Category Archives: Astronomy

[The moon of the distant object 2007 OR10 was spotted in Hubble images from 2009 and 2010. Credit:NASA,ESA, C. Kiss (Konkoly Observatory), and J. Stansberry (STScI)]

To be honest, theres not a huge amount we know about the distant solar system object provisionally named (225088) 2007 OR10. But nowwe know something new: It has a moon.

Thats actually very cool. And terribly important. Or it will be, soon.

Let me sum up. No, it is too important. Let me explain.

2007 OR10 is a member of our solar system, a world orbiting well past Neptune. And by well, I mean well: The closest it ever gets to the Sun is about 5 billion kilometers, roughly the same distance out as Pluto. But its orbit is very elliptical, and at its furthest, it gets 15 billion kilometers from the Sun. Thats a long, long way.

Which to be fair, is why we dont know much about it. Right now its about 13 billion km out. Thats a tremendous distance, making it difficult to observe. Heck, it was only discovered in 2007.

Besides its orbit,we know its very red; observations of it using different filters (as well as spectra; that is, breaking its light up into individual colors) indicate its much better at reflecting red light than blue. This happens a lot with worlds out in the distant solar system: The simple molecule methane breaks down when exposed to the ultraviolet light from the Sun, then build back up into more complex molecules called tholins, which can be various shades of red and brown. We see this on Pluto, for example, and OR10 is the right size and distance from the Sun to undergo this as well.

Its size can be estimated by its brightness ... though thats not easy. If you use visible light its hard; it could be small and shiny or bigger and dark. However, this can be nailed down by looking in the infrared, where warm objects emit light in well-understood ways. From those observations, OR10 was previously found to be about 1535 km (960 miles) across, about half the diameter of Earths moon. That makes it the third largest object in this region of the solar system known; only Pluto and Eris are known to be bigger.

Interestingly, every object in the solar system out past Neptune (called Trans Neptunian Objects or TNOs) bigger than 1000 km in size has been found to have at least one moon. It would actually be rather weird if OR10 didnt. Not only that, but careful measurements of its brightness over time showed it had a rotation period (a day) of about 45 hours, which is much longer than average for most TNOs (which are usually around 24 hours). A moon can interact gravitationally with its primary to slow the spin via tides, so astronomers got suspicious. Does OR10 have a moon?

Thats why a group of astronomers looked through archived observations of OR10 made by Hubble back in 2009 and 2010. Careful examination of the data revealed that yes, OR10 has a moon, so faint it was missed in previous analysis(Note: the moon was actually announced in 2016 at a conference; this news announcement coincides with the release of the official scientific paper)!

The moon is about 240 km (150 miles) across, so its pretty big compared to OR10...assuming its about the same composition and reflectance (that is, red). If its more reflective it could be smaller. Ill note that Plutos moon Charon is much darker than Pluto, so its possible the calculated diameter of OR10s moon will change with further observations.

Unfortunately, the moon is only seen in a handful of images (theres one set of observations made in 2009 and another in 2010). Thats not enough to determine its orbit, and thats the most critical aspect of all this! Why?

Once you can calculate the orbit of the moon, you can also find the mass of both objects. Thats huge! If we know the size and the mass, that means we can calculate the density, and that tells you (at least in part) what the objects are made of. Water ice, for example, is less dense than rock. A mix of the two would have a density somewhere in between. So seeing the moon move around enough to determine the orbit leads to great things.

I find that amazing; if you see an object with a moon and observe it for a while, you can determine their distance, orbits, separations, masses, and even guess at their composition! Thats so cool.

Weve found over the years that objects out there past Neptune are pretty diverse. Makemake, for example, is about the same size as OR10 but much more reflective. Other TNOs with moons show variations in reflectivity as well, so theres clearly a complicated and dynamic history to these objects. Moons are probably the product of collisions between bodies out there; the debris ejected coalesces to form a moon or moons. This isnt hugely well understood right now, so the more of these we find the more clues we have for their origins.

