Soon I will be off on an observing run in Hawaii. I will be using the 15m JCMT telescope on Mauna Kea to take spectral line data using an instrument called HARP.

Since this will be my first professional expedition I will be taking lots of pictures and notes as I try to get to grips with using a real telescope to doing real science.

As much as possible I will blog here, though at this stage I really don’t know what will be possible.
So in case you suddenly notice an absence of blog posts in the next while, fear not - it is just me being all busy and such.

If you have any questions about my trip drop me a line via the comments thread here and I will get back to you.

Astronomy Blog gives a great little overview of the upcoming meteor shower, including a top pic from Stellarium. I love this shower because I’m often in France for it where I can much better skies.

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The other day we were driving along and I found out that a friend of mine’s father is a commercial airline pilot. We chatted about it for a while - apparently his mother was an air hostess and that’s how they met - and I mentioned that he must have time travelled quite a bit.

I wasn’t being facetious by any means. It has always been a fascination of mine that Einstein’s special relativity is something you experience on long plane trips. During my physics A-Level I learned that one of the verifications of relativity was that some researchers placed took two synchronised atomic clocks and placed one of a boeing jet. they flew it around the world a few times at regular commerical speeds and low and behold when it came back the travelling clock had experienced less time than the stationary one.

Like the astronauts in Planet of the Apes, the moving clock had experienced time dilation and lost a few nanoseconds compare to its Earthbound counterpart. I suggest that my friend’s father would had experienced his fare share of time dilation himself, albeit only on the order of nanoseconds.

So here’s a little form to let you figure out how much time you’ve saved in the past year:

So there you are, have a go. See how many nanoseconds you can add to your life by flying endlessly around the world.

So I’m still musing about the reasons for studying star formation and so I have begun trying to think in a more positive way. This is what I came up with earlier today…

Star formation is a science at a turning point. It will not be long now before astronomers have the choice of several world-leading instruments capable of observing at millimetre and sub-millimetre wavelengths. NASA’s Spitzer telescope is already orbiting above our heads taking new and exciting images with an array of instruments. Herschel, an eagerly anticipated multiple-instrument space observatory akin to Hubble will be launched by ESA within a year or so. SCUBA-2 is a high-technology camera that will be fitted to the James Clerk Maxwell Telescope (JCMT) atop Hawaii’s Mauna Kea and allow rapid surveys of star forming regions to be made at speeds many tens of times faster than has been done previously.

Within the next decade it is hoped that several of the big questions of star formation may be answered. Why do stars form in clusters of hundreds or thousands of stars? Why do stars have the signature spread of masses that is observed? What are the initial conditions of planet formation? There are many more but these give a good example of the kind of thing that star formation theorists and observers are out to explain.

Whilst returning to the Moon and Mars will hold the public eye for decades to come, the nitty gritty of the origins of our creation are mostly hidden in understanding star and planet formation. To understand how the Sun and it’s ever-growing family of planets, dwarf-planets and other miscellany – including us – came to be here in this neck of the galactic woods is a vital part of the much larger puzzle that is star formation itself.

As a discipline, star formation slots neatly in almost all areas of astronomy and astrophysics. If you want to understand galaxies you’ll need to know what they’re made of and if you want to get to grips with nebulae then you’d better know where they’re headed. Even cosmology, so often seen by my own colleagues as putting the physics in astrophysics, has recently been bitten by the star formation question. Namely, they need to explain how stars formed so early in the universe after the big bang. If they can’t, then there is some explaining to do since we have observed stars at ages very close to that of the universe itself.

Those three examples are very overarching but they get the point across: star formation is vital to modern astronomy. Part of the mystery of the subject is that it often crosses huge orders of scale in the same physical process. A good example told to me recently is that if the Sun were a metre across then the nebula from which it formed would be the size of France. The Earth on this scale is only the size of a marble! To compress all that material down through a million orders of magnitude in size obviously involves complex physics, yet if you want to understand where we all ultimately came from, then you need to know. So to save you the trouble of having to figure it all out, the astronomers are willing to do it for you.

