Sunday, April 5, 2015

Seeking Ceres: Following the Brave New World Through 2015

Seeking Ceres: Following the Brave New World Through 2015:



Credit:


A misshapen crescent Ceres as seen from NASA’s Dawn spacecraft. Image credit: NASA/JPL/Caltech/UCLA/DLR/IDA
A little world is making big headlines in 2015. NASA’s Dawn spacecraft entered orbit around 1 Ceres on March 6th, 2015, gaving us the first stunning images of the ~900 kilometre diameter world. But whether you refer to Ceres as a dwarf planet, minor planet, or the king of the asteroid belt, this corner of the solar system’s terra incognita is finally open for exploration. It has been a long time coming, as Ceres has appeared as little more than a wandering, star-like dot in the telescopes of astronomers for over two centuries since discovery.



Untitled


The orbit of 1 Ceres. Credit: NASA/JPL
And the good news is, you can observe Ceres from your backyard if you know exactly where to look for it with binoculars or a small telescope. We’ll admit, we had an ulterior motive on pulling the trigger on this post three months prior to opposition on July 24th, as Dawn will soon be exiting its ‘shadow phase’ and start unveiling the world to us up close. The first science observations for Dawn begin in mid-April.



Credit


The path of Ceres through the remainder of 2015. Credit: Starry Night Software.
Ceres spends all of 2015 looping through the constellations of Capricornus, Microscopium and Sagittarius. This places it low to the south for northern hemisphere observers on April 1st in the early morning sky. Ceres will pass into the evening sky by mid-summer. Ceres orbits the Sun once every 4.6 years in a 10.6 degree inclination path relative to the ecliptic that takes it 2.6 AU to 3 AU from the Sun. The synodic period of Ceres is, on average, 467 days from one opposition to the next.



Ceres


Ceres, Vesta and Mars group together in 2014. Image credit and copyright: Mary Spicer
Shining at magnitude +8, April 1st finds Ceres near the Capricornus/Sagittarius border. Ceres can reach magnitude +6.7 during a favorable opposition. Note that Ceres is currently only 20 degrees east of the position of Nova Sagittarii 2015 No. 2, currently still shining at 4th magnitude. June 29th and November 25th are also great times to hunt for Ceres in 2015 as it loops less than one degree past the 4th magnitude star Omega Capricorni.



June 30


Ceres meets up with Omega Capricorni on June 29th. Credit: Stellarium.
You can nab Ceres by carefully noting its position against the starry background from night to night, either by sketching the suspect field, or photographing the region. Fans of dwarf planets will recall that 1 Ceres and 4 Vesta fit in the same telescopic field of view last summer, and now sit 30 degrees apart. Ceres is now far below the ecliptic plane, but will resume getting occulted by the passing Moon on February 3rd, 2017.



Left


The Palermo transit instrument used to discover Ceres. From Della Specola Astronomica (1792)
Ceres was discovered by Giuseppe Piazzi on the first day of the 19th century on January 1st, 1801. Ceres was located on the Aries/Cetus border just seven degrees from Mars during discovery. Piazzi wasn’t even on the hunt for new worlds at the time, but was instead making careful positional measurements of stars with the 7.5 centimetre Palermo Circle transit telescope.



Credit


A 1802 publication by Piazzi describing his discovery of Ceres. Credit: Image in the Public Domain.
At the time, the discovery of Ceres was thought to provide predictive proof of the Titus-Bode law: here was a new planet, just where this arcane numerical spacing of the planets said it should be. Ceres, however, was soon joined by the likes of Juno, Pallas, Vesta and many more new worldlets, as astronomers soon came to realize that the solar system was not the neat and tidy place that it was imagined to be in the pre-telescopic era.

To date, the Titus-Bode law remains a mathematical curiosity, which fails to hold up to the discovery of brave new exoplanetary systems that we see beyond our own.



Credit


Piazzi’s 1801 log describing the motion of Ceres against the starry background. Credit: Monatliche Correspondenz
The view from Ceres itself would be a fascinating one, as an observer on the Cererian surface would be treated to recurrent solar transits of interior solar system worlds. Mercury would be the most frequent, followed by Venus, which transits the Sun as seen from Ceres 3 times in the 21st century: August 1st, 2042, November 19th, 2058 and February 13th 2068. Mars actually transits the Sun as seen from Ceres even earlier on June 9th, 2033. Curiously, we found no transits of the Earth as seen from Ceres during the current millennium from 2000 to 3000 AD!



From Ceres, Jupiter would also appear 1.5’ in diameter near opposition, as opposed to paltry maximum of 50” in size as seen from the Earth. This would be just large enough for Jupiter to exhibit a tiny disk as seen from Ceres with the unaided eye. The four major Galilean moons would be visible as well.



Credit


The 2033 solar transit of Mars as seen from Ceres. Credit: Starry Night Education Software.
The mysteries of Ceres beckon. Does the world harbor cryovolcanism? Just what are those two high albedo white dots? Are there any undiscovered moons orbiting the tiny world? If a fair amount of surface ice is uncovered, Ceres may soon become a more attractive target for human exploration than Mars.

