Astronomical logbooks

Here’s an interesting subject for the budding astronomer – how do you note down what you’ve seen during an observing session. In many cases the answer will be ‘not at all’ – plenty of people enjoy having a look through the eyepiece, maybe take a picture or two and leave it at that. However, there are those who might want a more permanent record that they can refer back to and maybe share with others. In this internet era the entire thing may be, or may be later transferred to, a version that is done electronically. The records are known as logbooks and whilst there must be hundreds of ways of doing this, there are a few things that are considered normal practise.

When planning an observing session, the best results can be obtained through planning the session. Take a look at something like Stellarium to get an idea of what will be out in the night sky in the area you can see. Use metcheck or a weather satellite to get an idea of how long the clouds will give you. If you’ve selected a few targets for your telescope, now might be the time to work out how to set up your log book.

Observer information

Remember to identify yourself, and any co-observers, your observing site (latitude, longitude) and the full date on which you are observing. If you observe both sides of midnight, include both dates on which your observing sessions occurred This might best be done by writing down your start time and date and end time, plus new date if required.

Make a note of the weather conditions. Is it hazy? Is there much light pollution (reflected glow from streetlights or the glow from a nearby or full Moon)? How much of the sky is covered in clouds? These can be important in deciding whether or not you really had a chance of seeing those fainter stars or nebulae.

Observing information

Always remember to write down the tools of your trade. Which telescope (diameter, focal length) was used with which eyepiece (focal length). If you divide the telescope focal length by the eyepiece focal length, you get the magnification. The maximum useful magnification of a given telescope is either 50x the diameter of the telescope in inches, or 20x the diameter in millimeters. Anything above this will give you a bigger image, but it will be fainter and show no smaller details. Of course it is up to you whether you go for a small bright target or a faint but easier to see one. Did you use a diagonal (something that pops into the eyepiece holder so the eyepiece points upwards, making it easier to use at some telescope positions)? Alt-az or equatorial mount? Motor(s) on (tracking the motion of the heavens) or undriven? Maybe the observation was made using binoculars or the naked eye. In which case the magnification and diameter plus focal length of the binoculars is still required, though the eyes can just be written down as being used alone…

Also include all you can on any imaging devices you might use. Did you do a quick sketch of what you can see? Maybe you held a camera, or mounted a camera on the telescope – say which you did and any information on the camera, such as focal length etc that you can get off the web or just the make (if you have a few cameras, why not write this information down on an early page or a back page and give it a name, so you don’t have to copy everything out twice). Did the camera look through an eyepiece (afocal viewing) or was it acting as the eyepiece (prime focus viewing). Maybe the camera was out on its own without a telescope, doing star trails, getting the Moon with a planet or meteors etc. Write down what lens or lenses were used.

Other things to include, if you are using a telescope eyepiece combination. The field of view is the angular size of what you can see through the eyepiece. If there are several objects in the area you are looking at, it is sometimes useful to know how many should be in range of a given eyepiece, or in the case of large objects (like comet Lulin) whether or not the whole thing will fit in the fov of a given eyepiece. This can be calculated through something like an online calculator, or checked at the eyepiece. To check at the eyepiece, remember that the sky rotates (roughly) 360 degrees in one day. That’s 15 arc-minutes every minute and 15 arc-seconds every second (there are 60 arc-seconds in one arc-minute and 60 arc-minutes in one degree of arc). So if you measure the time taken for an object to pass from one side of the field of view to another (with no motors running), then multiply the times in seconds by 15, that gives you the f.o.v in arc-seconds, which can then be converted to degrees, minutes and seconds. Knowing how big your f.o.v. is will then tell you how big it is compared to the objects you might be looking at.

Another reason you might want to switch off the motors is to check the orientation of the things you are looking at. This is always important to put on a sketch or image to tell others which way up it is meant to be. If you, for example, want to know what satellite was on the left hand side of Jupiter and which was on the right and the next day you compare your image to where Stellarium says the moons were, it helps to know if your telescope has flipped the image left to right, or top to bottom or both or neither. To do this, firstly turn off your motors if you have any. Then watch the direction the stars drift in. This is the direction of the rotation of the Earth, they are headed towards the west and an arrow can be drawn to say whether this is left or right. If you’re using an equatorial mount, point the telescope down in declination. The direction the stars move is then the up direction (positive declination), which can be denoted with another arrow. If you’re using alt-az, do the same in both alt and az directions (up-down, left-right, respectively) to get your two arrows.

Observation Information

For objects in the sky such as planets, comets, stars, deep sky objects and the like (things that aren’t really moving that much). The name, if known, and basic co-ordinates (again if known) of the target you are looking at is always helpful. Some telescopes with control pads or setting circles will give you the RA and Dec co-ordinates, in other cases a compass and estimate of the angular altitude will be helpful. Mention what type of thing you are looking at (maybe even why if you have a reason). Is there an even like a occultation going on? Did someone say it was a pretty thing to look at? Are you ticking off everything on Messier’s list one by one?

Of course not all objects require this sort of an observation. Writing down the co-ordinates of the aurora might not be so helpful as writing down the forms of the aurora (corona, sharp curtain, sheet, flickering, green, red etc). Meteors you might not want to sketch every single one, but get an idea of where in the sky they are coming from (their radiant) and an idea of how many per minute are likely to fly overhead (Zenithal rate). Think about what you are seeing/going to see before making notes. If it’s a sporadic meteor happening during observations of other things, then get its direction, where it went to and from and maybe an idea of how bright it is.

