Daily Archives: 07/04/2010

Mercury and Venus tonight

An amazing thing happened tonight. After days, indeed almost a week, of clouds hanging over either the entire sky or just the bit on the horizon, they parted and provided a crystal clear night. Admittedly, they did so after the auroral events of last night were over, and well past the time when Venus and Mercury were at their closest, but the two inner planets remained close enough for a good bit of viewing. Not just in Kendal but all over if twitter is anything to go by (@NewburyAS tweeted loads of photos sent in by followers).

At around quarter past eight, I wheeled my telescope bag over a host of golden daffodils to view the most interesting sight of spring from Bowling Fell. Accompanied only by teenagers who left as soon as it got cold and a couple of dog walkers and photographers higher up, I looked to the West and after a moment or two spotted Venus through the bright sunset. If Venus was hard to spot, there was no chance yet of Mercury, so I took a few shots to see if the camera was better than the eye before turning to other matters.

I unpacked the Celestron 130SLT telescope and set it up. Turned the eyepiece onto Venus and slotted in the 25, 9 and then 4mm eyepieces to view the thick gibbous planet. I spun the telescope to the north using the azimuth control with the 25mm eyepiece in it and came swiftly to rest on tiny Mercury. As with the last time I observed the planet, it was just a pinprick in the 25mm eyepiece, but showed something closer to a phase when the 9 and then 4mm eyepieces were trained on it.

I took a few more shots, including some with the telescope in view, and took a few more looks at the planets until the town hall clock began to ring out nine o’clock. At this point, the planets were too low for my observing area, so I went to the steps that showed me a view over the town and a look to the north. I couldn’t see anything auroral happening, but I did see the rising of something orange and familiar. Yes, before you write in to report strange lights over Kendal or a UFO that definitely isn’t a Chinese Lantern – actually, it was. The picture, when zoomed into fully, shows the familiar shape. The zoomed out picture shows the orange blob that keeps getting reported (even at the stroke of midnight on New Year’s eve). The thing even flew over Stuart Atkinson, who was observing from Kendal Castle.

Then I packed everything away and wheeled back over the host of by now less golden daffodils and home in time for tea. In the sky as well as the vanishing forms of Mercury and Venus, Mars was close to overhead and Saturn was rising in the south east. Though I’ll have to catch that BBC4 program on Dame Jocelyn Bell-Burnell (Beautiful Minds) on BBC iPlayer at a later date. More photos can be seen on my flickr account.


More planetary confusion

As has been demonstrated repeatedly, the boundaries between a planet and another object are often hard to define. We’re all aware of the trouble in creating a definition at the lower end of the mass scale, but at the upper end it is even worse as the nearest clear cut brown dwarfs (the next step between a planet and a star) are quite a distance away and pretty dim.

The definition of a brown dwarf is that it is capable of fusing deuterium, but not quite able to deal with hydrogen. The lower end of the brown dwarf mass scale is around 7-13 times the mass of Jupiter and the upper end around 85 Jovian masses. This can only be confirmed by actually seeing brown dwarfs, high mass exoplanets and low mass stars and measuring their masses. The trouble with astronomy is that observations do sometimes tend to through up new conundrums – like a planetary candidate or two at brown dwarf masses. Now another spanner has been thrown into the works.

A binary system has been found that doesn’t seem to be two stars orbiting their common centre of mass, like other binaries. One of them appears to be an exoplanet. This is all fine and well, you might think, the planet merely formed quite a distance away from its host star – and the distance this companion is from its host star is but 3.6 billion km (ie between the distance that Uranus and Neptune orbit the Sun). However, the star it shares a centre of mass with is itself a brown dwarf, and the planetary disc it could support isn’t quite that wide. Also, the age of the system is just too young for the normal method of planetary formation to have taken place.

This method is known as core accretion and results from instabilities in the disc of matter surrounding a star creating cores around which gravitational collapse can occur. Over time, the core accretes matter onto it and a planet is the result.

This planet is however 5-10 times the mass of Jupiter. It is likely too low mass to fuse deuterium and so cannot be a Brown Dwarf on that criterium. However, the discoverer of the system says it should be called a Brown Dwarf based on the fact that the evidence points toward it forming directly from core collapse in the molecular cloud that formed the companion Brown Dwarf. Furthermore, observations suggest that the binary system is gravitationally connected to a second binary system of low mass objects – a red dwarf star and another Brown Dwarf. The discoverer, Dr Kevin Luhman of Penn State University, believes that this shows the same processes that form stars can be responsible for objects all the way down to planetary size.

The system, known as 2M044144, is located 450 light years away in the constellation of Taurus and was observed using the Hubble Space Telescope and the eight metre Gemini North telescope in Hawaii.

