Universe Today

November 7, 2010December 24, 2015 by Matt Williams

Precession of the Equinoxes

Semi Major Axis — Solstice and Equinox - Credit: NASA

When he was first compiling his famous star catalogue in the year 129 BCE the Greek astronomer Hipparchus noticed that the positions of the stars did not match up with the Babylonian measurements that he was consulting. According to these Chaldean records, the stars had shifted in a rather systematic way, which indicated to Hipparchus that it was not the stars themselves that had moved but the frame of reference – i.e. the Earth itself.

Such a motion is called precession and consists of a cyclic wobbling in the orientation of Earth’s axis of rotation. Currently, this annual motion is about 50.3 seconds of arc per year or 1 degree every 71.6 years. The process is slow, but cumulative, and takes 25,772 years for a full precession to occur. This has historically been referred to as the Precession of the Equinoxes.

The name arises from the fact that during a precession, the equinoxes could be seen moving westward along the ecliptic relative to the stars that were believed to be “fixed” in place – that is, motionless from the perspective of astronomers – and opposite to the motion of the Sun along the ecliptic.

This precession is often referred to as a Platonic Year in astrological circles because of Plato’s recorded remark in the dialogue of Timaeus that a perfect year could be defined as the return of the celestial bodies (planets) and the fixed stars to their original positions in the night sky. However, it was Hipparchus who is first credited with observing this phenomenon, according to Greek astronomer Ptolemy whose own work was in part attributed to him.

The precession of the Earth’s axis has a number of noticeable effects. First of all , the positions of the south and north celestial poles appear to move in circles against the backdrop of stars, completing one cycle every 25, 772 years. Thus, while today the star Polaris lies approximately at the north celestial pole, this will change over time, and other stars will become the “north star”. Second, the position of the Earth in its orbit around the Sun during the solstices, equinoxes, or other seasonal times slowly changes.

The cause of this was first discussed by Sir Isaac Newton in his Philosophiae Naturalis Principia Mathematica where he described it as a consequence of gravitation. Though his equations were not exact, they have since been revised by scientists and his original theory proven correct.

It is now known that precessions are caused by the gravitational source of the Sun and Moon, in addition to the fact that the Earth is a spheroid and not a perfect sphere, meaning that when tilted, the Sun’s gravitational pull is stronger on the portion that is tilted towards it, thus creating a torque effect on the planet. If the Earth were a perfect sphere, there would be no precession.

Today, the term is still widely used, but generally in astrological circles and not within scientific contexts.

We have written many articles about the equinox for Universe Today. Here’s an article about the astronomical perspective of climate change, and here’s an article about the Vernal Equinox.

If you’d like more info on Earth, check out NASA’s Solar System Exploration Guide on Earth. And here’s a link to NASA’s Earth Observatory.

We’ve also recorded an episode of Astronomy Cast all about Gravity. Listen here, Episode 102: Gravity.

Sources:
http://en.wikipedia.org/wiki/Axial_precession_%28astronomy%29
http://en.wikipedia.org/wiki/Chaldea
http://en.wikipedia.org/wiki/Ecliptic
http://en.wikipedia.org/wiki/Great_year
http://www.crystalinks.com/precession.html
http://en.wikipedia.org/wiki/Isaac_Newton

Reference:
NASA: Precession

November 7, 2010December 24, 2015 by Matt Williams

Pompeii Eruption

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Imagine if you will that it’s bright sunny day in summer. The festival of Vulcanalia, dedicated to the Roman God of Fire, has just passed. Now you’re out looking for some produce to stock up for the coming winter. You’ve just finished a tour of the marketplace and are on your way home when suddenly, the mountain that your town sits at the foot of inexplicably erupts! Fire and ash rain down upon your city, people are baked alive and the town is encased in soot and dirt several meters thick. But, silver lining here, your bodies are so well preserved that when you’re dug up two thousand years later, they’ll have a pretty good idea what life was like at the time of your death. Yes, that’s how the Pompeii Eruption took place. The year was 79 CE; the place, a prosperous town named Pompeii located in the Bay of Naples. It was one of the most significant natural disasters of the ancient world, a major archaeological find in the 18th century, and is now one of the biggest tourist draws in all of Italy.