The magnitude of an object is how astronomers denote how bright an object is. Originally, the 4000 or so visible stars were divided into six magnitudes of brightness. A sixth magnitude star was the faintest visible to the less polluted skies of the ancients, now you’re lucky to get a fifth magnitude sky. The magnitude scale has since been revised a little and now given a proper footing. Each magnitude represents a drop or increase in brightness of two and a half times. Magnitude one is two and a half times fainter than magnitude zero and so on – the bigger and more positive a number, the fainter the thing is. Some stars in the sky vary in their brightness, whilst others shine fairly constantly. I mentioned in yesterday’s skies over Kendal post that there are some good variables up this month. Why not pick a few stars in the area of known constant magnitude, compare Algol’s brightness to each of them and determine its change in brightness (its ‘light-curve’) during one of the dimming episodes?

Post observation notes

Of course observations don’t end just because you’ve packed away the telescope for the next cloud filled month. Further analysis can be done on what you’ve seen. Compare your notes with Stellarium’s predictions. Do some data reduction on your images to correct for light pollution (sky removal), thermal interference in CCDs, flattening out warping of the image by fast lenses (flat fielding) and so on. Note down what you’ve done and what the result is. Get names for what’s in your sketch or your image to see what you might not have noticed you had seen. Remember all the prediscovery recordings of Uranus and Neptune as background stars. Although you’re unlikely to have seen a new planet out there, there’s many an asteroid, satellite or comet waiting to pop up unexpectedly on a set of images. This may even provide you with a new target to observe the following night.

I watch as diploma students learn to record at the eyepiece

The Skies over Kendal this month…

Clouds.

Ok, if the clouds should happen to depart for a while (and here’s Kendal’s Met check to see if and when they might), here’s a brief roundup of what might be visible in the skies this month:

Solar System

The Comet Lulin remains high in the sky pleasing astronomers outside of our little cloud nursery. Although it will rise higher and earlier in the sky this month, the comet will also fade in brightness fast, going from nearly visible to the naked eye in excellent conditions at the moment to something around sixteen times dimmer, visible only through a good telescope. Observing in the early part of the month will give the best chance of seeing this visitor in a small telescope or binoculars, to find it, use a finder chart such as this one at Cumbrian Sky.

The Antihelion Source is a rather impressive name for a source of meteors. It should provide a couple of meteors every now and again from the radiant, which is moving into Virgo by the end of the month (the bit of the sky in the south at midnight, hence antihelion, or antisunward). Those that have managed to see the comet recently (including myself) have been reporting these meteors, and they’re nice and bright.

The asteroid Ceres (largest of the belt asteroids) passes through Leo minor this month. Ceres was at opposition in February (closest approach to the Earth) and so is fading in brightness now. It appears as an out of place star in binoculars at the beginning of the month, but fades to a more difficult to see object later in the month.

The Planets

Mercury hides behind the Sun this month, making a difficult to observe planet impossible to observe. Jupiter is similarly badly placed, but starts to appear low in the southern horizon at dawn. On the 17th of March, all the four Galilean moons of Jupiter line on to the west of the planet during the morning. On the 27th, at around 05:42:57 (at a rough guess), the moon Callisto occults the moon Ganymede, giving a good idea of how fast these things move. Uranus can be written off altogether this month, Mars and Neptune both appear in the very early morning at the end of the month, close to the horizon at sunrise.

Saturn, at least, continues to shine on in the sky, just beneath Leo. Its rings are almost edge on during this month, making them difficult to see (though as of last week, they still make an impressive bar of light). The moons of Saturn will be seen moving in front and behind the planet during this month, with transits of shadows of moons particularly visible in good telescopes. On the 8th of March, Saturn will be at Opposition, making it especially bright – though not enough to cut through thick clouds…

Venus takes advantage of being one of the few things happening outside of Leo. Shining bright in the evening sky, the overall size of the disc of Venus grows during this month, but the phase of Venus grows closer and closer to a ‘new Venus’, with only a very thin crescent by the end of the month as the planet moves between us and the Sun on the 27th and then out again during the morning hours at the very end of the month.

A few things outside the solar system

Algol, also known as the Demon Star, is visible in the constellation of Perseus. The brightness of the star changes so that it grows three times brighter and then dims again in just under three days. This is due to Algol actually being two stars, one of which passes in front of the other, dimming the system down. The eclipses last around ten hours, with the middle five hours containing the most noticeable changes in brightness. Minima of these eclipses, most favourable for our viewing, will occur at: 0:42hours on the 1st; 21:30 on the 3rd; 5:36 on the 18th; 2:24 on the 21st and 23:12 on the 23rd.

Lambda Tauri is another eclipsing binary star, this time in Taurus, but with a less pronounced dip in brightness and spread over a longer period of time (just under four days). The eclipses last about 14 hours. Favourable minima this month include: 23:30 on the 2nd; 22:24 on the 6th and 21:30 on the 10th.

