Astronomy Archives

March 13, 2009December 24, 2015 by Fraser Cain

Shield Volcanoes

Color mosaic of Mars' greatest mountain, Olympus Mons, viewed from orbit. Credit NASA/JPL

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Shield volcanoes are large volcanoes with gently sloping sides. In fact, the largest volcanoes on Earth (and even the Solar System) are shield volcanoes. They form when lava flows of low viscosity build up over long periods of time, creating volcanoes with huge internal volume. The best known shield volcanoes are ones that make up the Big Island of Hawaii: Mauna Loa and Mauna Kea.

The common feature with shield volcanoes is that they’re built up slowly over time from a very stable central summit vent. Flow after flow pours out of the vent, slides down the slopes of the volcano, and builds up the size. The largest volcanoes, like Mauna Loa and Mauna Kea would have been created from thousands of these flows.

Shield volcanoes can be found around the world. In northern California and Oregon, they can be 5-10 km across and about 500 meters high. But in the Hawaiian Islands, the volcanoes were atop very active vents for millions of years. Mauna Loa projects 4,168 meters above sea level, but if you measure it from the base of the ocean to its top, it measures 8,534 meters. (Mount Everest is 8,848 meters tall).

Volcanic activity is linked to plate tectonics, and the most of the world’s volcanoes are located near plate boundaries where subduction is happening. This is where one plate is passing under another plate, sinking into the Earth’s mantle.

The largest shield volcano in the Solar System is Olympus Mons on Mars. This monster measures 27 km above the surface of Mars, and is 550 km in width. It’s believed that Olympus Mons got so big because Mars lacks plate tectonics. A single volcanic hotspot was able to channel lava for billions of years, building up the volcano to such a great size.

We have written many articles about the Earth for Universe Today. Here’s an article about Olympus Mons, and here’s an article about Mauna Kea and Mauna Loa.

Want more resources on the Earth? Here’s a link to NASA’s Human Spaceflight page, and here’s NASA’s Visible Earth.

We have also recorded an episode of Astronomy Cast about Earth, as part of our tour through the Solar System – Episode 51: Earth.

March 13, 2009December 24, 2015 by Tammy Plotner

Weekend SkyWatcher’s Forecast – March 13-15, 2009

Greetings, fellow SkyWatchers! With the Moon gone from the early evening skies, it’s time for a little sky dancing this weekend. Are you ready for a little old stepping out and a little new? Then waltz this way as we check out some very new star clusters and interesting asterisms! Grab your binoculars and telescopes and I’ll meet you in the back yard….

Friday, March 13, 2009 – Today note the 1886 birth of Albert William Stevens, a daring balloonist who took the Explorer II to an altitude of 72,395 feet. He took the first photo showing Earth’s curvature and the first solar eclipse photo of the Moon’s shadow on Earth. Also, salute the 1855 birth on this date of Percival Lowell, who predicted the existence of Pluto (but Clyde Tombaugh was the one who actually discovered it, on Lowell’s 75th birthday!). Sir Percival was a determined soul who spent his life trying to find proof of life on Mars. He founded Lowell Observatory in 1894, where he studied Mars intensively, drawing the Red Planet covered with canals and oases. As Lowell once said: ‘‘Imagination is as vital to any advance in science as learning and precision are essential for starting points.’’

Tonight we’ll look at a bright collection of stars located less than a handspan west of Procyon. Its name is Collinder 106 (RA 06 37 19 Dec -05 57 55). At a combined magnitude of 4.5, this expansive open cluster can be spotted as a hazy patch with the unaided eye and comes to full resolution with binoculars. It contains only around 14 members, but this widely scattered galactic collection has helped scientists determine size scales and dispersion among groups of its type. Viewed telescopically at low power, the observer will find it rich in background stars and a true delight in a low power, wide field eyepiece. If you’d like a challenge, hop a half degree to the northeast to spot Collinder 111 (RA 06 38 42 Dec -06 54 00). While visually only about one-tenth the apparent size of its larger southwestern neighbor, spare little Collinder 111 also belongs to the same class of open clusters. Who knows what may lurk around these understudied clusters?

