Welcome back to Messier Monday! Today, we continue in our tribute to our dear friend, Tammy Plotner, by looking at the star cluster known as Messier 73.
During the 18th century, famed French astronomer Charles Messier noticed the presence of several “nebulous objects” while surveying the night sky. Originally mistaking these objects for comets, he began to catalog them so that others would not make the same mistake. Today, the resulting list (known as the Messier Catalog) includes over 100 objects and is one of the most influential catalogs of Deep Space Objects.
One of these objects is Messier 73, a four star asterism located approximately 2,500 light-years from Earth. It is visible in the southern part of the Aquarius constellation, near the border of Capricornus and just southeast of Messier 72. Given that Aquarius and Capricornus are relatively faint constellations, this object is one of the more challenging Messier objects to find in the night sky. Continue reading “Messier 73 – the NGC 6994 Star Cluster”
The Aries constellation and nearby Deep Sky Objects. Credit: thinglink.com
Welcome back to constellation Friday! Today, in honor of our dear friend and contributor, Tammy Plotner, we examine the Aries constellation. Enjoy!
In the 2nd century CE, Greek-Egyptian astronomer Claudius Ptolemaeus (aka. Ptolemy) compiled a list of the then-known 48 constellations. His treatise, known as the Almagest, would serve as the authoritative source of astronomy for over a thousand years to come. Since the development of modern telescopes and astronomy, this list has come to be expanded to include the 88 constellation that are recognized by the International Astronomical Union (IAU) today.
Of these constellations, Aries – named in honor of the Ram from classical Greek mythology – is featured rather prominently. This faint constellation has deep roots, and is believed to date all the way back to the astrological systems of the ancient Babylonians. Positioned on the ecliptic plane, it is bordered by constellations of Perseus, Triangulum, Pisces, Cetus and Taurus, and is also the traditional home of the vernal equinox.
The Wild Duck Cluster photographed on amateur astrophotography equipment. Credit: Creative Commons/Rawastrodata
Welcome back to another edition of Messier Monday! Today, we continue in our tribute to Tammy Plotner with a look at the M11 Wild Duck Cluster!
In the 18th century, French astronomer Charles Messier noted the presence of several “nebulous objects” in the night sky while searching for comets. Hoping to ensure that other astronomers did not make the same mistake, he began compiling a list of 1oo of them. This list came to be known as the Messier Catalog, and would have far-reaching consequences.
One of these objects is M11, otherwise known as The Wild Duck Cluster, an open cluster located in the constellation Scutum, near the northern edge of a rich Milky Way star cloud (the Scutum Cloud). This open star cluster is one of the richest and most compact of all those known, composed of a few thousand hot, young stars that are only a few million years old.
Full panoramic view of the constellations near the Milky Way by Matt Dieterich
What comes to mind when you look up at the night sky and spot the constellations? Is it a grand desire to explore deep into space? Is it the feeling of awe and wonder, that perhaps these shapes in the sky represent something? Or is the sense that, like countless generations of human beings who have come before you, you are staring into the heavens and seeing patterns? If the answer to any of the above is yes, then you are in good company!
While most people can name at least one constellation, very few know the story of where they came from. Who were the first people to spot them? Where do their names come from? And just how many constellations are there in the sky? Here are a few of the answers, followed by a list of every known constellation, and all the relevant information pertaining to them.
Definition:
A constellation is essentially a specific area of the celestial sphere, though the term is more often associated with a chance grouping of stars in the night sky. Technically, star groupings are known as asterisms, and the practice of locating and assigning names to them is known as asterism. This practice goes back thousands of years, possibly even to the Upper Paleolithic. In fact, archaeological studies have identified markings in the famous cave paintings at Lascaux in southern France (ca. 17,300 years old) that could be depictions of the Pleiades cluster and Orion’s Belt.
There are currently 88 officially recognized constellations in total, which together cover the entire sky. Hence, any given point in a celestial coordinate system can unambiguously be assigned to a constellation. It is also a common practice in modern astronomy, when locating objects in the sky, to indicate which constellation their coordinates place them in proximity to, thus conveying a rough idea of where they can be found.