The Usual Stuff

If you want to watch satellites flaring or passing in the sky (even sometimes during the day), then go to Heavens Above to get times and directions. If you need assistance in deciding where things are in the sky, why not install the free program Stellarium, which does all the work for you? Finally, to avoid the dreaded clouds, Met Check gives a quick forecast and the Met satellites or other satellites can be used to track breaks in the cloud, if you are truly determine to catch that comet (or even the moon at this rate)…

Public events

As part of the International Year of Astronomy 2009, the Eddington Society will be laying to rest the memory of the Venus watch with a public observing event – Saturn Watch, close to the time of Opposition on Friday the 6th from 9pm at Bowling Fell. This is round the corner from my place, so I may even be sticking my telescope in the mud with the rest of them. Either way, I’ll be there.

On the 28th, the Spring MoonWatch begins, lasting until the 5th of April. This is one of a couple of weeks when the Moon is in a favourable position for detail to be seen on the surface. Too close to new Moon and there’s nothing lit up, too close to the full Moon and there’s no shadow to bring out detail. As part of the International Year of Astronomy and the telescopes for schools initiative, the Society for Popular Astronomy has organised these country-wide watches to give everyone the chance to see… well… probably clouds.

We can but try…

Strange lights over Kendal

As with every other town, city and village in the UK and beyond, Kendal often gets reports of possible UFOs. Whilst I can hardly say I am in a position to definitively rule out alien visitors or presently unknown natural atmospheric phenomena happening, I would like to point out a few more down to Earth suggestions of what needs to be ruled out in such a sighting.

Sky lanterns are paper constructs with a candle below that slowly burns up the lantern. The effect is like a hot air balloon and the lanterns lift into the sky. These have become more popular in recent years, including here in Kendal. Here’s a video of several taking off in formation. The flickering candles can produce some flashing and they have been identified as culprits of UFO sightings during the last celebration of the Hindu Festival of Light in London.

Birds flying about in formation lit by streetlight it another possible explanation for orange UFO’s. They can seem to change direction very suddenly because firstly they actually can change direction quickly and secondly they may initially be flying partly towards you, then turn to put their full speed in a different direction. The flapping wings can produce a pulsating appearance.

On a clear night, satellites can be seen. Heavens Above can give an idea when a visible satellite may be passing over, or suddenly flaring in and out of view, but not really whether or not the satellite is rotating and therefore likely to appear to pulsate as the mirrors reflect different amounts of light.

Meteors. Again due to a trick of perspective, like birds they can come down at different angles. This might make one meteor streak across the sky, whilst others appear as a dot on the horizon and vanish. In an active shower, many may appear to do this or intermediate versions.

Planes – Kendal has a commercial plane route to the south. As I as trying to watch Comet Lulin, I was troubled by multiple flashing lights due to planes zipping about the place. They follow pretty straight paths, or obvious hyperbolic curves and are sometimes accompanied by rumblings so low you can miss them. Had I been in traffic and not listening out for the second plane after the first had shot overhead, I would’ve missed the sound entirely. In addition to this, Kendal is the RAF’s northern playground. When I lived on the Castle Estate, they used to use my house as target practise, and it was sometimes unnerving to see them diving at us. That sort of thing is better restricted now, but that may just make the fact we do have planes overhead less immediately obvious to the memory.

Of course, being Kendal, we probably have to rule out hot air balloons too. Lots of these pass over in the day and there is plenty of alcohol about.

The best thing to do if you do see something is to write down where you were, the general direction of the thing, how many, what colour, pulsating or not, estimate of speed and direction of travel and the time of the sighting. These will rule out or point to meteors (except sporadics, which appear outside of designated storm times), satellites, planes and the like – though sadly, the birds refuse to be so easily pigeonholed… though for those very interested in what’s up there, there’s nothing like astronomy as a hobby to keep your eyes on the skies and getting to recognise what ought to be there – and possibly what ought not.

UPDATE: During the MoonWatch on Friday the 3rd of April, there were a number of comments about a strange light drifting above us. That light was just an ordinary plane, but through the mist it looked like a slow moving orange ball (due to the wing lights shining through the fog). Of course aircraft lights often flash too, which can create pulsating orange balls, which is one reason why if you do see a UFO, it is best to note down the weather conditions at the time.

The Wanderers

Observing the planets has been a hobby of humanity since the dawn of time. Our fellow travellers in the solar system have weaved their strange helical paths in the sky, forcing thinking and rethinking over what they are doing and why. Geocentric models of the Universe, centred on the Earth, required ‘epicycles’, extra little spins the planets did to explain why they sometimes moved one way and then another in the sky. Of course, we now know that the planets do this because as well as their own orbit, taking them to and throe along the Zodiac bouncing between points aligned either side of the Sun, the orbit of the Earth changes our perspective on the planets. When we undertake them, or are undertaken by them, in the great race around the Sun they appear to undergo retrograde motion – they reverse their direction in the sky, moving to the West rather than the East. Then it all goes back to normal. During this time, known as Opposition, they are at their closest to the Earth. The modern world has a total of eight planets, neatly cut into the inner Terrestrial Planets (including the Earth) and the outer Gas Giants, the two separated by the asteroid belt. Outside the outer planets lies the Kuiper belt of icy comets in waiting. For the purpose of observing the planets from the Earth, the term ‘inner planets’ is taken to mean the planets inside the orbit of the Earth. ‘Outer planets’ refers to planets which orbit at distances greater than that of the Earth, which includes Mars as well as the Gas Giants.

