Sunday, 26 February 2017

Asteroid 2017 DF passes the Earth.

Asteroid 2017 DF passed by the Earth at a distance of 802 400 km (2.09 times the average distance between the Earth and the Moon, 0.54% of the average distance between the Earth and the Sun),slightly before 9.30 am GMT on Sunday 19 February 2017. There was no danger of the asteroid hitting us, though had it done so it would have presented no threat. 2017 DF has an estimated equivalent diameter of 9-28 m (i.e. it is estimated that a spherical object with the same volume would be 9.28 m in diameter), and an object of this size would be expected to explode in an airburst (an explosion caused by superheating from friction with the Earth's atmosphere, which is greater than that caused by simply falling, due to the orbital momentum of the asteroid) in the atmosphere between 30 and 17 km above the ground, with only fragmentary material reaching the Earth's surface.

The calculated orbit of 2017 DF. Minor Planet Center.

2017 DF was discovered on 17 Februaryy 2017 (two days before its closest approach to the Earth) by the University of Arizona's Mt. Lemmon Survey at the Steward Observatory on Mount Lemmon in the Catalina Mountains north of Tucson. The designation 2017 DF implies that the asteroid was the sixth object (object F) discovered in the second half of February 2017 (period 2017 D).

2017 DF has a 779 day orbital period and an eccentric orbit tilted at an angle of 0.86° to the plane of the Solar System, which takes it from 0.99 AU from the Sun (i.e. 99% of he average distance at which the Earth orbits the Sun) to 2.31 AU from the Sun (i.e. 2.31% of the average distance at which the Earth orbits the Sun, considerably outside the orbit of the planet Mars). It is therefore classed as an Apollo Group Asteroid (an asteroid that is on average further from the Sun than the Earth, but which does get closer). This means that close encounters between the asteroid and Earth are common, with the last having occurred in April 2000 and the next predicted in January 2036. 2017 DF also has occasional close encounters with the planet Mars, with the next predicted in November 2037.

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Saturday, 25 February 2017

Three confirmed fatalities as Atlantic Storm Doris sweeps across UK.

Parts of the UK are clearing up after Atlantic Storm Doris swept across the nation on Thursday 23 February 2017, bringing with it winds gusting as high as 140 kilometres per hour. The storm brought down trees, damaged power supplies and tore up fences across the country, causing a series of traffic accidents and widespread disruption to transport networks. Many people were left without power in Northern Ireland, Wales and England, flights were cancelled from airports and the Port of Liverpool was forced to close for part of the day.

Waves breaking over Newhaven Lighthouse on the south coast of England during Atlantic Storm Doris. Glyn Kirk/AFP.

At least three people have died during the storm, all of them in England. At the time of writing only one of these has been identified; 29-year-old Tahnie Martin of Stafford, who worked at the Department of English at the University of Wolverhampton, was killed by falling debris as she walked through the middle of Wolverhampton with colleagues. West Midlands Police are investigating the incident, and have not ruled out braining a criminal prosecution against the building's owners. 

Tahnie Martin of the University of Wolverhampton, who was killed by falling debris on 23 February 2017. SWNS.

In Swindon in Wiltshire, a 32-year-old woman was killed when the wind blew her into traffic, and a man in his 50s was killed in London when the high-sided vehicle he was driving was blown into a lamppost. In Stoke-on-Trent in Staffordshire a woman in her sixties is being treated for serious injuries after a carport collapsed on her, while in Milton Keynes a schoolgirl was injured after part of the roof of the school's gym collapsed while she was inside.

Vehicles damaged by a falling wall in Liverpool. Liverpool Echo.

In Wales the Storm caused part of the historic Colwyn Bay Pier to collapse, while the modern Turner Contemporary Gallery in Margate, Kent, was also damaged. The storm has also caused damage across parts of continental Europe, particularly in the Netherlands, Belgium, northern Germany and Poland.

Ocean storms form due to heating of air over the sea in tropical zones. As the air is heated the the air pressure drops and the air rises, causing new air to rush in from outside the forming storm zone. If this zone is sufficiently large, then it will be influenced by the Coriolis Effect, which loosely speaking means the winds closer to the equator will be faster than those further away, causing the storm to rotate, clockwise in the northern hemisphere and anticlockwise in the southern hemisphere.

Whilst the high winds associated these storms is extremely dangerous, the real danger from such storms is often the flooding. Each millibar drop in air pressure can lead to a 1 cm rise in sea level, and large storms can be accompanied by storm surges several meters high. This tends to be accompanied by high levels of rainfall, caused by water picked up by the storm while still at sea, which can lead to flooding, swollen rivers and landslides; which occur when waterlogged soils on hill slopes lose their cohesion and slump downwards, over whatever happens to be in their path.

