| | 10 new stories for 2016/02/02
Massive Ariane 5 To Launch Giant NextGen Telescope In Dynamic Deployment To L2 
The Ariane 5 rocket is a workhorse for delivering satellites and other payloads into orbit, but fitting the James Webb Space Telescope (JWST) inside one is pushing the boundaries of the Ariane 5's capabilities, and advancing our design of space observatories at the same time.The Ariane 5 is the most modern design in the ESA's Ariane rocket series. It's responsible for delivering things like Rosetta, the Herschel Space Observatory, and the Planck Observatory into space. The ESA is supplying an Ariane 5 to the JWST mission, and with the planned launch date for that mission less than three years away, it's a good time to check in with the Ariane 5 and the JWST.The Ariane 5 has a long track record of success, often carrying multiple satellites into orbit in a single launch. Here's its most recent launch, on January 27th from the ESA's spaceport in French Guiana. This is Ariane 5's 70th successful launch in a row.[embed]https://www.youtube.com/watch?v=cJBzLGljmg8[/embed]But launching satellites into orbit, though still an amazing achievement, is becoming old hat for rockets. 70 successful launches in a row tells us that. The Ariane 5 can even launch multiple satellites in one mission. But launching the James Webb will be Ariane's biggest challenge.The thing about satellites is, they're actually getting smaller, in many cases. But the JWST is huge, at least in terms of dimensions. The mass of the JWST—6,500 kg (14,300 lb)—is just within the limits of the Ariane 5. The real trick was designing and building the JWST so that it could fit into the cylindrical space atop an Ariane 5, and then "unfold" into its final shape after separation from the rocket. This video shows how the JWST will deploy itself.[embed]https://www.youtube.com/watch?v=bTxLAGchWnA[/embed]The JWST is like a big, weird looking beetle. Its gold-coated, segmented mirror system looks like multi-faceted insect eyes. Its tennis-court sized heat shield is like an insect's shell. Or something. Cramming all those pieces, folded up, into the nose of the Ariane 5 rocket is a real challenge.Because the JWST will live out its 10-year (hopefully) mission at L2, rather than in orbit around Earth, it requires this huge shield to protect itself from the sun. The instruments on the James Webb have to be kept cool in order to function properly. The only way to achieve this is to have its heat shield folded up inside the rocket for launch, then unfolded later. That's a very tricky maneuver.But there's more.The heart of the James Webb is its segmented mirror system. This group of 18 gold-coated, beryllium mirrors also has to be folded up to fit into the Ariane 5, and then unfolded once it's separated from the rocket. This is a lot trickier than launching things like the Hubble, which was deployed from the space shuttle.Something else makes all this folding and unfolding very tricky. The Hubble, which was James Webb's predecessor, is in orbit around Earth. That means that astronauts on Shuttle missions have been able to repair and service the Hubble. But the James Webb will be way out there at L2, so it can't be serviced in any way. We have one chance to get it right.Right now, the James Webb is still under construction in the "Clean Room" at NASA's Goddard Space Flight Centre. A precision robotic arm system is carefully mounting Webb's 18 mirrors.There's still over two years until the October 2018 launch date, and there's a lot of testing and assembly work going on until then. We'll be paying close attention not only to see if the launch goes as planned, but also to see if the James Webb—the weird looking beetle—can successfully complete its metamorphosis. The post Massive Ariane 5 To Launch Giant NextGen Telescope In Dynamic Deployment To L2 appeared first on Universe Today.
Messier 1 (M1) – The Crab Nebula 
In the 18th century, French astronomer Charles Messier kept noting the presence of fixed, diffuse objects in the night sky. Initially, he thought these were comets, which he was attempting to locate at the time. However, astronomers would later discover that these objects were in fact nebulae, galaxies and star clusters. Between the years of 1758 and 1782, Messier compiled a list of approximately 100 of these objects.His intention was to ensure that other astronomers would not mistake these objects for comets. But in time, this list - known as the Messier Catalog - served a higher purpose. In addition to being a collection of some of the most beautiful objects in the night sky, the catalog was also an important milestone in the discovery and research of Deep Sky objects. The first item in the catalog is the famous Crab Nebula - hence its designation as Messier Object 1, or M1. Description: Messier 1 (aka. M1, NGC 1952, Sharpless 244, and the Crab Nebula) is a supernova remnant located in the Perseus Arm of the Milky Way Galaxy, roughly 6500 ± 1600 light years from Earth. Like all supernova remnants, it is an expanding cloud of gas that was created during the explosion of a star. This material is spread over a volume approximately 13 ± 3 ly in diameter, and is still expanding at a velocity of about 1,500 km/s (930 mi/s).Based on its current rate of expansion, it is assumed that the overall deceleration of the nebula's expansion must has decreased since the initial supernova. Essentially, after the explosion occurred, the nebula's pulsar would have began to emit radiation that fed the nebula's magnetic field, thus expanding it and forcing it outward.In visible light, the Crab Nebula consists of an oval-shaped mass of filaments - whose spectral emission lines are split into both red and blue-shifted components - which surround a blue central region. The filament are leftover from the outer layers of the former star's atmosphere, and consist primarily of hydrogen and helium, along with traces of carbon, oxygen, nitrogen and heavier elements. The filaments' temperatures are typically between 11,000 and 18,000 K.The blue region, meanwhile, is the result of highly polarized synchrotron radiation, which is emitted by high-energy electrons in a strong magnetic field. The curved path of these electrons is due to the strong magnetic field produced by the neutron star at the center of the nebula (see below). One of the many components of the Crab Nebula is a helium-rich torus which is visible as an east-west band crossing the pulsar region.The torus accounts for about 25% of the nebula's visible ejecta and is believed to be made up of 95% helium. As yet, there has been no plausible explanation for the structure of the torus. And while it is very difficult to gauge the total mass of the nebula, official estimates place it at 4.6 ± 1.8 Solar masses - i.e 5.5664 to 12.7232 × 1030 kg.Crab Pulsar: At the center of the Crab Nebula are two faint stars, one of which