Planets appear star-like in the sky (always in the Zodiac, as this is where the ‘ecliptic’ plane lies where the planets and the Sun orbit) and identifying them, beyond being able to learn the stars of the constellations off by heart and noticing when an extra one pops in, is often a matter of looking at finder charts (perhaps in newspapers or local blogs). A more reliable way is to use a planetarium program like Stellarium.

The Inner Planets

The closest planet to the Sun is Mercury. Orbiting at some 58 million kilometres, observations of Mercury’s orbit played a crucial part in deciding that General Relativity and its predictions of how gravity worked was an improvement on the Classical Physics of Newton that went before. The planet itself resembles a shrivelled ball. It is a tiny planet, only around 5 thousand kilometres in diameter, and lacks a significant atmosphere. So insignificant does Mercury appear in the program of space exploration that the first full pictures of its surface have only been taken by probes orbiting the planet as I write. In many textbooks as a result, maps of Mercury have pieces missing.

This planet was first observed by the ancients. Its close orbit to the Sun means it follows the Sun very closely as it either sets of rises. By the time the Sun is far away enough set to be safe to look, Mercury is very close to the ground. This presents the obvious problem of how do you get a telescope to it before it has set as well as the less obvious problem of the warm air near the ground causing turbulence in the sky at dusk, and evaporating water causing much the same effect at dawn. If you do get to see this dot in the sky, you may be rewarded with the phases of Mercury, whose disk alters like that of the Moon. Of course, another time to see Mercury is when it transits the surface of the Sun, information on which can be seen in an earlier post.

Venus is the most obvious of the planets in the sky. A bright ball of light shining at either dawn or dusk, known as either the Morning or Evening star depending on where it is in its orbit, this planet might have caught your attention even when not looking for it. Venus is sometimes called Earth’s Twin, as at 12.1 thousand kilometres in diameter, it is closer to the Earth’s 12.7 thousand kilometres than any other planet. That is where the similarity stops. At 108 million kilometres from the Sun, Venus boils. Due to an atmosphere now composed mostly of CO2 and sulphurous compounds from the volcanoes on the surface, heat is trapped and heats up that surface above the temperature of the surface of Mercury. Venus is shrouded in clouds, with a surface only visible if a probe is fired underneath the clouds, where it will quickly melt and collapse on the surface. Recent observations have shown Venus to have tenuous aurorae over the entire dark side of the planet.

Observationally, Venus is very much like a more obvious version of Mercury. Being bigger, it reflects more light. Being further from the Sun, it appears in the hours of darkness, or is still present on the edge of darkness. Being an inner planet, it also shows phases and finally being shrouded in a single layer of cloud, it is generally featureless aside from these phases. It can also be seen transiting the Sun and has also been known since ancient times. Below is a picture of astronomers at the first event of the Eddington Astronomical Society in Kendal, which was formed at the meeting. It was a Venus watch with telescopes, binoculars, members of the public, a display on the planets and a feed showing the event as it was recorded from another observing site in case the haze defeated us (which in the end it didn’t).

The Eddington Society begins with Venus on the Sun

The Outer Planets

All of the outer planets show a constant, nearly phase-less sunlit face to us, however, most of these faces are actually quite interesting to look at. Every one of them has at least a couple of satellites, which can be seen with the right power telescope, and the first three even have changeable features.

The first of these four is Mars, the Red Planet. Known for its ability to harbour martians in fiction and its strange red soil. Currently undergoing a program of exploration through the actions of the Mars Rovers as well as a series of Mars orbiting artificial satellites, our knowledge of the planet is as tenuous as it’s CO2 based atmosphere, and equally as interesting (I am an atmospheric physicist, I find tenuous atmospheres interesting, even CO2 ones). Mars lies 228 million kilometres from the Sun and is roughly 6.8 thousand kilometres in diameter. The planet has a slightly odd shape, perhaps due to a massive collision undergone at a time called the Heavy Bombardment phase, when small planetesimals slammed together to form the things we see today. Recent satellite observations

Observationally, Mars is yet another planet seen by the ancients. It does have two tiny moons, but these are difficult to spot. Things a little easier to spot are the massive regions of darker under soil that contrast with the brighter red regions of dust. Mars also has ice caps that can easily be seen to change with the seasons (with a moderately sized telescope). Small telescopes and binoculars should pic out the strange red disc and perhaps some surface markings, depending on what part of the planet is facing us at the time. Opposition, when Mars shines its brightest, will allow even small instruments the chance to see the markings clearly. Recent satellite observations have shown Mars to have small localised aurorae around magnetic hot spots.

Jupiter is known as the King of the Planets. A giant 143 thousand kilometres in diameter, 778 million kilometres from the Sun, this is a giant and a half. The planet contains observed storms that rage over distances greater than the diameter of the Earth. It is a Gas Giant, meaning unlike the rocky Terrestrial planets, the thing we actually see is a ball of gas. It isn’t known if the core formed into a solid thing inside or whether the pressure and temperature have formed something a little weirder down there, but it is known that the outer atmosphere is very active. The planet is also magnetically active. The first satellite to get close to Jupiter was fried by the radiation there, though it recovered enough to continue on its way with its remaining instruments. Jupiter was the first planet photographed to have a comet slam into it whilst the world watched. Fireballs larger than the Earth developed in the Jovian atmosphere that collapsed to form shock waves even larger in the atmosphere. The scars remained visible for a few years afterwards before the storms covered them up and the planet returned to life as usual. The auroral system on Jupiter, like everything else, is very much on a larger scale. Generated by particles expelled from the satellite Io, which end up in orbit of Jupiter and get ionised by the Sun, the Jovian auroral system puts out one hundred times the power of the Earth’s auroral system. It does have an Earth like aurora happening inside the main oval, but that is so weak in comparison to be almost irrelevant to the main one.