And one last note. 2007 OR10 is the largest known object in the solar system that doesnt have a name. Astronomers who find these worlds get the honor of naming them, generally giving them a handle that reflects their nature in some way; TNOs are typically named after native culture gods of the underworld (following the path of Pluto, named for the Roman god). Hopefully, given this new discovery of a moon, we wont have to wait too much longer before we can call 207 OR10 by something a bit less prosaic.

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Bad Astronomy | Astronomers find a moon for a distant, frigid world ... - Blastr

More than four decades ago, astronomers discovered the first gamma-ray emission coming from outside the solar system. This high-energy signal is associated with the destruction of roughly 1043 positrons a type of antimatter each second. Despite extensive follow-up, astronomers today are still looking for the exact source (or sources) of this emission, which could run the gamut from mundane (natural processes in a stars life) to exotic (dark matter) origins. Recently, a group of astronomers has determined that positrons resulting from white dwarf mergers could contribute significantly to the signal we see.

The emission associated with galactic positron annihilation occurs when a positron meets its counterpart, an electron, destroying both particles in the process. Thus, this emission requires a ready source of antimatter, which has remained mysterious ever since its initial detection.

Measurements suggest that the signal is nearly one and a half times higher in the bulge, or central regions of the Milky Way, than in the arms. This particular aspect of the emission has led to the development of several models that speculate an overabundance of positrons in this area could be due to processes related to dark matter or our galaxys central supermassive black hole. However, many astronomers are still searching for less exotic ways the positrons were seeing undergo annihilation could be produced.

In a paper published May 22 in Nature Astronomy, first author Roland M. Crocker of the Research School of Astronomy and Astrophysics at Australian National University and his co-authors examine a possible stellar source of galactic positrons that could be responsible for the signal: white dwarf mergers.

White dwarfs are the remnant cores of Sun-like stars, left behind after the star runs out of fuel and dies. If two low-mass stars (between about 1.4 and 2 times the mass of our Sun) circle each other closely in a binary system, they can interact via a process called mass transfer, where gas from the stars is exchanged. The end result is two white dwarfs that may eventually merge, and that merger can result in the production of radioactive isotopes that decay into positrons.

There are several clues that have led Crocker and his co-authors to this conclusion. The ratio of the signals strength in the bulge and arms is similar to the ratio of the stellar mass (essentially the number of stars) in these two structures as well. This led the astronomers to consider that the positron production could be related to an older stellar population, such as white dwarfs. Additionally, by looking at the processes that produce positrons through radioactive decay, they determined that the decay of 44Ti into positrons is the most likely source.

However, this material is not produced in sufficient amounts in most core collapse supernovae, which occur when a massive star reaches the end of its life. While supernovae triggered by the merger of two white dwarfs are much rarer, these events should produce more 44Ti per merger, which would then decay and produce the number of positrons required to create the emission line from their subsequent annihilation.

The current resolution of instruments used to study this emission is not high enough to find point sources, such as individual supernova remnants, in the bulge. Thus, more precise measurements and computer simulations will be needed to determine the positron production rates from such events. The authors also state that white dwarf mergers are likely not the only source of antimatter in our galaxy, which still includes contributions from massive stars and black holes, even if dark matter is eventually ruled out as a viable source for this emission.

Read more here:

Merging white dwarfs may create most of our galaxy's antimatter ... - Astronomy Magazine

Children enjoy launching rockets at Astrofest on BYU campus. (Ari Davis)

The Erying Science Center was a flurry of sights, colors and sounds last Saturday during BYUs ninthannual Astrofest as hundreds of local children and parents participated in astronomy and physics themed games and activities.

Astrofest was started in the summer of 2009 by several BYU faculty members and students.

The main purpose of the event is to provide opportunities for families and kids to learn about physical science and astronomy in a fun environment, said BYU professor and event volunteer Darin Ragozzine. We offer a variety of activities that are fun for a variety of ages.

The ground floor of the Eyring Science Center was ground zero for activities as attendees signed in and experimented with all of the different displays available in the lobby. Tours of BYUs Multiple Agent IntelligentCoordination andControlLab and the Eyring Science Centers Research Labs bounced in and out,creating a steady streamof parents and wide-eyed children.