is its progenitor (i.e the one that created it). It is because of this star that M1 is a strong source of radio waves, X-rays and Gamma-ray radiation. The remnant of supernova SN 1054, which was widely observed on Earth in the year 1054, this star was discovered in 1968 and has since been designated as a radio pulsar.Known as the Crab Pulsar (or NP0532), this rapidly rotating star is believed to be about 28–30 km (17–19 mi) in diameter and emits pulses of radiation - ranging from radio wave and X-ray - every 33 milliseconds. Like all isolated pulsars, its period is slowing very gradually, and the energy released as the pulsar slows down is enormous. The Crab Pulsar is also the source of the nebula's synchrotron radiation, which has a total luminosity about 75,000 times greater than that of the Sun.The pulsar's extreme energy output also creates an unusually dynamic region at the center of the Crab Nebula. While most astronomical objects only show changes over timescales of many years, the inner parts of the Crab show changes over the course of only a few days. The most dynamic feature in the inner part of the nebula is the point where the pulsar's equatorial wind slams into the bulk of the nebula, forming a shock front (see above image).The Crab Pulsar is also surrounded by an expanding gas shell which encompasses its spectroscopic companion star, which in turn orbits the neutron star every 133 days. This pulsar was the first one which was also verified in the optical part of the spectrum. History of Observation: The very first recorded information on this supernova event reaches as far back as July 4, 1054 A.D. by Chinese astronomers who marked the presence of a "new star" visible in daylight for 23 days and 653 nights. The event may have also been recorded by the Anasazi, Navajo and Mimbres First Nations of North America in their artwork as well.In more modern times, the nebula was cataloged as a discovery by British amateur astronomer John Bevis in 1731, and independently by Charles Messier on August 28th, 1758 while looking for the return of Comet Halley. Although Bevis had added it to his "Uranographia Britannica", Messier recognized what he had located had no proper motion, and was therefore not a comet. However, Messier did credit Bevis' discovery when he learned of it years later.By September 12th, 1758, Messier hit upon the idea of compiling a catalog of objects that weren't comets, in order to help other astronomers avoid similar mistakes. Considering M1's position, only slightly more than a degree from the ecliptic plane, this was a very good idea. Especially since M1 was again confused with Halley's Comet when it returned in 1835.The name Crab Nebula was first suggested by William Parsons, the Third Earl of Rosse, who observed it while at Birr Castle in 1884. The name was apparently due to the drawing he made of it, which resembled a crab. When he observed it again in 1848 using a ]telescope with better resolution, he could not confirm the resemblance. But the name had become popular by this point and has stuck ever since.All of the early observers - including Herschel, Bode, Messier and Lassell - apparently mistook the filamentary structures of the Nebula as an indication of stellar structure. As Messier himself described it: "Nebula above the southern horn of Taurus, it doesn't contain any star; it is a whitish light, elongated in the shape of a flame of a candle, discovered while observing the comet of 1758. See the chart of that comet, Mem. Acad. of the year 1759, page 188; observed by Dr. Bevis in about 1731. It is reported on the English Celestial Atlas." Sir Williams Herschel's writing on the nebula appeared in the 74th volume of the Philosophical Transactions of the Royal Society of London, which was released in 1784. As he described it: "To these may added the 1st [M1], 3d, 27, 33, 57, 79, 81, 82, 101 [of Messier's catalog], which in my 7, 10, and 20-feet reflectors shewed a mottled kind of nebulosity, which I shall call resolvable; so that I expect my present telescope will, perhaps, render the stars visible of which I suppose them to be composed..." But it was Parsons (aka. Lord Rosse) who first recognized M1 for what we know it as today. As he recorded when viewing it for the first time (in 1844): "Fig. 81 is also a cluster; we perceive in this [36-inch telescope], however, a considerable change of appearance; it is no longer an oval resolvable [mottled] Nebula; we see resolvable filaments singularly disposed, springing principally from its southern extremity, and not, as is usual in clusters, irregularly in all directions. Probably greater power would bring out other filaments, and it would then assume the ordinary form of a cluster. It is stubbed with stars, mixed however with a nebulosity probably consisting of stars too minute to be recognized. It is an easy object, and I have shown it to many, and all have been at once struck with its remarkable aspect. Everything in the sketch can be seen under moderately favourable circumstances." Locating Messier 1: The Crab Nebula is easily visible in the night sky near the Taurus constellation, whenever light pollution is not an issue. It can be located by identifying Zeta Tauri, a third magnitude star located east/northeast of Aldebaran. With dark sky conditions, it can be seen as a tiny, hazy patch with binoculars and small telescopes with low magnification. If sky conditions are bright, it may be harder to locate with modest equipment.With a little more magnification, it is seen as a nebulous oval patch, surrounded by haze. In telescopes starting with 4-inch aperture, some detail in its shape becomes apparent, with some suggestion of mottled or streak structure in the inner part of the nebula. To the amateur astronomer, M1 does indeed look similar to a faint comet without a tail.As Messier 1 is situated only 1 1/2 degrees from the ecliptic, there are frequent conjunctions and occasional transits of planets, as well as occultations by the Moon. And for the sake of simplicity, here are the vital statistics on this Messier Object: Object Name: Messier 1 Alternative Designations: NGC 1952, M1, Sharpless 244, Crab Nebula Object Type: Supernova Remnant Constellation: Taurus Right Ascension: 05 : 34.5 (h:m) Declination: +22 : 01 (deg:m) Distance: 6.3 (kly) Visual Brightness: 8.4 (mag) Apparent Dimension: 6x4 (arc min)We wish you luck in locating it in the night sky. And should you find it, enjoy your observations!We have written many great articles about the Crab Nebula and Messier Objects here at Universe Today. Here's What Is The Crab Nebula?, The Peculiar Pulsar in the Crab Nebula, and Top Five Celestial Objects Anyone Can See With A Small Telescope.Be to sure to check out our complete Messier Catalog.For more information, check out the SEDS Messier Database. The post Messier 1 (M1) – The Crab Nebula appeared first on Universe Today.