Observationally, this is yet another planet known to the ancients (they did a lot of planet gazing) and yet another visible in the night sky as a star-like object without the aid of telescopes etc. If you do look at it with binoculars or a small telescope, you are likely to see a yellow disc, perhaps with a bit of a red dot on it (the Great Red Spot) and maybe with two faint brown lines going across. These are part of the cloud band system, which can be seen more clearly with a larger telescope. Jupiter rotates in less than half a day, so it is possible to do widely spaced observations and see the red spot has moved across the disc. Jupiter also has four bright moons that can be seen in any telescope or binoculars. Galileo’s observation of these moons and recordings of where they were at each time, gave him the chance to work out how fast they went round the planet, which proved to be a good test of Kepler’s laws (indeed this is the basis for an experiment many astronomy courses run to familiarise people with Kepler’s laws).

Jupiter, taken at ULO

Saturn is well known as the Ringed Planet. Presently under the undying eye of the Cassini Huygens probes, this planetary system has driven the imagination almost as much as Jupiter. A fellow gas giant, it lies 1.4 billion kilometres from the Sun and stands 125.1 thousand kilometres in diameter. It too has a strong magnetic field, but weaker than Jupiter. It has cloud bands, but they are fainter than Jupiter’s. It has an auroral system created through a combination of Earth like effects and ionisation of the rings, but these are less powerful than Jupiter’s, though they do save up their energy and produce massive bursts as the solar wind pulses rush over the planet.

Observationally, Saturn is the furthest of the eight planets to have been seen and recorded by the ancients. Through the smallest instruments, it can be seen to have rings (though, as it happens, they’re almost edge on at this moment in time, so they’re very hard to see for the first time in years). Saturn does have moons and yesterday four of them transited Saturn, due to the relative positions of the Sun, the Earth and Saturn, the shadows were visible on the planetary disc and even a small telescope would’ve seen the shadow of Titan. Sadly, this area was both clouded out and in the middle of the day at the time, so no show from here…

Saturn from ULO - note chromatic aberration (Fry refractor used)

Uranus is the first of the outer planets not to be discovered in ancient times. Or at least not to be recorded as such, it does appear to the naked eye (under excellent dark skies and only just) at Opposition, but then goes very slightly below it, so the planet may have been seen and then simply vanished. It lies 2.9 billion kilometres from the Sun and follows the pattern of Saturn, in that it has very few bands at all, it is colder and smaller than Jupiter (just 51.2 thousand kilometres in diameter). It has very strange magnetic configurations. Whereas the strongest part of the Earth’s field is dipole (it has two poles, North and South), Uranus has strong quadrupole (four poles) and even octupole (eight poles) components to it’s field. The aurorae are weak and blobby (as the strange magnetic field makes nice smooth ovals difficult to produce). It was first discovered by Herschel in 1781, but it’s brightness allowed it to be mistaken for a star by many others including the astronomer Flamsteed, who saw it on six occasions (during the years 1690, 1712 and 1715), La Monnier recorded the planet six times in 1769 and Mayer recorded it once in 1756. Each time, it was recorded as a faint star, and when it moved, it simply got recorded as different faint stars. Such was the difficulty of observing these things.

Observationally, Uranus can only be seen using the naked eye in very good conditions, with excellent skies and the Earth close to the planet. Telescopically, the planet makes a lovely green disc among the stars.

Finally Neptune. At 4.8 million kilometres from the Sun and 48.6 thousand kilometres in size, this is the furthest and the smallest of the gas giants. Very little is known about it’s magnetic configuration and there is scant evidence of auroral activity at this moment in time. It was officially discovered in 1846 by John Couch Adams, but it has since transpired Galileo sketched it slightly earlier… He saw it twice in 1612 and even recognised that it was moving. However, there were no bright stars in the area to compare it to, so he may have assumed his memory was playing up.

Observationally, Neptune is like a smaller, fainter Uranus.

UCL detects longest ever exoplanetary transit

Scientific paper of experiment and results

Students and a lecturer at University College London have been looking at transits of extrasolar planets for a while, using a C-14 telescope (a fourteen inch mirrored celestron made reflecting telescope). They use a method called ‘photometry’, where the brightness of the star is recorded. This brightness is adjusted for features such as atmospheric absorption. Should a planet pass in front of the star, the brightness drops a little. Ingress is when the planet goes in, egress when it heads out the other side.

The radial velocity method, where the gravitational pull of the rotating planet causes the star to wobble and the wobble is measured through the Doppler shift of spectral lines of the star, had previously been used by others to decide that there was a planet there. Closer observations and analysis revealed that it was a ‘hot Jupiter’ planet (massive, a gas giant 3.9 times the size of Jupiter called HD80606b, close in and spinning round the star fast) and also that it was very highly elliptical – the orbit of the planet was an ellipse, with the shorter diameter 0.93 times as long as the longer diameter.