Based on the letters of Pliny the Younger, historians now believe the eruption to have taken place between the 24th of August and November 23rd, in the year 79 CE. Witnessing the eruption from across the Bay of Naples, Pliny gave a fist-hand account of the destruction. Although it was generally assumed that the people of Pompeii died as a result of suffocation from volcanic ash, a recent multidisciplinary volcanological and bio-anthropological study, merged with numerical simulations and experiments, indicated that heat was the main cause of death. The results of this study show that temperatures would have reached 250 °C up to a distance of 10 kilometers, which would have been sufficient to cause instant death, even if people were sheltered within buildings. The people and buildings of Pompeii were covered in up to twelve different layers of soil which was 25 meters deep and were therefore not discovered for almost two thousand years.

However, rediscovery of the lost city started in 1738, beginning with Pompeii’s sister town of Herculaneum which had also been destroyed in the eruption. At the time, the discovery was the accidental result of workmen digging so that they could build the foundations of a new summer palace for the king of Naples. The discovery of ancient buildings, left largely intact, led to a subsequent intentional excavation of Pompeii itself in 1764 by Francisco la Vega. In addition to intact buildings, many of which contained perfectly preserved Roman frescos, human remains were also uncovered.

For over 20 years now, Pompeii has been one of the most popular tourist destinations in Italy, attracting almost 2.6 million visitors in 2008 alone. In 1997, it was designated a World Heritage Site by UNESCO and attempts are underway to ensure that it can be preserved for future generations. Though the life-blood of the local economy, the pressure exerted by millions of tourists annually is taking its toll on this once-perfectly preserved site.

We have written many articles about Pompeii Eruption for Universe Today. Here’s an article about Mt. Vesuvius, and here are interesting facts about volcanoes.

If you’d like more info on volcanoes, check out the U.S. Geological Survey Homepage. And here’s a link to NASA’s Earth Observatory.

We’ve also recorded related episodes of Astronomy Cast about Volcanoes. Listen here, Episode 141: Volcanoes, Hot and Cold.

Sources:
http://en.wikipedia.org/wiki/Pompeii#Vesuvius_eruption
http://en.wikipedia.org/wiki/Mount_Vesuvius
http://touritaly.org/pompeii/pompeii-main.htm
http://wikitravel.org/en/Pompeii

November 7, 2010December 24, 2015 by Nancy Atkinson

Sagan Day Essays

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Tuesday (11/09) is Carl Sagan Day — a chance to remember the legacy of one of the great spokespersons for science. The folks over at the Kepler spacecraft website held an essay contest, inviting the public to submit writings inspired by the imagery that Sagan created in his allegory of The Shores of the Cosmic Ocean. (Regrettably, I didn’t write about this beforehand to give Universe Today readers a heads-up.) The essays — which also include guest essays by notables such as Jill Tartar and Seth Shostak — are now available to read, and are all well worth the trip over to the Kepler website, especially if Sagan had an impact on your thought processes (as he did on mine). I hope you’ll check it out.

By the way, I am currently attending a joint meeting of the National Association of Science Writers ad the Council for the Advancement of Science Writing at Yale University and thus will not have the opportunity to post many articles the next couple of days. But the rest of the UT team will work to keep you updated on the news. While here, I’ll have the chance to talk with some astronomers and cosmologists, and have already met a lot of great and wonderful writers.

November 6, 2010December 24, 2015 by Tammy Plotner

New Supernova Lights Up Leo

A new supernova? Darn right. Lighting up Leo? Well… not without some serious visual aid, but the fact that someone out there is watching and has invited us along for the ride is mighty important. And just who might that someone be? None other than Tim Puckett.

Less than 24 hours ago, the American Association of Variable Star Observer’s Report #222 stated:

“Bright Supernova in UGC 5189A: SN 2010jl
November 5, 2010

We have been informed by Tim Puckett and by the Central Bureau for Astronomical Telegrams (CBET 2532, Daniel W. E. Green, Ed.) of the discovery of a bright supernova in UGC 5189A by J. Newton and Puckett, Portal, AZ, on November 3.52 UT at unfiltered magnitude 13.5. Confirming images (limiting magnitude 19.1) by Puckett on Nov. 4.50 UT showed the object at magnitude 12.9.