The excitement carried up through the higher floors of the Eyring Science Center as stations with origami, paper airplanes and star wheels were crowded with children and adults alike. The fourth floor planetarium was packed with strollers and attendees as the Planetarium offered free shows every half hour.

Oohs and aahs could be heard on the centers roof as BYU students, alumni and faculty taught about basic astronomy and positioned solar telescopes for attendees to view sun spots.

Astrofest is a great way to introduce difficult concepts like astronomy to kids, said recent BYU alumna and program volunteer Leanne Farnbach. Its a great way to really teach the science behind how the earth works in a friendly environment.

Outside, the trees of the Joseph Smith Building courtyard were littered with homemade rockets thanks to Astrofests main event. Prospective astronauts were able to create and launch their designs hundreds of feet in the air under the supervision of local high school and BYU students.

We have a modified sprinkler valve and an air compressor. Just put a rocket on top, press the button and the compressor will send them flying, said Mountain View High School junior Timothy Taylor.

Between the indoor and outdoor events, Astrofest typically attracts between 2000 and 3000 attendees in a single afternoon said BYU physics professor Eric Hintze.

We have the materials for about 1700 rockets and 550 patches for the Scouts, said Hintze. Almost all of them are gone by the end of the day.

Astrofest is held annually and overseen byBYU faculty and students.For those interested in volunteering or attending, the event is heldon an annual basis in the mid-spring.

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Astrofest teaches about astronomy and physics - Universe.byu.edu

Astronomer Te Kkau Himiona Te Pikiktuku's account of his people's Matariki tradition has been recorded by his great grandson Dr Rangi Mtmua in his new book Matariki, The Star of the Year.

The Waikato University academic took on the challenge of publishing the 400-page manuscript he inherited from his father Timi Rwiri, Te Kkau's grandson, in 1995.

Matariki is a symbolic cluster of stars that holds a number of traditions for Mori, the most significant being that it marks beginning of the Mori new year. However, Dr Matamua maintains that there is confusion between the moon calendar and solar calendar.

Mtmua says, I'm saying that we're looking for it at the wrong time, too early. Sometimes we are celebrating Matariki at a time when it's still below the earth.

Rangi says we shouldn't buy into the belief that the month we know as Pipiri is June. June is factored using the solar year and Pipiri is factored using the lunar year.

Most of the time, the right time to find Matariki is at the end of June, or the beginning or middle of July. Thats Pipiri on the Mori calendar.

Dr Rangi Mtmua wants to revive Mori astronomy.

The stories are there. Since Tne travelled to the heavens to hang the stars. The stars are a tribe of chiefs. Knowledge is the sustenance of chiefs. Therefore the knowledge is there amongst the chiefs suspended in the sky.

Wishing upon a star, Dr Rangi Mtmua has a vision that he hopes will attract and educate Mori youth and those passionate about astronomy and the knowledge and wisdom embedded within the stars.

I want to set up a Mori observatory. The idea is that it will be similar to the traditional observatories while incorporating knowledge from the modern world.

The Museum awards will be held tomorrow night,while the book Matariki - The Star of the Year will be formally launched on Wednesday.

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Dr. Rangi Mtmua hopes to revive Mori astronomy - Mori Television

Youve probably hear it many times the universe is expanding.

A harder question, at least for astronomers, is how fast is the universe expanding?

That speed is difficult to measure precisely. Several techniques are used to get the distance and speed of distant objects, but not all of these techniques agree with one another.

One method that uses the heat of radiation, or cosmic microwave background, left over from the Big Bang indirectly determines the expansion speed. This method uses a mathematical model of the expanding universe that includes mysterious dark energy.

Assuming this model is correct, it gives a precise value of the Hubble constant, or the speed of expansion.

Another method is a direct measurement of the expansion, but that is more difficult to perform.

This method involves observations of certain types of stars, called Cepheid variables, and also supernovas in distant galaxies. Astronomers have methods to determine the brightness of both of these at their source, and by comparing these to the light level measured by telescopes, the distance can be calculated.

Its like using the light in your eye from a distant light bulb and knowing whether it's a 60-watt or 100-watt bulb at the source to estimate the distance.