Saturday, March 14, 2009 – Before dawn, look for the close appearance of Spica and the Moon to celebrate today’s famous astro births, starting with astronaut Frank Borman (b. 1928), a crew member of Apollo 8, the first manned flight around the Moon. Next, astronaut Eugene Cernan (b. 1934), who floated in space for more than 2 hours during the Gemini 9 mission and piloted Apollo 10. How about Giovanni Schiaparelli (1835), the Italian astronomer who described Mars’s ‘‘canali’’ and named its ‘‘seas’’ and ‘‘continents.’’ Schiaparelli’s comet studies demonstrated that meteoroid swarms existed in the path of cometary orbits, and thus predicted annual meteor showers. He was first to suggest that Mercury and Venus rotate and discovered the asteroid Hesperia. Still not enough? Then wish a happy birthday to Albert Einstein (b.1879), the German–American physicist considered the most brilliant intellect in human history!

For a moment let’s reflect on Einstein’s Cross, proof of his genius. We can’t observe this Pegasus-based gravitational lens right now, but we can try to understand Einstein’s theory of gravity as an effect of the curvature in space–time. For example, if you draw a line around the center of a ball, the line would be straight, eventually coming back to its point of origin. We don’t see the point until we reach it, but we know it’s there. Einstein knew this dimension existed and predicted any object with mass will bend space and time around it, just like our line around the ball. He predicted light would also follow a curved path around an object… such as a distant quasar located behind a closer galaxy!

Tonight’s object is a ‘‘cross’’ astersim of stars. Begin at Procyon and shift about 10 degrees southwest (or 2 degrees south of 18 Monocerotis) to locate this pretty grouping of stars. Yes it’s true. It’s just an unknown, undocumented, and unnamed asterism, but how fitting to honor all these famous astro figures and a brilliant man who once said: ‘‘The fairest thing in life we can experience is the mysterious. It… stands at the cradle of true art and true science.’’

Now let’s go for a a challenging study. Larger telescopes should look for diminutive Bochum 2 less than half a degree northeast of ‘‘Einstein’s Asterism’’ (RA 06 48 50 Dec 00 22 35). At low power, it’s just a tight configuration of stars, but test the limit your telescope and increase magnification. This young open cluster has been studied for internal kinematics, spectroscopic binaries, and its motion in the galaxy, but its most interesting feature is a trapezium system at its heart. After a 4-year study, two of the members were documented as close binary stars with highly eccentric orbits, and one of the members is leaving as a runaway!

For smaller optics, continue another half degree east for NGC 2301 (RA 06 51 48 Dec -00 28 00). Even telescopes as small as Lacaille’s can see this bright, 2,500 light-year-distant open cluster. Studied for its variable stars, NGC 2301 is also on many binocular deep-sky observing lists!

Sunday, March 15, 2009 – Today marks the 1713 birth of Abbe Nicolas Louis de Lacaille, the French astronomer who named 15 of the 88 constellations. Using only a half-inch refractor, Lacaille made 26 new discoveries and charted 9,776 stars, creating the first southern star catalog. Sharing the date is William Rutter Dawes (b. 1799). ‘‘Eagle-eyed’’ Dawes made exhaustive measurements of binary stars, discovered Saturn’s inner Crepe Ring, and accurately mapped Mars. Dawes also devised the elegantly simple formula (Dawe’s Limit) of dividing the number 11 by the aperture in centimeters to give the arcseconds of resolution required to split a binary star.

Thankfully, somebody was watching the sky at 5:30 p.m. on this date in 1806, because the observed fall of a pristine 6-kilogram chondrite meteor made an indisputable case that chondrites carried carbon-based organic chemicals. Perhaps it was from one of the Corona Australid meteors whose shower peak is tonight after midnight? The fall rate is about 5–7 per hour, and best for our friends in the southern hemisphere!

Tonight let’s return to the Einstein’s Asterism and drop 15 degrees due southeast to study open cluster NGC 2360 (RA 07 17 42 Dec -15 38 00). At a distance of 4,600 light-years, magnificent NGC 2360 contains around 40 members, 7 of which are red giants. You have Caroline Herschel to thank for this lovely cluster… and her birthday is tomorrow!