Spectroscopic observations (CBET 2536, Daniel W. E. Green, Ed.) by S. Benetti and F. Bufano, Istituto Nazionale di Astrofisica, Osservatorio Astronomico di Padova, on behalf of a larger collaboration, and by J. Vinko, University of Szeged, G. H. Marion, Harvard-Smithsonian Center for Astrophysics and University of Texas, T. Pritchard, Pennsylvania State University, and J. C. Wheeler and E. Chatzopoulos, University of Texas, show that SN 2010jl is a type-IIn supernova. Vinko et al. also report that simultaneous measurements with Swift/UVOT in the ultraviolet bands confirm that the transient is ultraviolet-bright, as expected for young, interacting supernovae.

Coordinates: 09 42 53.33 +09 29 41.8 (J2000.0) This position is 2.4″ east and 7.7″ north of the center of UGC 5189A. This AAVSO Special Notice was prepared by Elizabeth O. Waagen.”

While magnitude 12-12.9 isn’t unaided eye bright by a long shot, it’s well within the reach of most of today’s backyard telescopes. The image you see here on the right is of UGC 5189A before the event and the lefthand image was taken at the time of the supernova report. Visually the SN event outshines the galaxy! While chasing a faint supernova event might not be everyone’s cup of tea, Mr. Puckett’s devotion is absolutely legendary and I strongly encourage you to have a look if you have the the tools and talent.

So many supernovae… So little time!

November 6, 2010December 24, 2015 by Steve Nerlich

Astronomy Without A Telescope – Indigenous Australian Astronomy

The Homunculus Nebula arising from the Eta Carinae star system - thought to be stellar material blown off by this massive star system during a 'supernova impostor' event that occurred around 1840.

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Eta Carinae is a massive binary system – of which the dominant member is an eruptive luminous blue variable star. The system’s last significant eruption – also known as the ‘great outburst’ – made Eta Carinae briefly the second brightest star system in the night sky after Sirius over the period of 1837 to 1845, after which it faded again. The great outburst left behind the Homunculus Nebula – and also left an impression on the indigenous Aboriginal people of Australia who observed it at that time.

Hamacher, with research interests in Australian archaeoastronomy – and Frew, an astrophysicist with research interests in the light curves of variable stars over long time periods, have collaborated on a paper which draws on historical records to build a case that the Boorong people of northwest Victoria incorporated the observation of Eta Carinae’s great outburst into their oral traditions.

This is of general interest as the only known observation of the Eta Carinae outburst by indigenous people – and of particular interest to Hamacher to support his assertion that Australian Aboriginal oral traditions are dynamic and evolving – and often incorporate transient astronomical events.

The Boorong clan apparently no longer exists as an entity and much of their traditional knowledge may have been lost. However, William Stanbridge published records of his encounters with them around 1860, particularly detailing their astronomical knowledge. His records include Aboriginal star names and stories associated with them – against which he either wrote down the relevant European star name or otherwise at least indicated the general vicinity of the star in question.

Of particular interest here is the star named Collowgullouric War by the Boorong – described as a ‘large red star in Rober Carol, marked 966’ by Stanbridge. In Boorong oral tradition at that time, Collowgullouric War was the wife of War – which Stanbridge directly identified as the star Canopus – and which today we consider the second brightest star in the night sky.

There are other examples of husband and wife pairings in Aboriginal astronomy – where the stars are generally closely associated in the sky and of similar apparent magnitude. Stanbridge noted Collowgullouric War as the third brightest star in a list that included Sirius as brightest, Canopus as second brightest and Alpha Centauri (or Rigil Kent) as fourth brightest. Today we would agree with most of that statement, except that Alpha Centauri is the third brightest star – and what the heck is Collowgullouric War?

The reference “large red star in Rober Carol, marked 966” refers in short-hand to a now-defunct constellation Rober Carolinum – and 966 is almost certainly a designation drawn from one of the first southern sky star catalogues, produced by La Caille in 1763. Lac 966 is actually the Carina nebula, while the Eta Carinae star is Lac 968 – but since it’s unlikely Stanbridge had his own copy of the rare La Caille catalogue, there is the possibility of a transcription error. And, in any case, in referring to a star associated the Carina Nebula, it seems reasonable to assume he really meant Eta Carinae.