So as well as fitting nicely into most areas of astronomy, star formation actually fits into your life – it’ll change the way you think of things. This isn’t just because the various stages of stars give you pretty objects like the Orion Nebula (Above) and the Pleiades (Top) to look at with your telescope. Star formation tells us something very fundamental: we are all made of stardust. The Sun, the planets and everything else you know were formed from the same giant cloud of material – most likely a cloud left over from an even older star when it died. Anything that wasn’t there to begin with was made inside the Sun and it is the Sun that protects from anything outside our Solar System with its enormous gravitational and magnetic fields. Only star formation can tell us how all of this works and how the cogs in the great celestial machine got turning in the first place.

Soon we will be in the position to look at other solar systems from the outside, a perspective we have never had before. If the current theories are correct then star formation is about to turn a corner. Astronomers will look at whole systems like our own at various stages of existence, from barely formed blobs about to start collapsing through multiple stars with their many shapes and sizes to single suns with rocky bodies in orbit and who knows what else. This will in turn allow us to see ourselves even more clearly then we ever have before and to figure out how we got here and why it happened.

This is inspirational science, and worth keeping an eye out for in the years to come. I welcome views on what I have written here from astronomers and non-astronomers alike - what do you think?

I’ve just spent the weekend in Rome. In fact I had one of the best holidays ever running around the Italian capital and generally being silly with my friends. We also visited the Vatican, naturally, and so upon returning home I thought I should do a Roman Catholic Orbiting Frog post.

So what did the Pope ever do for Astronomy? Well quite a lot it seems. There is a Vatican Observatory outside of Rome which operated for many centuries. Its origins can be traced back to the 16th century and research is still done there today.

The observatory was first thought of by Pope Gregory XIII who had a penchant for astronomy. It is actually him that grabbed my attention when looking up the history of the papacy’s astronomical ties since Gregory himself enacted something which has since affected most of the world today.

A thousand years ago, give or take a century, the Roman Empire created the Roman Calendar. It consisted of ten months (Martius, Aprilis, Maius, Junius, Quntilis, Sextilis, September, October, November, and December) in a year of 304 days. After December had finished there would be a period of Winter in which there were no numbered days until the King decided it was time to start over, based on thr advice of his astronomers.

One king had the bright idea to insert a specific Winter and so introduced January and February, although February came first for over 200 years! Then in 46 Bc, another 400 years later, Julius Caesar formalised the calendar (remaning some Months along the way in the form of July and August) into what is called the Julian Calendar. This was a system of years with 365 days and then every fourth year (a leap year) 366.

By the time Caesar did this, the months and the season were no longer at all in sync. He had to add in 90 days to the year 46BC in order to resynchronise them. But even this new system - the height of technological innovation at the time - wasn’t quite right.

So it was that in 1582 AD, Pope Gregory XIII devised a way to sort the calednar out once and for all. What he came up with was a system based on a cycle of 400 years comprising 146,097 days, in a year of an average length of 365.2425 days. The Gregorian calendar, as it  became known, is a modification of the Julian calendar in which leap years are omitted in years divisible by 100 but not divisible by 400. By this rule, the year 1900 was not a leap year (1900 is divisible by 100 and not divisible by 400), but the year 2000 will be a leap year (2000 is divisible by 400).

Pope Gregory’s calendar was constructed to approximate the tropical year, which is the true time taken for the Earth to complete one orbit around the Sun.

The Julian calendar was switched over to the Gregorian starting in 1582, at which point the 10 day difference between the actual time of year and traditional time of year on which calendrical events occurred became intolerable for framers and the general life. Pope Gregory decreed that the day after October 4th 1582 would be October 15th, and so the Catholic countries of France, Spain, Portugal, and Italy complied.
The Protestant German countries adopted the Gregorian reform in 1700. By this time, the calendar trailed the seasons by 11 days. England and what would become American finally followed suit in 1752, and Wednesday, September 2nd, 1752 was immediately followed by Thursday, September 14th This traumatic change resulted in widespread riots and the populace demanding “Give us the eleven days back!”, according to Vardi’s ‘The Gregorian Calendnar’.