Now, return to our Einstein’s Asterism and head slightly more than half a degree west to study scattered open cluster Dolidze 25 (RA 06 45 06 Dec -00 18 00). This low power, telescopic only, galactic cluster is a worthy study for those who seek the unusual. Located at the outer edges of our own galaxy, Dolidze 25 may very well be the product of the merger of the Milky Way and the Canis Major Dwarf galaxy. Extremely rich in oxygen and significantly deficient in metals, this huge starforming region contains young stars, pre-main sequence stars, and Delta Scuti types. With its thin veil of nebula, Do25 should prove to be challenging and quite to your liking! Hop another half degree west, and then slightly south for Dolidze 23 (RA 06 43 12 Dec -00 00 00). This telescope-only cluster reveals around a dozen easily resolvable stars at low power. Dolidze 23’s two brighter members are finderscope visible. Locate the cluster at low power, and place it at the south edge of the field of view. Turn off your drive units and allow the field to cruise by naturally as you observe. This allows Dolidze 25 to drift across your line of sight, a technique that often improves your ability to spot fine detail in fainter objects.

Celestial scenery alert on Tuesday, March 17! A few hours before dawn, the Moon and mighty Antares will be nearly touching, separated by only a fraction (0.2) of a degree. For some, this could be a wonderful occultation event, so be sure to check maps and resources! Although the occultation path is limited, even more so is the graze path, just a few kilometers wide. For these lucky viewers, brilliant red Antares may flash in and out of view several times as it moves slowly along behind the lunar mountains.

Until next week, dreams really do come true when you keep on reaching for the stars!

This week’s awesome photos are: Sir Percival Lowell (historical image), Collinder 106 (credit – Palomar Observatory, courtesy of Caltech), Einstein’s Cross (credit – HST/NASA), “Einstein’s Asterism’’ (Credit – Palomar Observatory, courtesy of Caltech), Bochum 2, NGC 2301, Dolidize 25 and NGC 2360 (credit – Palomar Observatory, courtesy of Caltech). Thank you so much!

March 12, 2009October 21, 2016 by Fraser Cain

What is Earth’s Magnetic Field?

You can’t see it, but there’s an invisible force field around the Earth. Okay, not a force field, exactly, but a gigantic magnetic field surrounding the Earth, and it acts like a force field, protecting the planet – and all the life – from space radiation. Let’s take a look at the Earth’s magnetic field.

The Earth is like a great big magnet. The north pole of the magnet is near the top of the planet, near the geographic north pole, and the south pole is near the geographic south pole. Magnetic field lines extend from these poles for tens of thousands of kilometers into space; this is the Earth’s magneto sphere.

The geographic poles and the magnetic poles are far enough apart that scientists distinguish them differently. If you could draw a line between the magnetic north and south poles, you would get a magnetic axis that’s tilted 11.3 degrees away from the Earth’s axis of rotation. And these magnetic poles are known to move around the surface, wandering as much as 15 km every year.

Scientists think that the Earth’s magnetic field is generated by electrical currents flowing in the liquid outer core deep inside the Earth. Although it’s liquid metal, it moves around through a process called convection. And the movements of metal in the core sets up the currents and magnetic field.

As I mentioned at the top of this article, the magnetic field of the Earth protects the planet from space radiation. The biggest culprit is the Sun’s solar wind. These are highly charged particles blasted out from the Sun like a steady wind. The Earth’s magnetosphere channels the solar wind around the planet, so that it doesn’t impact us. Without the magnetic field, the solar wind would strip away our atmosphere – this is what probably happened to Mars. The Sun also releases enormous amounts of energy and material in coronal mass ejections. These CMEs send a hail of radioactive particles into space. Once again, the Earth’s magnetic field protects us, channeling the particles away from the planet, and sparing us from getting irradiated.

The Earth’s magnetic field reverses itself every 250,000 years or so. The north magnetic pole becomes the south pole, and vice versa. Scientists have no clear theory about why the reversals happen. One interesting note is that we’re long overdue for a reversal. The last one happened about 780,000 years ago.

We have written many articles about Earth for Universe Today. Here’s an article about how the geomagnetic reversal doesn’t mean doomsday in 2012, and here’s an article about how a solar storm compressed the Earth’s atmosphere.

