Astronomy Archives

February 8, 2016February 11, 2016 by Markus Pössel

Gravitational Waves and How They Distort Space

Gravitational waves distort space in a rhythmic fashion. These simple animations show how. — That's not a space worm. It's what a gravitational wave does to space according to Einstein's theory of general relativity.

It’s official: on February 11, 10:30 EST, there will be a big press conference about gravitational waves by the people running the gravitational wave detector LIGO. It’s a fair bet that they will announce the first direct detection of gravitational waves, predicted by Albert Einstein 100 years ago. If all goes as the scientists hope, this will be the kick-off for an era of gravitational wave astronomy: for learning about some of the most extreme and violent events in the cosmos by measuring the tiny ripples of space distortions that emanate from them.

Time to brush up on your gravitational wave knowledge, if you haven’t already done so! Here’s a visualization to help you – and we’ll go step by step to see what it means:

Einstein’s distorted spacetime

In the words of the eminent relativist John Wheeler, Einstein’s theory of general relativity can be summarized in two statements: Matter tells space and time how to curve. And (curved) space and time tell matter how to move. (Here is a slightly longer version on Einstein Online.)

Einstein published the final form of his theory in November 1915. By spring 1916, he had realized another consequence of distorting space and time: general relativity allows for gravitational waves, rhythmic distortions which propagate through space at the speed of light.

For quite some time, physicists weren’t sure whether these gravitational waves were real or a mathematical artifact within Einstein’s theory. (For more about this controversy, see Daniel Kennefick’s book “Traveling at the Speed of Thought and this article.) But since the 1980s, there has been indirect evidence for these waves (which earned its discoverers a Nobel prize, no less, in 1993).

Gravitational waves are emitted by orbiting bodies and certain other accelerated masses. Right now, major international efforts are underway to detect gravitational waves directly. Once detection is possible, the scientists hope to use gravitational waves to “listen” to some of the most violent processes in the universe: merging black holes and/or neutron stars, or the core region of supernova explosions.

Just as regular astronomy uses light and other forms of electromagnetic radiation to learn about distant objects, gravitational wave astronomy will decipher the information contained within gravitational waves. And if you go by recent rumors, gravitational wave astronomy might already have kicked off in mid-September 2015.

What do gravitational waves do?

But what do gravitational waves do? For that, let us look at a simplified, entirely hypothetical situation. (The following are variations on images and animations originally published here on Einstein Online.) Consider particles drifting in space, far from any sources of gravity. Imagine that the particles (red) are arranged in a circle around a center (marked in black):

If a simple gravitational wave were to pass through this image, coming directly at the reader, distances between these particles would change rhythmically as follows:

Note the distinctive pattern: When the circle is stretched in the vertical direction, it is compressed in the horizontal direction, and vice versa. That’s typical for gravitational waves (“quadrupole distortion”).

It’s important to keep in mind that this animation, and the ones that will follow, exaggerate the gravitational wave’s effect quite considerably. The gravitational waves detectors such as aLIGO hope to measure are much, much weaker. If our hypothetical circle of particles were as large as the Earth’s orbit around the Sun, a realistic gravitational wave would distort it by less than the diameter of a hydrogen atom.

Gravitational waves moving through space

The animation above shows what could be called a “gravitational oscillation.” To see the whole wave, we need to consider the third dimension.

We talk about a wave when oscillations propagate through space. Consider a water wave: At each point of the surface, we have an oscillation, with the surface rising and falling rhythmically. But it’s only the fact that this oscillation propagates, and that we can see a crest moving over the surface, that makes this into a wave.

It’s the same with gravitational waves. To see that, we will look not at a single circle of freely floating particles, but at many such circles, stacked one behind the other, forming the surface of a cylinder:

In this image, it’s hard to see which points are in front and which in the back. Let us join each particle to its nearest neighbors with a blue line, and let us also fill out the area between those lines. That way, the geometry is much more obvious:

Just remember that neither the lines nor the whitish surface is physical. On the contrary, if we want the particles to be maximally susceptible to the effect of the gravitational wave, we should make sure they are truly floating freely, and certainly they shouldn’t be linked in any way!

