Boulders on the floor of Cerberus Fossae. Credit: NASA/JPL/University of Arizona
[/caption]
Compared to Earth, Mars is a relatively quiet planet, geologically speaking. Actually, very quiet, as in pretty much dead. While it has volcanoes much larger than any here, they have been inactive for a very long time; the latest studies suggest however that volcanic activity may have continued until only a matter of millions of years ago. That seems like an eternity to our human sense of time, but geologically, it is quite recent.
There is also the massive canyon system Valles Marineris, much larger than the Grand Canyon here on Earth, and evidence for ancient hot springs, glaciers, etc. which also show that Mars was once much more active than it is today.
Earthquakes are a common, daily occurrence on our planet, but what about Mars? If they do still happen, they would seem to be much more infrequent than they are here. The new study, however, supports the idea that Mars was geologically active for longer than previously thought, and perhaps still is.
Scientists in Europe have been examining images of a Martian fault system, Cerberus Fossae, taken by the Mars Reconnaissance Orbiter. They’ve found a spot where boulders have tumbled down cliffs near the fault; what’s interesting is that they are primarily found in one location, best explained by marsquakes rather than melting ice and avalanches. This grouping of boulders suggests that they were near the epicentre of a marsquake. The trails behind the rolling boulders are still visible, indicating that they must have fallen relatively recently, with not enough time yet for winds to erase the trails.
Closeup of boulders and trails in Cerberus Fossae. Credit: NASA/JPL/University of Arizona
Marsquakes would also be evidence for possible continued volcanism on the planet, even if only deep underground. That itself has further implications, since it is already known that there are massive ice deposits beneath the surface, even closer to the equator. Heat from any recent or current activity could create liquid water in places, which of course leads back to the question of possible present or past life.
Falling boulders, then, while an interesting observation in themselves, may actually also help to solve some of the ongoing mysteries about the Red Planet.
The study was published in the Journal of Geophysical Research. The paper is available here (by subscription or for $25.00 US).
This meteorite struck the Thomassen family's cabin in Oslo. (Photo: Rune Thomassen)
[/caption]
A family in Oslo got a surprise when they visited their allotment garden cabin for the first time this season and found that a 585-gram (20 oz.) meteorite had ripped a hole through the roof. The space rock was discovered “lying five or six metres away,” the cabin’s owner, Rune Thomassen, told the local newspaper VG.
Such an event is rare in Norway; since 1848 the country has noted only 14 meteorite discoveries.
Astrophysicist Knut Jørgen Røed Ødegaard from the University of Oslo investigated the report and found it to be genuine.
“You can tell immediately that it’s genuine from the burned crust, and you can also recognize it from how rough and unusual it is. It gives me goosebumps,” Ødegaard told VG.
NASA Astrobiology Institute’s Hans Amundsen noted the meteorite’s unusual composition: “This is a very rare meteorite because you can see from the cut of it that it contains fragments from many different kinds of rock that have cemented together, forming a so-called breccia.”
Such meteorites are caused by previous collisions, cementing together different types of material from impacts with asteroids or planets.This means the meteorite that landed on the Thomassens’ cabin may very well have been blown off the surface of Mars at some point in the distant past!
“This is unique. This is double-unique,” Ødegaard noted to VG.
According to Amundsen, such a meteorite is very valuable to researchers as well as private collectors, who may be willing to pay highly for it. Chunks of Mars have fetched USD $877 per gram in the past… making the Thomassens’ find potentially worth over $500,000!
Norway’s geological museum has the country’s only meteorite collection “and they’re the right ones to determine what kind of meteorite this is,” Amundsen said.
Read more on this story here, and see coverage with photos and video on the VG site here (in Norwegian).
Erasure's Andy Bell in front of ESO's Very Large Telescope array. Credit: S. Lowery/Erasure/ESO.
[/caption]
British synthpop band Erasure released a video today featuring lead singer Andy Bell in front of the telescopes of ESO’s Paranal Observatory, located high in the mountains of Chile’s Atacama Desert. The new single “Fill Us With Fire” honors ESO’s 50th anniversary this year. Watch the full video below!
The video features the Very Large Telescope as well as some of ESO’s stunning images of the night sky. This is the third single to be released from their 2011 album Tomorrow’s World.