All great thoughts to ponder, as this stellar speck in the eyepiece of your backyard telescope becomes a brand new world full of exciting possibilities.



About 

David Dickinson is an Earth science teacher, freelance science writer, retired USAF veteran & backyard astronomer. He currently writes and ponders the universe from Tampa Bay, Florida.

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Stunning Photo of Volcanic Lightning at Volcán de Colima in Mexico

Stunning Photo of Volcanic Lightning at Volcán de Colima in Mexico:



The Colima Volcano (Volcán de Colima) pictured on March 29, 2015 with lightning arcing through the ash plume. Credit and copyright: César Cantú.


The Colima Volcano (Volcán de Colima) pictured on March 29, 2015 with lightning arcing through the ash plume. Credit and copyright: César Cantú.
The Colima volcano in Mexico is active again, and has been spewing out large plumes of ash nearly 3 kilometers into the air. Astrophotographer César Cantú captured this spectacular picture of lightning slicing through the cloud of ash.

How can lightning strike in an ash cloud? Through friction, particles of the ash can charge each other by rubbing against each other during the eruption. When the energy is discharged, it can create lightning bolts.


The Colima volcano is one of the most active volcanoes in Mexico, and is also called ‘Volcán de Fuego’ or ‘Fire volcano.’ It has erupted more than 40 times since the first documented eruption in 1576.

The latest news on this current eruption is that local authorities have put the volcano on a yellow alert, meaning the volcano is showing increased activity, and residents who live nearby should prepare for a possible evacuation.

Stay safe César, and thanks for sharing your image with Universe Today! See a larger version on his website here.



About 

Nancy Atkinson is currently Universe Today's Contributing Editor. Previously she served as UT's Senior Editor and lead writer, and has worked with Astronomy Cast and 365 Days of Astronomy. Nancy is also a NASA/JPL Solar System Ambassador.

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A Red Moon – NOT a Sign of the Apocalypse!

A Red Moon – NOT a Sign of the Apocalypse!:



Composite picture of a dark red Moon during a total lunar eclipse. Credit: NASA/ Johannes Schedler (Panther Observatory)


Composite picture of a dark red Moon during a total lunar eclipse. Credit: NASA/Johannes Schedler (Panther Observatory)
Editor’s note: This is an article we wrote a few months ago, but are reposting it for the upcoming eclipse on April 4. Here is a complete guide on how to see this particular ‘red Moon’ lunar eclipse.

On most evenings, the Moon will appear as a bright yellow or white color in the night sky. But on occasion, the Moon can turn a beautiful and dramatic red, coppery color. Naturally, there are a number of superstitions associated with this stellar event. But to modern astronomers, a Red Moon is just another fascinating phenomenon that has a scientific explanation.

Since the earliest days of recorded history, the Moon has been believed to have a powerful influence over human and animal behavior. To the Romans, staring at a full Moon was thought to drive a person crazy – hence the term “lunatic”. Farmers in the past would plant their crops “by the moon”, which meant sowing their seeds in accordance with the Moon’s phases in the hopes of getting a better harvest.

So naturally, when the Moon turned red, people became wary. According to various Biblical passages, a Blood Moon was thought to be a bad omen. But of course, the Moon turns red on a semi-regular basis, and the world has yet to drown in fire. So what really accounts for a “Red Moon?” What causes Earth’s only satellite to turn the color of blood?

Ordinarily, the Moon appears as it does because it is reflecting light from the Sun. But on occasion, it will darken and acquire either a golden, copper, or even rusty-red color.

There are few situations that can cause a red Moon. The most common way to see the Moon turn red is when the Moon is low in the sky, just after moonrise or before it’s about to set below the horizon. Just like the Sun, light from the Moon has to pass through a larger amount of atmosphere when it’s down near the horizon, compared to when it’s overhead. The Earth’s atmosphere can scatter sunlight, and since moonlight is just scattered sunlight, it can scatter that too. Red light can pass through the atmosphere and not get scattered much, while light at the blue end of the spectrum is more easily scattered. When you see a red moon, you’re seeing the red light that wasn’t scattered, but the blue and green light have been scattered away. That’s why the Moon looks red.

The second reason for a red Moon is if there’s some kind of particle in the air. A forest fire or volcanic eruption can fill the air with tiny particles that partially obscure light from the Sun and Moon. Once again, these particles tend to scatter blue and green light away, while permitting red light to pass through more easily. When you see a red moon, high up in the sky, it’s probably because there’s a large amount of dust in the air.



Depiction of the Sun's rays turning the Moon red. Image Credit: NASA/Mars Exploration


Depiction of the Sun’s rays turning the Moon red. Image Credit: NASA/Mars Exploration
A third – and dramatic – way to get a red Moon is during a lunar eclipse. This happens when the Moon is full and passes into Earth’s shadow (also known as the umbra), which darkens it. At that point, the Moon is no longer being illuminated by the Sun. However, the red light passing through the Earth’s atmosphere does reach the Moon, and is thus reflected off of it. For those observing from the ground, the change in color will again be most apparent when the Moon appears low in the night sky, just after moonrise or before it’s about to set below the horizon. Once again, this is because our heavy atmosphere will scatter away the blue/green light and let the red light go straight through.