Makes daylight savings seem like child’s play.

Big doesn’t quite cover this blog post.

For the past few weeks in my role as a demonstrator in the first year undergraduates lab, I have been supervising the experiment titled Large Scale Structure of the Universe. The experiment itself is a slightly painful exercise involving a series of simulated optical telescopes on an odd piece of software installed on the lab computers. The students have to find the galaxies, which I give to them on a piece of paper, and then take a fake spectrograph reading for each one. This enables them to dot-by-dot create a small, 3D slice of the universe where they can see how far away each galaxy is from Earth and the structure the galaxies take on the largest scales.
They are, understandably, not too thrilled at this. Lab takes four hours and the preamble to this experiment takes a good hour on its own. When it is complete, and they have say, an hour remaining of lab, in which they must answer a series of questions based upon the data they have taken and the completed set of many more galaxies printed in their lab book already.

Now ignoring the fact that they seem to have taken the data for no reason at all and that this is a sure-fire way of ensuring they learn to loathe astronomy as a boring, long-winded science, what they end up with is quite interesting. Naturally none of them see it as interesting as they have been steadily bored by it for a whole afternoon, which is a great shame.

The reason it is so interesting is that on the very largest scales, the Universe has a structure. When one looks into the sky and sees the myriad of stars, nebula and galaxies one could be forgiven for thinking that the universe was pretty randomly distributed. Yet given a little thought this doesn’t seem obvious at all because eveything we have yet discovered seems to have an order.

The Earth goes around the Sun, the Sun around the centre of the galaxy. The galaxy itself is part of a larger collection of gravitationall bound galaxies called the Local Group. The Local Group is part of a larger collection known as a cluster. The clusters collect into super-clusters. There is structure at all levels. Yet at its highest order of size, the Universe still shows form and shape.

Taking every galaxy as simply a dot and then assembling all the dots together into a picture containing millions upon millions of galaxies we see the Universe looks a bit like foam. The matter (i.e. all the galaxies) mostly exisitng on the surface of bubbles, within which lies great voids of space. These regions are unimaginable large and if you were to sit at the centre of them it would be incredibly dark as there would be no stars to light things up.

There are many people studying the structure of the universe at this level. There is a survey, as a good example, called the Two degrees of freedom galaxy redshift survey, or the 2DF Survey which you can read more about at this link

What I wanted to post here though was deatils of the Millennium Simulation. In the words of the Virgo Consortium that carried out the simulation, it is

“…the largest [computer] Simulation ever carried out, containign over 10 billion particles. The simulation was carried out by the Virgo Consortium using the a cluster of 512 processors located at the Max Planck Institute for Astrophysics in Garching, Germany. The simulations took a total of 28 days (~600 hours) of wall clock time, and thus consumed around 343000 hours worth of cpu-time.”

What the simulation produced, amongst other things, was a series of movies and images from a simulated Universe. In these animations the camera flies around the universe, showing in rich detail the current best model for what the universe looks like at such large scales. It is quite beautiful to watch and I suggest you do. There are two versions of it: a 60 MB version called the Fast Flythru and then a 120 MB version which is the same journey but done more slowly so you can take more in. Both are DivX files.

A whole host of video and images are available on this website, which outlines what you’re looking at as well. You can look at the Universe as it is now or watch it evolve from its early stages to the present day.

Obviously even at 10 billion particles, the Millennium Simulation doesn’t even start to approach the actual resolution of the Universe but this is worth a look and certainly gives you an idea of exactly how teeny tiny we are here on Earth and how remarkable it is that we are able to discover such enormous ideas.

My friend Louis asked me the other day whether gravity is different at the equator than at the poles. This was in response to learning that the Earth is wider as the equator and not precisely spherical. Its a good question. He then followed it up with ‘how does gravity work?’ which is an even better question since no one really knows. So here are some thoughts on gravity.