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Magnitude 5.9 Earthquake in Northern Province, Zambia.

The United States Geological Survey recorded a Magnitude 5.9 Earthquake at a depth of 26.7 km roughly 846 km east of Kaputa in Northern Province, Zambia, slightly after 2.30 am local time (slightly after 0.30 am GMT) on Friday 24 February 2017. There are no reports of any damage or casualties arising from this quake, though people have reported feeling it across much of northeastern Zambia, and it is likely to have been felt in parts of neighbouring Tanzania and the Democratic Republic of Congo.

The approximate location of the 24 February 2017 Northern Province Earthquake. USGS.

Eastern Zambia lies within the the of the Great Rift Valley, which is slowly splitting the African Plate in two along a line from the Red Sea through Ethiopia, and which includes the great lakes and volcanoes of east-central Africa. This has the potential to open into a new ocean over the next few tens of millions of years, splitting Africa into two new, smaller, continents; Nubia to the west and Somalia to the east.

  Movement on the African Rift Valley, with associated volcanoes. Rob Gamesby/Cool Geography.
Witness accounts of Earthquakes can help geologists to understand these events, and the structures that cause them. The international non-profit organisation Earthquake Report is interested in hearing from people who may have felt this event; if you felt this quake then you can report it to Earthquake Report here.

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Loxodonta cyclotis: African Forest Elephant population undergoes sharp decline in Minkébé National Park, Gabon.

African Forest Elephants (Loxodonta cyclotis) are found in undisturbed forests in Central Africa. They were not recognised to be a separate species until 2010 largely due to the remote locations where they live, and are still poorly understood by zoologists and conservationists. Generic studies have found that they are not just distinct from other African Elephants, they are more closely related to the extinct European Straight-tusked Elephant (Palaeoloxodon antiquus) than to either of their living relatives. Despite living in areas hard to reach, these Elephants are thought to be particularly vulnerable to Human activities such as hunting, largely in the form of poaching for the (illegal) ivory trade and deforestation (which fragments the large areas of forests the Elephants leave, resulting in a network of forest patches too small to use separated by unsuitable open habitats.

50% of all African Forest Elephants are thought to live within the borders of Gabon, making conservation efforts in that country crucial to the survival of the species. The Minkébé National Park in northern Gabon was created in 2002 to provide a refuge for Elephants. It covers an area of about 7570 km² (34% larger than the average size of such parks in West and Central Africa, and is isolated, being 58 km from the nearest major highway. The location was chosen as it was home to a large population of Elephants, with one of the highest population densities in Central Africa.

The park was not initially well funded, limiting the staffing and resources available to either manage the park or protect the Elephants. In 2011 concern about poaching led to the government of Gabon to raise the status of the Forest Elephant to ‘Fully Protected’ and establish a National Park Police to man the park. However this does not appear to have been sufficient to remedy the situation, with staff in the park recording 161 poached Elephant carcases between 2012 and 2015, and a significant amount of ivory seized on the international market which has been sourced to the tri-national area of Cameroon, Gabon and Congo. 

In a paper published in the journal Current Biology on 20 February 2017, a team of scientist led by John Poulsen of the Nicholas School of the Environment at Duke University and the Agence Nationale des Parcs Nationaux in Gabon, describe the results of a study of the decline of the population of African Forest Elephants in the Minkébé National Park.

Poulsen et al. used data from two large scale surveys of Elephant dung in the park made in 2004 and 2014. The data obtained by these surveys was analysed using two separate analytical techniques; distance-sampling and dung-rainfall, in order to provide two separate estimates of the population in the two years. The distance-sampling method produced an estimate of 32 851 Elephants in 2004 and 7370 in 2014, a drop in population of 77.6%, while the dung-rainfall method produced an estimated population of 35 404 Elephants in 2004 and 6542 in 2014, a drop of 81.5%. 

Elephant in the Minkébé National Park. Poulsen et al. (2017). 

Either of these results points to a dramatic decline in Elephant numbers in the park, with poaching being the most likely source of the problem. Poulsen et al. speculate that much of the poaching in the north and central parts of the park can be attributed to organised crime syndicates operating out of Cameroon (to the north), noting that in 2011 park authorities discovered an illegal mining encampment in the centre of the park, where over 6000 migrants, principally from the town of Djoum in Cameroon, were also engaging in other illegal activities such as mining. However Gabon also appears to have its own home-grown poaching problem, with timber concessions to the west and south of the park providing logging roads that give access to the park.

Poulsen et al. observe that Elephant ivory is not currently listed on Appendix 1 of the Convention on the International Trade in Endangered Species (CITES), due to fears that some nations would pull out of the convention altogether if it were so listed. Similarly the African Forest Elephant is not currently recognised as a separate species under the terms of the International Union for the Conservation of Nature’s Red List of Threatened Species, for very much the same reasons They recommend that the African Forest Elephant should be recognised as a separate species on the Red List, and that all products derived from the species should be listed under Appendix 1 of the CITES convention.