Photometry of the egress of the planet has provided additional data on the orbital parameters of the planet. Analysis of the light curve adjusted for the limb darkening effect of the star’s edge provides data on the planet’s size and velocity. As well as this taking actual observations of the transit (which had been predicted using the already available data of the radial Doppler shift) allowed the theoretical idea of what would happen to be tested and improved.

The use of a 10″ and a 14″ telescope by lecturer Steve Fossey, PhD student Dave Kipping (of my very own APL) and Natural Sciences final year MSci student Ingo Waldmann shows how even the instruments available to the dedicated amateur can be used to proper scientific effect with the right tools behind the eyepiece.

Of course, the best bit is I get to use one of my pictures of the University of London Observatory – the domes with the telescopes used are the ones to the left of the picture. There are actually three in that block, the closest is the Meade, the furthest the C-14…

ULO

Chris Lintott’s Universe » See the Northern Lights with the Sky at Night

Chris Lintott’s Universe » See the Northern Lights with the Sky at Night.

A clip has been posted on youtube from the last episode of the sky at night. This deals with the aurora – or rather it deals with watching the aurora in a place where they are easy to see. The aurorae are the subject of my own research, and are of course also beautiful things in their own right. Things that, as it happens, are considered very low priority for government funding at the moment. Last year’s debacle at the STFC funding review almost left the UK with no funding for auroral physics, which would’ve meant several global projects we are involved in going to the wall. Even now, we only have a slight reprieve and the same people with the same aims and priorities continue to hold the purse strings. It may be that videos like the one above are all that the UK ever gets out of the aurora in the future…

Spectacular “cosmic eye”, Helix nebula, captured by telescope – Times Online

Spectacular ‘cosmic eye’, Helix nebula, captured by telescope – Times Online.

The Helix nebula is a thing of great beauty. Looking a little like an eye surrounded by lids and even a faint eyebrow, this is a prime example of a planetary nebula. Planetary nebulae are so called as in small telescopes they looked initially like planets (in that they were elongated rather than pinpricks like stars) that simply didn’t move anywhere. Nebula itself means cloud, so this is an eye shaped planetary cloud… sounds big, but not as big as it actually is.

In the sky, the Helix Nebula covers around half a degree (25 seconds of arc) and is just below visual magnitude at 6.58 (the level of visual magnitude is around 6 and larger numbers equal dimmer objects on this scale, with every new increment meaning a dimming or brightening of about two and a half times the previous increment). It is around 2.5 light years across and 700 light years away, making it relatively close compared to other planetary nebulae.

The Nebula was formed when the central star reached the end of its fusion burning life. With no further fuel to heat up the central core, the temperature and pressure falls off and the outer layers fall in. They crushed the core of the star, bouncing off it and heading out into space to form the nebula. The current nebula has two shells, one travelling outwards at around 40km per second and one at 31. Using this information, it is determined that the nebula is about 10,000 years old, give or take a millennium or two.

One thing imaged here that has turned out to be true of other planetary nebula are things called cometary knots. These are streaks of gas, shaped like a comet with their tails pointed away from the central star. About 20,000 of these solar system sized balls with even larger tails have been noted. In the middle of them all sits a stellar remnant, the crushed core still glowing white and slowly cooling off to become a white dwarf star.

UPDAT: Skymania has a version of the story that actually includes the picture being talked about, which is a help…

Discovery win an award with Nasa documentary website

CableFAX Announces Best of the Web Winners :: CableFax Portal.

Why do I want to flag up an awards ceremony? Well, the Discovery channel won the Supplemental Web Content award with the website based around the six part series on Nasa, “When we left the Earth”, which, according to the award’s citation:

Discovery’s 6-part series was impressive enough, but the interactivity and deeper dive of the companion Website was the perfect icing on a freeze-dried, astronaut-ready cake. Interactivity ranged from “Eyes on the Universe,” in which users could study the stars, to the “NASA Video Vault,” an incredible collection of rarely-seen mission videos from Apollo to the Space Shuttle. Visitors could even share their own “I-was-there-when” stories about historic space missions.

Solar astronomy

The daytime seems at first glance quite a bad time for astronomy. There seems to be no stars, the Moon sometimes appears when close to the new Moon phase, but apart from that and the occasional daytime satellite flare (see Heavens Above for timings) there’s only one thing out there – the Sun. It provides warmth and light, particles and photons, both of which can produce unusual effects in the sky. It also has features to observe, when done carefully and with a full awareness of the dangers.

Daytime Moon

The Sun, a profile

Our star is roughly 5 billion years old. Its surface glows at a temperature of 6 thousand degrees celsius, and its centre one of six million. It is more than one and a quarter million kilometres in diameter and it derives it’s energy through the process of nuclear fusion.

It was discovered during the twentieth century that the atom was composed of protons and neutrons and electrons. But it was also discovered that the mass of individual protons, neutrons and electrons when added together in the appropriate amount was greater than the mass of the same protons, neutrons and electrons when they are bound together in an atom. This excess mass, it seems, is converted into energy as the nucleus fuses together. The famous equation energy = mass x the square of the speed of light describes how we convert from the missing mass to the energy produced by nuclear fusion. And it is through various chains of light atomic nuclei fusing to form other light atomic nuclei that keeps the Sun shining.