Isaac Newton wasn’t the first to wonder what gravity was. Aristotle and Galileo are just two famous examples of philosophers who tried to address the issue. Aristotle believed that all bodies fell toward the centre of the Earth in proportional to their weight. Galileo famously (or mythically) dropped a cannonball and an apple off the Leaning Tower of Pisa to see which hit the ground first.

Newton was however the first to quanitfy gravity, in his Principia Mathematica. He outlined several of physics’ most fundamental laws in mathmatical form in that text and with his exploration of the understanding of the laws of motion he was able to explain the motions of that mythic cannonball as well as the bodies of the heavens as well.

Newton’s laws are sufficient to explain the motion of objects in out everday lives. From the acceleration of cars on motorways to the flight of planes through the sky to the weight of objects on a tabletop, Newton’s Laws can adequately explain them all. They can almost exactly explain the precise motion of the planets around the Sun.

But not quite.

Albert Einstein outlined his General Theory of Relativity in 1915 which showed gravity as the curvature of the fabric of spacetime. Why he did this isn’t worth going into here, but he did and he was right (so far as we know). We can now successfully predict the motions of the planets to within microseconds. Relativity along with Newton’s laws have allowed to send men to the Moon an spacecraft even further.

So how does it work? Well in Newton’s equation (which is s far as we’ll go here in terms of equations) the force of gravity between two objects is directly proportional to the sum of their masses and inversely proportional to the square of the distance between them. What does that all mean? Well if you double the masses, you double the force and if you double the distance you decrease the force by a factor of four (i.e. two squared).

We can now measure variations of the gravtational field to a high level of accuracy. Spacecraft and satelites have now been measuring the Earth’s delicately varying gravitational field for some time. Below is a map showing the variation of gravity across the globe, taken from the GRACE satellites.

GRACE (Gravity Recovery and Climate Experiment) are two satellites placed into orbit in March 2002 which monitor the Earth’s gravity among other things. It shows in red, regions where the gravitational field is slightly (and I do mean ever-so slightly) higher and in blue where it is lower. Here it is again but in 3D.

So this answers Louis’ question in as much as it can be answered. The answer is that yes, gravity changes across the surface of the Earth, although not perceptably by human standards. How it varies is shown above in the animation and in the map.

As for what gravity really is… well that is the subject if much observational and theoretical debate. It is out there, all pervasive and influencing everything. It shaped the universe from its earliest moments and may well shape its ultimate demise. At the moment it seems to be a good bet that, just as Einstein described it, gravity is the bending of spacetime. It is also a good bet that  the laws of gravity are the same here as they are anywhere else in the universe (although there are many who would argue this point).

If you have any other questions about gravity then I’d be happy to try and find out more for thr blog. Just drop me a line or leave a comment here.

In my blog post on Meteorites I mentioned the Moon formation theory regarding what is known as the Giant Impact Hypothesis. This theory is widely becoming regarded as the best model science has for the Moon’s formation.

Regardless of the evidence for and against this model, here is how it works…

We set the scene around 4 and a half billion years ago, just a few tens of millions of years after the Earth’s formation. At the same time as the Earth has formed, another body, dubbed Theia, has also been created at one of the Langrangian points (proably L5) along the Earth’s orbit. Lagrangian points are those at which the gravity forces of the Sun and Earth are minimal or non-existent - The Hubble Sapce telescope sits at L2 for example.

As Theia grew, it eventually got too big for its position (around the size of Mars) and began to sway in its orbit, eventually being flung at an angle toward the Earth, attracted by its gravitational pull.

It hit the Earth, throwing of huge amounts of debris and itself being destroyed in the impact, merging eventually with the Earth and also the material flung outward.

Caught in the Earth’s gravity, the debris coalesces itself into a body - the Moon - and settles into a tidally locked orbit, meaning that the same face always presents itself to the Earth.

I went looking for an animation of these events and found one on Wikipedia:

The object was named Theia after the greek Titan who gave birth to Selene, goddess of the Moon.

A good, straightforward question - I like it. They’re round because they’re huge!