Closeup of the Lascaux cave paintings, showing a bull and what could be the Pleiades Cluster (over the right shoulder) and Orion’s Belt (far left). Credit: ancient-wisdom.com
The word constellation has its roots in the Late Latin term constellatio, which can be translated as “set of stars”. A more functional definition would be a recognizable pattern of stars whose appearance is associated with mythical characters, creatures, or certain characteristics. It’s also important to note that colloquial usage of the word “constellation” does not generally differentiate between an asterism and the area surrounding one.
Typically, stars in a constellation have only one thing in common – they appear near each other in the sky when viewed from Earth. In reality, these stars are often very distant from each other and only appear to line up based on their immense distance from Earth. Since stars also travel on their own orbits through the Milky Way, the star patterns of the constellations change slowly over time.
History of Observation:
It is believed that since the earliest humans walked the Earth, the tradition of looking up at the night sky and assigning names and characters to them existed. However, the earliest recorded evidence of asterism and constellation-naming comes to us from ancient Mesopotamia, and in the form of etchings on clay tablets that are dated to around ca. 3000 BCE.
However, the ancient Babylonians were the first to recognize that astronomical phenomena are periodic and can be calculated mathematically. It was during the middle Bronze Age (ca. 2100 – 1500 BCE) that the oldest Babylonian star catalogs were created, which would later come to be consulted by Greek, Roman and Hebrew scholars to create their own astronomical and astrological systems.
Star map showing the celestial globe of Su Song (1020-1101), a Chinese scientist and mechanical engineer of the Song Dynasty (960-1279). Credit: Wikipedia Commons
In ancient China, astronomical traditions can be traced back to the middle Shang Dynasty (ca. 13th century BCE), where oracle bones unearthed at Anyang were inscribed with the names of star. The parallels between these and earlier Sumerian star catalogs suggest they did no arise independently. Astronomical observations conducted in the Zhanguo period (5th century BCE) were later recorded by astronomers in the Han period (206 BCE – 220 CE), giving rise to the single system of classic Chinese astronomy.
In India, the earliest indications of an astronomical system being developed are attributed to the Indus Valley Civilization (3300–1300 BCE). However, the oldest recorded example of astronomy and astrology is the Vedanga Jyotisha, a study which is part of the wider Vedic literature (i.e. religious) of the time, and which is dated to 1400-1200 BCE.
By the 4th century BCE, the Greeks adopted the Babylonian system and added several more constellations to the mix. By the 2nd century CE, Claudius Ptolemaus (aka. Ptolemy) combined all 48 known constellations into a single system. His treatise, known as the Almagest, would be used by medieval European and Islamic scholars for over a thousand years to come.
Between the 8th and 15th centuries, the Islamic world experienced a burst of scientific development, reaching from the Al-Andus region (modern-day Spain and Portugal) to Central Asia and India. Advancements in astronomy and astrology closely paralleled those made in other fields, where ancient and classical knowledge was assimilated and expanded on.
The Northern Constellations. Credit: Bodel Nijenhuis Collection/Leiden University Library
In turn, Islamic astronomy later had a significant influence on Byzantine and European astronomy, as well as Chinese and West African astronomy (particularly in the Mali Empire). A significant number of stars in the sky, such as Aldebaran and Altair, and astronomical terms such as alidade, azimuth, and almucantar, are still referred to by their Arabic names.
From the end of the 16th century onward, the age of exploration gave rise to circumpolar navigation, which in turn led European astronomers to witness the constellations in the South Celestial Pole for the first time. Combined with expeditions that traveled to the Americas, Africa, Asia, and all other previously unexplored regions of the planet, modern star catalogs began to emerge.
IAU Constellations:
The International Astronomical Union (IAU) currently has a list of 88 accepted constellations. This is largely due to the work of Henry Norris Russell, who in 1922, aided the IAU in dividing the celestial sphere into 88 official sectors. In 1930, the boundaries between these constellations were devised by Eugène Delporte, along vertical and horizontal lines of right ascension and declination.