Nuclear fusion only happens in the core, when the temperature is high enough and the pressure great enough to crush enough protons and neutrons together for something to happen. Directly outside the core, less fusion occurs. In fact, fusion occurs sporadically at some level in any gas, but for a self sustaining reaction continuously producing significant amounts of energy, the kinds of conditions found in stellar cores are required.

Surrounding the stellar core, there is an area known as the radiative zone. There are three ways of transferring heat in a fluid – conduction, convection and radiation. Conduction of heat, where one bit of gas warms up the next bit of gas etc isn’t the most efficient way of covering the distances required in the Sun. Convection doesn’t work at this level either as the rate at which the heat drops off from the central core is stable. Then we are left with radiation, with photons of energy emitted and travelling through this region of the sun, bouncing off every electron and proton that they find in their way. They get absorbed and re-emitted, transferring energy outwards.

Eventually, the warmth of the core gets close enough to the cold of space for an unstable temperature gradient to form and so for convection to begin. This is the process of hot fluid rising up to cool close to the surface and cold fluid dropping down to the hot core.

The visible part of the Sun is called the Photosphere, ie the sphere that produces the photons. This is a very thick layer, which is cooler and darker the further from the core it gets. For this reason, the edge of the solar disk, known as the ‘limb’ is darker than the centre.

Above the photosphere, and invisible in normal circumstances, is the solar corona. This is effectively the solar atmosphere and can normally only be seen during an eclipse of the Sun. People studying the solar corona often have to resort to creating an artificial eclipse, such as a sun block on their instrument lens.

The Sun is a highly magnetically active thing, with a complicated magnetic field. At the start of a solar cycle, the magnetic field looks pretty much like the dipole field of a bar magnet. However, the lines of force in the field are tethered to the Sun’s plasma, and that plasma rotates at different speeds at different solar latitudes (the equator spins round once every 25 or so days, the poles closer to once every 34 days). This ‘differential rotation’ of the plasma leads to the magnetic field lines getting warped and wrapped tightly round the star. Over the course of roughly eleven years, the winding becomes so extreme the field is forced to reorder itself, flipping over so the north becomes the south in a new dipole configuration. The solar cycle therefore flips the field direction from north to south and back to north again over an average of 22 years.

The Sun doesn’t stop at the corona. Protons, neutrons and electrons from the Sun act as they would do in any other gas. They expand outwards from the source of heat. They carry the solar magnetic field with them in an arrangement called the solar wind. There are in fact two sources of solar wind, a slow wind from the equator and a fast wind from the poles, in regions known as coronal holes as little x-ray emission is seen from them. The solar wind’s two components being of different speeds run into each other and form a pulsed wind. Although the pulsing has been seen quite easily happening before the wind reaches the Earth, it isn’t until the wind reaches the gas giants that it has time to form really distinct pulses, with the material from the slow solar wind given out in about three days bunched into a small wavefront. This wavefront then slowly dissipates as the solar wind spreads further out into the solar system, losing its density. The point at which the solar wind reaches the winds of other stars as well as any interstellar flow is the heliopause – the point at which Helios, the Sun, ceases to have a direct effect beyond shining like any other star.

What kind of effects does the sun produce on the Earth?

The Sun has a number of direct effects on the Earth. Ignoring the more obvious ones such as the difference between day and night and the small matter of life on Earth, light from the Sun gets bent by the atmosphere in a number of ways. The atmosphere acts a little like a lens in a refracting telescope, like a lens in a refracting telescope, it will both absorb some of the light and bend the rest of it, splitting the light into a spectrum as it does so. During the day, the blue part of the spectrum is most noticeable. At sunset and sunrise, red is in the ascendant. The picture below shows red light reflecting off the Moon during a lunar eclipse, having been bent around the Earth.

Red Moon.

Ice crystals and water droplets in the air can also cause further effects. These include Halos, such as that shown below around the Moon. More beautifully, circumzenithal arcs are rainbow like arcs that appear due to refraction through ice crystals. Circumhorizontal arcs are cirrus clouds refracting through ice crystals to provide a slab of rainbow coloured cloud. Finally, Sundogs are ‘false suns’ appearing one on either side of the sun, between 22 and 61 degrees from the solar centre in the sky. These are very common things.

Halo around the moon

Of course, the particles the Sun emits hit the Earth too. Or rather they strike the upper layers of our magnetic field, dividing that region into the heliosphere, where the Solar or Interplanetary Magnetic Field, is the dominant force and the Terrestrial Magnetosphere, where the Earth’s magnetic field is more dominant. Cycles of magnetic field reconnection and realignment force material gathered and accelerated in the magnetosphere to plunge back into the atmosphere. This can be seen in the Aurorae, either at the northern or southern polar circles. These will be discussed in much detail in many future posts as they are the subject of my own research.

Observing the Sun

As mentioned before, it isn’t a good idea to look at the Sun with the naked eye, never mind with a telescope. That is the easiest way to never look at anything else ever again. Nevertheless, there are ways to have a look.

The least technologically advanced way (and cheapest) is to put a pinhole in a piece of card and project the Sun onto another piece of card. A similar method, with similar results, is to point a telescope in the direction of the sun and project the image (focus the image onto a piece of white card or a screen, rather than looking through the telescope). You can use the shadow of the telescope to direct it (make the shadow as small as possible to have it pointing directly at the Sun) and remember to take off your finderscope rather than risk accidentally looking through it! This method will work for binoculars too.