Now, let us see what the same gravitational wave we saw before does to this assembly of particles. From this perspective, the wave is passing from the right-hand side in the back towards the left-hand side on the front: As you can see, the wave is propagating through space. For instance, the point where the vertical distances within the circle of particles is maximal is moving towards the observer. The wave nature can be seen even more clearly if we look at this cylinder directly from the side:

What the animations show is just one kind of simple gravitational wave (“linearly polarized”). Here is another kind (“circularly polarized”):

This, then, is what the gravitational wave hunters are looking for. Except that they do not have particles floating in free space. Instead, their detectors contain test masses (notably large mirrors) elaborately suspended here on Earth, with laser light to detect the minute distance changes caused by gravitational waves.

More realistic gravitational wave signals, which contain information about merging black holes or the bulk motion of matter inside a supernova explosion, are more complicated still. They combine many simple waves of different frequencies, and the strength of such waves (their amplitude) will change over time in a characteristic fashion.

In these animations, gravitational waves look a bit like wriggling space worms. But these space worms could become the astronomers’ best friends, carrying information about the cosmos that is hard or even impossible to obtain in any other way.

[Don’t miss the sequel: Gravitational wave detectors: how they work]

Update: Gravitational Waves Detected

February 8, 2016April 26, 2016 by Bob King

Peculiar ‘Cauliflower Rocks’ May Hold Clues To Ancient Mars Life

"Cauliflower" shaped silica-rich rocks photographed by the Spirit Rover near the Home Plate rock formation in Gusev Crater in 2008. Could microbes have built their nodular shapes? Credit: NASA/JPL-Caltech

Evidence of water and a warmer, wetter climate abound on Mars, but did life ever put its stamp on the Red Planet? Rocks may hold the secret. Knobby protuberances of rock discovered by the Spirit Rover in 2008 near the rock outcrop Home Plate in Gusev Crater caught the attention of scientists back on Earth. They look like cauliflower or coral, but were these strange Martian rocks sculpted by microbes, wind or some other process?

Close-up of the lobed silica rocks on Mars photographed by the Spirit Rover on Sol 1157. Credit: NASA/ JPL-Caltech — Close-up of the lobed silica rocks on Mars photographed by the Spirit Rover’s microscopic imager on Sol 1157. It’s not known where wind (or other non-biological process) or micro-life had a hand in creating these shapes. Credit: NASA/ JPL-Caltech

When analyzed by Spirit’s mini-TES (Mini-Thermal Emission Spectrometer), they proved to be made of nearly pure silica (SiO2), a mineral that forms in hot, volcanic environments. Rainwater and snow seep into cracks in the ground and come in contact with rocks heated by magma from below. Heated to hundreds of degrees, the water becomes buoyant and rises back toward the surface, dissolving silica and other minerals along the way before depositing them around a vent or fumarole. Here on Earth, silica precipitated from water leaves a pale border around many Yellowstone National Park’s hot springs.

The Grand Prismatic Spring at Yellowstone National Park. Could it be an analog to similar springs, hydrothermal vents and geysers that may once have existed in Gusev Crater on Mars? Credit: Jim Peaco, National Park Service

Both at Yellowstone, the Taupo Volcanic Zone in New Zealand and in Iceland, heat-loving bacteria are intimately involved in creating curious bulbous and branching shapes in silica formations that strongly resemble the Martian cauliflower rocks. New research presented at the American Geophysical Union meeting last month by planetary geologist Steven Ruff and geology professor Jack Farmer, both of Arizona State University, explores the possibility that microbes might have been involved in fashioning the Martian rocks, too.

A sizzling visit to El Tatio’s geysers

The researchers ventured to the remote geyser fields of El Tatio in the Chilean Atacama Desert to study an environment that may have mimicked Gusev Crater billions of years ago when it bubbled with hydrothermal activity. One of the driest places on Earth, the Atacama’s average elevation is 13,000 feet (4 km), exposing it to considerably more UV light from the sun and extreme temperatures ranging from -13°F to 113°F (-10° to 45°C). Outside of parts of Antarctica, it’s about as close to Mars as you’ll find on Earth.

Ruff and Farmer studied silica deposits around hot springs and geysers in El Tatio and discovered forms they call “micro-digitate silica structures” similar in appearance and composition to those on Mars (Here’s a photo). The infrared spectra of the two were also a good match. They’re still analyzing the samples to determine if heat-loving microbes may have played a role in their formation, but hypothesize that the features are “micro-stromatolites” much like those found at Yellowstone and Taupo.