The reddish light projected on the Moon is much dimmer than the full white sunlight the Moon typically reflects back to us. That’s because the light is indirect and because the red-colored wavelengths are only a part of what makes up the white light from the sun that the Moon usually receives.

In other words, when you see a red Moon, you’re seeing the result of blue and green light that has been scattered away, and the red light remaining.



Path of the Moon through Earth's umbral and penumbral shadows during the Total Lunar Eclipse of April 15, 2014. Image Credit: NASA/Eclipse


Path of the Moon through Earth’s umbral and penumbral shadows during the Total Lunar Eclipse of April 15, 2014. Image Credit: NASA/Eclipse Website
And that’s the various ways how we get a Red Moon in the night sky. Needless to say, our ancient forebears were a little nervous about this celestial phenomenon occurrence.

For example, Revelations 6:12/13 says that a Red Moon is a sign of the apocalypse: “When he opened the sixth seal, I looked, and behold, there was a great earthquake, and the sun became black as sackcloth, the full moon became like blood, and the stars of the sky fell to the earth as the fig tree sheds its winter fruit when shaken by a gale.”

But rest assured that if you see one, it’s not the end of the world. The Sun and Moon will rise again.

We have covered lunar eclipses many times on Universe Today, and often explain the red Moon phenomenon. Here’s another good explanation of the science behind a Red Moon, and why the recent series of lunar eclipses in 2014 and 2015 (known as a tetrad) do not mean anything apocalyptic, and here’s another article about how to see a lunar eclipse. Here’s an article that includes a stunning array of images of the Moon during an eclipse in 2014.

Of course, NASA has some great explanations of the red Moon effect during a lunar eclipse. Here’s another one.

You can listen to a very interesting podcast about the formation of the Moon from Astronomy Cast, Episode 17: Where Did the Moon Come From?

Sources: NASA Science: Lunar Eclipse, NASA: Mars Exploration, Discovery News, NASA: Eclipse Website



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Author, freelance writer, educator, Taekwon-Do instructor, and loving hubby, son and Island boy!

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Hangout with New Horizons on April 3, 2015

Hangout with New Horizons on April 3, 2015:

New Horizons
New Horizons spacecraft by Johns Hopkins University Applied Physics Laboratory/Southwest Research Institute


Are you excited about the upcoming NASA New Horizons flyby to Pluto? Even though the flyby will happen on July 14, 2015, Pluto is getting closer and closer in the spacecraft’s cameras. And there’s lots of science to be done between now and then.


Join me today, Friday April 3 at 10 am PDT / 1 pm EDT for a special Hangout with NASA and members from the New Horizons science team to discuss the state of the mission and what we can expect over the next few months as we finally meet Pluto up close. Ask the team your questions live.

We’ll be joined by:

Click here to learn more about the event, or watch it live at 10am PDT.

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A Flag Shaped Aurora over Sweden

A Flag Shaped Aurora over Sweden: APOD: 2015 March 30 - A Flag Shaped Aurora over Sweden


Discover the cosmos! Each day a different image or photograph of our fascinating universe is featured, along with a brief explanation written by a professional astronomer.

2015 March 30


See Explanation. Clicking on the picture will download the highest resolution version available.
A Flag Shaped Aurora over Sweden

Image Credit & Copyright: Mia Stålnacke
Explanation: It appeared, momentarily, like a 50-km tall banded flag. In mid-March, an energetic Coronal Mass Ejection directed toward a clear magnetic channel to Earth led to one of the more intense geomagnetic storms of recent years. A visual result was wide spread auroras being seen over many countries near Earth's magnetic poles. Captured over Kiruna, Sweden, the image features an unusually straight auroral curtain with the green color emitted low in the Earth's atmosphere, and red many kilometers higher up. It is unclear where the rare purple aurora originates, but it might involve an unusual blue aurora at an even lower altitude than the green, seen superposed with a much higher red. As the Sun continues near its top level of surface activity, colorful nights of auroras over Earth are likely to continue.

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Corona from Svalbard

Corona from Svalbard: APOD: 2015 March 31 - Corona from Svalbard


Discover the cosmos! Each day a different image or photograph of our fascinating universe is featured, along with a brief explanation written by a professional astronomer.

2015 March 31


See Explanation. Clicking on the picture will download the highest resolution version available.
Explanation: During a total solar eclipse, the Sun's extensive outer atmosphere, or corona, is an inspirational sight. Streamers and shimmering features that engage the eye span a brightness range of over 10,000 to 1, making them notoriously difficult to capture in a single photograph. But this composite of 29 telescopic images covers a wide range of exposure times to reveal the crown of the Sun in all its glory. The aligned and stacked digital frames were recorded in the cold, clear skies above the Arctic archipelago of Svalbard, Norway during the Sun's total eclipse on March 20 and also show solar prominences extending just beyond the edge of the solar disk. Remarkably, even small details on the dark night side of the New Moon can be made out, illuminated by sunlight reflected from a Full Earth. Of course, fortunes will be reversed on April 4 as a Full Moon plunges into the shadow of a New Earth, during a total lunar eclipse.