Andy spent one day at Paranal in February 2012, during which time footage was shot of him singing Erasure’s latest single. The footage was edited with some of ESO’s best astronomical images. Andy, thrilled with the result, decided to dedicate it to ESO’s 50th Anniversary and make it the exclusive video for the single.
Shooting the Fill Us With Fire video. (F. Huber/Erasure/ESO)
Standing on a 20-foot-high platform in front of the VLT, Andy didn’t have a lot of room to move around during the shooting of the video. Say what you will about the choreography, I think it’s awesome to see the observatory and some of its amazing images featured in a new music video!
Personally, I would have wanted to be standing on top of one of the telescope domes but I’m not sure if that’s allowed.
Credit: Erasure/ESO (S. Lowery)
Directed by: Simon Lowery
Editing: Simon Lowery, Lars Lindberg Christensen & Patrick Geeraert
Music: Erasure/Andy Bell
Footage and photos: ESO, Guillaume Blanchard & Simon Lowery
Neptune's system of moons and rings visualized. Credit: SETI
Neptune is one of four planets in our Solar System with planetary rings. Neptune was not discovered until 1846 and its rings were only discovered definitively in 1989 by the Voyager 2 probe. Although the rings were not discovered until the late 1900’s, William Lassell who discovered Titan recorded that he had observed a ring. However, this was never confirmed. The first ring was actually discovered in 1968, but scientists were unable to determine if it was a complete ring. The Voyager’s evidence was the definitive proof for the existence of the rings.
Neptune has five rings: Galle, Le Verrier, Lassell, Arago, and Adams. Its rings were named after the astronomers who made an important discovery regarding the planet. The rings are composed of at least 20% dust with some of the rings containing as much as 70% dust; the rest of the material comprising the rings is small rocks. The planet’s rings are difficult to see because they are dark and vary in density and size. Astronomers think Neptune’s rings are young compared to the age of the planet, and that they were probably formed when one of Neptune’s moons was destroyed.
The Galle ring was named after Johann Gottfried Galle, the first person to see the planet using a telescope. It is the nearest of Neptune’s rings at 41,000–43,000 km. The La Verrier ring was named after the man who predicted Neptune’s position. Very narrow, this ring is only about 113 kilometers wide. The Lassell ring is the widest of Neptune’s rings. Named after William Lassell, it lies between 53,200 kilometers and 57,200 kilometers from Neptune, making it 4,000 kilometers wide. The Arago ring is 57,200 kilometers from the planet and less than 100 kilometers wide.
The outer ring, Adams, was named after John Couch Adams who is credited with the co-discovery of Neptune. Although the ring is narrow at only 35 kilometers wide, it is the most famous of the five due to its arcs. Adams’ arcs are areas where the material of the rings is grouped together in a clump. Although the Adams ring has five arcs, the three most famous ones are Liberty, Equality, and Fraternity. The arcs are the brightest parts of the rings and the first to be discovered. Scientists are unable to explain the existence of these arcs because according to the laws of motion they should distribute the material uniformly throughout the rings.
The rings of Neptune are very dark, and probably made of organic compounds that have been baked in the radiation of space. This is similar to the rings of Uranus, but very different to the icy rings around Saturn. They seem to contain a large quantity of micrometer-sized dust, similar in size to the particles in the rings of Jupiter.
It’s believed that the rings of Neptune are relatively young – much younger than the age of the Solar System, and much younger than the age of Uranus’ rings. They were probably created when one of Neptune’s inner moons got to close to the planet and was torn apart by gravity.
The innermost ring of Neptune orbits at a distance of 41,000 km from the planet, and extends to a width of 2,000 km. It’s named after Johann Gottfried Galle, the first person to see Neptune through a telescope. The next ring is the narrower LeVerrier ring, named after Neptune’s co-discoverer, Urbain Le Verrier. It’s only 113 km wide. Then comes the Lassell ring, the widest ring in the system at about 4,000 km. Then comes the Arago ring, and finally the very thin Adams ring, named after Neptune’s other co-discoverer.
Five of the planets in the night sky are easy to see with the unaided eye, and have been known since ancient times. Uranus is just bright enough that you can see it in a perfectly dark place if you know where to look. But Neptune can only be seen in a telescope. And since telescopes have only been around for a few hundred years, Neptune was discovered recently. So, who discovered Neptune?