The IAU list is also based on the 48 constellations listed by Ptolemy in his Almagest, with early modern modifications and additions by subsequent astronomers – such as Petrus Plancius (1552 – 1622), Johannes Hevelius (1611 – 1687), and Nicolas Louis de Lacaille (1713 – 1762).
The modern constellations, color-coded by family, with a dotted line denoting the ecliptic. Credit: NASA/Scientific Visualization Studio
However, the data Delporte used was dated to the late 19th century, back when the suggestion was first made to designate boundaries in the celestial sphere. As a consequence, the precession of the equinoxes has already led the borders of the modern star map to become somewhat skewed, to the point that they are no longer vertical or horizontal. This effect will increase over the centuries and will require revision.
Not a single new constellation or constellation name has been postulated in centuries. When new stars are discovered, astronomers simply add them to the constellation they are closest to. So consider the information below, which lists all 88 constellations and provides information about each, to be up-to-date! We even threw in a few links about the zodiac, its meanings, and dates.
The Big Dipper is big. Come on, it’s right there in the name. But how big is the Big Dipper if you could see it from all angles?
Ask someone to name a constellation and they’ll usually say the Big Dipper. Anyone living in the Northern hemisphere who can draw a spoon generally can recognize it in the sky.
I am about to shake the foundations of your reality with a level of pedantry that at bare minimum should earn me a solid shaking and possibly even a face punch or two. The Big Dipper is not, and never will be a constellation.
It’s an asterism, a familiar pattern of stars in the sky. There are 88 constellations, and the Big Dipper isn’t one of them. It’s a part of the constellation of Ursa Major. In fact, the handle of your familiar spoon is actually the tail of the great bear.
Now that I’ve lulled you to sleep with some painfully uninteresting specifics, which you can bust out to make yourself unpopular at your AV Club pop and chip parties whenever someone refers to the “Big D” as a constellation. I strongly suggest whatever it is you tell them, you start off with *ACTUALLY….*
And now that you’ve made it this far, I shall reward you with what you’re seeking. Just how big is that Big Dipper? There are a couple of ways to skin this bear’s tail. We can say its size relative to the amount of sky real estate it occupies, or we can do the end to end Kessel run.
This chart shows the constellation of Carina (The Keel) and includes all the stars that can be seen with the unaided eye on a clear and dark night. Credit: ESO
You might be surprised to know how much of the sky it takes up. Astronomers measure the sky in degrees. 360 degrees takes you all the way around the sky, and our Moon measures half a degree across.
Dubhe and Merak are the pointer stars in the Big Dipper. You could put 11 full Moons side to side in the gap between them. And about 40 full Moons from bottom corner of the Dipper to the end of its handle. So, the Big Dipper measures about 20 degrees.
Here are some easy ways to measure sizes. Your pinkie nail, held at arm’s length is half a degree. 3 fingers is 5 degrees, your fist is 10 degrees. Rocking out with devil horns are 15 degrees and hang loose or the inspector gadget phone is 25 degrees.
Trekkers and Trekkies may prefer to use the Vulcan live long and prosper measurement, which is about the same number of degrees you are from getting a romantic companion.
Big Dipper Past. Credit: Alexander Meleg
So, stem to stern, how big is our giant celestial ladle? I know you know those things aren’t in anything resembling a straight line. Some of the stars are closer, and some of the stars are further out. If you could make a box that completely surrounded them, how big would it be?
The closest star in the asterism is Megrez at 58 light years. and the most distant is Dubhe at 124 light-years. And yet, they all look roughly the same brightness. This means that Dubhe is a much brighter star than Megrez, and it’s just further away. Because these stars are moving in the sky what we see as a Big Dipper today didn’t always look this way. 150,000 years ago, the Big Dipper looked like this (above).
Big Dipper Future. Credit: Alexander Meleg
And in 150,000 years from now it’ll look like this (left). Less dipper, more plow-like. Or maybe a shoe form? Shoes are kind of like ladles, right? Super gross, terribly unhygenic ladles.