Guide to the Constellations and Messier Objects by Tammy Plotner 
The first person to ever write an article for Universe Today (apart from me) was Tammy Plotner. Tammy was an experienced amateur astronomer, and had already dedicated her life to sharing her love of the night sky with the public. She spoke at astronomy clubs, did plenty of sidewalk astronomy, and in 2004, she contributed her first article to Universe Today.By 2006, Tammy had written dozens of articles for Universe Today, and embarked on a weekly astronomy series called What's Up This Week. We later turned those into actual books (printed on paper, no less), and did another edition in 2007.In 2015, Tammy passed away after a long struggle with MS, and we mentioned it here on Universe Today.One of my favorite projects that Tammy ever embarked on for Universe Today was to publish a guide to every single Messier Object, and every single Constellation in the sky. There are more than 100 Messier Objects, and 88 recognized constellations, and Tammy wrote an in-depth guide to each and every one.To honor Tammy, we've decided to bring these wonderful guides back to the surface - you probably never even realized they were in the vast Universe Today archives. The Guide to Space Curator, Matt Williams, will be completely revised Tammy's guides, adding plenty of new pictures and links to additional resources.We'll release one a week from both collections until they're all republished, starting with M1: the Crab Nebula, today.I hope you enjoy them, I sure did. The post Guide to the Constellations and Messier Objects by Tammy Plotner appeared first on Universe Today.
What is the Higgs Boson? What is this thing we keep hearing about – the Higgs Boson, and why is it important?
It's been said that the best way to learn is to teach. And so, today I'm going to explain everything I can about the Higgs boson. And if I do this right, maybe, just maybe, I'll understand it a little better by the end of the episode. I'd like to be clear that this video is for the person whose eyes glaze over every time you hear the term Higgs boson. You know it's some kind of particle, Nobel prize, mass, blah blah. But you don't really get what it is and why it's important. First, let's start with the Standard Model. These are essentially the laws of particle physics as scientists understand them. They explain all the matter and forces we see all around us. Well, most of the matter, there are a few big mysteries, which we'll discuss as we get deeper into this. But the important thing to understand is that there are two major categories: the fermions and the bosons.  Bosons, fermions and other particles after a collsion. Credit: CERN Fermions are matter. There are the protons and neutrons which are made up of quarks, and there are the leptons, which are indivisible, like electrons and neutrinos. With me so far? Everything you can touch are these fermions. The bosons are the particles that communicate the forces of the Universe. The one you're probably familiar with is the photon, which communicates the electromagnetic force. Then there's the gluon, which communicates the strong nuclear force and the W and Z bosons which communicate the weak nuclear force. Mystery number 1, gravity. Although it's one of the fundamental forces of the Universe, nobody has discovered a boson particle that communicates this force. So, if you're looking for a Nobel Prize, find a gravity boson and it's yours. Prove that gravity doesn't have a boson, and you can also get a Nobel Prize. Either way, there's a Nobel Prize in it for you. ![Credit: PBS NOVA [1], Fermilab, Office of Science, United States Department of Energy, Particle Data Group](https://lh3.googleusercontent.com/blogger_img_proxy/AEn0k_vRupGrAYnZW1AxR6HGXBN6d7BjptAHbY2NPnoRPNjieIZ1UJ_4bjMdSxmhTRMvczejEH-T_rkbBozNfpKiOEV62XiNFRcQJQbet-Rps4bMm8o9pNz7OfzevZtNIKf6J3jp_bZ03JIYeMhRXrCH_Uek1Sz5KgJ1EWho8v_qSnoQTasymstQbguYTRVT4hVQ_4Ddew=s0-d) Credit: PBS NOVA [1], Fermilab, Office of Science, United States Department of Energy, Particle Data Group Again, this is the Standard Model, and it accurately describes the laws of nature as we see them around us. One of the biggest unsolved mysteries in physics was the concept of mass. Why does anything have mass at all, or inertia? Why does the amount of physical "stuff" in an object define how easy it is to get moving, or how hard it is to make it stop? In the 1960s, physicist Peter Higgs predicted that there must be some kind of field that permeates all of space and interacts with matter, sort of like a fish swimming through water. The more mass an object has, the more it interacts with this Higgs field. And just like the other fundamental forces in the Universe, the Higgs field should have a corresponding boson to communicate the force – this is the Higgs boson. The field itself is undetectable, but if you could somehow detect the corresponding Higgs particles, you could assume the existence of the field.  Cross-section of the Large Hadron Collider where its detectors are placed and collisions occur. LHC is as much as 175 meters (574 ft) below ground on the Frence-Swiss border near Geneva, Switzerland. The accelerator ring is 27 km (17 miles) in circumference. (Photo Credit: CERN) And this is where the Large Hadron Collider comes in. The job of a particle accelerator is to convert energy into matter, via the formula e=mc2. By accelerating particles – like protons – to huge velocities, they give them an enormous amount of kinetic energy. In fact, in its current configuration, the LHC moves protons to 0.999999991c, which is about 10 km/h slower than the speed of light. When beams of particles moving in opposite directions are crashed together, it concentrates an enormous amount of energy into a tiny volume of space. This energy needs somewhere to go so it freezes out as matter (thanks Einstein). The more energy you can collide, the more massive particles you can create. And so, in 2013, the LHC allowed physicists to finally be able to confirm the presence of the Higgs Boson by tuning the energy of the collisions to exactly the right level, and then detecting the cascade of particles that occur when Higgs bosons decay. Because the right particles are detected, you can assume the presence of the Higgs boson, and because of this, you can assume the presence of the Higgs field. Nobel prizes for everyone.  Particle collision. Credit: CERN I said there were a few mysteries left; gravity was one, of course, but there are a few more. The reality is that physicists now know that the matter I described is really just a fraction of the entire Universe. Cosmologists estimate that just 4% of the Universe is the normal baryonic matter that we're familiar with. Another 23% is dark matter, and a further 73% is dark energy. So there are still plenty of mysteries to keep physicists busy for years. And so, in 2013, the Large Hadron Collider finally turned up the particle that physicists had predicted for 50 years. The last piece of the Standard Model was finally proven to exist, and we're closer to understanding what 4% of the Universe is. The other 96% (oh, and gravity), are still a total mystery. Physicists are cranking up the LHC to higher and higher levels of energy, to search for other particles, to understand dark matter, and see if they can generate microscopic black holes. This mighty instrument has plenty more science to reveal, so stay tuned. That's the Higgs Boson in a nutshell. Let me me know if there are other concepts in particle physics you'd like to talk about. Put your ideas into the comments below. The post What is the Higgs Boson? appeared first on Universe Today.