Want more resources on the Earth? Here’s a link to NASA’s Human Spaceflight page, and here’s NASA’s Visible Earth.

We have also recorded an episode of Astronomy Cast about Earth, as part of our tour through the Solar System – Episode 51: Earth.

Reference:
NASA: Is the Earth’s magnetic field changing?

March 12, 2009December 24, 2015 by Anne Minard

Stars at Milky Way Core ‘Exhale’ Carbon, Oxygen

Carbon exists only in a fine-tuned universe( 'Cat's Eye' Planetary Nebula) — Cat's Eye Nebula. Researchers have found carbon and oxygen in dusty planetary nebulae surrounding stars at the center of the Milky Way. Credit: NASA/JPL-Caltech/J. Hora (Harvard-Smithsonian CfA

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Carbon and oxygen have been spotted in the dust around stars in the center of the Milky Way galaxy, suggesting that the stars have undergone recent disruptions of some kind — and hinting how stars can send heavy elements — like oxygen, carbon, and iron — out across the universe, paving the way for life.

Scientists have long expected to find carbon-rich stars in our galaxy because we know that significant quantities of carbon must be created in many such stars. But carbon had not previously shown up in the clouds of gas around these stars, said Matthew Bobrowsky, an astrophysicist at the University of Maryland and a co-author of a new study reporting the discovery.

“Based on our findings, this is because medium-sized stars rich in carbon sometimes keep that carbon hidden until very near the end of their stellar lives, releasing it only with their final ‘exhalations’,” explained Bobrowsky.

The new results appear in the February issue of the journal Astronomy and Astrophysics.

Bobrowsky and his team, led by J. V. Perea-Calderón at the European Space Astronomy Centre in Madrid, Spain, used the Spitzer Space Telescope to view each star and its surrounding clouds of dust and particles, called a planetary nebulae. The researchers measured the light emitted by the stars and the surrounding dust and were able to identify carbon compounds based on the wavelengths of light emitted by the stars. Looking in an area at the center of the Milky Way called the “Galactic Bulge,” the team observed 26 stars and their planetary nebulae and found 21 with carbon “signatures.”

But the scientists did not just find carbon around these stars; they also found oxygen in these 21 dust clouds, revealing a surprising mixture of ingredients for space dust. They report in their paper that this is likely due to a thermal pulse where a wave of high-pressure gas mixes layers of elements like carbon and oxygen and spews them out into the surrounding cloud.

The finding of carbon and oxygen in the dust clouds surrounding stars suggests a recent change of chemistry in this population of stars, according to the authors.

“Stars in the center of the Milky Way are old and ‘metal-rich’ with a high abundance of heavy elements,” Bobrowsky said. “They are different in chemical composition than those found in the disc, farther out from the center.”

Studying the chemistry of the stars helps scientists learn how the matter that makes up our earth and other planets in our galaxy left its stellar birthplaces long ago.

As a star burns hotter and hotter, the hydrogen gas that originally made up almost all of its mass is converted, through nuclear fusion, first to helium, and then to progressively heavier elements. The hottest region in the core fuses together the heaviest elements. And these can reach the surface of the star only when its life is almost over.

“The Big Bang produced only hydrogen and helium,” Bobrowsky said. “Heavier elements like carbon and oxygen only come from getting ‘cooked up’ in stars. Nuclear reactions in stars created the heavier elements found in ‘life as we know it’.”

In the last 50,000 years of their 10 billion-year lives, sun-sized stars expel carbon atoms along with hydrogen and helium to form a surrounding cloud of gas that soon disperses into space, perhaps to eventually become the stuff of new stars, solar systems, or perhaps even life on some earth-like planet. Much larger stars expel their heavier matter in massive explosions called supernovae.

“All the heavy elements [which astronomers call ‘metals,’ and include all elements heavier than hydrogen and helium] on Earth were created by nuclear fusion reactions in previous generations of stars,” said Bobrowsky. “Those earlier stars expelled those elements into space and then our solar system formed out of that gas containing all the heavy elements that we now find in Earth and in life on Earth.”