The mathematician Alexis Bouvard published a series of astronomical tables detailing the orbit of Uranus. Over time, several astronomers realized that there had to be some additional planet deeper out in the Solar System that was influencing the motion of Uranus with its gravity. They set to work calculating where this additional planet might be located in the Solar System.
Two astronomers, Britain’s John Couch Adams and France’s Urbain Le Verrier had worked out the position of the hypothetical 8th planet independently from each other. And both had a difficult time convincing their colleagues to spend any time actually looking where they suggested the planet might be.
The Berlin Observatory astronomer Johann Gottfried Galle used the calculations by Le Verrier to find Neptune within just 1° of its predicted location, and just 12° of Adams’ predictions. Both astronomers claimed that they were the first to discover the planet, and it led to an international dispute.
After the discovery, there was rivalry between England and France about who should get credit for finding Neptune, Adams or Le Verrier. The international astronomy community agreed that the two astronomers should share credit for the discovery. Eventually both Le Verrier and Adams were given credit for discovering Neptune in 1846.
The planet was named after the Roman god of the oceans; the same as the Greek God Poseidon.
Of course, this is just a shortened version of the discovery of Neptune. If you’d like to read more, check out this article that talks about the mathematical discovery of planets. And here’s more information on Le Verrier.
The "surface" of Neptune, its uppermost layer, is one of the most turbulent and active places in the Solar System. Credit: NASA/JPL
How did Neptune get its name? Shortly after its discovery, Neptune was only referred to as “the planet exterior to Uranus” or as “Le Verrier’s planet”. The first suggestion for a name came from Johann Galle, who proposed the name Janus. Another proposal was Oceanus. Urbain Le Verrier, who discovered the planet, claimed the right to name his discovery: Neptune. Soon Neptune became the internationally accepted name.
In roman mythology, Neptune was the god of the sea. The demand for a mythological name seemed to be in keeping with the nomenclature of the other planets, all of which, except for Earth, were named for Greek and Roman mythology. Most languages today use some variant of the name “Neptune” for the planet.
Now that you know how the planet was named, how about some facts about the planet itself. Size wise, the planet has an equatorial radius 24,764 km, a polar radius of 24,341 km, and a surface area of 7.6408×10,sup>9km2. It has a volume of 6.254×1013km3, a mass of 1.0243×1026kg, and a mean density of 1.638 g/cm3.
Its atmosphere is composed primarily of hydrogen and helium along with traces of hydrocarbons and nitrogen. It also contains a high proportion of ices like: water, ammonia, and methane. Astronomers occasionally categorize Neptune as an ice giant. The interior of Neptune is primarily composed of ices and rock. Traces of methane in the outermost regions account for the planet’s blue appearance. Neptune’s atmosphere is notable for its active and visible weather patterns. These weather patterns are driven by the strongest sustained winds of any planet in the Solar System, with recorded wind speeds as high as 2,100 km/h.Because of its great distance from the Sun, Neptune’s outer atmosphere is one of the coldest places in the Solar System, with temperatures at its cloud tops approaching ?218°C. Temperatures at the planet’s center are approximately 5,000°C. Neptune is one of the most interesting planets in our solar system. There are plenty of other articles about the planet here on Universe Today.
We have written many articles about Neptune for Universe Today. Here’s an article about the size of Neptune, and here’s an article about the atmosphere of Neptune.
An auroral display sparked by the Sun’s recent outbursts was captured by photographer Antti Pietikäinen in the sky over Muonio, Finland, on March 11, 2012. Watch this short but oh-so-sweet video and wish you were there!
Venus & Jupiter above Backyard Observatory - Credit: John Chumack
[/caption]
Greetings, fellow SkyWatchers! What an awesome display of planets! Please take the time to walk outdoors just after skydark – regardless of where you live – and enjoy the bright display of Venus and Jupiter! However, this isn’t the only planetary action going on this week… Mars and M96 pair up, as well as Uranus and the Moon. There’s even a Southern Hemisphere meteor shower to enjoy! Pretty exciting, huh? Join the party by getting out your binoculars or telescopes and meet me for more in the backyard…
Monday, March 12 – No. That’s not the “headlights” of a UFO on the western horizon tonight… It’s a very cool pairing of Venus and Jupiter! It’s not often you see the two visually brightest planets making a close visual pass at each other and tonight you’ll spot the inner planet to the south and the outer planet to the north. This would make a great photo opportunity! Why not consider adding something interesting to your picture like a scenic building, tree, or even a person? Watch in the days ahead as Jupiter appears to stay in the same spot at the same time, yet Venus will climb higher.