Flyover Video of Ceres Shows the Grandeur of Space Exploration 
Wow. This video will knock your socks off ... at least it did mine. This new flyover video of Ceres was created using enhanced images taken by the Dawn spacecraft's framing camera. It was produced by the camera team at the German Aerospace Center, DLR, using images from Dawn's high-altitude mapping orbit of 900 miles (1,450 kilometers) above Ceres' surface. The video shows a stark and stunning world."The viewer can observe the sheer walls of the crater Occator, and also Dantu and Yalode, where the craters are a lot flatter," said Ralf Jaumann, a Dawn mission scientist at DLR.  The enhanced color used here helps to highlight subtle differences in the appearance of surface materials. There's additional info at the end of the video, but for a quick reference, area with shades of blue contain younger, fresher material such as flows, pits and cracks, while brown areas clays, which, enticingly, usually form in the presence of water.I had the chance to visit with Marc Rayman, Dawn's chief engineer and mission director at JPL earlier this month, when I interviewed him for a book I'm working on about robotic space exploration. One thing he really stressed is that Ceres is a big place, with diverse terrain and a variety of features. This video really brings that home."Ceres has a surface area of 2,770,000 square kilometers ... It's a big surface and we haven't seen all of it," Rayman said. "It will be great to see what the new detail shows from the low altitude orbit, because those pictures will be four times better resolution than pictures we were able to get at our previous orbit."Dawn is now in its final and lowest mapping orbit, at about 240 miles (385 kilometers) from the surface.This animated flight over Ceres emphasizes the most prominent craters, such as Occator, Dantu, and the tall, conical mountain Ahuna Mons.The bright features seen in Occator Crater have been determined to be salts, which are quite reflective and look bright to our eyes (sorry no alien city lights) and the team will be providing more details and images soon.Additional info: JPL, Dawn mission home pageThe post Flyover Video of Ceres Shows the Grandeur of Space Exploration appeared first on Universe Today.
SpaceX Crew Dragon Conducts Propulsive Hover and Parachute Drop Tests; Videos 
On the road to restoring US Human spaceflight from US soil, SpaceX conducted a pair of key tests involving a propulsive hover test and parachute drop test for their Crew Dragon vehicle which is slated to begin human missions in 2017.SpaceX released a short video showing the Dragon 2 vehicle executing a "picture-perfect propulsive hover test" on a test stand at the firms rocket development facility in McGregor, Texas.The video published last week shows the Dragon 2 simultaneously firing all eight of its side mounted SuperDraco engines, during a five second test carried out on Nov. 22, 2015.Using the SuperDragos will eventually enable pinpoint propulsive soft landings like a helicopter in place of parachute assisted landings in the ocean or on the ground.The video clip seen below includes both full speed and slow motion versions of the test, showing the vehicle rising and descending slowly on the test stand.https://youtu.be/07Pm8ZY0XJI Video caption: SpaceX Dragon 2 crew vehicle, powered by eight SuperDraco engines, conducts propulsive hover test firing at rocket development facility in McGregor, Texas.The eight SuperDraco thrusters are mounted in sets 90 degrees apart around the perimeter of the vehicle in pairs called "jet packs." The SuperDracos generate a combined total of 33,000 lbs of thrust.SpaceX is developing the Crew Dragon under the Commercial Crew Program (CCP) awarded by NASA to transport crews of four or more astronauts to the International Space Station. "This test was the second of a two-part milestone under NASA's Commercial Crew Program," said SpaceX officials. "The first test—a short firing of the engines intended to verify a healthy propulsion system—was completed November 22, and the longer burn two-days later demonstrated vehicle control while hovering."The first unmanned and manned orbital test flights of the crew Dragon are expected sometime in 2017. A crew of two NASA astronauts should fly on the first crewed test before the end of 2017.Initially, the Crew Dragon will land via parachutes in the ocean before advancing to use of pinpoint propulsive landing.Thus SpaceX recently conducted a parachute drop test involving deployment of four red-and-white parachutes unfurling high above the desert near Coolidge, Arizona using a mass simulator in place of the capsule.https://youtu.be/4PG438XSarg Video Caption: SpaceX performed a successful test of its parachute system for the Crew Dragon spacecraft near Coolidge, Arizona, as part of its final development and certification work with NASA's Commercial Crew Program. Using a weight simulant in the place of a boilerplate spacecraft, four main parachutes were rigged to deploy just as they would when the Crew Dragon returns to Earth with astronauts aboard. Credit: NASA/SpaceX"The mass simulator and parachutes were released thousands of feet above the ground from a C-130 cargo aircraft. This test evaluated the four main parachutes, but did not include the drogue chutes that a full landing system would utilize," said NASA.Since the CCP program finally received full funding from Congress in the recently passed Fiscal Year 2016 NASA budget, the program is currently on track to achieve the orbital test flight milestones.Boeing and SpaceX were awarded contracts by NASA Administrator Charles Bolden in September 2014 worth $6.8 Billion to complete the development and manufacture of the privately developed Starliner CST-100 and Crew Dragon astronaut transporters under the agency's Commercial Crew Transportation Capability (CCtCap) program and NASA's Launch America initiative.The Crew Dragon will launch atop a SpaceX Falcon 9 rocket from launch Complex 39A at the Kennedy Space Center. The historic launch pad has been leased by SpaceX from NASA and is being refurbished for launches of the Falcon 9 and Falcon Heavy.Stay tuned here for Ken's continuing Earth and planetary science and human spaceflight news. Ken KremerThe post SpaceX Crew Dragon Conducts Propulsive Hover and Parachute Drop Tests; Videos appeared first on Universe Today.