There is a new method to measure the Hubble constant, and it uses a technique called gravitational lensing, which was first predicted using Einsteins equations for gravity.

Maybe youve heard that light bends near massive objects such as black holes. Also, its been known for centuries that light bends when it enters glass, such as in the lens of a magnifying glass.

That means light from distant objects, such as quasars, can bend when traveling past a massive galaxy. The massive galaxy acts as a lens and bends the quasar light to a focal point.

This forms multiple images in a telescope on Earth if the quasar and the galaxy are lined up just right. Such a result of gravitational lensing is shown in the picture accompanying this column. In it, four images of a quasar surround the galaxy in the center.

Using gravitational lensing, a team of astronomers called the H0LiCOW collaboration (as in holy cow, Batman!) announced earlier this year a direct measure of the Hubble constant.

The key result is that H0LiCOW agrees with the Hubble constant found by the other direct measurements and disagrees with that found from the cosmic microwave background.

So whats going on? After all, we have only one universe, and its speed of expansion is fixed by nature. Obviously, one (or more) of the measurement techniques is flawed.

In my view, the most likely explanation is that the mathematics used to describe the dark energy in the cosmic microwave measurements is incorrect. There are other models proposed by theoretical physicists that put the effect of dark energy into the equations in a different way, so maybe one of these alternate models is correct.

The bottom line is that there are some details about the expansion of the universe that we still dont understand. All measurements agree that the universe is expanding, but whether the Hubble constant has a value of 66 or 73 (in the appropriate measuring units) is still an issue.

While this might seem a small difference between the different ways to measure the speed of expansion, precise measurements have the effect of telling us whether or not we have a correct physical model of the universe.

Kenneth Hicks is a professor of physics and astronomy at Ohio University in Athens.

hicks@ohio.edu

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Astronomy: HoLiCOW! Measuring speed of universe expansion is no easy task - The Columbus Dispatch

Quasars are extremely bright, extremely distant objects. They are the disks of material around supermassive black holes, which heat up and glow as material streams inward toward the event horizon. And now, the Sloan Digital Sky Survey (SDSS)has identified more than 147,000 of these objects in the distant universe to create a first-of-its-kind 3-dimensional map of the early universe that is also the largest such map available to date.

The observations were taken over the course of two years as part of the SDSS Extended Baryon Oscillation SpectroscopicSurvey, abbreviated eBOSS, which uses the Sloan Foundation 2.5m Telescope at Apache Point Observatory. eBOSS aims to more accurately measure the expansion history of the universe. The quasars in the study were spotted shining at a time when the universe was between 3 and 7 billion years old.

This new, more complete map of the universe and its expansion history agrees with the standard cosmology astronomers have developed over the past two decades and are currently using today, which includes properties such as Einsteins general theory of relativity and the existence of dark matter and dark energy.

Studying this time frame is particularly important because its the epoch leading up to when the universes expansion changed from a decelerating to an accelerating expansion. That happened when the universe was roughly 7.8 billion years old, or about 6 billion years ago. Today, that acceleration continues in short, objects farther away from us are receding faster, and continue to do so because of a cosmological component called dark energy. Characterizing the exact nature of this transition from a decelerating to accelerating universe can place further constraints on the nature of dark energy, which is the dominant component in our universe at the present time.

In a recent press release, Will Percival, a professor of cosmology at the University of Portsmouth and the eBOSS survey scientist, explains, Even though we understand how gravity works, we still do not understand everything there is still the question of what exactly dark energy is. We would like to understand dark energy further.

eBOSS is looking into the nature of dark energy by studying baryonic acoustic oscillations, or BAOs. BAOs are the remnant signature of sound waves traveling through the very early universe; when the universe was about 380,000 years old, these sound waves were essentially frozen in place by changing conditions. Since then, their signature has been stretched by the expansion of the universe. But astronomers have a good idea of what the BAOs should have looked like at the time they were frozen, making the changes we see in BAOs over time a clear record of the universes expansion over time.