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The Owl and the Galaxy

The Owl and the Galaxy: APOD: 2015 April 2 - The Owl and the Galaxy


Discover the cosmos! Each day a different image or photograph of our fascinating universe is featured, along with a brief explanation written by a professional astronomer.

2015 April 2


See Explanation. Clicking on the picture will download the highest resolution version available.
Explanation:

The Owl and the Galaxy sail these skies

With blue and yellow star.


They go together beneath the Big Dipper,
If you wonder where they are.

The Galaxy's light shines through the night,
Ten millions of light-years away.

But never fear the Owl is near,
Inside the Milky Way.

A cosmic shroud, the Owl is proud,
its central star a must.

And the spiral Galaxy lies on edge
To show off all its dust,
Its dust,
Its dust,
To show off all its dust.
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Sun and Moon Halo

Sun and Moon Halo: APOD: 2015 April 3 - Sun and Moon Halo


Discover the cosmos! Each day a different image or photograph of our fascinating universe is featured, along with a brief explanation written by a professional astronomer.

2015 April 3


See Explanation. Clicking on the picture will download the highest resolution version available.
Explanation: Two pictures captured on April 1 are combined in this creative day and night composite. Separated in time by about 10 hours the images otherwise match, looking along the coast at Östersund Sweden. The relative times were chosen to show the Sun and a nearly full Moon at the same place in the cold, early springtime sky. In the night scene Jupiter also shines above the waterfront lights, while Sun and Moon are both surrounded by a beautiful circular ice halo. The Sun and Moon halos really do align, each with an angular radius of 22 degrees. That radius is a constant, not determined by the brightness of Sun or Moon but only by the hexagonal geometry of atmospheric ice crystals and the reflection and refraction of light. Of course tomorrow, April 4, will find the Sun and Moon on opposite sides of planet Earth for a total lunar eclipse.

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Voorwerpjes in Space

Voorwerpjes in Space: APOD: 2015 April 4 - Voorwerpjes in Space


Discover the cosmos! Each day a different image or photograph of our fascinating universe is featured, along with a brief explanation written by a professional astronomer.

2015 April 4



See Explanation. Clicking on the picture will download the highest resolution version available.
Explanation: Mysterious Hanny's Voorwerp, Dutch for "Hanny's Object", is really enormous, about the size of the Milky Way Galaxy and glowing strongly in the greenish light produced by ionized oxygen atoms. It is thought to be a tidal tail of material left by an ancient galaxy merger, illuminated and ionized by the outburst of a quasar inhabiting the center of distant spiral galaxy IC 2497. Its exciting 2007 discovery by Dutch schoolteacher Hanny van Arkel while participating online in the Galaxy Zoo project has since inspired a search and discovery of eight more eerie green cosmic features. Imaged in these panels by the Hubble Space Telescope, all eight appear near galaxies with energetic cores. Far outside their associated galaxies, these objects are also likely echoes of quasar activity, illuminated only as light from a core quasar outburst reaches them and ultimately fading tens of thousands of years after the quasar outburst itself has faded away. Of course a galaxy merger like the impending merger of our own Milky Way and the Andromeda Galaxy, could also trigger the birth of a quasar that would illuminate our distant future version of Hanny's Voorwerp.

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Monday, March 30, 2015

"Mini Supernova" Explosion Could Have Big Impact

"Mini Supernova" Explosion Could Have Big Impact:



GK Persei*


In Hollywood blockbusters, explosions are often among the stars of the show. In space, explosions of actual stars are a focus for scientists who hope to better understand their births, lives, and deaths and how they interact with their surroundings.

Using NASA's Chandra X-ray Observatory, astronomers have studied one particular explosion that may provide clues to the dynamics of other, much larger stellar eruptions.

A team of researchers pointed the telescope at GK Persei, an object that became a sensation in the astronomical world in 1901 when it suddenly appeared as one of the brightest stars in the sky for a few days, before gradually fading away in brightness. Today, astronomers cite GK Persei as an example of a "classical nova," an outburst produced by a thermonuclear explosion on the surface of a white dwarf star, the dense remnant of a Sun-like star.

A nova can occur if the strong gravity of a white dwarf pulls material from its orbiting companion star. If enough material, mostly in the form of hydrogen gas, accumulates on the surface of the white dwarf, nuclear fusion reactions can occur and intensify, culminating into a cosmic-sized hydrogen bomb blast. The outer layers of the white dwarf are blown away, producing a nova outburst that can be observed for a period of months to years as the material expands into space.

Classical novas can be considered to be "miniature" versions of supernova explosions. Supernovas signal the destruction of an entire star and can be so bright that they outshine the whole galaxy where they are found. Supernovas are extremely important for cosmic ecology because they inject huge amounts of energy into the interstellar gas, and are responsible for dispersing elements such as iron, calcium and oxygen into space where they may be incorporated into future generations of stars and planets.