Tonight let’s return again to NGC 2362 and start at the cluster’s north-northeast corner to have a look at a single, unusual star – UW Canis Majoris. At magnitude 4.9, this super-giant spectroscopic binary is one of the most massive and luminous in our galaxy. Its two stars are separated by only 27 million kilometers (17 million miles) and revolve around each other at a frenzied pace – in less than four and a half days. This speed means the stars themselves are flattened and would appear to be almost egg-shaped. The primary itself is shedding material that’s being collected by the secondary star.
Now drop southwest of NGC 2362 for another open cluster – NGC 2354 (Right Ascension: 7 : 14.3 – Declination: -25 : 44). While at best this will appear as a small, hazy patch to binoculars, NGC 2354 is actually a rich galactic cluster containing around 60 metal-poor members. As aperture and magnification increase, the cluster shows two delightful circle-like structures of stars, similar to a figure 8. Be sure to make a note… You’ve captured another Herschel 400 object!
Tuesday, March 13 – On this day in 1781, Uranus was discovered by William Herschel. Also on this day, in 1855, Percival Lowell was born in Boston. Educated at Harvard, Lowell went on to found the observatory which bears his name in Flagstaff, Arizona, and spent a lifetime studying Mars. During the early morning hours, you can honor Lowell by seeing Mars yourself – it’s best viewed when as high a possible on the ecliptic. While there won’t be a great many details, think of how many strides have been made since Lowell’s time and how advanced our knowledge of Mars has become!
Tonight let’s hop about four fingerwidths east-northeast of Sirius. Look for 5th magnitude SAO 152641 to guide you to a faint patch of stars in binoculars and a superb cluster in a telescope – NGC 2360 (Right Ascension: 7 : 17.8 – Declination: -15 : 37). Comprised of around eighty 10th magnitude and fainter stars, this particular cluster will look like a handful of diamond dust scattered on the sky. Discovered by Caroline Herschel in 1783, this intermediate-aged galactic cluster is home to red giants and heavy in metal abundance. Mark your notes, because not only is this a Herschel object, but is known as Caldwell 58 as well!
Wednesday, March 14 – Today is the birthday of Albert Einstein. Born in 1879, Einstein was one of the finest minds of our times. He developed the theory of gravity in terms of spacetime curvature – dependent on the energy density. Winner of the 1921 Physics Nobel prize, Einstein’s work on the photoelectric effect is the basis of modern light detectors.
Tonight let’s hop about a fistwidth north of bright Eta Canis Majoris and have a look at a “double cluster” – NGC 2383 (Right Ascension: 7 : 24.8 – Declination: -20 : 56) and NGC 2384 (Right Ascension: 7 : 25.1 – Declination: -21 : 02). Just showing in binoculars as a faint patch, this pair will begin resolution with larger scopes. Studied photometrically, it would appear these fairly young clusters have contaminated each other by sharing stars – which has also occurred in some clusters located in the Magellanic Clouds. Enjoy this unusual collection of stars…
Thursday, March 15 – Today celebrates the birth of Nicolas Lacaille. Born in 1713, Lacaille’s measurements confirmed the Earth’s equatorial bulge. He also named fourteen southern constellations. To honor Lacaille tonight, let’s begin some explorations in a constellation he named – Puppis!
For SkyWatchers living in high northern latitudes, you’ll never see all of this constellation, but there will be some things for you to explore, as well as a great deal for our friends in the southern hemisphere. The first is a Herschel object that lies directly on the galactic equator around five degrees north-northwest of Xi.
NGC 2421 (Right Ascension: 7 :36.3 – Declination: -20 : 37) is a magnitude 8.3 open cluster that will look like an exquisitely tiny “Brocchi’s Cluster” in binoculars and begin good resolution of its 50 or so members to an intermediate telescope, in an arrowhead-shaped pattern. It’s bright, it’s fairly easy to find, and it’s a great open cluster to add to your challenge study lists!