How Does The Earth Rotate? 
Beginning in the 16th century, humanity's understanding of our world and the cosmos was revolutionized as we became aware of a simple fact. The Earth moved! Not only did it move about the Sun, but it also rotates. And while it would take several centuries before this became universally accepted (aka. a few people had to endure persecution and house arrest) the fact that the Earth rotates about our Sun and on its axis soon became accepted fact.In fact, the rotation of our planet on its axis and around the Sun are the cause of just about every stellar phenomenon we humans have come to take for granted. It is the reason the Sun rises in the East and sets in the West, the reason why the Moon goes through phases, and the reason the stars appear to rotate around the Earth once every day. So let's address this whole " Eppur Si Mouve" business, shall we? As already noted, Earth experiences two kinds of rotation. On the one hand, there is the rotation of Earth on its axis, which is known as sidereal rotation. This is what allows for the diurnal cycle and makes it appear as if the heavens are revolving around us. On the other hand, the Earth orbits about the Sun, which is known as its orbital period. This revolution (among other things) is responsible for the seasons, the length of the year, and variations in our diurnal cycle. Let's break these rotational habits down by the numbers... Sidereal Rotation: Earth rotates once on its axis every 23 hours, 56 minutes and 4.1 seconds. Also known as a sidereal day, this period of rotation is measured relative to the stars. Meanwhile, Earth's solar day (i.e. the amount of time it takes for the Sun to reappear in the same place in the sky) is an even 24 hours. Naturally, we use this latter value when it comes time to measure calendar days.Earth's sidereal rotation is responsible for the pattern of sunrises and sunsets that we are so familiar with. Using celestial objects as a reference point (i.e. the Moon, the stars, etc) the Earth rotates at a rate of 15°/h (or 15'/min) in a western direction. If viewed from space above the North Pole, Earth would appear to be rotating counter-clockwise. Hence why the Sun rises in the East and sets in the West.The speed of the rotation of Earth has had various effects over time, including the Earth's shape (an oblate spheroid with flattening at the poles), Earth's climate, the depth and currents of its oceans, as well as tectonic forces. This should come as no surprise, considering that it's rotational velociy is 1,674.4 km/h.However, the planet is slowing slightly with the passage of time, due to the tidal effects the Moon has on Earth's rotation. Atomic clocks show that a modern day is longer by about 1.7 milliseconds than a century ago, slowly increasing the rate at which UTC is adjusted by leap seconds. The Earth's rotation also goes from the west towards east, which is why the Sun rises in the east and sets in the west.https://youtu.be/YKswo9Nq0Uo Orbital Period: Earth orbits the Sun at an average distance (aka. semi-major axis) of 149,598,023 km or 92,955,902 mi (about 1 AU), and completes a single rotation every 365.2564 mean solar days. This is what is known as a sidereal year, or Earth's orbital period. This creates the appearance of the Sun moving eastward through the sky at a rate of about 1° per day.At this rate, it takes the Sun the equivalent of 24 hours - i.e. one solar day - to complete a full rotation about the Earth's axis and return to the meridian (a point on the globe that runs from north to south through the poles). Viewed from the vantage point above the north poles of both the Sun and Earth, Earth orbits in a counterclockwise direction about the Sun.This Earth's rotation around the Sun, or the precession of the Sun through the equinoxes, is the reason a year lasts approximately 365.2 days. It is also for this reason that every four years, an extra day is required (a February 29th during every Leap Year). Also, Earth's rotation about the Sun is sujbect to a slight eccentricity of (0.0167°), which means that it is periodically closer or farther from the Sun at certain times of the year.https://youtu.be/nRzAu1yG_uwEarth's perihelion (147,098,074 km) occurs around January 3rd, and the aphelion around July 4th (152,097,701 km). The changing Earth-Sun distance results in an increase of about 6.9% in solar energy reaching the Earth at perihelion as related to aphelion. The southern hemisphere is tilted toward the Sun at about the same time that the Earth reaches the closest approach to the Sun, so the southern hemisphere receives slightly more energy from the Sun than does the northern over the course of a year.It is also the reason for the Moon's apparent phases, and the occasional lunar and solar eclipse. A lunar eclipse occurs where the Moon passes into the shadow of the Earth (umbra) relative to the Sun, which causes it to darken and take on a reddish appearance (aka. a "Blood Moon" or "Sanguine Moon".)A solar eclipse occurs during a new Moon, when the Moon is between the Sun and Earth. Since they are the same apparent size in the sky, the moon can either partially block the Sun (annular eclipse) or fully block it (total eclipse). In the case of a total eclipse, the Moon completely covers the disc of the Sun and the solar corona becomes visible to the naked eye.Were it not for Earth's axial tilt (which is inclined 24.3° to the ecliptic), there would be an eclipse every two weeks, alternating between lunar eclipses and solar eclipses. It is also because of it's axial tilt that the amount of sunlight reaching the Earth's surface varies over the course of the year. This is what causes seasonal changes, changes in the diurnal cycle, and changes in the Sun's position in the sky relative to equator. When one hemisphere is tilted towards the Sun, it experiences summer, characterized by warmer temperatures and longer days. Every six months, this situation is reversed. History of Study: In ancient times, astronomers naturally believed that the Earth was a fixed body in the cosmos, and that the Sun, the Moon, the planets and stars all rotating around it. By classical antiquity, this became formalized into cosmological systems by philosophers and astronomers like Aristotle and Ptolemy - which later came to be known as the Ptolemaic Model (or Geocentric Model) of the universe.However, there were those during Antiquity that questioned this convention. One point of contention was the fact that the Earth was not only fixed in place, but that it did not rotate. For instance, Aristarchus of Samos (ca. 310 – 230 BCE) published writings on the subject that were cited by his contemporaries (such as Archimedes). According to Archimedes, Aristarchus espoused that the Earth revolved around the Sun and that the universe was many times greater than previously thought.And then there was Seleucis of Seleucia (ca. 190 – 150 BCE), a Hellenistic astronomer who lived in the Near-Eastern Seleucid empire. Seleucus was a proponent of the heliocentric system of Aristarchus, and may have even proven it to be true by accurately computing planetary positions and the revolution of the Earth around the Earth-Moon 'center of mass'. The geocentric model of the universe would also be challenged by medieval Islamic and Indian scholars. For instance, In 499 CE, Indian astronomer Aaryabhata published his magnum opus Aryabhatiya, in which he proposed a model where the Earth was spinning on its axis and the periods of the planets were given with