A stromatolite from Wyoming made of many layers of bacteria-cemented mineral grains. Credit: Bob King

Stromatolites form when a sticky film of bacteria traps and cements mineral grains to create a thin layer. Other layers form atop that one until a laminar mound or column results. The most ancient stromatolites on Earth may be about 3.5 billion years old. If Ruff finds evidence of biology in the El Tatio formations in the punishing Atacama Desert environment, it puts us one step closer to considering the possibility that ancient bacteria may have been at work on Mars.

Scientists have found evidence that Home Plate at Gusev crater on Mars is composed of debris deposited from a hydrovolcanic explosion. The finding suggests that water may have been involved in driving an eruption that formed the deposits found on Home Plate. Spirit found the silica-rich rocks at lower right near Tyrone in 2008. Credit: NASA/JPL-Caltech

Silica forms may originate with biology or from non-biological processes like wind, water and other environmental factors. Short of going there and collecting samples, there’s no way to be certain if the cauliflower rocks are imprinted with the signature of past Martian life. But at least we know of a promising place to look during a future sample return mission to the Red Planet. Indeed, according to Ruff, the Columbia Hills inside Gusev Crater he short list of potential sites for the 2020 Mars rover.

More resources:

Steve Ruff paper comparing El Tatio with an early hot springs environment in Gusev Crater
Spirit Rover raw image archive
Details about the Spirit’s discovery of silica

February 5, 2016April 26, 2016 by Matt Williams

NASA Says “No Chance” Small Asteroid Will Hit Earth On March 5th

Artist's impression of a Near-Earth Asteroid passing by Earth. Credit: ESA

On October 6th, 2013, the Catalina Sky Survey discovered a small asteroid which was later designated as 2013 TX68. As part Apollo group this 30 meter (100 ft) rock is one of many Near-Earth Objects (NEOs) that periodically crosses Earth’s orbit and passes close to our planet. A few years ago, it did just that, flying by our planet at a safe distance of about 2 million km (1.3 million miles).

And according to NASA’s Center for NEO Studies (CNEOS) at the Jet Propulsion Laboratory, it will be passing us again in a few weeks time, specifically between March 2nd and 6th. Of course, asteroids pass Earth by on a regular basis, and there is very rarely any cause for alarm. However, there is some anxiety about 2013 TX68’s latest flyby, mainly because its distance could be subject to some serious variation.

Continue reading “NASA Says “No Chance” Small Asteroid Will Hit Earth On March 5th”

February 5, 2016December 10, 2021 by Tammy Plotner

What Are The Constellations?

milky way constellations — 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 one section of the cave painting at the Lascaux cave complex, showing what could be Pleiades and Orion's Belt. Credit: ancient-wisdom.com — *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 — *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.

Enjoy your reading!

-A

-B

-C

-D

-E

-F

Fornax

-G

-H

-I

Indus

-L

-M

-N

Norma

-O

-P

-R

Reticulum

-S

-T

-U

-V

February 4, 2016March 18, 2016 by Evan Gough

The Highest-Resolution Image Ever Seen in Astronomy

A jet of material being ejected out of a black hole at the centre of the galaxy BL Lacertae. Image: Dr. Jose L. Gomez

What do you get when you combine 15 radio telescopes on Earth and one in space? You get an enormous “virtual telescope” that is 63,000 miles across. And when you point it at a distant black hole, you get the highest resolution image every seen in astronomy.

Although it looks just like a big green blob, it’s actually an enormously energetic jet of matter streaming out of a black hole. And this black hole is 900 million light years away.

As reported at Popular Science, it required an array of 15 radio telescopes on Earth, and the Russian space telescope Spektr-R, to capture the image. This technique—called interferometry—is like creating a telescope that is 63,000 miles across. The detail it provides is like seeing a 50 cent coin on the Moon.

For perspective, the object in the image is 186 billion miles long, at minimum, and would just barely fit in the Oort Cloud.

The jet at the heart of BL Lacertae, with the Oort Cloud and Alpha Centauri for comparison. Image: Gomez et. al., A Lobanov, NRAO.

February 3, 2016 by David Dickinson

A Challenge in Visual Athletics: Hunting the Gegenschein

The gegenschein visible as the bright 'knot' in the zodiacal glow high above the VLT. Image credit: ESO/Y. Beletsky

Looking for something truly elusive? Astronomy has no shortage of the fleeting and ephemeral when it comes to challenges. This week’s challenge will require supremely dark skies and persistence.