If you’re looking for a curiosity, then look no further than Leo and Mars. Tonight the happy red planet is situated just to the east of Messier 96 (Right Ascension: 10 : 46.8 – Declination: +11 : 49)! Enjoy celestial mechanics over the next few nights as Mars gently changes its position in relation with this distant galaxy… and gets much closer!
Friday, March 16 – On this day in 1926, Robert Goddard launched the first liquid-fuel rocket. But he was first noticed in 1907 when a cloud of smoke issued from a powder rocket fired in the basement of the physics building in Worcester Polytechnic Institute. Needless to say, the school took an interest in the work of this shy student. Thankfully they did not expel him, and thus began his lifetime of work in rocket science. Goddard was also the first to realize the full implications of rocketry for missiles and space flight, and his lifetime of work was dedicated to bringing this vision to realization. While most of what he did went unrecognized for many years, tonight we celebrate the name of Robert H. Goddard. This first flight may have gone only 12 meters, but forty years later on the date of his birth, Gemini 8 was launched, carrying Neil Armstrong and David Scott into orbit!
Let’s begin our observing evening with Mars. While you may have been keeping track of its position, did you know that it’s less than a degree away from a Messier object tonight? That’s right! You’ll find the dusty red planet just to the north of M96 (Right Ascension: 10 : 46.8 – Declination: +11 : 49).
Tonight we’ll pick up a challenge cluster and a planetary nebula on the Herschel list by returning to NGC 2421 and hopping about a fingerwidth northeast for NGC 2432 (Right Ascension: 7 : 40.9 – Declination: -19 : 05). This small, loose open cluster is rather dim and contains around 20 or so faint members shaped like the letter B. About another degree northeast is NGC 2440 – an elongated, small 11th magnitude planetary nebula. Look for its central star to cause a brightening and up the magnifying power to reveal it.
While out, be on watch for the Corona-Australids meteor shower. While the fall rate is low – 5 to 7 per hour – our friends in the southern hemisphere might stand a chance with this one!
Saturday, March 17 – On this day in 1958, the first solar-powered spacecraft was launched. Named Vanguard 1, it was an engineering test satellite. From its orbital position, the data taken from its transmission helped to redefine the true shape of the Earth.
Tonight let’s return to Xi Puppis and head less than a fingerwidth east-northeast for Herschel study NGC 2482 (Right Ascension: 7 : 54.9 – Declination: -24 : 18). At magnitude 7, this small fuzzy spot in binoculars will resolve into around two dozen stars to the telescope. Look for the diagonal chain of stars along its edge.
Now let’s have a look at an open cluster easily located in northeastern Orion. This 5.9 magnitude scattered group of stars may have been first observed by Giovanni Batista Hodierna in the mid-17th century. While bright enough to have been a Messier object, William Herschel added it to his log of discoveries on October 15, 1784, as H VIII.24. Of the 30 known stars associated with this 3,600 light-year distant group, the brightest is 50 million years old. A half-dozen of the cluster’s very brightest members can be seen in small scopes at mid-range powers. Look for NGC 2169 (Right Ascension: 6 : 08.4 – Declination: +13 : 57) slightly less than a fist width north-northeast of Betelguese and slightly south of Xi and Nu Orionis.
Sunday, March 18 – Although you can’t see it with just your eyes, Uranus is less than a degree from the Moon this morning. For some areas this could be an occultation, so be sure to check IOTA information!
Today in 1965, the first ever spacewalk was performed by Alexei Leonov onboard the Soviet Voskhod spacecraft. The “walk” only lasted around 20 minutes and Alexei had problems in re-entering the spacecraft because his space suit had enlarged slightly. Imagine his fear as he had to let air leak out of his space suit in order to squeeze back inside. When they landed off target in the heavily forested Ural Mountains, the crew of two had to spend the night in the woods surrounded by wolves. It took over twenty-four hours before they were located and workers had to chop their way through the forest and recover them on skis. Brave men!
Tonight let’s honor them by studying a small area which contains not only three Herschel objects – but two Messiers as well – M46 and M47. You’ll find them less than a handspan east of Sirius and about a fistwidth north of Xi Puppis.