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Wednesday, 22 February 2017

Annular Eclipse to be visible from Africa, Antarctica and South America.

An annular eclipse of the Sun (eclipse in which the Moon passes in front of the Sun, but does not completely block it, leaving visible ring of light) will be visible from parts of Angola, Argentina and Chile on Sunday 26 February 2017, with a partial eclipse visible from much of the rest of Sub-Saharan Africa, Antarctica, the southern half of South America and the islands of the South Atlantic.

The path of the 26 February 2017 Annular Solar Eclipse. The annular eclipse will be visible along the central dark grey path. A partial eclipse will be visible from the shaded areas; in the lighters area the full eclipse will not be visible as it will have started before dawn (west) or will continue after sunset (east). The solid red lines are the Equator and the Greenwich Meridian, the dotted red lines are the Topics of Cancer (north) and Capricorn (south). HM Nautical Almanac Office.

Eclipses are a product of the way the Earth, Moon and Sun move about one-another. The Moon orbits the Earth every 28 days, while the Earth orbits the Sun every 365 days, and because the two Sun and Moon appear roughly the same size when seen from Earth, it is quite possible for the Moon to block out the light of the Sun. At first sight this would seem likely to happen every month at the New Moon, when the Moon is on the same side of the Earth as the Sun, and therefore invisible (the Moon produced no light of its own, when we see the Moon we are seeing reflected sunlight, but this can only happen when we can see parts of the Moon illuminated by the Sun). 

The relative positions of the Sun, Moon and Earth during a Solar eclipse. Starry Night.

An Annular Eclipse is a type of Solar Eclipse, in which the Moon passes between the Earth and the Sun while the moon is close to aphelion (when it is furthest from the Earth). The Moon has a variable orbit, getting considerably closer and further from the Earth at different times, which alters its size as seen from the Earth. Thus when it is at its furthest from the Earth it appears considerably smaller than the Sun so an eclipse occurring at this time will produce a ring of sunlight, rather than a period of darkness. A Partial Annular Eclipse resembles a regular Partial Eclipse, in that the light of the Sun will be partially blocked by the Moon passing in from of it, though the disk of the Moon will be smaller.

An Annular Eclipse on 20 May 2013, photographed from Middlegate, Nevada. Wikipedia.

However the Moon does not orbit in quite the same plane as the Earth orbits the Sun, so the Eclipses only occur when the two orbital planes cross one-another; this typically happens two or three times a year, and always at the New Moon. During Total Eclipses the Moon entirely blocks the light of the Sun, however most Eclipses are Partial, the Moon only partially blocks the light of the Sun.

How the differing inclinations of the Earth and Moon's orbits prevent us having an eclipse every 28 days. Starry Skies.

Although the light of the Sun is reduced during an Eclipse, it is still extremely dangerous to look directly at the Sun, and eclipses should only be viewed with specialized equipment.

 Animation showing the shadow of the Moon at five minute intervals on Sunday 26 February 2017. Andrew Sinclair/HM Nautical Almanac.

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Tuesday, 21 February 2017

Thousands of homes flooded in Jakarta, Indonesia.

Thousands of homes have been flooded in Jakarta, Indonesia, after 144 mm of rain fell in the city in 24 hours from 6.00 am on Monday 20 February 2017 till 6.00 am on Tuesday 21 February. Water levels as high as 1.5 m have been reported in parts of the city, leading to flooded homes, abandoned cars and closures of schools and businesses. However there are no reports of any injuries or fatalities; which local authorities are claiming is due to a campaign of river dredging and slum clearances initiated after a flood in 2013 that killed 20 people.

Flooding in the Petogokan District of south Jakata on Tuesday 21 February 2017. Edy Susanto/Gresnews.

Jakata has a tropical monsoon climate, with peak rainfall in January and February, but this weeks rains have exceeded the typical amount for the entire of February. This is likely to be linked to a La Niña weather system over the southern Pacific, which has brought flooding to many parts of Southeast Asia. 

The effects of a La Niña weather system in December-February. NOAA.

The La Niña weather system is the opposite of the El Niño weather system, in which unusually cold surface temperatures spread across the equatorial Pacific from the upwelling zone on the South American coast. This traps warm water from the western Pacific, preventing it from spreading east and warming the central Pacific. This leads to lower evaporation over the (cooler) east Pacific, leading to low rainfall on the west coast of South America, and higher evaporation over the (warmer) west Pacific, leading to higher rainfall over East and Southeast Asia and northern Australia.

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