Argo Navis (the ship Argo) was one of Ptolemy's 48 constellations - since split into the modern constellations Vela (the sails), Puppis (the stern) and Carina (the keel). Another now-defunct constellation, Robur Carolinum (the Oak of King Charles) introduced by Edmond Halley, also overlies this region of the sky. Around the 1840's, Eta Carinae (red arrow) might have been classified as a star of the Robur Carolinum constellation - but is now considered part of the Carina constellation. Canopus (or Alpha Carinae) is the large, bright star to the right of the drawing of the ship's rudder. Credit: Johannes Hevelius' star catalogue *Firmamentum*, circa 1690 - as sourced from Hamacher and Frew. And... for reasons unknown, Hevelius did his star catalogues from the point of view of an outsider looking in, so this map is kind of back the front. The same approach is used on the flag of Brazil - for reasons unknown. What a long caption this is.

So for a brief period of a decade or so – Eta Carinae rivalled Canopus in brightness, during the period of its variable brightening from 1837 to 1845.

On this basis, it is reasonable to assume that an indigenous people with an interest in the night sky would certainly have noted the Eta Carinae outburst – and might well have developed a story based on its close association with the similarly bright star Canopus, which was present in the sky nearby.

It remains to be discovered what other southern sky events the Indigenous Australians may have gained a privileged view of during their 40,000 year colonization of the Australian continent.

Further reading: Hamacher and Frew An Aboriginal Australian Record of the Great Eruption of Eta Carinae

November 6, 2010January 20, 2016 by Nancy Atkinson

Hartley 2 in Motion: Stunning Morph Animation of Flyby Images

The folks from UnmannedSpaceflight.com have done it again. Daniel Machácek created this wonderful animation from just the five initial images of Hartley 2 that were released by the Deep Impact team immediately following its flyby on November 4, 2010, using Sqirlz Morph software. Time in the animation is five times faster than the actual speed of the flyby. Hartley 2 really does look like a flying bowling pin, except this one is 2km (1.25 miles) long and about .2 km in diameter. Thanks to Daniel for sharing his animation.

November 5, 2010December 24, 2015 by Jon Voisey

What was SN 1961V?

NGC 1058. Image credit: Bob Ferguson and Richard Desruisseau/Adam Block/NOAO/AURA/NSF

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Up there in the sky! It’s a supernova! It’s a Luminous Blue Variable eruption! It’s…. well, we’re not sure….

In July of 1961, a star in the spiral galaxy NGC 1058 blew up, but in a very odd fashion. The time to reach its peak brightness was several months as well as a slow decline including a three year plateau. Narrow spectral lines revealed a slow expansion velocity of 2,000 km sec^-1. Some proposed it was an unusual supernova. Others claimed it was an especially energetic eruption of a Luminous Blue Variable (LBV) star like Eta Carinae. The infamous Fritz Zwicky called it a “Type V Supernova” which meant a supernova in name only, but could be anything as it was simply an “impostor”. For nearly 50 years, astronomers have been trying to sort out what this supernova impostor truly was.

One front on which much of the effort has focused is on the nature of the star before the explosion. The host galaxy is a beautiful face on spiral galaxy and was a tempting target for many observations well before the eruption. This has allowed astronomers to use archival images to determine properties of the parent star. And what a whopper it was. The star had an absolute magnitude near -12! Even Eta Carinae, one of the most massive stars currently known, only has an absolute magnitude of around -5.5. This extreme luminosity led astronomers towards early estimates for its mass to be as much as a staggering 2,000 M_☉! While this is certainly incorrect, it still reveals just how massive SN 1961V’s progenitor truly was. Most estimates now put it in the range of 100 – 200 M_☉.

A key difference between a supernova and an eruption is the remnant. In the case of a supernova, it is expected that the result would be a neutron star or black hole. If the object were an eruption, even a large one, the star would remain intact. In this vein, many astronomers have also attempted to inspect the remnant. However, due to the shell of gas and dust created in either scenario, imaging the objects has proven to be a challenge. While prior to the event, the culprit stuck out like a sore thumb, the remnant is lost in a haze of other stars.