LEAD IMAGE CAPTION: Cat’s Eye Nebula. Researchers have found carbon and oxygen in dusty planetary nebulae surrounding stars at the center of the Milky Way. Credit: NASA/JPL-Caltech/J. Hora (Harvard-Smithsonian CfA)

Source: Astronomy & Astrophysics and Spitzer, via AAS

March 12, 2009December 24, 2015 by Fraser Cain

Earth, Sun and Moon

From our perspective, the three objects that have the greatest impact on our lives are the Earth, Sun, and Moon. The Earth, of course, is the planet beneath our feet. Without it, well, we wouldn’t have anything at all. The Sun warms our planet, and with the Moon, creates the tides.

The Moon orbits the Earth and in turn, the Earth orbits the Sun. We see the Universe from a platform that is both rotating on its axis, and traveling in an elliptical orbit around the Sun. The Earth’s rotation on its axis makes the Sun rise in the east and set in the west, and is a big part of why the Moon rises and sets too; although the Moon takes 29 days to complete an orbit around the Earth as well.

The average distance from the Earth to the Moon is 384,403 km. And the average distance from the Earth to the Sun is 149,597,887 km. If you divide these two numbers, you get approximately 389. Now, if you divide the diameter of the Sun (1.4 million km) by the diameter of the Moon (3,474 km), you get 403. Those two numbers are pretty close. This is why the Moon and the Sun appear to be the same size in the sky; it’s a total coincidence.

Because they appear to be the same size in the sky, the Sun, Earth and Moon work together to create eclipses. When the Moon is directly in between the Earth and Sun, we see a solar eclipse. The Moon appears to pass in front of the Sun and darken it completely. And in the opposite situation, when the Earth is in between the Sun and the Moon, the Earth’s shadow darkens the Moon. This is a lunar eclipse. We don’t see eclipses every month because the Moon’s orbit it tilted slightly away from the Earth’s orbit around the Sun. Sometimes the Moon is above this orbit and sometimes it’s below, so it doesn’t block the light from the Sun, or get caught in the Earth’s shadow.

The Sun and the Moon work together to create the tides we experience here on Earth. Most of the rise of the tides comes from the gravitational pull of the Moon, but a small amount comes from the Sun. When the two objects are on the same side of the Earth, we get the highest and lowest tides, and when they’re on opposite sides of the Earth, the tides are less extreme.

The brightest object in the Sky is the Sun. Astronomers measure its apparent magnitude as -26.73. This makes it 449,000 times brighter than the full Moon. The brightness of the Moon is only -12.6. Of course all of the Moon’s brightness is just reflected light from the Sun.

We have written many articles about the Earth for Universe Today. Here’s a more detailed article about the Sun and the Moon.

Want more resources on the Earth? Here’s a link to NASA’s Human Spaceflight page, and here’s NASA’s Visible Earth.

We have also recorded an episode of Astronomy Cast about Earth, as part of our tour through the Solar System – Episode 51: Earth.

Reference:
NASA Earth Observatory

March 11, 2009December 24, 2015 by Fraser Cain

Who Discovered the Earth?

Earth as seen from the ISS. Credit: NASA

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When I was first asked this question, “who discovered the Earth”, I thought it was ridiculous. If you use your eyes and look down beneath your feet, you’d be able to discover the Earth. This was how the first humans would have done it hundreds of thousands of years ago. But maybe a better question is: who discovered that the Earth is a planet?

In ancient times, people thought the Earth was the center of the Universe, and that the Sun, Moon, planets and stars rotated around us. Although some thought the Earth was flat, the ancient Greeks, like Plato, were convinced that the Earth was a sphere. They thought that each of the worlds and stars were in crystal spheres surrounding us.

This idea is natural and intuitive. Anyone who stands outside and looks up can clearly see that the stars and the planets are turning around the Earth. But ancients astronomers who studied the heavens found a few problems. Instead of following a straight path in the sky, some of the planets would appear to stop, move backwards, stop again, and then move forwards. To explain this, the Greek astronomer Ptolemy said that the planets were in tiny spheres and made little circles as they orbited around the Earth.

