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Why is Earth’s spin axis drifting?
Unlike a plastic globe of Earth, the real planet Earth isn’t perfectly round and doesn’t spin smoothly. The imaginary line around which Earth spins – passing through the North and South Poles – is called its spin axis. Scientists have known for a long time that Earth’s spin axis drifts and wobbles. Measurements over the 20th century show that Earth’s spin axis drifts by about 4 inches (10 cm) per year. Over the course of a century, that’s more than 11 yards (10 meters). This week (September 19, 2018), NASA scientists announced they’ve used observational and model-based data spanning the 20th century in order to identify – for the first time – three processes primarily responsible for this drift.
The three processes are mass loss due to melting ice (mostly in Greenland), the lifting of land masses as glaciers have melted since the last ice age (aka glacial rebound), and the slow creeping motion of rocky material in Earth’s interior mantle, caused by convection currents carrying heat from our planet’s interior to its surface (this third process is called mantle convection).
Scientists call the drift of Earth’s spin-axis its polar motion. Surendra Adhikari of NASA’s Jet Propulsion Laboratory in Pasadena, California is first author on the new paper describing the causes for the drift. He said:
The traditional explanation is that one process, glacial rebound, is responsible for this motion of Earth’s spin axis. But recently, many researchers have speculated that other processes could have potentially large effects on it as well.
We assembled models for a suite of processes that are thought to be important for driving the motion of the spin axis. We identified not one but three sets of processes that are crucial – and melting of the global cryosphere (especially Greenland) over the course of the 20th century is one of them.
His team’s statement said:
In general, the redistribution of mass on and within Earth – like changes to land, ice sheets, oceans and mantle flow – affects the planet’s rotation. As temperatures increased throughout the 20th century, Greenland’s ice mass decreased. In fact, a total of about 7,500 gigatons – the weight of more than 20 million Empire State Buildings – of Greenland’s ice melted into the ocean during this time period. This makes Greenland one of the top contributors of mass being transferred to the oceans, causing sea level to rise and, consequently, a drift in Earth’s spin axis.
While ice melt is occurring in other places (like Antarctica), Greenland’s location makes it a more significant contributor to polar motion.
Full moon falls on September 24, 2018 for us in the Americas, and on September 25 for much of the rest of the world (more about exact times below). It’s the first full moon of autumn for the Northern Hemisphere and first full moon of spring for the Southern Hemisphere. It’s the closest full moon to the September equinox. That makes it the Northern Hemisphere’s Harvest Moon!
No matter where you live worldwide, the moon will appear plenty full to you on both September 24 and 25, lighting up the night from dusk until dawn.
The exact time of full moon comes for all of us at same instant worldwide, but our clocks read differently by time zone.
Although several dozen minor galaxies lie closer to our Milky Way, the Andromeda galaxy is the closest large spiral galaxy to ours. Excluding the Large and Small Magellanic Clouds, which can’t be seen from northerly latitudes, the Andromeda galaxy – also known as M31 – is the brightest galaxy you can see. At 2.5 million light-years, it’s also the most distant thing visible to your unaided eye.
To the eye, this galaxy appears as a smudge of light larger than a full moon.
APPROACHING GREEN COMET EXPLODES: A comet that could become visible to the naked eye in August has exploded in brightness, suddenly increasing its luminosity 16-fold. Whatever happened on Comet PANSTARRS (C/2017 S3) on July 1st has given it an expanding green atmosphere almost twice the size of the planet Jupiter. Visit today's edition of Spaceweather.com for pictures and more information about this approaching comet.
It’s that magical time of year again, when the solar system’s favorite planet – Saturn – is well placed for viewing in our sky. Shining with a distinct golden color, Saturn is a lovely object to view with the eye alone. Binoculars will enhance its color … but to see Saturn’s rings you need a small telescope. And we do mean small. Veteran observer Alan MacRobert at SkyandTelescope.com has written:
The rings of Saturn should be visible in even the smallest telescope at 25x [magnified by 25 times]. A good 3-inch scope at 50x [magnified by 50 times] can show them as a separate structure detached on all sides from the ball of the planet.
Space Weather News for May 25, 2018
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JELLYFISH SPRITES OVER OKLAHOMA: Last night in Oklahoma, a swarm of jellyfish sprites flashed above an intense thunderstorm approaching Oklahoma City. A photographer caught the display at nearly point-blank range, only ~80 miles away, which is unusually close for these forms of upward-directed lightning. Visit today's edition of Spaceweather.com to learn more about jellyfish sprites and why more of them may be in the offing.
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Asteroid 2010 WC9 will safely pass at about half’s the moon’s distance on Tuesday, May 15, 2018. Estimates of its size range from 197 to 427 feet (60-130 meters), making the May 15 pass one of the closest approaches ever observed of an asteroid of this size. This asteroid was “lost” and then found again. The Catalina Sky Survey in Arizona first detected it on November 30, 2010, and astronomers watched it until December 1, when it became too faint to see. They didn’t have enough observations to track its orbit fully and so predict its return. On May 8, 2018 – almost eight years later – astronomers discovered an asteroid and gave it the temporary designation ZJ99C60. Then they realized it was asteroid 2010 WC9, returning.