We’re talking about the gegenschein, the elusive counter glow lying opposite to the Sun across the plane of the ecliptic. Continue reading “A Challenge in Visual Athletics: Hunting the Gegenschein”

February 1, 2016April 26, 2016 by Evan Gough

Massive Ariane 5 To Launch Giant NextGen Telescope In Dynamic Deployment To L2

The Ariane5 lifting off from Kourou in French Guiana. Image: ESA/Arianespace.

The Ariane 5 rocket is a workhorse for delivering satellites and other payloads into orbit, but fitting the James Webb Space Telescope (JWST) inside one is pushing the boundaries of the Ariane 5’s capabilities, and advancing our design of space observatories at the same time.

The Ariane 5 is the most modern design in the ESA’s Ariane rocket series. It’s responsible for delivering things like Rosetta, the Herschel Space Observatory, and the Planck Observatory into space. The ESA is supplying an Ariane 5 to the JWST mission, and with the planned launch date for that mission less than three years away, it’s a good time to check in with the Ariane 5 and the JWST.

The Ariane 5 has a long track record of success, often carrying multiple satellites into orbit in a single launch. Here’s its most recent launch, on January 27th from the ESA’s spaceport in French Guiana. This is Ariane 5’s 70th successful launch in a row.

But launching satellites into orbit, though still an amazing achievement, is becoming old hat for rockets. 70 successful launches in a row tells us that. The Ariane 5 can even launch multiple satellites in one mission. But launching the James Webb will be Ariane’s biggest challenge.

The thing about satellites is, they’re actually getting smaller, in many cases. But the JWST is huge, at least in terms of dimensions. The mass of the JWST—6,500 kg (14,300 lb)—is just within the limits of the Ariane 5. The real trick was designing and building the JWST so that it could fit into the cylindrical space atop an Ariane 5, and then “unfold” into its final shape after separation from the rocket. This video shows how the JWST will deploy itself.

The JWST is like a big, weird looking beetle. Its gold-coated, segmented mirror system looks like multi-faceted insect eyes. Its tennis-court sized heat shield is like an insect’s shell. Or something. Cramming all those pieces, folded up, into the nose of the Ariane 5 rocket is a real challenge.

Because the JWST will live out its 10-year (hopefully) mission at L2, rather than in orbit around Earth, it requires this huge shield to protect itself from the sun. The instruments on the James Webb have to be kept cool in order to function properly. The only way to achieve this is to have its heat shield folded up inside the rocket for launch, then unfolded later. That’s a very tricky maneuver.

But there’s more.

The heart of the James Webb is its segmented mirror system. This group of 18 gold-coated, beryllium mirrors also has to be folded up to fit into the Ariane 5, and then unfolded once it’s separated from the rocket. This is a lot trickier than launching things like the Hubble, which was deployed from the space shuttle.

Something else makes all this folding and unfolding very tricky. The Hubble, which was James Webb’s predecessor, is in orbit around Earth. That means that astronauts on Shuttle missions have been able to repair and service the Hubble. But the James Webb will be way out there at L2, so it can’t be serviced in any way. We have one chance to get it right.

Right now, the James Webb is still under construction in the “Clean Room” at NASA’s Goddard Space Flight Centre. A precision robotic arm system is carefully mounting Webb’s 18 mirrors.

A robotic arm positions one of James Webb's 18 mirrors. Image: NASA/Chris Gunn — A robotic arm positions one of James Webb’s 18 mirrors. Image: NASA/Chris Gunn

There’s still over two years until the October 2018 launch date, and there’s a lot of testing and assembly work going on until then. We’ll be paying close attention not only to see if the launch goes as planned, but also to see if the James Webb—the weird looking beetle—can successfully complete its metamorphosis.

February 1, 2016December 2, 2019 by Tammy Plotner

Messier 1 (M1) – The Crab Nebula

The Crab Nebula (aka. Messier Object 1) is an example of a supernova explosion that emitted cosmic rays. Credit: NASA

In the 18th century, French astronomer Charles Messier kept noting the presence of fixed, diffuse objects in the night sky. Initially, he thought these were comets, which he was attempting to locate at the time. However, astronomers would later discover that these objects were in fact nebulae, galaxies and star clusters. Between the years of 1758 and 1782, Messier compiled a list of approximately 100 of these objects.