Although the remnants of supernovas are much more massive and energetic than classical novas, some of the fundamental physics is the same. Both involve an explosion and creation of a shock wave that travels at supersonic speeds through the surrounding gas.

The more modest energies and masses associated with classical novas means that the remnants evolve more quickly. This, plus the much higher frequency of their occurrence compared to supenovas, makes classical novas important targets for studying cosmic explosions.

More information at http://chandra.harvard.edu/photo/2015/gkper/index.html

-Megan Watzke, CXC

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Dark Matter is Darker Than Once Thought

Dark Matter is Darker Than Once Thought:



Six Galaxy Clusters*


This panel of images represents a study of 72 colliding galaxy clusters conducted by a team of astronomers using NASA's Chandra X-ray Observatory and Hubble Space Telescope. The research sets new limits on how dark matter - the mysterious substance that makes up most of the matter in the Universe - interacts with itself, as reported in the press release. This information could help scientists narrow down the possibilities of what dark matter may be.

Galaxy clusters, the largest objects in the Universe held together by their own gravity, are made up of three main components: stars, clouds of hot gas, and dark matter. When galaxy clusters collide, the clouds of gas enveloping the galaxies crash into each other and slow down or stop. The stars are much less affected by the drag from the gas and, because they occupy much less space, they glide past each other like ships passing in the night.

Because the clouds of gas are very hot - millions of degrees - they glow brightly in X-ray light (pink). When combined with visible-light images from Hubble, the team was able to map the post-collision distribution of stars and also of the dark matter (blue). Astronomers can map the distribution of dark matter by analyzing how the light from distant sources beyond the cluster is magnified and distorted by gravitational effects (known as "gravitational lensing.")

The collisions in the study happened at different times, and are seen from different angles - some from the side, and others head-on. The clusters in the panel are from left to right and top to bottom: MACS J0416.1­2403, MACS J0152.5-2852, MACS J0717.5+3745, Abell 370, Abell 2744 and ZwCl 1358+62.

More information at http://chandra.harvard.edu/photo/2015/dark/index.html

-Megan Watzke, CXC

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Using 19th Century Technology to Time Travel to the Stars

Using 19th Century Technology to Time Travel to the Stars:



This image of a spiral galaxy, taken on a glass photographic plate, is one in a series of photos taken over decades. From the Harvard Plate collection. Image courtesy American Museum of Natural History.


This image of a spiral galaxy, taken on a glass photographic plate, is one in a series of photos taken over decades. From the Harvard Plate collection. Image courtesy American Museum of Natural History.
In the late 19th century, astronomers developed the technique of capturing telescopic images of stars and galaxies on glass photographic plates. This allowed them to study the night sky in detail. Over 500,000 glass plate images taken from 1885 to 1992 are part of the Plate Stacks Collection of the Harvard-Smithsonian Center for Astrophysics (CfA), and is is the largest of its kind in the world.

“The images captured on these plates remain incredibly valuable to science, representing a century of data on stars and galaxies that can never be replaced,” writes astronomer Michael Shara, who is Curator in the Department of Astrophysics at the American Museum of Natural History in New York City, who discussed the plates and their significance in a new episode of AMNH’s video series, “Shelf Life.”

These plates provide a chance to travel back in time, to see how stars and galaxies appeared over the past 130 years, allowing astronomers to do what’s called “time domain astronomy”: studying the changes and variability of objects over time. These include stars, galaxies, and jets from stars or galactic nuclei.




But viewing these plates is difficult. The glass plates can still be viewed on a rather archaic plate viewer—a device that’s like an X-ray light box in a doctor’s office. But those aren’t readily available, and Harvard is hesitant about shipping the 100-plus-year-old glass plates around the world. If astronomers travel to Cambridge to dig through the archives, they can spend hours poring over logbooks or just looking for the right plate. Plus, there’s not an easy way to compare these plates to today’s digital imagery.

AMNH is helping CfA to digitize the glass plates, which is discussed in the video. There’s also a citizen science project called DASCH to help digitize the telescope logbooks record that hold vital information associated with a 100-year-long effort to record images of the sky. By transcribing logbook text to put those historical observations in context, volunteers can help to unlock hidden discoveries.

Find out more about DASCH here, and you can read the news release from last year about it here.

Find out more about AMNH’s digitization project here, where you can also see more episodes of “Shelf Life.”

Past episodes usually focus on the “squishy/hold-in-your-hand side of natural history collections,” said Kendra Snyder from AMNH’s communications department, adding that this latest episode about astronomy offers a different take on what people think is in museum collections.



About 

Nancy Atkinson is currently Universe Today's Contributing Editor. Previously she served as UT's Senior Editor and lead writer, and has worked with Astronomy Cast and 365 Days of Astronomy. Nancy is also a NASA/JPL Solar System Ambassador.

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Predicting Eclipses: How Does the Saros Cycle Work?