The brighter of the two clusters is M47 (Right Ascension: 7 : 36.6 – Declination: -14 : 30) and at 1600 light-years away, it’s a glorious object for binoculars. It is filled with mixed magnitude stars that resolve fully to aperture with the double Struve 1211 near its center. While M47 is in itself a Herschel object, look just slightly north (about a field of view) to pick up another cluster which borders it. At magnitude 6.7, NGC 2423 isn’t as grand, but it contains more than two dozen fairly compressed faint stars with a lovely golden binary at its center.
Now return to M47 and hop east to locate M46 (Right Ascension: 7 : 41.8 – Declination: -14 : 49). While this star cluster will appear to be fainter and more compressed in binoculars, you’ll notice one star seems brighter than the rest. Using a telescope, you’ll soon discover the reason. 300 million year old M47 contains a Herschel planetary nebula known as NGC 2438 in its northern portion. The cluster contains around 150 resolvable stars and may involve as many as 500. The bright planetary nebula was first noted by Sir William Herschel and then again by John. While it would appear to be a member of the cluster, the planetary nebula is just a little closer to us than the cluster. Be sure to mark your notes… There’s a lot there in just a little area!
Until next week? May all of your journeys be at light speed!
Many thanks to John Chumack for the inspiring image!
[/caption] Mass: 1.98892 x 1030 kg Diameter: 1,391,000 kilometers Radius: 695,500 km Surface gravity of the Sun: 27.94 g Volume of the Sun: 1.412 x 1018 km3 Density of the Sun: 1.622 x 105 kg/m3
How Big is the Sun?
The Sun is the largest object in the Solar System, accounting for 99.86% of the mass.
As stars go, the Sun is actually a medium-sized, and even smallish star. Stars with much more mass can be much larger than the Sun. For example, the red giant Betelgeuse, in the constellation of Orion is thought to be 1,000 times larger than the Sun. And the largest known star is VY Canis Majoris, measuring approximately 2,000 times larger than the Sun. If you could put VY Canis Majoris into our Solar System, it would stretch out past the orbit of Saturn.
The size of the Sun is changing. In the future when it runs out of usable hydrogen fuel in the core, it will become a red giant as well. It will engulf the orbits of Mercury and Venus, and possibly even the orbit of the Earth. For a few million years, the Sun will be about 200 times bigger than its current size.
After the Sun becomes a red giant, it will shrink down to become a white dwarf star. Then the size of the Sun will only be roughly the size of the Earth.
Mass of the Sun
The mass of the Sun is 1.98892 x 1030 kilograms. That’s a really big number, and it’s really hard to put it into context, so let’s write out the mass of the Sun, with all the zeros.
Still need to wrap your head around this? Let’s give you some comparisons. The mass of the Sun is 333,000 times the mass of the Earth. It’s 1,048 times the mass of Jupiter, and 3,498 times the mass of Saturn.
In fact, the Sun accounts for 99.8% of all the mass in the entire Solar System; and most of that non-Sun mass is Jupiter and Saturn. To say that the Earth is an insignificant speck is an understatement.
When astronomers try to gauge the mass of another star-like object, they use the mass of the Sun for comparison. This is known as a “solar mass”. So the mass of objects, like black holes, will be measured in solar masses. A massive star might have 5-10 solar masses. A supermassive black hole could have hundreds of millions of solar masses.
Astronomers will refer to this with an M beside a symbol that looks like a circle with a dot in the middle – M⊙. To show a star that has 5 times the mass of the Sun, or 5 solar masses, it would be 5 M⊙. Eta Carinae, one of the most massive stars known. Image credit: NASA
The Sun is massive, but it’s not the most massive star out there. In fact, the most massive star we know of is Eta Carinae, which has a mass of 150 times the mass of the Sun.
The Sun’s mass is actually slowly decreasing over time. There are two processes at work here. The first is the fusion reactions in the core of the Sun, converting atoms of hydrogen into helium. Some of the Sun’s mass is lost through the fusion process, as atoms of hydrogen are converted into energy. The warmth we feel from the Sun, is the Sun’s lost mass. The second way is the solar wind, which is constantly blowing protons and electrons into outer space.
Mass of the Sun in kilograms: 1.98892 x 1030 kg
Mass of the Sun in pounds: 4.38481 x 1030 pounds
Mass of the Sun in tons: 2.1924 x 1027 tons
Diameter of the Sun
The diameter of the Sun is 1.391 million kilometers or 870,000 miles.