Thus, BAOs can be used as a sort of standard ruler by cosmologists. The size of the oscillations corresponds to the most likely distance between galaxies, including the quasars that reside within them. According to Pauline Zarrouk, a PhD student at the University Paris-Saclay, You have metres for small units of length, kilometers or miles for distances between cities, and we have the BAO for distances between galaxies and quasars in cosmology.

Today, the distribution of galaxies (and their quasars) is a reflection of the frozen-in BAOs, so the better we can map the universe, the better we can understand how its expansion has changed over time, independent of other ways of measuring that expansion, such as using supernovae or lensed quasars.

Thus far, Our results are consistent with Einsteins theory of general relativity says Hector Gil-Marin of the Laboratoire de Physique Nuclaire et de hautes nergies in Paris. Gil-Marin is one of the astronomers who contributed to the analysis of the quasars and the creation of the map. We now have BAO measurements covering a range of cosmological distances, and they all point to the same thing: the simple model matches the observations very well.

See the article here:

Astronomers create the largest map of the universe | Astronomy.com - Astronomy Magazine

Theres a star 1,300 light years away that has exhibited some of the strangest behavior ever seen: something dims 20 percent of its light, something that is beyond the size of a planet. Its called KIC 8462852, but most people shorthand it Tabbys Star, or Boyajians Star for its discoverer, Tabitha Boyajian.

Heres the thing, though. Absolutely nobody knows why its dimming that much. It could be a massive fleet of comets or the debris of a planet. But its not giving off much infrared excess, which is a sort of "heat glow" from reflected starlight. And now, it seems to be dimming again, either helping or complicating the search for a solution.

Boyajian and co-investigator Jason Wright first put out the alert, hoping to garner observations from telescopes worldwide. Theyre hoping at least one of telescope can grab spectra from the star to see what is causing the dimming.

So far the dimming is at 2-3 percent, meaning the transit of something is just starting. Tabbys Star has a dedicated telescope waiting to find such an event, so the big observation period could yield further clues to whats occurring.

Ok, its time we tell you: some people think its aliens. The hypothesis, put forth by Wright, states that in the absence of a good hypothesis, all avenues must be explored, and that includes giant Dyson Swarm machines harnessing the power of the star. Gathering the spectra could help rule that out or bolster the case for that all other avenues exhausted scenario.

Heres the thing, too: you can get in on the action. Amateur astronomers use smaller scopes to track the star, which is bigger and older than the Sun. Its at around 12th magnitude in the direction of Cygnus. So get out there tonight and hunt for some aliens.

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The weird star that totally isn't aliens is dimming again | Astronomy ... - Astronomy Magazine

2007 OR10 is the largest body in the solar system with no common name. And now, the no-name dwarf planet with a diameter between 800 and 950 miles (1,2901,528km) has been discovered to have a moon.

As the name implies, 2007 OR10 was initially discovered in 2007. Its the third or fourth largest object in the Kuiper Belt, just after Pluto, Eris, and Makemake. There is some debate as to its size. Dwarf planet planetary scientist Mike Brown lists it as the fourth largest, while other estimates place it above Makemake in diameter. Browns graduate student at the time, Meg Schwamb, discovered the world. It is a bright, red, icy world that swings from 33 to 101 AU in its orbit. (One AU is the distance between the Earth and the Sun, and Neptune is at 30 AU.)

OR10 has a very slow rotation rate, which hid the moon in plain sight from Hubble for quite some time. Its a large moon for OR10s size, estimated at 150 to 250 miles (240400km) in diameter. The higher estimate places the moon at the lower limits of dwarf planet status, had it orbited the Sun on its own. A body is considered a dwarf planet if it can attain a round shape and is only in orbit around the Sun and not another body. The moon is about one-quarter the size of OR10, a similar ratio to the Moon and Earth.

So now theres a dwarf planet without a name with a fairly large moon around it. Maybe this boosts the case for giving it a real name.

