The September Equinox

The September Equinox falls on Monday 22 September this year (2025), when the day and night will be of equal length in both of the Earth's hemispheres. The Earth spins on its axis at an angle to the plain of the Solar System. This means that the poles of the Earth do not remain at 90° to the Sun, but rather the northern pole is tilted towards the Sun for six months of the year (the northern summer), and the southern pole for the other six months (the southern summer). This means that twice a year neither pole is inclined towards the Sun, on days known as the equinoxes.

Simplified diagram showing the tilt of the Earth throughout the year. Not to scale. The Human Adventures in Space Exploration.

The equinoxes fall each year in March and September, with the March Equinox being the Spring (or Vernal) Equinox in the Northern Hemisphere and the Autumn Equinox in the Southern Hemisphere, while the September Equinox is the Autumn Equinox in the Northern Hemisphere and the Spring Equinox in the Southern Hemisphere. On these two days the day and night are both exactly twelve hours long at every point on the planet, the only days on which this happens.

How the combination of the Earth's equatorial plane (horizontal circle labelled as Celestial equator) and the plane of the Earth's orbit (diagonal circle labelled as Path of the Sun) creates the Solstices and Equinoxes that we observe. Christopher Crockett.

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Suspected poacher shot in Kruger National Park, South Africa.

A suspected poacher has been shot in a confrontation with field rangers near the Crocodile Bridge entrance to the Kruger National Park in South Africa. The incident happened on Thursday 18 September 2025, after the rangers discovered and followed a set of Human tracks leading towards the southern boundary of the park. At about 8.00 pm local time they reported encountering two armed men, who fled, successfully climbing over the boundary fence. One of the men then allegedly turned and raised his riffle towards the rangers, causing them to fire. The other fled into a cornfield and escaped.

When the rangers reached the man they had shot they found he was alive, and called for a doctor and police support. A search revealed that a bag the man was carrying contained two Rhino horns, and that he did not posses a permit to enter the park or carry a firearm. He was arrested at the scene, but then transferred to a local hospital where he will be held until he is deemed fit to appear before magistrates. 

A pair of White Rhinoceros, Ceratotherium simum, in the Kruger National Park, South Africa. Roger de la Harpe/Kruger National Park.

South Africa is home to more than half of the world's surviving Rhinoceros population, but has (like many other countries) faced significant problems from poaching of the Animals for their horns. This reached a peak between 2013 and 2017, with more than a thousand Rhinos being killed each year in South Africa, according to Save the Rhino, although the number fell each year from 2015 until 2020. During the COVID 19 pandemic there was an increase in poaching, with the number killed rising slowly each year until 2023. There was a drop of about 15% in 2024, although this still resulted in 420 known Rhinoceros poaching incidents. The majority of Rhino poaching is thought to be carried out by organised crime syndicates, rather than opportunistic local hunters. 

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Magnitude 6.5 Earthquake beneath Central Papua Province, Indonesia.

The Indonesian Meteorological, Climatological, and Geophysical Agency recorded a Magnitude 6.5 Earthquake at a depth of about 24 km, to the south of the town of Nabire in Central Papua Province, Indonesia slightly before 3.20 am on Friday 19 September 2025, Eastern Indonesian Time (slightly before 6.20 pm on Thursday 18 September, GMT). The event was felt across much of western Central Papua Province and parts of eastern West Papua Province, and is reported to have caused the collapse of the main bridge in Nabire, as well as two houses. Other buildings, including the airport, have recorded minor damage, although no casualties have been reported.

The approximate location of the 18 September 2025 Central Papua Earthquake. USGS.

The tectonic situation underlying the island of Papua is complex, with the island being made up of a number of small tectonic plates being squeezed between the larger Pacific/Caroline and Australian plates. Beneath Central Papua Province the Pacific Plate is being subducted beneath the Australian Plate along the New Guinea Trench, however, this is not a simple tectonic boundary with one plate disappearing beneath another, as a sliver of an older, now almost completely subducted plate caught between the two and being displaced to the west along the Sorong-Yapen Fault. This creates a complex situation in which the various plates stick together until pressure builds up sufficiently to overcome the friction and causes sudden movements we experience as Earthquakes.

(a) Block diagram illustrating kinematic partitioning of oblique convergence (without scale) in northwestern New Guinea. The diagram shows partitioning  as is occurring in the last 4 million years and also notes the timing of major shortening events in the region. Note that shortening in the Lengguru Fold Belt region (including the adjacent Wandamen Peninsula) was replaced by extension after 3 million years ago. Black arrows show GPS vectors. (b) Block diagram showing oblique convergence. Saputra et al. (2023).

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Partial Lunar Eclipse to be visible from New Zealand and parts of Antarctica, Oceania, and Australia.

A partial Solar Eclipse will occur on Sunday 21 September 2025, which will be visible from all of New Zealand and parts of Antarctica, Oceania, and Australia. The event will occur between 5.31 pm and 9.53 pm GMT.

The Moon's shadow projected onto the Earth as the eclipse proceeds. The hemisphere of the Earth facing the Sun is shown. Contours show where various fractions of the Sun's disk is covered. In-The-Sky.

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.

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 an eclipse should always be viewed using appropriate equipment. 

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Thirty one known deaths in an Ebola Virus outbreak in Kasai Province, Democratic Republic of Congo.