Predicting Eclipses: How Does the Saros Cycle Work?:



Image credit and copyright:


A sequence of images from the April 15th 2014 ‘Tax Day’ total lunar eclipse. Image credit and copyright: Kenneth Brandon
Boy, how about that total solar eclipse last Friday? And there’s more in store, as most of North America will be treated to yet another total lunar eclipse on the morning of April 4th. This eclipse is member three of four of a quartet of lunar eclipses, known as a tetrad.

Solar and lunar eclipses are predictable, and serve as a dramatic reminder of the clockwork nature of the universe. Many will marvel at the ‘perfect symmetry’ of eclipses as seen from the Earth, though the true picture is much more complex. Yes, the Sun is roughly 400 times larger in diameter than the Moon, but also about 400 times farther away. This distance isn’t always constant, however, as the orbits of both the Earth and Moon are elliptical. And to complicate matters, the Moon is currently moving 3 to 4 centimetres farther away from the Earth per year. Already, annular eclipses are more common in the current epoch than are total solar eclipses, and about 1.4 billion years from now, total solar eclipses will cease to happen entirely.

This has an impact on lunar eclipses as well. The dark inner umbra of the Earth is an average of about 1.25 degrees across at the distance from Earth to the Moon. The Moon’s orbit is inclined 5.1 degrees relative to the ecliptic plane, which traces out the Earth’s path around the Sun.  If this inclination was equal to zero, we’d be treated to two eclipses — one solar and one lunar — every 29.5 day synodic month.



This inclination assures that we have, on average, two eclipse seasons year, and that eclipses occur in groupings of 2-3.  The maximum number of eclipses that can occur in a calendar year is 7, which next occurs in 2038, and the minimum is 4, as occurs in 2015.

A solar eclipse occurs at New Moon, and a lunar eclipse always occurs at Full — a fact that many works of film and fiction famously get wrong. And while you have to happen to be in the narrow path of a solar eclipse to witness totality, the whole Moonward facing hemisphere of the Earth gets to witness a lunar eclipse. Ancient cultures recognized the mathematical vagaries of the lunar and solar cycles as they attempted to reconcile early calendars. Our modern Gregorian calendar strikes a balance between the solar mean and tropical year. The Muslim calendar uses strictly lunar periods, and thus falls 11 days short of a 365 day year. The Jewish and Chinese calendars incorporate a hybrid luni-solar system, assuring that an intercalculary ‘leap month’ needs to be added every few years.

But trace out the solar and lunar cycles far enough, and something neat happens. Meton of Athens discovered in the 5th century BC that 235 synodic periods very nearly equals 19 solar years to within a few hours. This means that the phases of the Moon ‘sync up’ every 19-year Metonic cycle, handy if you’re say, trying to calculate the future dates for a movable feast such as Easter, which falls on (deep breath) the first Sunday after the first Full Moon after the March equinox.



Credit


A unique ‘moondial’ in front of the Flandrau observatory on the University of Arizona Tucson campus. Image credit: David Dickinson
But there’s more. Take a period of 223 synodic months, and they sync up three key lunar cycles which are crucial to predicting eclipses;

Synodic month- The time it takes for the Moon to return to like phase (29.5 days).

Anomalistic month- The time it takes for the Moon to return to perigee (27.6 days).

Draconic month- the time it takes for the Moon to return to a similar intersecting node (ascending or descending) along the ecliptic (27.2 days).

That last one is crucial, as eclipses always occur when the Moon is near a node. For example, the Moon crosses ascending node less than six hours prior to the start of the April 4th lunar eclipse.



Credit


The evolution of a solar saros. Image credit: A.T. Sinclair/NASA/GSFC/Wikimedia Commons
And thus, the saros was born. A saros period is just eight hours shy of 18 years and 11 days, which in turn is equal to 223 synodic, 242 anomalistic or 239 draconic months.

The name saros was first described by Edmond Halley in 1691, who took it from a translation of an 11th century Byzantine dictionary. The plural of saros is saroses.

This also means that solar and lunar eclipses one saros period apart share nearly the same geometry, shifted 120 degrees in longitude westward. For example, the April 4th lunar eclipse is member number 30 in a cycle of 71 lunar eclipses belonging to saros series 132. A similar eclipse occurred one saros ago on March 24th, 1997. Stick around until April 14th, 2033 and you’ll complete a personal triple saros of eclipses, known as an exeligmos.



Credit:


A tale of three eclipses spanning 1997-2033 from lunar saros 132. Credit: Fred Espenak/NASA/GSFC
Dozens of saros series — both solar and lunar — are underway at any particular time.

But there’s something else unique about April’s eclipse. Though saros 132 started with a slim shallow penumbral eclipse way back on May 12th, 1492, this upcoming eclipse features the very first total lunar eclipse of the series. You can tell, as the duration of totality is a short 4 minutes and 43 seconds, a far cry from the maximum duration of 107 minutes that can occur during a central eclipse.



Created by author.


The evolution of lunar saros 132, showing five key eclipses out of the 71 in the series. Created by author
This particular saros cycle of eclipses will continue to become more central as time goes on. The final total lunar eclipse of the series occurs on August 2nd, 2213 AD, and the saros finally ends way out on June 26th, 2754.