Basically the spherical shape of planets and stars comes from the fact that they contain so much mass that they have reasonably sized gravitational fields. The mass in any object pulls other masses in toward it. Just as you and I feel the pull of the Earth downward so does the Earth itself.

So every point on the Earth (or any other planet) pulls on every other point. This results in a sphere since it is the only shape where all the gravity forces are balanced throughout the body.

Smaller objects like some of the asteroids and Mars’ moon’s Phobos and Deimos are not spherical. They are not big enough and do not contain enough mass for the gravity to be more powerful than the rock’s internal structure - known as rigid body forces. This condition, that an object can overcome these rigid forces and be spherical, is one of the parameters that the IAU used recently to determine what is a planet and what is not. Spherical objects are planets (or dwarf planets) and non-spherical ones are not.

This is also why we not have 100 mile high mountains on the Earth. If we did then they would collapse under their own gravity.

Some forces can overcome this spherical shape however. The spin of the Earth on its axis is fast enough that the resulting centrifugal force creates a bulge around the equator, making the Earth a little fat. In facts its about 25 miles wider at its middle than at its top.

In Jupiter, the planet is larger and made of less rigid material (i.e. liquid gases) and so the bulge in its middle is pronounced enough to see in pictures like the one above.

The other day there was a partial Lunar eclipse (shown in this photo from NASA’s Astronomy Picture of the Day website). A friend of mine, James, noted that the Moon was really big that night too as it rose with a chunk missing in the evening. The size is exaggerated in the above image by a clever use of a zoom lens but regardless the moon was a little larger than usual.

The Moon goes through a cycle during its orbit, being at one point closest and at another, farthest. If these points occur during the Full Moon the effect is very obvious to the eye as shown in the two comparison photos below.

The Moon’s orbit is not circular in shape but rather it is elliptical (as are all orbits) and thus it cycles between being nearer to us, at what is called perigee (~348,000 km), and then farthest from us at apogee (~398,000 km). In August, this year perigee occurred just one day before full moon.

The Moon takes 27 days and 7 hours to complete a rotation around the Earth. However during that time, the Earth has moved in its own orbit around the Sun and so it takes 29 and a half days to go from Full Moon to Full Moon since the lunar phases depend on the angle between the Sun, Moon and Earth.

Therefore if apogee or perigee occur at Full Moon in any given Month they will next occur slightly earlier in the next Month and so on back through the lunar cycle. This neat animation shows both effects quite nicely in one complete lunar phase cycle.

Therefore if apogee or perigee occur at Full Moon in any given Month they will next occur slightly earlier in the next Month and so on back through the lunar cycle.

So large moons occur once a month, but the effect is most pronounce at Full Moon. They occur at a different time each month and the cycle is not annual. It takes many decades for a large, full moon to land exactly on the same day in the year.

As a side note, down the left hand side of the answer is a scale picture of the Earth Moon system. The moon here is shown midway between apogee and perigee but it does give you an idea of the sizes and angles involved.

There are many categories, or classes, into which a star can form, based its temperature and luminosity. The size of the star is related to these factors. Supergiant stars are typically 10,000 times brighter than the Sun and 100 to 1000 time larger (that is that they have a radius 100 to 1000 times larger).

But how big is the biggest star? Well firstly lets explain that biggest is not necessarily brightest nor most massive. You might for example have a very dense, small star which is technically more massive than a low density giant star.

If we take biggest to mean physical dimension we can say that we looking for the star with the largest radius. The southern hemisphere star, Eta Carinae is almost 11 AUs in radius. AU stands for Astronomical Unit and is the distance between the Sun and Earth. 11 AU means that if you swapped Eta Carinae for the Sun, it would extend outward to engulf Jupiter’s orbit.

However it seems that the generally accepted winner in the largest star category is the Pistol Star, with an radius 340 times larger than the Sun’s. It is also 150 times more massive than our Sun and a million times more luminous.

Like Eta Carinae, it is part of the category of stars known as Luminous Blue Variables. It can found in the constellation of Sagittarius and only ranks in at a measly magnitude +4 when viewed from Earth compared to Sirius at -1.47 and Venus which sometimes reaches -4 or more (I should point out that the lower the magnitude, the brighter the star).