Thirty one people are now known to have died and a further seventeen people have received hospital treatment in an outbreak of Ebola Virus in Kasai Province, Democratic Republic of Congo. The first reported case was a woman in the 34th week of a pregnancy, who was admitted to Bulape General Reference Hospital on 20 August 2025 suffering from high fever, bloody diarrhoea, haemorrhaging and extreme weakness, according to a press release issued by the World Health Organization. This first patient died from multiple organ failure on 25 August, and was subsequently confirmed to have been infected with Ebola Virus through analysis of samples sent to the Institut National de Recherche Biomédicale in Kinshasa. Two healthcare workers who had come into contact with the patient also subsequently died of the Virus.

By the 4 September 28 cases of the Virus had been reported, with fifteen fatalities including four healthcare workers (a 54% case fatality ratio), all within the Bulape and Mweka health zones, with 80% of cases in persons above the age of fifteen. By 18 September 48 cases had been reported, with 31 known fatalities (a 64% case fatality ratio), and the Virus had spread to four healthcare districts. 

A team of medics from Medecins Sans Frontiers helping to set up an Ebola treatment centre in Bulape in September 2025. Medecins Sans Frontiers.

Ebola Virus Disease is caused by RNA Viruses of the genus Ebolavirus (sometimes referred to as Orthoebolavirus because it belongs to the Kingdom Orthornavirae). It has a reputation for being the world's deadliest viral disease, at least in part due to the 1995 film Outbreak, though this is probably slightly inaccurate as about 50% of victims survive, making it less deadly than diseases such as Rabies. However, it is extremely contagious, with know known cure, and has a tendency to rapidly overwhelm local health systems as health workers themselves are infected.

Electron micrograph of an Ebola Virus particle. Frederick Murphy/Centers for Disease Control and Prevention/Wikimedia Commons.

Ebola begins with a fever similar to that caused by Influenza or Malaria, which tends to come on rapidly two-to-three weeks after infection (during at least part of which time the patient is already infectious). This tends to be followed by extreme respiratory tract infection, headaches, confusion, rashes and tissue necrosis and heavy bleeding. Death is generally caused by multiple organ failure.

The only known treatment for Ebola is intensive rehydration, which can improve the survival prospects of patients greatly, accompanied by anticoagulants and procoagulants to mange the diseases attacks on the circulatory system, analgesia to cope with the pain of the disease and antibiotics and antimycotics to prevent secondary infection. Due to the highly contagious nature of the disease it is recommended that healthcare workers wear full-body protection to maintain a barrier between them and their patients; a daunting prospect in the tropical regions of Africa where the disease is endemic. A vaccine is now available for the disease.

Ebolavirus is thought to have a non-human animal vector, since its rapid onset and high mortality rate appears to preclude a permanent residence within Human hosts. Surveys of wild animals have found Ebola infections in Rodents and Great Apes, however these were affected by the disease in a similar way to Humans, and are therefore unlikely permanent hosts. The most likely vectors are thought to be Fruit Bats or small Primates, which are endemic to the areas where the disease occurs and which are widely eaten; cooking meat probably kills the virus, but there is a distinct danger of infection while preparing carcasses. 

Following the conformation that the outbreak in Kasai Province was caused by the Ebola Virus, the World Health Organization delivered 14 tonnes of emergency supplies to Bulape, including personal protective equipment, mobile laboratory equipment and medical supplies. Additional medical personnel, experienced in dealing with Ebola outbreaks, have also been sent to the area by the Congolese Ministry of Health, the World Health Organization, and Medecins Sans Frontiers. 

A specialist 34-bed Ebola treatment centre has been set up in Bulape, There are reported to be 2000 doses of Ebolavirus vaccine available in the Democratic Republic of Congo, which have been dispatched to Kasai Province, with the 523 front line healthcare workers having been the first recipients of the vaccines; a further 45 000 doses of vaccine are being sent to the area by international agencies. A testing lab has also been set up in Bulape, allowing for results to be obtained within 4-6 hours of samples being taken, as opposed to the 4-5 days needed to get a result from samples shipped to Kinshasa. 

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Magnitude 7.8 Earthquake off the coast of the Kamchatka Peninsula, Russian Far East.

The United States Geological Survey recorded a Magnitude 7.8 Earthquake at a depth of 19.5 km off the east coast of the Kamchatka Peninsula in the Russian Far East slightly before 2.00 am local time on Friday 19 September 2025 (slightly before 7.00 pm on Thursday 18 September, GMT). Despite the size of this event, no casualties have been reported, although tsunami warnings were triggered across the Pacific. The event is thought to have been an aftershock of a Magnitude 8.8 Earthquake recorded off the coast of the Kamchatka Peninsula in July this year.

The approximate location of the 19 September 2025 Kamchatka Earthquake. USGS.

The Kamchatka Peninsula lies on the eastern edge of the Okhotsk Plate, close to its margin with the Pacific and North American Plates. The Pacific Plate is being subducted along the margin, and as it does so it passes under the southern part of the Kamchatka Peninsula. This is not a smooth process, the rocks of the two plates continuously stick together then, as the pressure builds up, break apart again, causing Earthquakes.

Simple diagram showing the subduction of the Pacific Plate beneath the Okhotsk Plate along the Kuril Trench. Auburn University.

Earthquakes along subductive margins are particularly prone to causing tsunamis, since these often occur when the overlying plate has stuck to the underlying plate, being pulled out of shape by its movement.. Eventually the pressure builds up to far and the overlying plate snaps back, causing an Earthquake and a tsunami.

Simplified graphic showing tsunami generation along a convergent margin. NASA/JPL/CalTech.

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