I needed a diagram for an article on noctilucent clouds. They range from pretty (and copyrighted) to pretty ugly online so I had a go at making my own. As usual this was done with LaTeX (via LyX) and PSTRICKS.
Here's the finished picture:
The diagram is simple: part of a circle, some tangent lines, cloud symbols and labels. Then shade between the various curves and lines. Finally, a multi-do loop to draw the Sun.
Details below the fold.
If the Earth suddenly stopped moving around the Sun - how long would it take to fall into the Sun?
First of all, this is a situation that will never, ever happen! It would take a phenomenal amount of energy to stop planet Earth in its tracks. A passing malevolent alien attack fleet imparting that much energy to the Earth would likely destroy it! (Another problem for another day :-p ) Nevertheless it's an interesting maths problem to think about (maybe only to me) on a lazy afternoon.
We can use conservation of energy to solve this. The Earth has kinetic energy (from its motion) and gravitational potential energy because of its position in the gravitational field of the Sun. Ignoring the effects of other planets, the sum of those energies is constant and we can use that fact to figure out the fall time. Click below if you want to avoid the maths and just to skip to the answer!
Last night I watched an asteroid --- 2004 BL86 --- drift past the Earth. There was never any danger of a collision and it never got closer than about 3x the distance of the Moon. Nevertheless it was an interesting event to watch through the telescope. The asteroid was tracking north through the evening sky. At around 7.30pm, when I arrived home from work, it was too low in the southeast sky in Hydra. As the evening went on it raced north towards the constellation Cancer.
The animation below was made from frames taken over a ten minute period at around 9.30pm. The asteroid moved across a patch of sky about the size of the full moon during this period.
I stacked the images to make this picture:
I'm not sure why the asteroid has a strong green colour! It may be that the presence of moonlight in the sky messed up the colour balance during post processing.
Just to put this into some kind of perspective: the asteroid is about half a mile in diameter and it was around 1 milliion miles away when I took the pictures. Shining at around 9th magnitude, the asteroid was much too faint to be seen without optical aid. I saw several articles on astronomy and science websites suggesting that binoculars would have been enough. The fact of the matter is that at least a small telescope would have been needed by most observers unfamiliar with searching for faint objects.
Radar surveys of the asteroid carried out yesterday showed this tiny asteroid had a moon!
This is second time I've caught an asteroid close approach. I was lucky enough to catch the even closer approach by an asteroid called Duende (formerly 2012DA14) in 2013.
Comet 2014 Q2 Lovejoy will be at its closest point to the Sun on January 30th - a mere 120 million miles from it. Despite being further from the Sun (by 27 million miles) than us, Comet Lovejoy is glowing in our northern sky more brightly than any comet since Comet 2011 L4 PANSTARRs in 2013. Comet Lovejoy is starting to fade but remains excellently placed in the northern sky for UK astronomers.
The chart below shows the path of Comet Lovejoy from the last week of January until the start of March. During this period the comet is expected to fade from magnitude +5 to +8. Comets are somewhat unpredictable and those estimates don't take account of sudden outbursts caused by unstable conditions on the comet.
During the past few weeks I've tried to get pictures of Comet Lovejoy on lots of occasions. Here are a couple of my best pictures:
That delicate ion tail has been very difficult to see both visually through the telescope eyepiece and on camera. It's not helped that someone thought it a good idea to build Newcastle not far from here. And even less of a good idea to fill it with streetlights. Makes it almost impossible to get dark skies from my back garden.
The comet begins February in the constellation Andromeda, near second magnitude star Almach (itself a superb double star through telescopes). An excellent photographic opportunity occurs on the evening of February 20th/21st when the comet will be very close to the Little Dumbbell nebula (M76) in Perseus.
During March the comet will fade to the point where only telescopes can resolve the coma as it begins to blend into the rich starfields of Cassiopeia.
Comet 2014 Q2 Lovejoy is really starting to put on a great show for UK astronomers. At last, it is north of the celestial equator and shining brightly enough to be visible to the naked eye. My camera remote control has died so the pictures below were taken with my dad's superior Nikon D90.