What are you likely to see through this method? Well that depends on what is actually going on. During the most active phases of the solar cycle, when the magnetic field is highly twisted, the field buckles and loops of it come out of the body of the Sun. The feet of these loops are areas of high magnetic density that prevent plasma from moving sideways – it effectively cools it down. As a result, the plasma shines less brightly and appears black against the more bright rest of the surface – you have a sunspot. A good sunspot (and they can be good, with a fairly recent one filling a quarter of the sun’s visible disk at one point) will be seen to have an umbra and a penumbra – a middle dark bit and an outer dark bit. They may, if your image is good enough, also be associated with plages, which are the opposite in terms of being whiter than the rest of the solar surface. Also, if there is something transiting the solar surface – a planet (either Mercury or Venus) passing between the Earth and the Sun, for example – that will show as a big black dot too. The photograph below shows something a little closer to home making a partial transit of the Sun as shown project onto a screen - the Moon. Solar eclipses happen when the Moon is in the New phase and happens to be at a part of its orbit where it crosses the path of the Sun. This is as opposed to the Lunar eclipse, where the Moon is full and the Earth passes between it and the Sun, due to the Moon being on the right part of its orbit. The Moon’s orbit is tilted with respect to the Earth’s orbit of the Sun, meaning usually, the full and new Moons go ahead with no eclipses bothering them at all.

Partially eclipsed Sun, with added cloud, projected onto a screen

The next stage up from viewing the Sun through a projection would be to view the Sun through some sort of filter. The easiest filters to use are solar eclipse glasses, such as those lovingly modelled by two passing policemen in the picture below. The image of the Sun through these glasses is also shown in the picture below that. It is very similar to the image projected, but a lot smaller, which is why they tend to be saved for eclipses, and maybe a transit or unusually large sunspot for the eagle eyed.

Ello, ello, ello, what's all this then?

Quick look at the tiny Sun

Telescopes too can have filters attached to them. These can include Mylar filters, with arrive in sheets and have to be cut to shape, as well as more expensive glass filters, such as those available here. Before using a filter on a telescope, camera or binoculars, it is best to hold it up to the Sun and make sure that there are no small or large holes that may then allow dangerous amounts of light through. Also ensure you only ever by filters that cover the main aperture, not ones that get stuck onto the eyepiece. These second ones promote build ups of heat, which can be very dangerous in enclosed tubes. The advantages in using filters include the ability to use the telescope as a normal telescope with all the comfort that entails and the ability to see more than projection will give. As well as sunspots, plages, faculae(bright areas) and filaments (long wirey things), you may see granulation, which is caused by the convective cells of material spewing out of the centre of the cell and falling, when cooled back down the sides. In fact, what you’ll see is supergranulation, which is groups of these granules. Other things to see include solar flares and coronal mass ejections, where matter moves from the surface of the sun outwards in apparently small ejections that nevertheless dwarf something like the Earth. Then there are coronal loops, these are the loops of magnetic field that sprout from sunspots. Electrons and protons whizz up and down them, creating radio emissions, which can also be observed using something like Radio Jove’s equipment.

Of course, you might want to go one further than that and purchase a dedicated solar telescope, a thing which has become quite popular in recent years. The Coranado Personal Solar Telescope is shown below at the same event as the photos above. This is a telescope with filters already built in optimized for solar viewing in a few selected wavelengths (to bring out certain features). The PST is just a small refractor, which gives an indication of how smaller instruments can be well used in solar astronomy.

Personal Solar Telescope

If you want to know what the Sun’ll look like right now (perhaps to check for sunspots in advance), then SOHO provides this website. MDI continuum is best for seeing how the sun looks through projection, with the different filters in the top row showing a very high resolution version of what you might see through filters (the actual view is a lot less high quality from the Earth).

Professional Observations

Of course, it isn’t just the amateurs at it, professional astronomers point telescopes at the Sun as well. The Swedish Solar Telescope is one of the largest refracting telescopes in the world, with a lens a metre across. Most observations are now space based, with SOHO – the Solar Heliospheric Orbiter and STEREO – the Solar Terrestrial Relations Observatory spacecraft leading the way in light collecting. In the case of STEREO, as its name suggests two telescopes are used to provide a stereoscopic picture of the Sun, with the various solar flares and coronal loops shown in three dimensions, where previously we’d have to wait to view them off the limb. Numerous Earth and near Earth orbiting satellites also examine conditions in the solar wind and magnetosphere.

All this activity feeds into our knowledge of our closest star, how stars work, what they do things we can apply to unusual phenomena suggested by observations of other stars. There is also that small point about the Sun’s influence on life on Earth and the planet in general. Always nice to keep an occasional eye on that…

NASA – Expedition 18 Mission Logs: Sandra Magnus

NASA – Expedition 18 Mission Logs: Sandra Magnus.

What’s life like for astronauts on the International Space Station as it whizzes overhead us all? Well, you can find out by visiting the journals of those on board, such as Sandra Magnus who has recently been taking a few pictures of things inside and out of the space station.

Don’t forget to track the orbiting delight on Heavens Above, which contains information on whether and when the ISS will be passing above YOU.