Eclipses, both lunar and solar, have also made their way into the annuals of history. A rising partial eclipse greeted the defenders of Constantinople in 1453, fulfilling a prophecy in the mind of the superstitious when the city fell to the Ottoman Turks seven days later. And you’d think we’d know better by now, but modern day fears of the ‘Blood Moon‘ seen during an eclipse still swirl around the internet even today. Lunar eclipses even helped mariners get a onetime fix on longitude at sea: Christopher Columbus and Captain James Cook both employed this method.



Credit


The rising partial eclipse as seen from Constantinople on May 22nd 1453. Image credit: Stellarium
All thoughts to ponder as you watch the April 4th total lunar eclipse. This eclipse will be visible for observers across the Pacific, the Asian Far East, Australia and western North America, after which you’ll have one more shot at total lunar eclipse in 2015 on September 28th. The next total lunar eclipse after that won’t be until January 31st 2018, favoring North America.

Welcome to the saros!

Read Dave Dickinson’s eclipse-fueled sci-fi tales Exeligmos and Shadowfall.



About 

David Dickinson is an Earth science teacher, freelance science writer, retired USAF veteran & backyard astronomer. He currently writes and ponders the universe from Tampa Bay, Florida.

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Posted by Nelio Inacio at 12:30 PM 0 comments

Living with a Capricious Star: What Drives the Solar Cycle?

Living with a Capricious Star: What Drives the Solar Cycle?:



Solar energy energizes the drama of life on Earth, such as the bird caught transiting the solar disk as seen here. Image credit and copyright: Roger Hutchinson


Solar energy fuels the drama of life on Earth, such as the bird seen here transiting the solar disk. Image credit and copyright: Roger Hutchinson
You can be thankful that we bask in the glow of a relatively placid star. Currently about halfway along its 10 billion year career on the Main Sequence, our Sun fuses hydrogen into helium in a battle against gravitational collapse. This balancing act produces energy via the proton-proton chain process, which in turn, fuels the drama of life on Earth.

Looking out into the universe, we see stars that are much more brash and impulsive, such as red dwarf upstarts unleashing huge planet-sterilizing flares, and massive stars destined to live fast and die young.

Our Sun gives us the unprecedented chance to study a star up close, and our modern day technological society depends on keeping a close watch on what the Sun might do next. But did you know that some of the key mechanisms powering the solar cycle are still not completely understood?



Image credit: David Dickinson


One of the exceptionally active sunspot groups seen for Cycle #24 in early 2014. Image credit: David Dickinson
One such mystery confronting solar dynamics is exactly what drives the periodicity related to the solar cycle. Follow our star with a backyard telescope over a period of years, and you’ll see sunspots ebb and flow in an 11 year period of activity. The dazzling ‘surface’ of the Sun where these spots are embedded is actually the photosphere, and using a small telescope tuned to hydrogen-alpha wavelengths you can pick up prominences in the warmer chromosphere above.

This cycle is actually is 22 years in length (that’s 11 years times two), as the Sun flips polarity each time. A hallmark of the start of each solar cycle is the appearance of sunspots at high solar latitudes, which then move closer to the solar equator as the cycle progresses. You can actually chart this distribution in a butterfly diagram known as a Spörer chart, and this pattern was first recognized by Gustav Spörer in the late 19th century and is known as Spörer’s Law.



Sunspot_butterfly_graph


The ‘Butterfly diagram’ of sunspot distribution by latitude over previous solar cycles. Image credit: NASA/Marshall Spaceflight Center
We’re currently in the midst of solar cycle #24, and the measurement of solar cycles dates all the way back to 1755. Galileo observed sunspots via projection (the tale that he went blind observing the Sun in apocryphal). We also have Chinese records going back to 364 BC, though historical records of sunspot activity are, well, spotty at best. The infamous Maunder Minimum occurred from 1645 to 1717 just as the age of telescopic astronomy was gaining steam. This dearth of sunspot activity actually led to the idea that sunspots were a mythical creation by astronomers of the time.

But sunspots are a true reality. Spots can grow larger than the Earth, such as sunspot active region 2192, which appeared just before a partial solar eclipse in 2014 and could be seen with the unaided (protected) eye. The Sun is actually a big ball of gas, and the equatorial regions rotate once every 25 days, 9 days faster than the rotational period near the poles. And speaking of which, it is not fully understood why we never see sunspots at the solar poles, which are tipped 7.25 degrees relative to the ecliptic.



Other solar mysteries persist. One amazing fact about our Sun is the true age of the sunlight shining in our living room window. Though it raced from the convective zone and through the photosphere of the Sun at 300,000 km per second and only took 8 minutes to get to your sunbeam-loving cat here on Earth, it took an estimated 10,000 to 170,000 years to escape the solar core where fusion is taking place. This is due to the terrific density at the Sun’s center, over seven times that of gold.

Another amazing fact is that we can actually model the happenings on the farside of the Sun utilizing a new fangled method known as helioseismology.

Another key mystery is why the current solar cycle is so weak… it has even been proposed that solar cycle 25 and 26 might be absent all together. Are there larger solar cycles waiting discovery? Again, we haven’t been watching the Sun close enough for long enough to truly ferret these ‘Grand Cycles’ out.