Our brains keep from exploding by being pattern making machines. We see collections of stars in the sky and turn them into shapes. But it’s all just a matter of perspective. You’ve got to be right here and now to see the sky we do. Unless you’re looking for a giant “W” in which case you’ll always find one of those. It may not be the constellation Cassiopeia, but it’ll still be a pattern in the stars.
What’s your favorite asterism? Tell us in the comments below.
Junocam image of the stars that make up the "Big Dipper" asterism
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All right, it may look just like any other picture you’ve ever seen of the Big Dipper. Maybe even a little less impressive, in fact. But, unlike any other picture, this one was taken from 290 million km away by NASA’s Juno spacecraft en route to Jupiter, part of a test of its Junocam instrument! Now that’s something new concerning a very old lineup of stars!
“I can recall as a kid making an imaginary line from the two stars that make up the right side of the Big Dipper’s bowl and extending it upward to find the North Star,” said Scott Bolton, principal investigator of NASA’s Juno mission. “Now, the Big Dipper is helping me make sure the camera aboard Juno is ready to do its job.”
Diagram of the Juno spacecraft (NASA/JPL)
The image is a section of a larger series of scans acquired by Junocam between 20:23 and 20:56 UTC (3:13 to 3:16 PM EST) on March 14, 2012. Still nowhere near Jupiter, the purpose of the imaging exercise was to make sure that Junocam doesn’t create any electromagnetic interference that could disrupt Juno’s other science instruments.
In addition, it allowed the Junocam team at Malin Space Science Systems in San Diego, CA to test the instrument’s Time-Delay Integration (TDI) mode, which allows image stabilization while the spacecraft is in motion.
Because Juno is rotating at about 1 RPM, TDI is crucial to obtaining focused images. The images that make up the full-size series of scans were taken with an exposure time of 0.5 seconds, and yet the stars (brightened above by the imaging team) are still reasonably sharp… which is exactly what the Junocam team was hoping for.
“An amateur astrophotographer wouldn’t be very impressed by these images, but they show that Junocam is correctly aligned and working just as we expected”, said Mike Caplinger, Junocam systems engineer.
As well as the Big Dipper, Junocam also captured other stars and asterisms, such as Vega, Canopus, Regulus and the “False Cross”. (Portions of the imaging swaths were also washed out by sunlight but this was anticipated by the team.)
These images will be used to further calibrate Junocam for operation in the low-light environment around Jupiter, once Juno arrives in July 2016.
Read more about the Junocam test on the MSSS news page here.
As of May 10, Juno was approximately 251 million miles (404 million kilometers) from Earth. Juno has now traveled 380 million miles (612 million kilometers) since its launch on August 5, 2011 and is currently traveling at a velocity of 38,300 miles (61,600 kilometers) per hour relative to the Sun.
The handle of the Big Dipper just got stronger! Astronomers have found an additional star located in the Dipper’s gripper that is invisible to the unaided eye. Alcor, one of the stars that makes the bend in the Big Dipper’s handle has a smaller red dwarf companion orbiting it. Now known as “Alcor B,” the star was found with an innovative technique called “common parallactic motion,” and was found by members of Project 1640, an international collaborative team that gives a nod to the insight of Galileo Gallilei.
“We used a brand new technique for determining that an object orbits a nearby star, a technique that’s a nice nod to Galileo,” says Ben R. Oppenheimer, Curator at the Museum of Natural History. “Galileo showed tremendous foresight. Four hundred years ago, he realized that if Copernicus was right—that the Earth orbits the Sun—they could show it by observing the ‘parallactic motion’ of the nearest stars. Incredibly, Galileo tried to use Alcor to see it but didn’t have the necessary precision.”
If Galileo had been able to see change over time in Alcor’s position, he would have had conclusive evidence that Copernicus was right. Parallactic motion is the way nearby stars appear to move in an annual, repeatable pattern relative to much more distant stars, simply because the observer on Earth is circling the Sun and sees these stars from different places over the year.
The collaborative team that found the star includes astronomers from the American Museum of Natural History, the University of Cambridge’s Institute of Astronomy, the California Institute of Technology, and NASA’s Jet Propulsion Laboratory.