His intention was to ensure that other astronomers would not mistake these objects for comets. But in time, this list – known as the Messier Catalog – served a higher purpose. In addition to being a collection of some of the most beautiful objects in the night sky, the catalog was also an important milestone in the discovery and research of Deep Sky objects. The first item in the catalog is the famous Crab Nebula – hence its designation as Messier Object 1, or M1.

Description:

Messier 1 (aka. M1, NGC 1952, Sharpless 244, and the Crab Nebula) is a supernova remnant located in the Perseus Arm of the Milky Way Galaxy, roughly 6500 ± 1600 light years from Earth. Like all supernova remnants, it is an expanding cloud of gas that was created during the explosion of a star. This material is spread over a volume approximately 13 ± 3 ly in diameter, and is still expanding at a velocity of about 1,500 km/s (930 mi/s).

Based on its current rate of expansion, it is assumed that the overall deceleration of the nebula’s expansion must has decreased since the initial supernova. Essentially, after the explosion occurred, the nebula’s pulsar would have began to emit radiation that fed the nebula’s magnetic field, thus expanding it and forcing it outward.

The supernova that produced the Crab Nebula was detected by naked-eye observers around the world in 1054 A.D. This composite image uses data from NASA’s Great Observatories, Chandra, Hubble, and Spitzer, to show that a superdense neutron star is energizing the expanding Nebula by spewing out magnetic fields and a blizzard of extremely high-energy particles. The Chandra X-ray image is shown in light blue, the Hubble Space Telescope optical images are in green and dark blue, and the Spitzer Space Telescope’s infrared image is in red. The size of the X-ray image is smaller than the others because ultrahigh-energy X-ray emitting electrons radiate away their energy more quickly than the lower-energy electrons emitting optical and infrared light. The neutron star is the bright white dot in the center of the image. — The supernova that produced the Crab Nebula was detected by naked-eye observers around the world in 1054 A.D. This composite image uses data from NASA’s Great Observatories, Chandra, Hubble, and Spitzer.

In visible light, the Crab Nebula consists of an oval-shaped mass of filaments – whose spectral emission lines are split into both red and blue-shifted components – which surround a blue central region. The filament are leftover from the outer layers of the former star’s atmosphere, and consist primarily of hydrogen and helium, along with traces of carbon, oxygen, nitrogen and heavier elements. The filaments’ temperatures are typically between 11,000 and 18,000 K.

The blue region, meanwhile, is the result of highly polarized synchrotron radiation, which is emitted by high-energy electrons in a strong magnetic field. The curved path of these electrons is due to the strong magnetic field produced by the neutron star at the center of the nebula (see below). One of the many components of the Crab Nebula is a helium-rich torus which is visible as an east-west band crossing the pulsar region.

The torus accounts for about 25% of the nebula’s visible ejecta and is believed to be made up of 95% helium. As yet, there has been no plausible explanation for the structure of the torus. And while it is very difficult to gauge the total mass of the nebula, official estimates place it at 4.6 ± 1.8 Solar masses – i.e 5.5664 to 12.7232 $\times 10 30 kg.$

Crab Pulsar:

At the center of the Crab Nebula are two faint stars, one of which is its progenitor (i.e the one that created it). It is because of this star that M1 is a strong source of radio waves, X-rays and Gamma-ray radiation. The remnant of supernova SN 1054, which was widely observed on Earth in the year 1054, this star was discovered in 1968 and has since been designated as a radio pulsar.

The Crab Nebula Pulsar, M1. Both are sequences of observations that show the expansion of shock waves emanating from the Pulsar interacting with the surrounding nebula. The Crab Pulsar actually pulsates 30 times per second a result of its rotation rate and the relative offset of the magnetic pole. Charndra X-Rays (left), Hubble Visible light (right). (Credit: NASA, JPL-Caltech) — Observation sequences of M1, showing the expansion of shock waves emanating from the Pulsar interacting with the surrounding nebula. Charndra X-Rays (left), Hubble Visible light (right). (Credit: NASA, JPL-Caltech)

Known as the Crab Pulsar (or NP0532), this rapidly rotating star is believed to be about 28–30 km (17–19 mi) in diameter and emits pulses of radiation – ranging from radio wave and X-ray – every 33 milliseconds. Like all isolated pulsars, its period is slowing very gradually, and the energy released as the pulsar slows down is enormous. The Crab Pulsar is also the source of the nebula’s synchrotron radiation, which has a total luminosity about 75,000 times greater than that of the Sun.