respect to the Sun.The 10th-century Iranian astronomer Abu Sa'id al-Sijzi contradicted the Ptolemaic model by asserting that the Earth revolved on its axis, thus explaining the apparent diurnal cycle and the rotation of the stars relative to Earth. At about the same time, Abu Rayhan Biruni 973 – 1048) discussed the possibility of Earth rotating about its own axis and around the Sun – though he considered this a philosophical issue and not a mathematical one.At the Maragha and the Ulugh Beg (aka. Samarkand) Observatory, the Earth's rotation was discussed by several generations of astronomers between the 13th and 15th centuries, and many of the arguments and evidence put forward resembled those used by Copernicus. It was also at this time that Nilakantha Somayaji published the Aryabhatiyabhasya (a commentary on the Aryabhatiya) in which he advocated a partially heliocentric planetary model. This was followed in 1500 by the Tantrasangraha, in which Somayaji incorporated the Earth's rotation on its axis.In the 14th century, aspects of heliocentricism and a moving Earth began to emerge in Europe. For example, French philosopher Bishop Nicole Oresme (ca. 1320-1325 to 1382 CE) discussed the possibility that the Earth rotated on its axis. However, it was Polish astronomer Nicolaus Copernicus who had the greatest impact on modern astronomy when, in 1514, he published his ideas about a heliocentric universe in a short treatise titled Commentariolus ("Little Commentary").Like others before him, Copernicus built on the work of Greek astronomer Atistarchus, as well as paying homage to the Maragha school and several notable philosophers from the Islamic world (see below). Intrinsic to his model was the fact that the Earth, and all the other planets, rolved around the Sun, but also that the Earth revolved on its axis and was orbited by the Moon.In time, and thanks to scientists sch as Galileo and Sir Isaac Newton, the motion and revolution of our planet would become an accepted scientific convention. With the advent of the Space Age, the deployment of satellites and atomic clocks, we have not only confirmed that it is in constant motion, but have been able to measure the its orbit and rotation with incredibly accuracy.We have written many interesting articles about the motions of the Earth here at Universe Today. Here's How Fast Does The Earth Rotate?, Earth's Orbit Around The Sun, How Fast Does The Earth Rotate?, Why Does The Earth Spin?, What Would Happen If The Earth Stopped Spinning?, and What Is The Difference Between the Heliocentric and Geocentric Models Of The Solar System?Astronomy Cast also has a relevant episode on the subject - Episode 171: Solar System Movements and PositionsFor more information, be sure to check out NASA: Why Do We Study the Sun? NASA Eclipse, and all about Earth. The post How Does The Earth Rotate? appeared first on Universe Today.
Book Review: Lunar and Interplanetary Trajectories 
I've always been amazed when watching the game of billiards. Some person, with great concentration and aim, uses a long wooden stick to strike one ball which then, by design, causes reactions to other balls. The balls travel along precisely predetermined paths! Now imagine doing this in 3-D. Sound impossible? Well, that's what mission designers must do when preparing to send a probe to another orbiting body in our solar system. And their methodology is wonderfully presented in Robin Biesbroek's book "Lunar and Interplanetary Trajectories".  This book could be described as 'precise.' The author describes it as being written for a systems approach. He then goes on to proclaim that he presents and uses only one equation. This may be a good thing as the book has more than enough numerical data without adding the analytics. And the information flows along smoothly, as if presenting a case study so the reader won't get overwhelmed.First Biesbroek presents the significant parameters; the C3 launch energy and the co-ordinate system. Remember that I mentioned things were in three dimensions? Well, this book has us also realize that the co-ordinate system can come in many guises. As well, there's lots of angular momentum with which to deal. To aid the reader, the author includes many, many charts, graphs and plots. The plots of trajectories from Earth to beyond are particularly revealing and indeed necessary at times to grasp the nuances of positive and negative notations and maximum energy usage. To entice the reader further, Biesbroek includes many resolved missions, such as New Horizons, Phobos Grunt and Cassini/Huygens. Last, with almost a teasing presence, the author adds to the end of each chapter a few scholarly exercises. But don't worry, the solutions immediately follow!Sounds intriguing doesn't it? Well there's more. Biesbroek utilizes his systems approach when looking at pros and cons for many situations. For example, he's got the Low Earth Orbit mass delivery for the Falcon rocket as a condition. And he wants us to constrain the timing of our approach to Mars to minimize the chances of intersecting with a seasonal dust storm. Then there's the challenge of visiting Jupiter without getting harmed by its magnetic field.Further, and perhaps most insightful, is the expectation for any mission to be ten years or less. Apparently we may lose interest with anything that takes longer! But what if the designer gets it wrong? You'll just have to read the book to see why just this happened with the Surveyor lander. Apparently the controllers got a bit of a surprise as the lander didn't quite settle as expected. Nevertheless, with lots of errors of margin, the lander did survive and contribute to our knowledge base of space. As a reader will see, it's quite an accomplishment to design and build something for launch from Earth many years beforehand.Yes, this book presents what appears to be a carefully chosen mix of useful data and background information. Being that the author uses a systems design approach in the book, then there are limits to what the reader can use. Even with an appendix full of data tables, the reader may feel constrained by the finite options provided. That is, there are look-up tables throughout and it's up to the reader to figure out the best way to use them. You may want to go into more depth, but I suspect it'd take a good deal more training before you could comfortably prepare your own Molniya orbits. Thus, know that there is a mix of information in this book and after reading it you won't come out an expert in anything. But you will come out with a lot more knowledge on mission design and constraint parameters.When sitting back in a chair and looking at fantastic colour images of the surface of Pluto it's no surprise that it seems so easy and straightforward. Yet, as with almost anything that looks easy, there's a huge amount of effort riding along in the background, supporting every moment. And it all starts with turning an idea into reality.That's where Robin Biesbroek's book "Lunar and Interplanetary Trajectories" steps in. It will show you some of the tricks of the trade in optimizing missions, whether choosing the best launch system or balancing an orbit about a Lagrange point. Most people who appreciate the photos of distant worlds may appreciate the effort involved. Yet, for them, and for others who may think it`s quite simple, this book will have you appreciating all that's involved with travelling in space. The post Book Review: Lunar and Interplanetary Trajectories appeared first on Universe Today.