Excerpt from:

Researchers find a tiny moon around a large unnamed dwarf planet - Astronomy Magazine

Composite image of the Fomalhaut star system. The ALMA data, shown in orange, reveal the distant and eccentric debris disk in never-before-seen detail. The central dot is the unresolved emission from the star, which is about twice the mass of our sun. Optical data from the Hubble Space Telescope is in blue; the dark region is a coronagraphic mask, which filtered out the otherwise overwhelming light of the central star. Credit: ALMA (ESO/NAOJ/NRAO), M. MacGregor; NASA/ESA Hubble, P. Kalas; B. Saxton (NRAO/AUI/NSF)

An international team of astronomers using the Atacama Large Millimeter/submillimeter Array (ALMA) has made the first complete millimeter-wavelength image of the ring of dusty debris surrounding the young star Fomalhaut. This remarkably well-defined band of rubble and gasis likely the result of exocomets smashing together near the outer edges of a planetary system 25 light-years from Earth.

EarlierALMA observations of Fomalhaut taken in 2012 whenthe telescope was still under construction revealed only about one half of the debris disk. Though this first image was merely a test of ALMAs initial capabilities, it nonetheless providedtantalizing hints about the nature and possible origin of the disk.

The new ALMA observations offer a stunningly complete view of this glowing band of debris and also suggest that there are chemical similarities between its icy contents and comets in our own solar system.

ALMA has given us this staggeringly clear image of a fully formed debris disk, said Meredith MacGregor, an astronomer at the Harvard-Smithsonian Center for Astrophysics in Cambridge, Mass., and lead author on one of two papers accepted for publication in theAstrophysical Journaldescribing these observations. We can finally see the well-definedshape of the disk, which may tell us a great deal about the underlyingplanetary systemresponsible for its highly distinctive appearance.

Fomalhaut is a relatively nearby star system and one of only about 20 in which planets have been imaged directly. The entire system is approximately 440 million years old, or about one-tenth the age of our solar system.

As revealed in the new ALMA image, a brilliant band of icy dust about 2 billion kilometers wide has formed approximately 20 billion kilometers from the star.

Debris disks are common features around young stars and represent a very dynamic and chaotic period in the history of a solar system. Astronomers believe they are formed by the ongoing collisions of comets and other planetesimalsin the outer reaches of a recently formed planetary system.The leftover debris from these collisions absorbs light from its central star and reradiates that energy as a faint millimeter-wavelength glow that can be studied with ALMA.

Using the new ALMA data and detailed computer modeling, the researchers were able to calculate the precise location, width, and geometry of the disk. These parameters confirm that such a narrow ring is likely produced through the gravitational influence of planets in the system, noted MacGregor.

The new ALMA observations are also the first to definitively show apocenter glow, a phenomenon predicted in a 2016 paper by Margaret Pan, a scientist at the Massachusetts Institute of Technologyin Cambridge, who is also a co-author on the new ALMA papers. Like all objects with elongated orbits, the dusty material in the Fomalhaut disk travels more slowly when it is farthest from the star. As the dust slows down, it piles up, forming denser concentrations in the more distant portions of the disk. These dense regions can be seen by ALMA as brighter millimeter-wavelength emission.

Using the same ALMA dataset, but focusing on distinct millimeter-wavelength signals naturally emitted by molecules in space, the researchers also detected vast stores of carbon monoxide gas in precisely the same location as the debris disk.

These data allowed us to determine that the relative abundance of carbon monoxide plus carbon dioxide around Fomalhaut is about the same as found in comets in our own solar system, said Luca Matr with the University of Cambridge, UK, and lead author on the teams secondpaper. This chemical kinship may indicate a similarity in comet formation conditions between the outer reaches of this planetary system and our own. Matr and his colleaguesbelieve this gas is either released from continuous comet collisions or the result of a single, large impact between supercomets hundreds of times more massive than Hale-Bopp.

The presence of thiswell-defined debris disk around Fomalhaut, along with its curiously familiar chemistry, may indicate that this system is undergoing its own version of the Late Heavy Bombardment, a period approximately 4 billion years ago when the Earth and other planets were routinely struck by swarms of asteroids and comets left over from the formation of our solar system.

Twenty years ago, the best millimeter-wavelength telescopes gave the first fuzzy maps of sand grains orbiting Fomalhaut. Now with ALMAs full capabilities the entire ring of material has been imaged, concluded Paul Kalas, an astronomer at the University of California at Berkeley and principal investigator on these observations. One day we hope to detect the planets that influence the orbits of these grains.