The pulsar’s extreme energy output also creates an unusually dynamic region at the center of the Crab Nebula. While most astronomical objects only show changes over timescales of many years, the inner parts of the Crab show changes over the course of only a few days. The most dynamic feature in the inner part of the nebula is the point where the pulsar’s equatorial wind slams into the bulk of the nebula, forming a shock front (see above image).

The Crab Pulsar is also surrounded by an expanding gas shell which encompasses its spectroscopic companion star, which in turn orbits the neutron star every 133 days. This pulsar was the first one which was also verified in the optical part of the spectrum.

History of Observation:

The very first recorded information on this supernova event reaches as far back as July 4, 1054 A.D. by Chinese astronomers who marked the presence of a “new star” visible in daylight for 23 days and 653 nights. The event may have also been recorded by the Anasazi, Navajo and Mimbres First Nations of North America in their artwork as well.

Charles Messier, French astronomer, at the age of 40, by Ansiaume. Credit: Public Domain. — *Charles Messier, French astronomer, at the age of 40, by Nicolas Ansiaume. Credit: Public Domain.*

In more modern times, the nebula was cataloged as a discovery by British amateur astronomer John Bevis in 1731, and independently by Charles Messier on August 28th, 1758 while looking for the return of Comet Halley. Although Bevis had added it to his “Uranographia Britannica”, Messier recognized what he had located had no proper motion, and was therefore not a comet. However, Messier did credit Bevis’ discovery when he learned of it years later.

By September 12th, 1758, Messier hit upon the idea of compiling a catalog of objects that weren’t comets, in order to help other astronomers avoid similar mistakes. Considering M1’s position, only slightly more than a degree from the ecliptic plane, this was a very good idea. Especially since M1 was again confused with Halley’s Comet when it returned in 1835.

The name Crab Nebula was first suggested by William Parsons, the Third Earl of Rosse, who observed it while at Birr Castle in 1884. The name was apparently due to the drawing he made of it, which resembled a crab. When he observed it again in 1848 using a ]telescope with better resolution, he could not confirm the resemblance. But the name had become popular by this point and has stuck ever since.

Our eyes would never see the Crab Nebula or Messier 1 as this Hubble image shows it. Image credit: NASA, ESA, J. Hester and A. Loll (Arizona State University) — *Our eyes would never see the Crab Nebula as this Hubble image shows it. Credit: NASA, ESA, J. Hester and A. Loll (Arizona State University)*

All of the early observers – including Herschel, Bode, Messier and Lassell – apparently mistook the filamentary structures of the Nebula as an indication of stellar structure. As Messier himself described it:

“Nebula above the southern horn of Taurus, it doesn’t contain any star; it is a whitish light, elongated in the shape of a flame of a candle, discovered while observing the comet of 1758. See the chart of that comet, Mem. Acad. of the year 1759, page 188; observed by Dr. Bevis in about 1731. It is reported on the English Celestial Atlas.”

Sir Williams Herschel’s writing on the nebula appeared in the 74th volume of the Philosophical Transactions of the Royal Society of London, which was released in 1784. As he described it:

“To these may added the 1st [M1], 3d, 27, 33, 57, 79, 81, 82, 101 [of Messier’s catalog], which in my 7, 10, and 20-feet reflectors shewed a mottled kind of nebulosity, which I shall call resolvable; so that I expect my present telescope will, perhaps, render the stars visible of which I suppose them to be composed…”

Reproduction of the first depiction of the Messier 1 nebula by Lord Rosse (1844) (colour-inverted to appear white-on-black) William Parsons, 3rd Earl of Rosse - http://messier.seds.org/more/m001_rosse.html — *Reproduction of the first depiction of the nebula by Lord Rosse (1844). Credit: messier.seds.org*

But it was Parsons (aka. Lord Rosse) who first recognized M1 for what we know it as today. As he recorded when viewing it for the first time (in 1844):

“Fig. 81 is also a cluster; we perceive in this [36-inch telescope], however, a considerable change of appearance; it is no longer an oval resolvable [mottled] Nebula; we see resolvable filaments singularly disposed, springing principally from its southern extremity, and not, as is usual in clusters, irregularly in all directions. Probably greater power would bring out other filaments, and it would then assume the ordinary form of a cluster. It is stubbed with stars, mixed however with a nebulosity probably consisting of stars too minute to be recognized. It is an easy object, and I have shown it to many, and all have been at once struck with its remarkable aspect. Everything in the sketch can be seen under moderately favourable circumstances.”