Solar cycle


The sunspot number predicted for the current Cycle #24 versus reality. Image credit: NASA
Are sunspot numbers telling us the whole picture? Sunspot numbers are calculated using formula that includes a visual count of sunspot groups and the individual sunspots in them that are currently facing Earthward, and has long served as the gold standard to gauge solar activity. Research conducted by the University of Michigan in Ann Arbor in 2013 has suggested that the orientation of the heliospheric current sheet might actually provide a better picture as to the goings on of the Sun.

Another major mystery is why the Sun has this 22/11 year cycle of activity in the first place. The differential rotation of the solar interior and convective zone known as the solar tachocline drives the powerful solar dynamo.  But why the activity cycle is the exact length that it is is still anyone’s guess. Perhaps the fossil field of the Sun was simply ‘frozen’ in the current cycle as we see it today.

There are ideas out there that Jupiter drives the solar cycle. A 2012 paper suggested just that. It’s an enticing theory for sure, as Jupiter orbits the Sun once every 11.9 years.



The motion of the solar barycenter through the last half of the 20th century. Image credit: Carl Smith/Wikimedia Commons


The motion of the solar barycenter through the last half of the 20th century. Image credit: Carl Smith/Wikimedia Commons
And a recent paper has even proposed that Uranus and Neptune might drive much longer cycles…

Color us skeptical on these ideas. Although Jupiter accounts for over 70% of the planetary mass in the solar system, it’s 1/1000th as massive as the Sun. The barycenter of Jupiter versus the Sun sits 36,000 kilometres above the solar surface, tugging the Sun at a rate of 12.4 metres per second.



Rigs to view the Sun in both hydrogen-alpha and visible light. Credit: David Dickinson


Rigs to view the Sun in both hydrogen-alpha and visible light. Credit: David Dickinson
I suspect this is a case of coincidence: the solar system provides lots of orbital periods of varying lengths, offering up lots of chances for possible mutual occurrences. A similar mathematical curiosity can be seen in Bode’s Law describing the mathematical spacing of the planets, which to date, has no known basis in reality. It appears to be just a neat play on numbers. Roll the cosmic dice long enough, and coincidences will occur. A good test for both ideas would be the discovery of similar relationships in other planetary systems. We can currently detect both starspots and large exoplanets: is there a similar link between stellar activity and exoplanet orbits? Demonstrate it dozens of times over, and a theory could become law.

That’s science, baby.



About 

David Dickinson is an Earth science teacher, freelance science writer, retired USAF veteran & backyard astronomer. He currently writes and ponders the universe from Tampa Bay, Florida.

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Posted by Nelio Inacio at 12:29 PM 0 comments

Naked Eye Nova Sagittarii 2015 No 2

Naked Eye Nova Sagittarii 2015 No 2: APOD: 2015 March 25 - Naked Eye Nova Sagittarii 2015 No 2


Discover the cosmos! Each day a different image or photograph of our fascinating universe is featured, along with a brief explanation written by a professional astronomer.

2015 March 25


See Explanation. Clicking on the picture will download the highest resolution version available.
Explanation: It quickly went from obscurity to one of the brighter stars in Sagittarius -- but it's fading. Named Nova Sagittarii 2015 No. 2, the stellar explosion is the brightest nova visible from Earth in over a year. The featured image was captured four days ago from Ranikhet in the Indian Himalayas. Several stars in western Sagittarius make an asterism known as the Teapot, and the nova, indicated by the arrow, now appears like a new emblem on the side of the pot. As of last night, Nova Sag has faded from brighter than visual magnitude 5 to the edge of unaided visibility. Even so, the nova should still be easily findable with binoculars in dark skies before sunrise over the next week.

Posted by Nelio Inacio at 12:26 PM 0 comments

Orion Spring

Orion Spring: APOD: 2015 March 26 - Orion Spring


Discover the cosmos! Each day a different image or photograph of our fascinating universe is featured, along with a brief explanation written by a professional astronomer.

2015 March 26


See Explanation. Clicking on the picture will download the highest resolution version available.
Explanation: As spring comes to planet Earth's northern hemisphere, familiar winter constellation Orion sets in early evening skies and budding trees frame the Hunter's stars. The yellowish hue of cool red supergiant Alpha Orionis, the great star Betelgeuse, mingles with the branches at the top of this colorful skyscape. Orion's alpha star is joined on the far right by Alpha Tauri. Also known as Aldebaran and also a giant star cooler than the Sun, it shines with a yellow light at the head of Taurus, the Bull. Contrasting blue supergiant Rigel, Beta Orionis, is Orion's other dominant star though, and marks the Hunter's foot below center. Of course, the sword of Orion hangs from the Hunter's three blue belt stars near picture center, but the middle star in the sword is not a star at all. A slightly fuzzy pinkish glow hints at its true nature, a nearby stellar nursery visible to the unaided eye known as the Orion Nebula.

Posted by Nelio Inacio at 12:26 PM 0 comments
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