Numerous telescopes have been aimed at the region to attempt to ferret out the leftovers including the powerful Hubble, but many attempts have remained inconclusive. Recently, the Spitzer Space telescope was employed to study the region, and although not intended for studying individual stars, its infrared vision can allow it to pierce the veil of dust and potentially find the source responsible. If there is still an intense IR source, it would mean the star survived, and the supernova truly was an impostor.

This attempt at identification was recently undertaken by a team of astronomers from Ohio State University, led by Christopher Kochanek. Upon inspection, the team was unable to conclusively identify a source with sufficient intensity as to be a survivor of the SN 1961V event. As such, the team concluded that the event Zwicky defined as a “supernova impostor” was a “‘supernova impostor’ impostor”.

The team compared it to another recent supernova, SN 2005gl, which also had a supermassive progenitor and was observed prior to detonation. Previous studies of this supernova suggested that, just prior to the explosion itself, the star underwent a heavy phase of mass loss. If a similar scenario occurred in 1961V, it could explain the unusual expansion velocity. During this time, the star may quake ferociously, imitating LBV eruptions which could explain the pre-nova plateau.

While this comparison relies on a single strongly similar case, it underscores the need “that studies of SN progenitors should evolve from simple attempts to obtain a single snapshot of the star to monitoring their behavior over their final years.” Hopefully, future studies and observations will provide better theoretical simulations and the numerous large surveys will provide sufficient data on stars prior to eruption to better constrain the behavior of these monsters.

November 5, 2010April 26, 2016 by Fraser Cain

Another Project I’m Working On

If there are any webmasters or web marketers out there, you might want to check out another project I’m working on. It’s called the Keyword Strategy tool, and it’s what we built internally to handle all the pages and content for the Guide to Space. If you’re doing any search engine optimization, check it out.

November 5, 2010July 21, 2020 by Matt Williams

What is the Multiverse Theory?

*Could our Universe be part of a wider Multiverse? And could these other Universes support life? Credit: Jaime Salcido/EAGLE Collaboration*

If you’re a fan of science fiction or fantasy then chances are, at some point, you’ve read a book, seen a movie, or watched a series that explored the concept of multiple universes. The idea being that within this thing we call time and space, there are other dimensions where reality differs from our own, sometimes slightly, sometimes radically. Interestingly enough, this idea is not restricted to fiction and fantasy.

In science, this is known as the Multiverse Theory, which states that there may be multiple or even an infinite number of universes (including the universe we consistently experience) that together comprise everything that exists: the entirety of space, time, matter, and energy as well as the physical laws and constants that describe them. In this context, multiple universes are often referred to as parallel universes because they exist alongside our own.

The term was coined in 1895 by the American philosopher and psychologist William James. However, the scientific basis of it arose from the study of cosmological forces like black holes and problems arising out of the Big Bang theory. For example, within black holes it is believed that a singularity exists – a point at which all physical laws cease – and where it becomes impossible to predict physical behavior.

Beyond this point, it is possible that there may be an entirely new set of physical laws, or just slightly different versions of the ones that we know, and that a different universe might exist. Theories like cosmic inflation support this idea, stating that countless universes emerged from the same primordial vacuum after the Big Bang, and that the universe as we know it is just what is observable to us.

Max Tegmark’s taxonomy of universes sums up the different theories on multiple universes. IN this model, there are four levels that classify all major schools on thought on the subject.

In Level One, different universes are arranged one on top of the other in what is called Hubble Volumes, all having the same physical laws and constants. Though each will likely differ from our own in terms of distribution of matter, there will eventually be Hubble volumes with similar, and even identical, configurations to our own.

In Level Two, universes with different physical constants exist and the multiverse as a whole is stretching and will continue to do so forever, but some regions of space stop stretching and form distinct bubbles, like gas pockets in a loaf of rising bread.

In Level Three, known as the Many Worlds Interpretation of Quantum Mechanics, observations cannot be predicted absolutely but a range of possible observations exist, each one corresponding to a different universe. Level Four, aka.the Ultimate Ensemble devised by Tegmark himself, considers as equally real all universes that can be defined by mathematical structures. In other words, universes with the same or different constants may exist.