It wasn’t until the 16th century that the Polish mathematician and astronomer Nicolaus Copernicus presented the heliocentric model of the Solar System, where the Earth and the other planets orbited around the Sun. His model of the Solar System was backed up by observations by Galileo, who saw that Jupiter had moons of its own, and that Venus went through phases like the Moon.

It took a few years for the ideas to catch on, and for the scientific establishment to agree that yes, the Earth is just another planet, orbiting the Sun, and it’s not the center of the Universe.

We have written many articles about the Earth for Universe Today. Here’s an article about a new telescope that will let you see what Galileo saw.

Want more resources on the Earth? Here’s a link to NASA’s Human Spaceflight page, and here’s NASA’s Visible Earth.

We have also recorded an episode of Astronomy Cast about Earth, as part of our tour through the Solar System – Episode 51: Earth.

Reference:
NASA Earth Observatory: Planetary Motion

March 11, 2009December 24, 2015 by Nancy Atkinson

Top Ten Gamma Ray Sources from the Fermi Telescope

This view from NASA's Fermi Gamma-ray Space Telescope is the deepest and best-resolved portrait of the gamma-ray sky to date. The image shows how the sky appears at energies more than 150 million times greater than that of visible light. Among the signatures of bright pulsars and active galaxies is something familiar -- a faint path traced by the sun. Credit: NASA/DOE/Fermi LAT Collaboration

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The Fermi Telescope is seeing a Universe ablaze with Gamma Rays! A new map combining nearly three months of data from the Fermi Gamma-ray Space Telescope is giving astronomers an unprecedented look at the high-energy cosmos.

“Fermi has given us a deeper and better-resolved view of the gamma-ray sky than any previous space mission,” said Peter Michelson, the lead scientist for the spacecraft’s Large Area Telescope (LAT) at Stanford University. “We’re watching flares from supermassive black holes in distant galaxies and seeing pulsars, high-mass binary systems, and even a globular cluster in our own.”

The sources of these gamma rays come from within our solar system to galaxies billions of light-years away. To show the variety of the objects the LAT is seeing, the Fermi team created a “top ten” list comprising five sources within the Milky Way and five beyond our galaxy.

The top five sources within our galaxy are:

The Sun. Now near the minimum of its activity cycle, the sun would not be a particularly notable source except for one thing: It’s the only one that moves across the sky. The sun’s annual motion against the background sky is a reflection of Earth’s orbit around the sun.

“The gamma rays Fermi now sees from the sun actually come from high-speed particles colliding with the sun’s gas and light,” Thompson notes. “The sun is only a gamma-ray source when there’s a solar flare.” During the next few years, as solar activity increases, scientists expect the sun to produce growing numbers of high-energy flares, and no other instrument will be able to observe them in the LAT’s energy range.

LSI +61 303. This is a high-mass X-ray binary located 6,500 light-years away in Cassiopeia. This unusual system contains a hot B-type star and a neutron star and produces radio outbursts that recur every 26.5 days. Astronomers cannot yet account for the energy that powers these emissions.

PSR J1836+5925. This is a pulsar — a type of spinning neutron star that emits beams of radiation — located in the constellation Draco. It’s one of the new breed of pulsars discovered by Fermi that pulse only in gamma rays.

47 Tucanae. Also known as NGC 104, this is a sphere of ancient stars called a globular cluster. It lies 15,000 light-years away in the southern constellation Tucana.

The Large Area Telescope (LAT) on Fermi detects gamma-rays through matter (electrons) and antimatter (positrons) they produce after striking layers of tungsten. Credit: NASA/Goddard Space Flight Center Conceptual Image Lab

Click here to view an animation of the LAT

Unidentified. More than 30 of the brightest gamma-ray sources Fermi sees have no obvious counterparts at other wavelengths. This one, designated 0FGL J1813.5-1248, was not seen by previous missions, and Fermi’s LAT sees it as variable. The source lies near the plane of the Milky Way in the constellation Serpens Cauda. As a result, it’s likely within our galaxy — but right now, astronomers don’t know much more than that.

The top five sources beyond our galaxy are:

NGC 1275. Also known as Perseus A, this galaxy at the heart of the Perseus Galaxy Cluster is known for its intense radio emissions. It lies 233 million light-years away.