How Long Is A Year On The Other Planets? 
Here on Earth, we to end to not give our measurements of time much thought. Unless we're griping about Time Zones, enjoying the extra day of a Leap Year, or contemplating the rationality of Daylight Savings Time, we tend to take it all for granted. But when you consider the fact that increments like a year are entirely relative, dependent on a specific space and place, you begin to see how time really works.Here on Earth, we consider a year to be 365 days. Unless of course it's a Leap Year, which takes place every four years (in which it is 366). But the actual definition of a year is the time it takes our planet to complete a single orbit around the Sun. So if you were to put yourself in another frame of reference - say, another planet - a year would work out to something else. Let's see just how long a year is on the other planets, shall we? A Year On Mercury: To put it simply, Mercury has an orbital period of 88 days (87.969 to be exact), which means a single year is 88 Earth days - or the equivalent of about 0.241 Earth years. But here's the thing. Because of Mercury's slow rotation (once every 58.646 days) and its rapid orbital speed (47.362 km/s), one day on Mercury actually works out to 175.96 Earth days.So basically, a single year on Mercury is half as long as a Mercurian (aka. Hermian) day. This is due to Mercury being the closest planet to the Sun, ranging from 46,001,200 km at perihelion to 69,816,900 km at aphelion. At that distance, the planet shoots around the Sun faster than any other in our Solar System and has the shortest year.In the course of a year, Mercury experiences intense variations in surface temperature - ranging from 80 °K (-193.15 °C;-315.67 °F) to 700 °K (426.85 °C; 800.33 °F). However, this is due to the planet's varying distance from the Sun and its spin, which subjects one side to extended periods of extremely hot temperatures and one side to extended periods of night. Mercury's low axial tilt (0.034°) and its rapid orbital period means that there really is no seasonal variation on Mercury. Basically, one part of the year is as hellishly hot, or horribly cold, as any other. A Year On Venus: The second closest planet to our Sun, Venus completes a single orbit once ever 224.7 days. This means that a single year on Venus works out to about 0.6152 Earth years. But, once again, things are complicated by the fact that Venus has an unusual rotation period. In fact, Venus takes 243 Earth days to rotate once on its axis - the slowest rotation of any planet - and its rotation is retrograde to its orbital path. Combined with its orbital period, this means that a single solar day on Venus (the time between one sunup to the next) is 117 Earth days. So basically, a single year on Venus is lasts 1.92 Venusian (aka. Cytherean) days. Again, this would make for some confusing time-cycles for any humans trying to make a go of it on Venus! Also, Venus has a very small axial tilt - 3° compared to Earth's 23.5° - and its proximity to the Sun makes for a much shorter seasonal cycle - 55-58 days compared to Earth's 90-93 days. Add to that its unusual day-night cycle, variations are very slight. In fact, the temperate on Venus is almost always a brutal 736 K (463 °C ; 865 degrees °F), which is hot enough to melt lead! A Year On Earth: Comparatively speaking, a year on Earth is pretty predictable, which is probably one of the reasons why life is able to thrive here. In short, our planet takes 365.2564 solar days to complete a single orbit of the Sun, which is why we add an extra day to the calendar every four years (i.e. a Leap Year, which 2016 happens to be).But because our axis is tilted, there is considerable variation in the seasons during the course of a year. During the winter, when one hemisphere is pointed away from the Sun, the Sun's distance from the equator changes by up to 23.5°. As a result, between the summer and winter, the length of days and nights, temperatures, and seasons will go through significant changes.https://youtu.be/aSNs15sEINMAbove the Arctic Circle, an extreme case is reached where there is no daylight at all for part of the year - up to six months at the North Pole itself, in what is known as a "polar night". In the southern hemisphere the situation is exactly reversed, with the South Pole experiencing a midnight sun, a day of 24 hours, again reversing with the South Pole. Every six months, the order of this is reversed. A Year On Mars: Mars has one of the highest eccentricities of any planet in the Solar System, ranging from 206,700,000 km at perihelion and 249,200,000 km at aphelion. This large variation and its greater distance from the Sun, leads to a rather long year. Basically, Mars takes the equivalent of 687 (Earth) days to complete a single orbit around the Sun, which works out to to 1.8809 Earth years, or 1 year, 320 days, and 18.2 hours. On the other hand, Mars has a rotation period that is very similar to Earth's - 24 hours, 39 minutes, and 35.244 seconds. So while the days on Mars are only slightly longer, the seasons are generally twice as long. But this is mitigated by the fact that seasonal changes are far greater on Mars, owing to its eccentricity and greater axial tilt ( 25.19°). During the winter, the global atmospheric pressure on Mars is 25% lower than during summer. This is due to temperature variations and the complex exchange of carbon dioxide between the Martian dry-ice polar caps and its CO 2 atmosphere. As a result, Martian seasons vary greatly in duration than those on Earth, change roughly every six months, and do not start on the same Earth day every Martian year. A