During the 2018 return, closest approach of asteroid 2010 WC9 will happen on May 15 at 22:05 UTC (6:05 pm EDT; translate to your time). At that time, the asteroid will be 0.53 lunar-distances from Earth (126,419 miles or 203,453 km from Earth). According to orbit calculations made by NASA’s Jet Propulsion Laboratory, the May 15 close approach is the closest of this particular asteroid in nearly 300 years.
Is this a large asteroid? No, not by any absolute measure. But it is larger than the estimated size of the Chelyabinsk meteor, which entered Earth’s atmosphere, breaking windows in six Russian cities and causing some 1,500 people to seek medical attention, in 2013. Estimates of asteroid 2010 WC9’s diameter range from 197 to 427 feet (60-130 meters); estimates of the Chelyabinsk meteor’s size before encountering Earth’s atmosphere center around 65 feet (20 meters).
Asteroid 2010 WC9 is an Apollo type space rock. At no time will it be visible to the eye as it sweeps past Earth. It might get as bright as magnitude +11, which would make it bright enough to be seen in amateur telescopes pointed at the correct location and time.
Asteroid 2010 WC9 is travelling though space at a speed of 28,655 miles per hour (46,116 km/h).
Asteroid 2010 WC9 at Minor Planet Center; at CNEOS
Want to view the asteroid online? Guy Wells at Northolt Branch Observatories in London, England – which specializes in observations of near-Earth asteroids and other small solar system objects – emailed EarthSky on Friday to say:
We are planning to broadcast this asteroid live to our Facebook page on the night of May 14, likely around midnight, if the weather forecast remains positive. The broadcast will be less than 25 minutes in duration, as the asteroid will cross our field of view within that period of time. The asteroid will be moving quite rapidly (30 arcseconds per minute). Our display will update every five seconds. We are of course collecting astrometric data whilst this is happening, but the motion of the asteroid will be apparent every five seconds!
Daniel Bamberger, also at Northolt Branch Observatories, sent along the two images below. He wrote:
We imaged this object twice: First on May 9, when it was still known by its temporary designation ZJ99C60; then again on May 10, after it was identified as asteroid 2010 WC9, which had been a lost asteroid for eight years.
It is still a faint object of 18th magnitude, but it is brightening very rapidly: 2010 WC9 will be brighter than 11th magnitude at closest approach, making it visible in a small telescope!
A magnetosphere is that area of space, around a planet, that is controlled by the planet's magnetic field. The shape of the Earth's magnetosphere is the direct result of being blasted by solar wind. The solar wind compresses its sunward side to a distance of only 6 to 10 times the radius of the Earth. A supersonic shock wave is created sunward of Earth called the Bow Shock. Most of the solar wind particles are heated and slowed at the bow shock and detour around the Earth in the Magnetosheath. The solar wind drags out the night-side magnetosphere to possibly 1000 times Earth's radius; its exact length is not known. This extension of the magnetosphere is known as the Magnetotail. The outer boundary of Earth's confined geomagnetic field is called the Magnetopause. The Earth's magnetosphere is a highly dynamic structure that responds dramatically to solar variations.
Credit: NASA/Goddard/Aaron Kaase
A camera mounted ahead caught this image of Starman, in Elon Musk’s red Tesla Roadster, as car and mannequin left Earth behind. Calculations by astronomers in the days after the launch suggest the payload reached a speed of 20.8 miles per second (33.5 km/sec) after the last burn, a faster speed than expected. Image via SpaceX. Last Tuesday (February 6, 2018), SpaceX’s Falcon Heavy successfully lifted off from Launch Complex 39A at Kennedy Space Center in Florida. Falcon Heavy is now the world’s most powerful operational rocket by a factor of two, providing a heavy-lift capability not seen since the Apollo era in the late 1960s and early ’70s, when mighty Saturn V rockets lifted astronauts to the moon. Falcon Heavy’s launch last Tuesday was a test flight, its maiden voyage, meant to prove the concept of the rocket itself (which is in essence three of SpaceX’s Falcon 9 rockets joined together). It definitely did! But SpaceX founder and CEO Elon Musk, as always, went further. He and his team placed Musk’s 2008 Tesla Roadster at the top of the rocket, with the goal of blasting it into an elliptical orbit between Earth and Mars. The orbit would, at times, bring the car – with its passenger, a mannequin nicknamed Starman, dressed for space – near Mars.
The Falcon Heavy rocket test was a major success and a thrill for space fans. After livestreaming views from StarMan’s vantage point in Earth orbit SpaceX reignited the upper stage’s engine one last time, giving the Tesla a push beyond Earth’s orbit.
Humanity’s farthest and longest-lived spacecraft, Voyager 1 and 2, achieve 40 years of operation and exploration this August and September. Despite their vast distance, they continue to communicate with NASA daily, still probing the final frontier.