Hubble Space Telescope image of a blazar galaxy. Credit: NASA

3C 454.3. This is a type of active galaxy called a “blazar.” Like many active galaxies, a blazar emits oppositely directed jets of particles traveling near the speed of light as matter falls into a central supermassive black hole. For blazars, the galaxy happens to be oriented so that one jet is aimed right at us. Over the time period represented in this image, 3C 454.3 was the brightest blazar in the gamma-ray sky. It flares and fades, but for Fermi it’s never out of sight. The galaxy lies 7.2 billion light-years away in the constellation Pegasus.

PKS 1502+106. This blazar is located 10.1 billion light-years away in the constellation Boötes. It appeared suddenly, briefly outshone 3C 454.3, and then faded away.

PKS 0727-115. This object’s location in the plane of the Milky Way would lead one to expect that it’s a member of our galaxy, but it isn’t. Astronomers believe this source is a type of active galaxy called a quasar. It’s located 9.6 billion light-years away in the constellation Puppis.

Unidentified. This source, located in the southern constellation Columba, is designated 0FGL J0614.3-3330 and probably lies outside the Milky Way. “It was seen by the EGRET instrument on NASA’s earlier Compton Gamma Ray Observatory, which operated throughout the 1990s, but the nature of this source remains a mystery,” Thompson says.

The LAT scans the entire sky every three hours when operating in survey mode, which is occupying most of the telescope’s observing time during Fermi’s first year of operations. These snapshots let scientists monitor rapidly changing sources.

The all-sky image released today shows us how the cosmos would look if our eyes could detect radiation 150 million times more energetic than visible light. The view merges LAT observations spanning 87 days, from August 4 to October 30, 2008.

Source: NASA

March 10, 2009December 24, 2015 by Fraser Cain

Earth’s Interior

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Take a look down beneath your feet. You’re standing on the Earth’s crust. Although it seems limitless, the Earth’s crust only accounts for less than 1% of the Earth’s interior. Let’s take a look at everything that’s inside the Earth.

The Earth’s crust is the outer shell of the Earth. This is the part that has cooled down enough to solidify into rock. The crust extends down 30 km to 80 km underneath the continents, and only 5 km beneath the oceans. As you travel down through the crust, temperatures increase. The crust is broken up into several tectonic plates which “float” on top of the Earth’s mantle. In some regions, plates are sliding underneath one another, recycling rocks into the Earth. The crust beneath the middle of the oceans is spreading apart, and new material is welling up.

Beneath the crust is the largest part of the Earth’s interior: the mantle, which makes up about 84% of the Earth’s volume. This region extends down to a depth of 2,890 km. As you travel down through the mantle, temperatures increase immensely; they start at 500 C near the crust, and get to well over 4000 C at the boundary to the core. The mantle is mostly solid, but it acts like a viscous fluid, and experiences convection. Hot blobs of rock rise up from regions around the core through the mantle, give up their heat, and then sink back down.

At the very center of the Earth lies the core. This is a solid sphere of metal 2,440 km across surrounded by a layer of liquid metal. Scientists think that mostly made of iron (80%), with the rest composed of other heavy metals, like nickel, gold, platinum and even uranium. The core is slowly rotating compared to the crust, so that the core completes one rotation every 1000 years or so. The Earth’s magnetic field is though to be generated by the convection of hot metal in the Earth’s outer core. This field protects the Earth from the Sun’s solar wind; there probably wouldn’t be life on Earth without this field.

We have written many articles about the Earth for Universe Today. Here’s an article about the discovery of the Earth’s inner, inner core.

Want more resources on the Earth? Here’s a link to NASA’s Human Spaceflight page, and here’s NASA’s Visible Earth.

We have also recorded an episode of Astronomy Cast about Earth, as part of our tour through the Solar System – Episode 51: Earth.

Sources:
http://www.portal.gsi.gov.in/portal/page?_pageid=127,687643&_dad=portal&_schema=PORTAL
http://en.wikipedia.org/wiki/Mantle_%28geology%29
http://www.windows2universe.org/earth/Interior_Structure/interior.html

March 10, 2009May 4, 2017 by Fraser Cain

Why is the Earth Round?