Year On Jupiter: Jupiter is another interesting case. Whereas the gas giant only takes 9 hours 55 minutes and 30 seconds to rotate once on its axis, it also takes alson 11.8618 Earth years to complete an orbit around the Sun. This means that a year on Jupiter is not only the equivalent of 4,332.59 Earth days, but 10,475.8 Jovian days. That's a lot of sunrises!Much like Venus, Jupiter has an axial tilt of only 3 degrees, so there is literally no seasonal variation between the hemispheres. In addition, temperature variations are due to chemical compositions and depths rather than seasonal cycles. So while it does have "seasons", which change very slowly due to its distance from the Sun - each season lasts 3 years - they are not similar to what terrestrial planets experience. A Year On Saturn: Much like its fellow gas giant Jupiter, Saturn takes it time completing a single orbit of the Sun, but rotates on its axis very rapidly. All told, a year on the planet lasts the equivalent of 10,759 Earth days (or about 29 1?2 years). But since it only takes 10 hours, and 33 minutes to complete a single rotation on its axis, a year on Saturn works out to 24,491.07 Saturnian (aka. Cronian) days.Due to its axial tilt of almost 27 degrees (slightly more than Mars), Saturn experiences some rather long seasonal changes. But due to it being a gas giant, this does not result in variations in temperature. Combined with its distance from the Sun (at an average distance of 1,429.39 million km or 9.5 AU), a single season lasts more than seven years. A Year On Uranus: Uranus has some of the strangest annual and seasonal variations of any planet in the Solar System. For one, the gas/ice giant takes about 84 Earth years (or 30,688.5 Earth days) to rotate once around the Sun. But since the planet takes 17 hours, 14 minutes and 24 seconds to complete a single rotation on its axis, a year on Uranus lasts 42,718 Uranian days.However, this is confounded due to Uranus' axial tilt, which is inclined at 97.77° towards the Sun. This results in seasonal changes that are quite extreme, and unique to Uranus. In short, when one hemisphere is pointed towards the Sun (i.e. in summer), it will experience 42 years of continuous light. In winter, the situation is reversed, with this same hemisphere experiencing 42 years of continuous darkness. A Year On Neptune: Given its distance from the Sun, Neptune has the longest orbital period of any planet in the Solar System. As such, a year on Neptune is the longest of any planet, lasting the equivalent of 164.8 years (or 60,182 Earth days). But since Neptune also takes comparatively little time to rotate once on its axis (16 hours, 6 minutes and 36 seconds), a single year lasts a staggering 89,666 Neptunian days.What's more, with an axial tilt close to Earth and Mars' (28.5 degrees), there is some seasonal variation on the planet. Essentially, a single season lasts more than 40 years. But like all gas/ice giants, this does not result in noticeable temperature variations.We have written many interesting articles about the Solar System here at Universe Today. Here's How Long Is A Year on Earth?, How Long Is A Year On Mercury?, How Long Is A Year on Venus?, How Long Is A Year on Mars?, How Long Is A Year On Jupiter?, How Long Is A Year On Saturn?, How Long Is A Year On Pluto?, and Orbits Of The Planets.If you are looking for more information, try NASA's Solar System exploration page, and here's a link to NASA's Solar System Simulator.Astronomy Cast has episodes on all the planets, including Episode 49: Mercury, Episode 50: Venus, Episode 62: Uranus. The post How Long Is A Year On The Other Planets? appeared first on Universe Today.
Weekly Space Hangout – Jan. 29, 2016: Largest Solar System, Future Missions, and Remembering Our Lost Astronauts Host: Fraser Cain (@fcain) Guests:
Carolyn Collins Peterson (thespacewriter.com / space.about.com / @spacewriter )
Morgan Rehnberg (cosmicchatter.org / @MorganRehnberg )
Kimberly Cartier (@AstroKimCartier )
Dave Dickinson (www.astroguyz.com / @astroguyz)
Jolene Creighton (fromquarkstoquasars.com / @futurism)
Paul Sutter (pmsutter.com / @PaulMattSutter)
Their stories this week:
Largest solar system Elon Musk and the quest for Mars (plans for manned mission by 2025) This Week in Bezos Twelve years on Mars for Opportunity Remembrance Stories of Apollo 1 and Challenger Hunting for planets around Proxima Centauri Hubble Sees Monstrous Cloud Boomerang Back to our Galaxy Making New Stars By 'Adopting' Stray Cosmic Gases Work begins on NASA’s *other* telescope, WFIRST Telescopes team up to produce highest-resolution astronomical image We’ve had an abundance of news stories for the past few months, and not enough time to get to them all. So we’ve started a new system. Instead of adding all of the stories to the spreadsheet each week, we are now using a tool called Trello to submit and vote on stories we would like to see covered each week, and then Fraser will be selecting the stories from there. Here is the link to the Trello WSH page (http://bit.ly/WSHVote), which you can see without logging in. If you’d like to vote, just create a login and help us decide what to cover! We record the Weekly Space Hangout every Friday at 12:00 pm Pacific / 3:00 pm Eastern. You can watch us live on Google+, Universe Today, or the Universe Today YouTube page. You can also join in the discussion between episodes over at our Weekly Space Hangout Crew group in G+! The post Weekly Space Hangout – Jan. 29, 2016: Largest Solar System, Future Missions, and Remembering Our Lost Astronauts appeared first on Universe Today.
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