The National Radio Astronomy Observatory is a facility of the National Science Foundation, operated under cooperative agreement by Associated Universities, Inc.

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[ 19 May 2017 ] Icy ring around Fomalhaut observed in new wavelength News - Astronomy Now Online

This image of Jupiter was taken on 3April 2017 when the planet was at a distance of 414million miles (667million kilometres) from Earth. The NASA/ESA Hubble Space Telescope reveals the intricate, detailed beauty of Jupiters clouds as arranged into bands of different latitudes. Lighter coloured areas, called zones, are high-pressure where the atmosphere rises. Darker low-pressure regions where air falls are called belts. Constantly stormy weather occurs where these opposing east-to-west and west-to-east flows interact. The planets Great Red Spot (GRS, lower left), is a long-lived storm roughly the diameter of Earth. Oval BA, affectionately referred to as the Little Red Spot (lower right), transits roughly 90minutes ahead of the GRS. Image credit: NASA, ESA, and A. Simon (GSFC).Observers in the heart of the British Isles have already entered that time of the year when astronomical twilight lasts all night. But even if the sky never truly gets dark, take solace in the sight of Jupiter, currently highest in the sky to the south around 10pmBST.

The Solar Systems largest planet is now seven weeks past opposition, but still presents a magnitude-2.3 disc with an angular width of 42arcseconds. This is means that a telescope magnification of just 45 is sufficient to enlarge it to the same apparent size of an average full Moon as seen with the unaided eye.

Even the smallest telescope (and powerful binoculars, if suitably steadied) will reveal Jupiters four largest Galilean moons Io, Europa, Ganymede and Callisto in their orbital dance around their parent planet.

With a quality telescope of 3-inch (7.6-cm) aperture or greater at magnifications of 100 and more you can occasionally observe (subject to good seeing conditions) the shadows of these moons slowly drift slowly across the face of Jupiter, like ink-black dots. The timings of the start and end of such events visible from the UK for the remainder of the month are tabulated below. The times that the moons themselves are occulted (hidden) by Jupiter, or pass into or emerge from the planets shadow (eclipsed) are also shown.On the UK morning of Sunday 28May 2017, the shadows of Jupiters Galilean moons Io and Ganymede may be seen simultaneously on the face of their parent planet from 1:16am to 1:39amBST. This computer simulation depicts the scene at 1:20amBST. Note that this is an erect-image view (north up, east left). Users of Newtonian/Dobsonian telescopes should rotate this image 180degrees to match the eyepiece view, while owners of refractors, Maksutov- and Schmidt-Cassegrain telescopes with a star diagonal should mirror the image left to right. AN graphic by Ade Ashford/SkySafari.Great Red Spot and OvalBA (aka Little Red Spot) Jupiters Great Red Spot (GRS) also puts on an appearance at times suitable for observing from the UK during the remainder of the month, also shown in the table below. The GRS is said to transit when it lies on an imaginary line joining Jupiters north and south poles. Owing to the planets fast rotation (at the latitude of the Great Red Spot it takes little more than 9h55m to make one revolution), the GRS is well seen for roughly an hour either side of the transit time. The Great Red Spot has an unmistakable brick red hue at present, making it an easy object to identify in quality telescopes capable of 100 magnification or more when seeing conditions are good.

For observers with 8-inch (20-cm) and larger telescopes, try to see the smaller OvalBA (also shown in the image at the top of the page), popularly known as the Little Red Spot though do bear in mind that it transits the central meridian of Jupiter around 1hours before the times given for the GRS.Predictions for the start and end times of Galilean shadow transits, plus information on their eclipses and occultations for any given date in a slightly more user friendly format may also be obtained through our Almanac. To see the satellite events for any given day, ensure that the Add phenomena of Jupiter? checkbox is ticked. Like the Great Red Spot predictions, all Galilean moon phenomena events are in Universal Time (UT). For help using the Almanac, see this article.

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Don't miss Jupiter's moons and Great Red Spot during May - Astronomy Now Online