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Perseid Meteor Shower
Written by Michael Wilby   
Tuesday, 13 August 2013 18:53

NASA Picture of the day 13/08/2013                                     NASA Picture of the day 21/08/2013

The Perseid Meteor Shower is now subsiding following a high peak of 120'mph' (that's meteors per hour, or more officially the Zenithal Hourly Rate) early on Tuesday 13th August.

Last Updated on Thursday, 17 October 2013 18:54
 
March 2012 - The Return of the Virgo Cluster PDF Print Email
Written by Michael Wilby   
Sunday, 29 July 2012 15:14

There is a lot of planetary activity again this month, and though we are still in the process of losing some of our long-standing winter targets, both Mars and Saturn are continuing to rise into the evening skies. The clocks go back on the 25th March, which will put rising times back to almost what they are currently; while this is a welcome indicator that spring is finally on the way, for astronomy this also spells the beginning of the end for the lovely dark winter skies we are currently enjoying.

 

In terms of solar system news, for anyone who didn’t see the news the earth’s magnetosphere received another glancing blow from the sun, due to a double X-class flare on the 7th which was supposedly the largest in five years. Had this hit the earth straight on this would have had the potential to knock out satellite communications and other solar-sensitive technology, but as it was this only resulted in more auroral displays in high latitudes. Unfortunately Durham was once again clouded out at the peak of the activity and so we were not treated to any such displays. Mars is currently situated in southern Leo and is identifiable as a magnitude -1.2 star of very red hue to the unaided eye. The red planet has in fact just passed its opposition on the 3rd of March so is roughly at its maximum size for the year; as those who saw it through the Dob during telescope training last Saturday can tell you however, even at its peak there is not much to see. Due to Mars’ relatively high ellipticity, closest separation points can vary significantly from one year to the next and with a disk diameter of 13.9 arcseconds this year was almost maximum separation (angular size at opposition has varied between 13.8’’ and 25.1’’ in recent years). As such, anyone intending to tease surface details from the red planet will need large apertures and high magnification, though the white polar caps should be visible on high power through more modest equipment.

 

Saturn is finally becoming visible in the evening skies, and is currently rising around 9:30pm in Virgo, visible to the naked eye as a as a magnitude 0.8 star. The year-on-year opening of the planet’s rings is continuing since the ring plane crossing in 2008, which are lying at approximately a 15 tilt with respect to earth. While the ringed planet will continue to become more prominent in the sky, within Virgo there lies a cluster of the same name, which is best taken advantage of while the skies are still dark. The Virgo cluster contains over 1300 and is the central hub for the Virgo supercluster, which incorporates the Milky Way and surrounding local group; included in these are a number of bright galaxies, including the behemoth central elliptical M87. This has grown the over 200 times the mass of the Milky Way by accreting smaller galaxies fall into the cluster! As a by-product of this, the galaxy also produces a central jet as material falls onto the central supermassive black hole, but this is only seen in the best images (such as the Hubble image attached). Other cluster galaxies observable through a small telescope include the nearby M49 and M60, though all of these are fairly faint and are best revealed by wide-field imaging of the cluster.

 

 
February 2012 - The Earth’s Celestial Companion PDF Print Email
Written by Michael Wilby   
Thursday, 26 July 2012 16:20

 

The February sky is fairly sparse this year in terms of predictable transient events, though as the recent solar activity showed this does not necessarily mean it is going to be a quiet month! Though I only found out about the storm near its peak, the initial M3 class flare* was released from the sun on the 19th of Jan as observed by the STEREO solar satellites, which hit the earth’s magnetosphere on the 22nd (a day later than expected). This was swiftly followed by a larger M9 class flare which hit on the 24th, causing extensive auroral activity across Northern Europe and Greenland. Unfortunately any attempts to spot this from Durham were hampered by the thick cloud which set in from the 23rd. There was also an X-class flare (the most powerful category) on the 28th, though this is likely to deliver only a glancing blow to earth and as such is not rated as highly as those preceding it.

 

Elsewhere in the solar system, two of the inner planets are gearing up for a show next month; Mars will be at opposition on the 3rd whilst Mercury reaches greatest eastern elongation on the 5th and is observable for almost two hours after sunset. Jupiter is slowly nearing the end of its apparition, setting at 10pm by the end of the month, but Saturn has begun to edge into the evening sky; it seems there won’t be any evenings without one of the pair visible! Venus is still prominent in the evening sky as it moves towards greatest Eastern elongation in March; shining at magnitude -4 this is unmissably bright (though not to be confused with Jupiter) and is visible for a good four hours after sunset by the end of the month.

 

Normally the closest natural body to earth, the near side of the moon has been studied in great detail from everything from the naked eye to the Apollo missions. Due to its synchronous rotation** the far side on the moon is much less well understood, and the notable contrasts between the two hemispheres give rise to a number of interesting theories regarding the moon’s formation and early life. In terms of lunar phase activity this month, the moon is currently waxing towards full on the 7th and reaches new on the 21st.