Their story has not only impacted generations of current and future scientists and engineers, but also Earth’s culture, including film, art and music. Each spacecraft carries a Golden Record of Earth sounds, pictures and messages. Since the spacecraft could last billions of years, these circular time capsules could one day be the only traces of human civilization.
The Kentucky Handshake Full Moon on June 9, 2017. Taken by VE3UYI
Mars seen by the Viking oriter. Image via NASA/JPL/USGS
By Andrew Coates, UCL
Europe has been trying to land on Mars since 2003, but none of the attempts have gone exactly according to plan. A couple of months ago, the ExoMars Schiaparelli landing demonstrator crashed onto the planet’s surface, losing contact with its mothership. However, the mission was partially successful, providing information that will enable Europe and Russia to land its ExoMars rover on the Red Planet in 2021.
Now European research ministers have finally agreed to give the mission the outstanding €400m it needs to go ahead. A lot is at stake as the rover is poised to uniquely drill under the harsh Martian surface to search for signs of past, or even present, life. With the best of human endeavor, we must learn, try again and not give up. As leader of the international Panoramic Camera team on the rover, which will among other things provide surface geological and atmospheric context for the mission, I am one of many scientists working very hard to make it work. PanCam is one of nine state-of-the-art instruments which will help us analyze subsurface samples.
The reason it is so hard to land on Mars is that the atmospheric pressure is low, less than 1% of Earth’s surface pressure. This means that any probe will descend very rapidly to the surface, and must be slowed. What’s more, the landing has to be done autonomously as the light travel time from Earth is three to 22 minutes. This delay transmission means we can’t steer the rapid process from Earth. NASA and Russia have had their own problems with landings in the past, before the spectacular successes with the US missions Viking, Pathfinder, Spirit,Opportunity, Phoenix and Curiosity
Our sun is located about two-thirds of the way out from the center of the Milky Way. Illustration via Caltech.
The planets in our solar system orbit around the sun. One orbit of the Earth takes one year. Meanwhile, our entire solar system – our sun with its family of planets, moon, asteroid and comets – orbits the center of the Milky Way galaxy. Our sun and solar system move at about about 500,000 miles an hour (800,000 km/hr) in this huge orbit. So in 90 seconds, for example, we all move some 12,500 miles (20,000 km) in orbit around the galaxy’s center.
Our Milky Way galaxy is a big place. Even at this blazing speed, it takes the sun approximately 225-250 million years to complete one journey around the galaxy’s center.
This amount of time – the time it takes us to orbit the center of the galaxy – is sometimes called a cosmic year.
Do you see the starship Enterprise – from the famed Star Trek franchise – in these 2 nebulae? Image via NASA/JPL-Caltech.
Just in time for the 50th anniversary of the TV series Star Trek – created by writer and producer Gene Roddenberry – the Spitzer Space Telescope gives us this image of two nebulae that resemble the legendary starship Enterprise.
Star Trek first aired September 8,1966.
NASA said in a statement:
On the right of the image, with a little scrutiny, you may see hints of the saucer and hull of the original USS Enterprise, captained by James T. Kirk, as if it were emerging from a dark nebula. To the left, its Next Generation successor, Jean-Luc Picard’s Enterprise-D, flies off in the opposite direction …
Astronomically speaking, the region pictured in the image falls within the disk of our Milky Way galaxy and displays two regions of star formation hidden behind a haze of dust when viewed in visible light. Spitzer’s ability to peer deeper into dust clouds has revealed a myriad of stellar birthplaces like these, which are officially known only by their catalog numbers, IRAS 19340+2016 and IRAS19343+2026.
Trekkies, however, may prefer using the more familiar designations NCC-1701 and NCC-1701-D.
This artist’s concept puts solar system distances in perspective, but you have to think about it a bit to understand it. The scale bar is in astronomical units (AU), with each set distance beyond 1 AU representing 10 times the previous distance. One AU is the distance from the sun to the Earth, by the way, which is about 93 million miles or 150 million kilometers. Neptune, the most distant planet from the sun, is about 30 AU.
Informally, the term solar system is often used to mean the space surrounding our sun, out to the last planet. Astronomers, however, might speak of the solar system as the heliosphere, or sphere of the sun’s influence. Our dominates its own region of space and creates a sort of bubble of charged particles in the space surrounding it. These particles are “blown” out from the sun by the solar wind. It’s this heliosphere that Voyager 1 has now left. NASA says Voyager 1 actually crossed the heliopause, the boundary around the region of the sun’s influence, over a year ago, on August 25, 2012.
It’s also possible, though, to picture the solar system as going out to the Oort Cloud, the source of the comets that swing by our sun on long time scales. Beyond the outer edge of the Oort Cloud, the sun’s gravitational influence begins to wane. The inner edge of the main part of the Oort Cloud could be as close as 1,000 AU from our sun. The outer edge is estimated to be around 100,000 AU. So that’s 100,000 times the Earth-sun distance.