This was my view of the southern sky at about 6.30pm last night:
Comet Lovejoy was easily visible in the sky. At first glance it looks like a faint star but using averted vision it does look somewhat fuzzy. The cometary nature is revealed easily with binoculars.
A closer view of Comet Lovejoy as it passes through a beautiful part of the sky near Taurus, the Bull.
Finally, here's a telescope view of the comet revealing many delicate streams of material pushed away from the comet by the solar wind.
Comet Lovejoy was about 45 million miles from Earth last night. Although it's getting further away from us, it is continuing to approach the Sun. It will remain an easy target over the next couple of weeks for binoculars and small telescopes.
The clouds cleared for a couple of hours yesterday afternoon and I got a chance to see Mercury catching up to Venus in the evening sky. This was the view from my garden in Red Row.
The distance between them was about half a degree; closer than your little finger at arms length! You can just about see my telescope in the foreground of the picture. When I put the camera on that I got this view:
Venus is much brighter than Mercury. Both planets are almost behind the Sun as seen from Earth but Mercury is nearest to us. However, Venus is much bigger and has very reflective clouds whilst Mercury has no atmosphere and a dark, dusty surface. The upshot is that Venus always outshines Mercury.
The Cassini spacecraft captured this breathtaking view of Saturn on May 4th 2014 but I just noticed it today.
Cassini captured this view at a distance of approximately 2 million miles (3 million kilometers) from Saturn using a near infrared filter. Cassini was high above the ring plane and this is a view of the planet we never get from Earth. From our position near the centre of the solar system Saturn (and most of the planets beyond Earth) look fully illuminated all of the time.
One of the features that immediately catches the eye is that hexagon shape around the north pole of Saturn. The hexagon at Saturn's north pole isn't a new feature. It was seen in images taken by the Voyager 1 and 2 probes back in the 1980s.
Here are some closer Cassini views of it:
For some sense of scale: each side of the hexagon is a bit wider than the Earth.
Saturn is a rapidly rotating gas giant planet. How can a regular and seemingly long-lived feature like this arise in the atmosphere of Saturn? Astronomers don't have the definitive explanation yet although there is experimental evidence from laboratories on Earth which might give a clue.
The video shows an experiment to simulate conditions that might lead to a regular structure being set up in the atmosphere of Saturn. They built a cylindrical tank capable of varying the fluid flow within concentric regions inside. A hexagon appeared at the chaotic boundary between fluids moving at very different speeds. A number of vortices formed in the region separating the fluid flow and distributed themselves evenly around the pole at centre. Why a hexagon? Actually the experimenters could fine tune the spin rates to produce a hexagon but they could also generate other regular polygons too. You can see some them here.
The experiment showed how stability and order could arise from chaotic conditions induced by large differences in wind speeds at different latitudes on Saturn. There are still questions to be answered. For instance why is there no comparable feature at the south pole of Saturn? There is a huge, long-lived storm at the south pole, but no polygonal structure.
I love trawling through the raw image section of the Cassini website. It can lead to serious distraction no matter if they're images of the rings, the moons or Saturn itself. But I'm aware that this mission won't last forever; Cassini's time is running out and sometime in 2017 NASA scientists will place it in a final series of orbits which will send it crashing into Saturn.
Just put the finishing touches to a planetary elongation chart. Here it is in all of its glory:
A high quality PDF can be downloaded here.
This chart shows the positions of the naked-eye planets to the east (left) or west (right) of the Sun. The vertical axis represents the days and months of the year. The diagonal bands represent constellation boundaries. The wavy yellow band is a region close to the Sun in which it would be difficult to observe the planets. This chart behaves like a game of PacMan; any planets reaching opposition 180 degrees west of the Sun wrap straight over to the evening sky on the far left. Think of this as being like an unwrapped cylinder!
The places where the paths of the planets intersect represent conjunctions. These are visually striking opportunities to see bright planets shining together in the sky. In 2015 there are at least 12 such opportunities.