Again, let’s put this number into perspective. The diameter of the Sun is 109 times the diameter of the Earth. It’s 9.7 times the diameter of Jupiter. Really, really big.
Pardon the pun, but the Sun doesn’t hold a candle to some of the largest stars in the Universe. The biggest star we know of is called VY Canis Majoris, and astronomers think it could be 2,100 times the diameter of the Sun. The Earth compared to Sunspot 1312 on 10-10-11. Credit: Ron Cottrell.
Diameter of the Sun in kilometers: 1,391,000 km
Diameter of the Sun in miles: 864,000 miles
Diameter of the Sun in meters: 1,391,000,000 meters
Diameter of the Sun compared to Earth: 109 Earths
Radius of the Sun
The radius of the Sun, the measurement from the exact center of the Sun out to its surface, is 695,500 kilometers.
This radius is essentially the same however you measure it, from the center to the equator, or the from the center to the Sun’s poles. But you need to be careful with other objects, however, because the speed of their rotation affects the radius.
The Sun takes about 25 days to turn once on its axis. Because it rotates relatively slowly, the Sun doesn’t flatten out at all. The distance from the center to the poles is almost exactly the same as the distance from the center to the equator.
There are stars out there which are dramatically different, though. For example, the star Achernar, located in the constellation Eridanus, is flattened by 50%. In other words, the distance from the poles is half the distance across the equator. In this situation, the star actually looks like spinning-top toy.
So, relative to out stars out there, the Sun is almost a perfect sphere.
Astronomers use the Sun’s radius, or “solar radius” to compare the sizes of stars and other celestial bodies. For example, a star with 2 solar radii is twice as large as the Sun. A star with 10 solar radii is 10x as large as the Sun, and so on. VY Canis Majoris. The biggest known star.
Polaris, the North Star, is the brightest star in the constellation Ursa Minor (Little Dipper) and, because of its proximity to the north celestial pole, is considered the current northern pole star. Polaris is primarily used for navigation and has a solar radius of 30. That means, it is 30 times bigger than the Sun.
Sirius which is the brightest star in the night sky. In terms of apparent magnitude, the second brightest star, Canopus, has only half that of Sirius’. No wonder it really stands out. Sirius is actually a binary star system, with Sirius A having a solar radius of 1.711 and B, which is much smaller, at about 0.0084.
Radius of the Sun in kilometers: 695,500 km
Radius of the Sun in miles: 432,200 miles
Radius of the Sun in meters: 695,500,000 meters
Radius of the Sun compared to Earth: 109 Earths
Gravity of the Sun
The Sun has an enormous amount of mass, and so it has a lot of gravity. In fact, the mass of the Sun is 333,000 times more than the mass of the Earth. Forget that the surface temperature of the Sun is 5,800 Kelvin and made of hydrogen – what would you feel if you could walk on the surface of the Sun? Think about this, the gravity of the Sun at the surface is 28 times the gravity of the Earth.
In other words, if your scale says 100 kg on Earth, it would measure 2,800 kg if you tried to walk on the surface of the Sun. Needless to say, you would die pretty quickly just from the pull of gravity, not to mention the heat, etc.
The Sun’s gravity pulls all of its mass (mostly hydrogen and helium) into an almost perfect sphere. Down at the core of the Sun, the temperatures and pressures are so high that fusion reactions are possible. The tremendous amount of light and energy pouring out of the Sun counteracts the pull of gravity trying to collapse it down. The layout of the solar system, including the Oort Cloud, on a logarithmic scale. Credit: NASA
Astronomers define the Solar System as the distance under the influence of gravity from the Sun. We know that the Sun holds distant Pluto in orbit (5.9 billion km away on average). But astronomers think that the Oort Cloud extends out to a distance of 50,000 astronomical units (1 AU is the distance from the Earth to the Sun), or 1 light-year. In fact, the influence of the Sun’s gravity could extend out to 2 light-years away, the point at which the pull from other stars is stronger.
Surface gravity of the Sun: 27.94 g
Density of the Sun
The density of the Sun is 1.4 grams per cubic centimeter. Just to give you a comparison, the density of water is 1 g/cm3. In other words, if you could find a pool large enough, the Sun would sink down and not float. And this seems kind of counter-intuitive. Isn’t the Sun made of hydrogen and helium, the two lightest elements in the Universe? So how can the density of the Sun be so high?