Possibly one of the easiest objects to observe, the moon is instantly recognisable even through cloud; you don’t even need brilliant eyesight to begin picking out surface details without an optical aid. Binoculars or a small telescope with low magnification presents a stunning image of the whole moon, though for binoculars a steadying tripod improves the view dramatically. During the full moon most features will be visible, but the best time to observe individual targets is when the terminator (the line of twilight bisecting the moon) lies nearby. Normally objects like craters are fairly washed out by high surface brightness but are thrown into sharp relief by the low light levels cast near the terminator, revealing details which are not visible at any other time. Despite being tidally locked, we can actually observe a total of 59% of the moon’s surface from earth due to the effects of libration (a rolling effect caused by the moon’s slightly elliptical orbit around the earth); this explains why some prominent features on the lunar limb such as Mare Crisium sometimes appear less foreshortened than at other times of the lunar cycle.

The near side of the moon is littered with dark Maria; young, very flat and lightly cratered surfaces which were created when the moon was young and still had a molten interior. Large impactors punched through the crust and released vast lava flows which levelled and solidified; a particularly good example of this process is Plato crater, a 109km diameter circular crater located towards the lunar North Pole, the floor of which has been filled by the lava flow resulting from the forming impact. One of the most prominent craters on the moon is Tycho, which is young (relatively, at an estimated age of 108 million years); this can be seen since lines of bright ejecta from the impact lie over the older features (including the Maria) and stretch most of the way around the near side of the moon. In contrast to Plato, this has no lava floor and is fairly rugged; a central peak is also clearly visible where the material at the centre of the crater rebounded upwards after the collision. I recently found out by chance that the 389th largest crater on the moon is called Klute! An old heavily-worn crater 75km in diameter, it is sadly located on the far side of the moon so is not observable, and is named after a Dr. Daniel Klute (a contributor to the Saturn V rocket programme) rather than the nightclub.

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* A common system of flare classification is an alphanumeric system which represents the intensity of solar material hitting the Earth’s atmosphere. The M class flares are the second most powerful class (with an intensity range of 10-5 < I < 10-4 Wm-2), with the subsequent number denoting a multiplier of the intensity. E.g., the M9 class flare had a peak intensity of 9x10-5 Wm-2.

** Tidal friction during the earth-moon system’s early years fixed the moon’s rotation period such that it matches the lunar orbital period. Many small moons in the solar system (especially inner gas giant moons) seem to have suffered the same fate.

 

Last Updated on Thursday, 26 July 2012 16:22
 
January 2012 - Uranus and Neptune; the Neglected Siblings PDF Print Email
Written by Michael Wilby   
Thursday, 26 July 2012 16:05

 

As we move into the New Year there is no shortage of good astronomical targets, just perhaps a lack of willpower to stay outside (due to a combination of the cold weather and a recent excess Christmas festivities)! Many of the targets from last month’s bulletin are still very much visible, and the constellation of Orion still visibly dominating the night sky.

 

After the somewhat clouded out Geminids of last month, there is once again a chance to observe some meteors; this time in the form of the Quadrantids. These peak over the nights of the 3rd and 4th with a radiant lying between the constellations of Boötes, Ursa Major and Draco; the average ZHR for this shower is 40, but in recent years very sharp peaks have been observed, reaching as high as 120 for a few hours. Over these two nights the radiant will rise around midnight, making the shower not best placed for viewing in the UK. For those willing to stay up and brave the winter cold however, the lack of moonglow and consistently high yearly rates mean that this should be a good show!

 

The outer gas giants get somewhat left out by most solar system round-ups; while their greater distance from earth renders them smaller, fainter and hence harder to observe, they are nonetheless fascinating objects. Uranus and Neptune lie average orbital radii of 19.6AU*and 30AU respectively, with disk sizes of 3.5 and 2.2 arcseconds, or approximately 500x and 800x smaller than the diameter of the full moon. Large diameter telescopes with high magnifications are required to resolve these planets instead of seeing a dot of bluish tint, but this is well within the scope of dedicated amateur equipment. This month, both planets are located in the early evening sky, with Neptune setting at around 8pm early in the month and Uranus following around 10:30pm; Neptune becomes lost to the evening twilight by the 25th. Both planets are fairly close to their respective conjunctions**, but due to their large orbital radii compared to the earth this does not overly affect their visibility (of course assuming that the sun is not still above the horizon!). Visibly, both planetary disks have the same turquoise hue due to the presence of methane clouds in their upper atmosphere. Each also has an extensive moon system, but in the case of Neptune these are extremely faint and little is known about all but the largest, Triton. If you have access to a telescope which can resolve the moons of Uranus there is quite a show to be had; the five brightest moons are all approximately 15th magnitude (Miranda, Ariel, Umbriel, Titania and Oberon).

 

If the weather isn’t kind this month however (this is Durham, after all!), one of the major astronomical events which can be enjoyed from the comfort of your own armchair is the return of the Stargazing Live series. To be aired between the 16th and 18th Jan, Prof. Brian Cox and Dara O’Briain return to deal with practical observing tips, space news and even dabble in some astrophysics; based on last year’s show this should definitely be worth watching. AstroSoc is also running an affiliated event on the 21st, so keep your eye out for more details which will be coming your way shortly!

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*AU: Astronomical Unit, the mean radius of the orbit of the earth, equal to 1.5x1011 m

**Conjunction: When a planet lies in the same direction as the sun in the sky as viewed from Earth; this is the point at which the object is furthest from Earth.

Last Updated on Thursday, 26 July 2012 16:07
 
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