We have written many articles about multiverse for Universe Today. Here’s an article about searching life in the multiverse, and here’s an article about parallel universe.

If you’d like more info on the Multiverse, check out some Recent Innovations about the Concept of Universe, and here’s a link to an article about the Size of the Universe.

We’ve also recorded an entire episode of Astronomy Cast all about Multiverses. Listen here, Episode 166: Multiverses.

Sources:
http://en.wikipedia.org/wiki/Multiverse
http://www.sciencedaily.com/releases/2010/01/100112165249.htm
http://www.astronomy.pomona.edu/Projects/moderncosmo/Sean%27s%20mutliverse.html
http://en.wikipedia.org/wiki/William_James
http://en.wikipedia.org/wiki/Big_Bang
http://en.wikipedia.org/wiki/Inflation_%28cosmology%29

November 5, 2010December 24, 2015 by Matt Williams

Morning Star

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If you look to the morning sky – to the east that is, as the sun’s rising – you will notice a bright star in the firmament, one that should not be there. Theoretically, stars only come out at night and should be well on their way to bed by the time the sun rises, correct? Well, that’s because the Morning Star, as it’s known, isn’t a star at all, but the planet Venus. It is both the morning and evening star, the former when it appears in the east during sunrise and the latter when it appears in the west during sunset. Because of its unique nature and appearance in the sky, this “star” has figured prominently in the mythologies of many cultures.

In ancient Sumerian mythology, it was named Inanna (Babylonian Ishtar), the name given to the goddess of love and personification of womanhood. The Ancient Egyptians believed Venus to be two separate bodies and knew the morning star as Tioumoutiri and the evening star as Ouaiti. Likewise, believing Venus to be two bodies, the Ancient Greeks called the morning star Phosphoros (or Eosphoros) the “Bringer of Light” (or “Bringer of Dawn”) and the evening star they called Hesperos (“star of the evening”). By Hellenistic times, they had realized the two were the same planet, which they named after their goddess of love, Aphrodite. The Phoenicians, never ones to be left out where astronomy and mythology were concerned, named it Astarte, after their own goddess of fertility. In Iranian mythology, especially in Persian mythology, the planet usually corresponds to the goddess Anahita, and sometimes AredviSura, the goddesses of fertility and rivers respectively. Mirroring the ancient Greeks, they initially believed the planet to be two separate objects, but soon realized they were one.

The Romans, who derived much of their religious pantheon from the Greek tradition and near Eastern tradition, maintained this trend by naming the planet Venus after their goddess of love. Later, the name Lucifer, the “bringer of light”, would emerge as a Latinized form of Phosphoros (from which we also get the words phosphorus and phosphorescence). This would prove influential to Christians during the Middle Ages who used it to identify the devil. Medieval Christians thusly came to identify the Morningstar with evil, being somewhat more concerned with sin and vice than fertility and love! However, the identification of the Morningstar as a symbol of fertility and womanhood remains entrenched, best demonstrated by the fact that the astronomical symbol for Venus happens to be the same as the one used in biology for the female sex: a circle with a small cross beneath.

The Morningstar also figures prominently in the mythology of countless other cultures, including the Mayans, Aborigines, and Maasai people of Kenya. To all of these cultures, the Morningstar still serves as an important spiritual, agricultural and astrological role. To the Chinese, Japanese, Koreans and Vietnamese, she is known literally as the “metal star”, based on the Five Elements.

We have written many articles about the Morning Star for Universe Today. Here’s an article about how to find Venus in the sky, and here’s an article about the brightest planet.

If you’d like more information on the Morning Star, check out Hubblesite’s News Releases about Venus, and here’s a link to NASA’s Solar System Exploration Guide on Venus.

We’ve also recorded an entire episode of Astronomy Cast all about Venus. Listen here, Episode 50: Venus.

Sources:
http://en.wikipedia.org/wiki/Morning_Star
http://en.wikipedia.org/wiki/Lucifer
http://en.wikipedia.org/wiki/Eosphorus
http://en.wikipedia.org/wiki/Venus
http://en.wikipedia.org/wiki/Isis
http://en.wikipedia.org/wiki/Evening_star