Alcor is a relatively young star twice the mass of the Sun. Stars this massive are relatively rare, short-lived, and bright. Alcor and its cousins in the Big Dipper formed from the same cloud of matter about 500 million years ago, something unusual for a constellation since most of these patterns in the sky are composed of unrelated stars. Alcor shares a position in the Big Dipper constellation with another star, Mizar. In fact, both stars were used as a common test of eyesight—being able to distinguish “the rider from the horse”—among ancient people. One of Galileo’s colleagues observed that Mizar itself is actually a double, the first binary star system resolved by a telescope. Many years later, the two components Mizar A and B were themselves determined each to be tightly orbiting binaries, altogether forming a quadruple system.
In March, members of Project 1640 attached their coronagraph and adaptive optics to the 200-inch Hale Telescope at the Palomar Observatory in California and pointed to Alcor. “Right away I spotted a faint point of light next to the star,” says Neil Zimmerman, a graduate student at Columbia University who is doing his PhD dissertation at the Museum. “No one had reported this object before, and it was very close to Alcor, so we realized it was probably an unknown companion star.”
The team retuned a few months later and found the star had the same motion as Alcor, proving it was a companion star.
Alcor and its smaller companion Alcor B are both about 80 light-years away and orbit each other every 90 years or more. The team was also able to determine Alcor B is a common type of M-dwarf star or red dwarf that is about 250 times the mass of Jupiter, or roughly a quarter of the mass of our Sun. The companion is much smaller and cooler than Alcor A.
“Red dwarfs are not commonly reported around the brighter higher mass type of star that Alcor is, but we have a hunch that they are actually fairly common,” says Oppenheimer. “This discovery shows that even the brightest and most familiar stars in the sky hold secrets we have yet to reveal.”
The team plans to use parallactic motion again in the future. “We hope to use the same technique to check that other objects we find like exoplanets are truly bound to their host stars,” says Zimmerman. “In fact, we anticipate other research groups hunting for exoplanets will also use this technique to speed up the discovery process.”
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The Big Dipper is an asterism (well-known to those who live in the northern hemisphere), so is the False Cross (well-known to those who live in the southern hemisphere). Asterisms are easily recognized pattern of *s*t*a*r*s* (but not a constellation).
The sky is full of asterisms easily seen without a telescope or binoculars: Summer Triangle, Great Square of Pegasus, the W in Cassiopeia, Frying Pan, Orion’s Belt, … it’s a long list.
The Southern Cross is not an asterism, strictly speaking, because it’s a constellation (Crux).
An asterism can take in parts of more than one constellation; for example, the Square of Pegasus has three stars in Pegasus (the three brightest, alpha, beta, and gamma Peg), and one in Andromeda (alpha And).
Some well-known asterisms are visible only through a telescope or binoculars; for example the Coathanger, and Kemble’s Cascade.
A couple (at least) of open clusters are also asterisms – the Hyades and the Pleiades (also known as the Seven Sisters).
Some clear, fixed features in the night sky, with well-known names, are not asterisms or constellations … the Coalsack for example, is a dark cloud in the plane of the Milky Way which blocks its light, and the Magellanic Clouds are dwarf, satellite galaxies of our own.
As astronomy in many cultures developed independently of the West (ancient Greece, Rome, etc), many of the commonly recognized constellations in those cultures correspond to asterisms … see if you can recognize some of the Chinese ones!
A particularly interesting kind of constellation is the dark constellation; instead of joining up bright stars to make an easily recognized figure, some cultures linked various dark nebulae in the Milky Way; for example the Emu in the Sky of the Australian Aborigines (and no, these are not asterisms).
SEDS (Students for the Exploration and Development of Space) has a concise list of asterisms easily visible without binoculars, or a telescope (though you may have to go to the opposite hemisphere to see them all!).
Asterisms are mentioned in many of Universe Today’s Weekend SkyWatcher’s Forecasts (August 21-23, 2009, for example), in its articles on Constellations (e.g. Orion), and Kids Astronomy ones (e.g. Finding the Summer Triangle).