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Don’t listen to the Flat Earth Society, they’re wrong; the Earth is round. But did you ever wonder why the Earth is round? It all comes down to gravity.

One of the effects of mass is that it attracts other mass. For small objects, like your computer, your car, and even a building, the force of gravity is tiny. But when you have millions, and even trillions of tonnes of mass, the effect of the gravity really builds up. All of the mass pulls on all the other mass, and it tries to create the most efficient shape… a sphere.

For smaller objects, like asteroids, the force of gravity trying to pull the object into a sphere isn’t enough to overcome the strength of the rock keeping it in shape. But once you get above a certain mass and size, the strength of the object can’t stop the force of gravity from pulling it into a sphere. Objects larger than about 1,000 km in size are able to pull themselves into a sphere.

In fact, the International Astronomical Union decided in 2006 that this ability was one of the requirements for an object to be considered a planet. They must orbit the Sun, they need to have cleared out all the smaller objects in their orbit, and they need to have enough gravity to pull themselves into a sphere.

When an object has the gravity to pull itself into a sphere, astronomers say that it’s in hydrostatic equilibrium. And that’s why the Earth is round.

Of course, the Earth isn’t perfectly round. Because it’s turning on its axis approximately once every 24 hours, the Earth’s equator bulges outwards. And there are mountains and valleys that make the Earth’s surface rough.

We have written many articles about the Earth for Universe Today. Here’s an article about how round the Earth really is.

Want more resources on the Earth? Here’s a link to NASA’s Human Spaceflight page, and here’s NASA’s Visible Earth.

We have also recorded an episode of Astronomy Cast about Earth, answering a few questions, like why is Earth round. This was part of our tour through the Solar System – Episode 51: Earth.

March 10, 2009December 24, 2015 by Jerry Coffey

Density of the Earth

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The density of the Earth is 5.513 g/cm³. This is an average of all of the material on the planet. Water is much less dense than iron, hence an average is needed for ease of use. Earth is the most dense planet in the Solar System; however, if gravitational compression where factored out, the second most dense planet, Mercury, would be more dense. The density of Earth is calculated by dividing the planet’s mass by its volume, then simplifying from kg/km to g/cm cubed.

Here is the density of the other planets in our Solar System so you can compare to Earth’s.

Mercury	5.43 g/cm³
Venus	5.243 g/cm³
Mars	3.934 g/cm³
Jupiter	1.326 g/cm³
Saturn	0.687 g/cm³
Uranus	1.270 g/cm³
Neptune	1.638 g/cm³
The Sun	1.408 g/cm³

Just knowing the density of a planet is not much information. It sort of only gives a partial picture. Here are a few more interesting facts about the Earth that may help you understand our planet a little more.

The Moon is thought to have been formed when a large asteroid or a planetesimal impacted Earth. The Moon is the portion that was thrown back into space and the particles that accreted to it. Scientist think that other planets may have obtained some of their moons in a similar manner. The Earth is the only planet with a single Moon, but has two quasi-satellites 3753 Cruithne and 2002 AA₂₉.

The Sun is constantly evolving. In a few billion years it will begin to heat up on its way to the red giant phase of a star’s life. Along the way it will become hot enough to destroy life on Earth. The question will become how will humans survive. Colonizing other celestial objects is one option. Some scientists have developed a theoretical way to move the entire planet. It would require finding an asteroid large enough to perturb Earth’s orbit and push away from the Sun. Colonizing another planet could actually be easier.

Despite a lot of internet hype, there is no credible threat to the Earth that will coincide with the end of the Mayan calendar. The Mayan calender does not even end, 2012 marks the end of the current long-count period. 2013 marks the beginning of another.

The density of Earth is one of thousands of interesting facts that you find about your home planet. Here at Universe Today, we hope that you want to find many more and continue to research the world around you.

We have written many articles about density for Universe Today. Here’s an article about the density of the Sun, and here’s one about the density of Mars.

Want more resources on the Earth? Here’s a link to NASA’s Human Spaceflight page, and here’s NASA’s Visible Earth.

We have also recorded an episode of Astronomy Cast about Earth, as part of our tour through the Solar System – Episode 51: Earth.

Sources:
NASA
Physics Forums