest star in Scorpius the Scorpion.

The post Find M4: An easy to spot globular cluster near Antares first appeared on EarthSky.

Omega Nebula and Eagle Nebula

The Omega Nebula, also known as the Swan Nebula or M17, is just barely visible to the unaided eye on a dark, moonless night. So, to get a good look, it’s best to use binoculars or a telescope with low-power magnification. Also, the Omega Nebula is very near another prominent nebula, known as M16 or the Eagle Nebula. M16 is the home of the famous Pillars of Creation. In the sky, M16 and M17 appear as two closely-knit patches of haze. Indeed, they fit readily within the same binocular field of view.

You can find them within the hazy band of our Milky Way galaxy that crosses the sky on a northern summer evening. This region of the sky is crowded with deep-sky objects, and to be sure, these two nebulae are among the best of the bunch!

How to see the Omega Nebula

If you want to see M17 and many other deep-sky objects, learn to recognize the constellation Sagittarius the Archer, with its famous Teapot asterism. The Teapot is located in the direction of the star-rich center of our Milky Way galaxy. So there are many beautiful star clusters and nebulae in this part of the sky. And, it’s an easy star-hop from the Teapot to M17 and its nearby companion on the sky’s dome, M16.

As an illustration, draw an imaginary line from the star Kaus Australis (also known as Epsilon Sagittarii) in the Teapot and pass to the left of the star Kaus Media (or Delta Sagittarii) to locate M16 and M17. These two nebulae are close together and located about one fist-width above the Teapot.

As seen from the Northern Hemisphere, M16 and M17 are summertime objects. They’re highest up when they’re due south on late August evenings. And in addition, they’re wintertime objects in the Southern Hemisphere, where they’re closer to being overhead.

The nebula of many names

Objects in astronomy often have more than one name. They get their names from being observed and studied by various astronomers over the years. Amateur astronomers tend to call deep-sky objects by their “M” names, or Messier names. But all of these objects have proper names as well. M17, in particular, has at least five proper names: the Omega Nebula, Horseshoe Nebula, Checkmark Nebula, Swan Nebula and Lobster Nebula. Learn where these names came from here.

The science of M17

The Omega Nebula is a vast interstellar cloud of dust and gas giving birth to young, hot stars. It spans some 15 light-years in diameter, with a mass of around 800 solar masses. And it’s part of a larger cloud, roughly 40 light-years in diameter with a mass of 30,000 solar masses.

Astronomers don’t know the distance to M17 with precision. But they estimate that it’s around 5,000 light-years away. For comparison, the more brilliant Orion Nebula is some 1,300 light-years distant. While the Orion Nebula resides within the Milky Way’s Orion spiral arm (just like our solar system), when you look at M17 or M16 you’re seeing wonders from our galaxy’s next arm inward: the Sagittarius arm.

Competing nebulae

There are many glorious deep-sky objects in this part of the night sky. Two of the most famous patches of nebulosity – M8 and M20 – also vie for your attention from the Sagittarius arm. And like M16 and M17, they couple up within the same binocular field. Judge for yourself which pair of stellar nurseries is most impressive!

Bottom line: Barely visible to the unaided eye on a dark night, the star-forming region known as the Omega Nebula is best seen through binoculars, or low power in a telescope.

The post The Omega Nebula is a star-forming region first appeared on EarthSky.