Well, it all comes down to gravity. But first, let’s calculate the density of the Sun for ourselves.
Formula for density is to divide mass by volume. The mass of the Sun is 2 x 1033 grams, and the volume is 1.41 x 1033 cm3. And so, if you do the math, the density of the Sun works out to be 1.4 g/cm3. Interior of the Sun. Image credit: NASA
The Sun holds itself together with gravity. Although the outermost layers of the Sun might be less dense, the intense gravity crushes the inner regions to enormous pressures. At the core of the Sun, the pressure is more than 1 million metric tons/cm sq – that’s equivalent to more than 10 billion times the atmosphere of the Earth. And once you get those kinds of pressures, fusion can ignite.
Density of the Sun: 1.622 x 105 kg/m3
Volume of the Sun
The volume of the Sun is 1.412 x 1018 km3. That’s a lot of cubic kilometers. Do you need something to compare this with? The volume of the Sun is so great that it would take 1.3 million planets the size of the Earth to fill it up. Or you could fill it with almost 1000 planets the size of Jupiter.
Volume of the Sun in cubic kilometers: 1.412 x 1018 km3
Volume of the Sun compared to Earth: 1,300,000
Circumference of the Sun
The circumference of the Sun is 4,379,000 km.
Just for comparison, the equatorial circumference of the Earth is 40,075 km. So, the circumference of the Sun is 109 times larger than the circumference of the Earth. And the circumference of the Sun is 9.7 times bigger than the circumference of Jupiter.
Today's Journal Club is about a new addition to the Standard Model of fundamental particles.
[/caption]
According to Wikipedia, a journal club is a group of individuals who meet regularly to critically evaluate recent articles in the scientific literature. And of course, the first rule of Journal Club is… don’t talk about Journal Club.
So, without further ado – today’s journal article is about dark matter being in the wrong place at the wrong time.
This time, rather than someone suggesting what the next journal club article would be (like that happens), I thought I would pick a topical scientific paper mentioned in one of Universe Today’s fabulously thought-provoking stories and enlarge on that a bit.
So, some might remember the Bullet Cluster – a seemingly clinching proof of dark matter, where two galactic clusters had collided in the past and what we see post-collision is that most of the mass of each cluster has passed straight through and out the other side. The only material remaining at the collision site is a huge jumbled clump of intergalactic gas.
This means that each galactic cluster, that has since moved on, has been stripped of much of its intergalactic gas. But lo and behold the seemingly empty intergalactic space within each of these stripped galactic clusters continues to distort the background field of view (a phenomenon known as weak gravitational lensing).
This seemed strong proof that the intergalactic spaces of each cluster must be filled with gravitationally-inducing, but otherwise invisible, stuff. In other words, dark matter. It makes sense that this dark matter would have moved straight on through the collision site because it is weakly interacting – whereas the gas caught up in the collision was not.
So, a cool finding and almost identical findings were discovered within the cluster collisions MACS J0025.4-1222, Abell 2744 and a couple of others. But now along comes Abell 520 with a completely counter example. Two or more galaxy clusters have collided, most of the visible contents have passed straight through, but back at the collision point is an apparent big clump of invisible stuff creating weak gravitational lensing – i.e. dark matter. It is the region labelled 3 on the figure at page 5 of the article.
This finding requires us to consider that we had naively concluded that the Bullet Cluster’s post-collision appearance was easily interpretable and that its outcome would surely be repeated in any equivalent collision of galaxy clusters.
But in the wake of Abell 520 we now may need to consider that the outcome of a collision between rapidly moving and utterly gargantuan collections of mass is much more complex and unpredictable than we had initially assumed. This doesn’t mean that the dark matter hypothesis has been debunked, it just means that the Bullet Cluster might not have been the clinching proof that we thought it was.
If we subsequently find fifty new Bullet cluster analogues and no more Abell 520 analogues, we might then assume that Abell 520 is just a weird outlier, which can be dismissed as an unrepresentative anomaly. But with only five or six such collision types known, one of which is Abell 520 – we can’t really call it an outlier at the moment.
So… comments? The authors offers six possible scenarios to explain this finding – got a seventh? Did we jump to conclusions with the Bullet Cluster? Could suggestions for an article for the next edition of Journal Club represent a form of negative energy?