UPDATE: Even as I was writing, a report came through of the discovery of the closest ever brown dwarf to Earth. UGPSJ0722-05 was found through looking at surveys of the sky in the infrared light these objects glow brightest in. The closeness of the object means it is relatively bright compared to others of its ilk as observed from Earth, making it a good thing to study. It was discovered by the UK Infrared Telescope in Hawaii, which the STFC has decided must shut to save money. As well as being the closest brown dwarf, this one is the coolest at a mere 400 K (the next closest being a rather warm 500K). The article also gives a third definition of brown dwarfs – it has a homogeneous composition due to the heat in its core convecting through the body, whereas planet’s differentiation their chemical composition (similar to the definition that works in the lower end of the planetary mass). The brown dwarf also has water, methane and an unexplained chemical absorbing at 1.25 microns.

Sunny skies on Triton

Triton is a cold, distant world. At 2,700km diameter, it is the largest moon of Neptune and the seventh largest satellite in the solar system, its host planet takes one hundred and sixty five years to complete an orbit of the Sun. Seasons on Triton therefore last forty years.

The surface of the cold world lies at a balmy 235 degrees Celsius below freezing. Its surface is on the move with cryovulcanism (volcanoes spurting out frigid liquids, in this case ammonia and water, rather than hot lava) pushing matter into the upper reaches of the atmosphere, where the winds whip it away. It is covered in a shell of ices including water, nitrogen and carbon dioxide.

The atmosphere of Triton has been a subject of some interest for some time. It is believed to have originated from the same area of the solar system as the dwarf planet Pluto, meaning their compositions are likely to be the same. Looking at Triton, we can start to infer something about the atmosphere of Pluto, which spends most of its time frozen to the tiny world’s surface, except for that little part of the orbit where it comes within the extent of the orbit of Neptune.

Triton’s atmosphere was once thought to be as thick as that of Mars (about 6 millibars), but in fact turned out to be a lot thinner, 14 microbars or around 70,000 times thinner than Earth’s atmosphere (roughly 500 times thinner than expected). The measurements, by the Voyager 2 spacecraft, also revealed the atmosphere was predominantly Nitrogen. Now ground based measurements have been made of the Southern Hemisphere, presently basking in the summer light, revealing some interesting facets of the evolutionary processes of Triton’s atmosphere.

As with its proposed likeness, Pluto and its near namesake Titan, there are gases in the atmosphere of Triton that only exist during the summer, being frozen to the surface during winter months. One of these has turned out to be Carbon Monoxide, which has been detected to be present in roughly ten times the amount on upper surfaces as there is on lower surfaces. The new measurements have also shown that this sublimates (turns from solid to gas with no liquid phase) directly into the atmosphere. The effect of sublimating gases is shown in measurements of atmospheric surface pressure during the summer decades; 40-65 microbars, four or so times as thick as the Voyager 2 measurements.

The measurements were the first ground based investigations of the atmosphere at this high resolution and were made with the Cryogenic High-Resolution Infrared Echelle Spectrograph (CRIRES) instrument on the Very Large Telescope, part of the European Southern Observatory.

Some snippets of astronomical information

There’s a couple of new videos and webpages of interest, giving historical or basic explanations of topics with relevance to astronomy.

The European Space Agency has a new video relating to the Sun and how we observe it. Admittedly, it misses out nearly two thousand year’s worth of sunspot observations and promotes an inaccurate pronunciation of the word magnetosphere, but a good watch nevertheless.

Meanwhile, over at NASA, there’s a brief introduction to the history of women in space. Tonight at 9pm on BBC4, there’s a program called Beautiful minds on Professor Jocelyn Bell, who discovered pulsars and there’s also a snippet to be broadcast on PBS in the USA on Caroline Herschel, another woman with some significant contribution to astronomy, which is shown below:

Astronomy Now are continuing their series on the Search for Extraterrestrial Intelligence with an article on the founding of Project Ozma and how it led to SETI itself being established.

More Global Astronomy Month activities

Following the successful online Messier Marathon, the next big venture of Global Astronomy Month will be Saturn Watch, lasting from the 11th-16th of April. If you want to know where Saturn is, then Astronomy Now has an interactive sky map to help.

GAM also has a new Youtube Channel and a trailer, shown below:

For those of us in the dark heart of Kendal, the Eddington Society has an ask the astronomers panel event coming up on our public beginners’ night meeting at Kendal Museum on the 12th of April at 7pm. Our own views of Saturn will be taken on the 21st of April from 8pm as we have a public observing night scheduled on that date.

…and if you can’t wait for all that, keep your eyes on the Western horizon at sunset for the appearance of Mercury and Venus, then turn your eyes to the North when it gets dark for a higher than has recently been average chance of seeing the aurora (if you live at the right latitude…).