Locating Messier 1:

The Crab Nebula is easily visible in the night sky near the Taurus constellation, whenever light pollution is not an issue. It can be located by identifying Zeta Tauri, a third magnitude star located east/northeast of Aldebaran. With dark sky conditions, it can be seen as a tiny, hazy patch with binoculars and small telescopes with low magnification. If sky conditions are bright, it may be harder to locate with modest equipment.

The constellation Taurus. Credit: iau.org — *Messier Object 1 sits between the Taurus, Orion, and Auriga constellations. Credit: iau.org*

With a little more magnification, it is seen as a nebulous oval patch, surrounded by haze. In telescopes starting with 4-inch aperture, some detail in its shape becomes apparent, with some suggestion of mottled or streak structure in the inner part of the nebula. To the amateur astronomer, M1 does indeed look similar to a faint comet without a tail.

As Messier 1 is situated only 1 1/2 degrees from the ecliptic, there are frequent conjunctions and occasional transits of planets, as well as occultations by the Moon. And for the sake of simplicity, here are the vital statistics on this Messier Object:

Object Name: Messier 1
Alternative Designations: NGC 1952, M1, Sharpless 244, Crab Nebula
Object Type: Supernova Remnant
Constellation: Taurus
Right Ascension: 05 : 34.5 (h:m)
Declination: +22 : 01 (deg:m)
Distance: 6.3 (kly)
Visual Brightness: 8.4 (mag)
Apparent Dimension: 6×4 (arc min)

We wish you luck in locating it in the night sky. And should you find it, enjoy your observations!

We have written many great articles about the Crab Nebula and Messier Objects here at Universe Today. Here’s What Is The Crab Nebula?, The Peculiar Pulsar in the Crab Nebula, and Top Five Celestial Objects Anyone Can See With A Small Telescope.

Be sure to check out our complete Messier Catalog.

For more information, check out the SEDS Messier Database.

February 1, 2016 by Fraser Cain

Guide to the Constellations and Messier Objects by Tammy Plotner

The first person to ever write an article for Universe Today (apart from me) was Tammy Plotner. Tammy was an experienced amateur astronomer, and had already dedicated her life to sharing her love of the night sky with the public. She spoke at astronomy clubs, did plenty of sidewalk astronomy, and in 2004, she contributed her first article to Universe Today.

By 2006, Tammy had written dozens of articles for Universe Today, and embarked on a weekly astronomy series called What’s Up This Week. We later turned those into actual books (printed on paper, no less), and did another edition in 2007.

In 2015, Tammy passed away after a long struggle with MS, and we mentioned it here on Universe Today.

One of my favorite projects that Tammy ever embarked on for Universe Today was to publish a guide to every single Messier Object, and every single Constellation in the sky. There are more than 100 Messier Objects, and 88 recognized constellations, and Tammy wrote an in-depth guide to each and every one.

To honor Tammy, we’ve decided to bring these wonderful guides back to the surface – you probably never even realized they were in the vast Universe Today archives. The Guide to Space Curator, Matt Williams, will be completely revised Tammy’s guides, adding plenty of new pictures and links to additional resources.

We’ll release one a week from both collections until they’re all republished, starting with M1: the Crab Nebula, today.

I hope you enjoy them, I sure did.

January 29, 2016May 30, 2023 by Matt Williams

The Orbit of the Planets. How Long Is A Year On The Other Planets?

Here on Earth, we to end to not give our measurements of time much thought. Unless we’re griping about Time Zones, enjoying the extra day of a Leap Year, or contemplating the rationality of Daylight Savings Time, we tend to take it all for granted. But when you consider the fact that increments like a year are entirely relative, dependent on a specific space and place, you begin to see how time really works.

Here on Earth, we consider a year to be 365 days. Unless of course it’s a Leap Year, which takes place every four years (in which it is 366). But the actual definition of a year is the time it takes our planet to complete a single orbit around the Sun. So if you were to put yourself in another frame of reference – say, another planet – a year would work out to something else. Let’s see just how long a year is on the other planets, shall we?

Continue reading “The Orbit of the Planets. How Long Is A Year On The Other Planets?”