There's a particularly striking gathering of the planets in the morning sky during October 2015. The planets Mercury, Venus, Mars and Jupiter will all appear together before sunrise on many of those autumn mornings.
The Taurid meteor shower reaches peaks on November 3rd and again on the 12th. For many amateur astronomers the month of November is associated with the Leonids - a much more famous shower which has occasional stormy outbursts. But I have to say, I prefer the Taurids because they have a more interesting backstory!
About 20,000 to 30,000 years ago a huge comet - perhaps 50 km in diameter or more - became embroiled in a series of close approaches to the planet Jupiter. Nothing unusual about that - Jupiter has a huge family of comets even today and we;ve seen first hand how Jupiter can change comet orbits and even tear comets apart.
These days, all we have left of the original giant progenitor comet is a small, faint comet with an orbital period of 3.3 years (called Encke's Comet) and a complex series of dust streams which the Earth encounters in November each year. The dust released by the fragmented nuclei over periods of thousands of years have gradually been spread out into a broad swathe of the inner solar system. Actually, the Earth also encounters one of the streams during June but during the daylight hours. It is speculated that the devastating Tunguska event of 1908 was due to a larger fragment disintegrating in the Earth's atmosphere. That's another story.
On Earth, each November, we see the remains of a giant comet, streaking into our atmosphere as a shower of shooting stars and appearing to come from the constellation Taurus. It takes the Earth weeks to cross these lanes of dust and in doing so we encounter two distinct peaks - evidence of the complex evolution of the meteor orbits. So in November we see the Northern Taurids near the start of the month and and the Southern Taurids around two weeks later. Activity is fairly low - typically about seven or eight per hour. Compare this to, say, the short sharp spike in activity of the Perseids in August or the Geminids in December.
Will we see another giant comet? Interestingly, there is evidence to suggest a big comet, seen in our skies in 1106, broke apart and the sun-grazing fragments have produced several of the best comets of past millennium.
There's also the possibility that a swarm of Kreutz sungrazing comets (probable fragments of the Great Comet of 1106) are en-route to the inner solar system and will arrive in the coming decades. If true then there are good prospects of seeing another Great Comet (or Comets).
So, no major showers this month. But chances are good this month that if you spend enough time outside watching the sky you will see the remnants of an ancient, giant comet ending their existence in a brief flash of light.
For a more in depth technical article about the Taurids --- see here.
* Had to fight an urge to add the word Batman! to this title.
Here, in one place, are some photos of our home world taken by humans and robots from low Earth orbit and beyond.
That final picture remains the most distant picture of the Earth ever taken. Taken at the request of Carl Sagan, the Voyager 1 spacecraft captured a series of images which were stitched into Family Portrait of the major planets of the solar system:
The Voyager Portrait was from taken by a camera leaving the solar system and looking in towards home. A more recent portrait was assembled by the MESSENGER mission team, this time looking out from a vantage point the near the centre of the solar system:
Clearly, these images put our place in the solar system (and universe) into perspective! You don't have to travel too far before the Earth is rapidly scaled down from an entire planet with oceans, cities and people to less than a single bluish pixel before spacecraft have left the outer solar system,
I'll leave the final word to Carl Sagan, who said this about The Pale Blue Dot:
“Look again at that dot. That's here. That's home. That's us. On it everyone you love, everyone you know, everyone you ever heard of, every human being who ever was, lived out their lives. The aggregate of our joy and suffering, thousands of confident religions, ideologies, and economic doctrines, every hunter and forager, every hero and coward, every creator and destroyer of civilization, every king and peasant, every young couple in love, every mother and father, hopeful child, inventor and explorer, every teacher of morals, every corrupt politician, every "superstar," every "supreme leader," every saint and sinner in the history of our species lived there-on a mote of dust suspended in a sunbeam."
Dr Adrian Jannetta
Guitar strummin' explorer of the universe. Mild mannered maths teacher by day and astronomer by night.