According to Space.com, there are now over 10,000 man-made satellites orbiting the Earth. A few hundred are big enough and fly close enough to the Earth that they are visible. This list includes the International Space Station (ISS) and NASA’s space shuttles.

In the case of the latter two examples, the objects are large enough (i.e. at least six meters in length) and orbit at just 240 miles above the Earth. This means that the sunlight that falls on them is easily seen from the Earth, albeit for only brief periods of time - the ISS can traverse the sky in just a couple of minutes. You can find out when to see the ISS in your area using the Heaven’s Above website.

These days however, the main satellite spotting buzz comes from trying to spot an Iridium Flare. The Iridium satellites are a large fleet of recent additions to the sky. They have large mirror-like solar panels (seen in image above) which are Teflon coated and act like mirrors, briefly reflecting a bright burst, or flare, of sunlight from almost 500 miles up in the sky. The flares range in brightness and can even be seen in the daytime, if you know where to look. This information can also be found on the Heaven’s Above site.

A star or constellation that is always visible (i.e. that never sets) is known as circumpolar. Dependent on where you are in the world different stars will be circumpolar. To explain this more fully we need to understand why the stars set at all.

The stars above our heads are to any casual observer, fixed in their positions above us. In reality they move but the motion is so small and subtle from our distant perspective that they can be considered motionless for the sake of this example. As the Earth rotates they seem to move across the sky and as we moved around the sun they rise and set a different times just as the Sun does, with the seasons.

If you imagine the Earth’s surface extended outward as a sphere. First you have the molten mantle and then the Earth’s crust on which we live. Then you have the lower atmosphere which we breathe and in which mountains and oceans exist. Go even higher and we have a larger sphere on which planes fly about. Higher still there is an imaginary sphere which Satellites move around on and then a larger one still going outward farther and farther until we have what the Greek’s coined the Celestial Sphere. Although they believed it more literally, the idea of a giant Celestial Sphere on which the stars sit is very useful, it acts like a globe for the constellations and it is shown in the graphic above.

So extended outward from the Earth’s north and south pole are lines which reach out to the Celestial north and south pole. The Celestial equivalents of longitude and latitude are Right Ascension and Declination. The celestial equator lies in line with the Earth’s own equator (by definition).

Because the Earth is tilted on its axis, the Sun traces a path around this sphere known as the Ecliptic. If the Earth were not tilted then the Ecliptic would lie exactly on the Celestial equator. But in reality the two are slightly at an angle.

The Sun, the Moon and the planets all move around our sky along the Ecliptic and therefore the twelve constellations which lie on the Ecliptic are always home to the planets. These are the constellations of the Zodiac.

Now all of this explanation is to put in context the fact that if you sit at the North Pole and look directly upward, you will see the star Polaris (or the North Star, in the constelation Ursa Minor), which conveniently lies almost directly over the North Celestial Pole. It will not move at all because of your location on the Earth. At the Horizon you will see the signs of the Zodiac rising slightly over the horizon and then dip slightly under it, following the Ecliptic over the course of the year. In between you have various other constellations which never leave the sky. In fact almost all of the stars in the Celestial Northern Hemisphere will remain visible to you on any night of the year.

A similar situation would present itself if you sat at the South Pole, only this would involved the constellation Crux, rather than Polaris, and all the Southern stars would remain with you. However if you sat on the Equator or in the Tropics, you would not see a sky that rotated but kept the same stars, instead you see a vast rolling sky with one constellation of the Zodiac high above your head at all times and Polaris and Crux sitting at opposite ends of the horizon.

So the question of whether there are any constellations which are always visible is only answered by knowing your location. So, at the poles, all constellations that you can see are circumpolar; at the equator none of them are. In between the answer is that some of them are.

From Cardiff and other similar latitudes the following are circumpolar constellations:

Ursa Major
Ursa Minor
Draco
Cephus
Cassiopeia
Camelopardalis
Lynx

This answer also explains why you need a different planisphere for different locations.