Hot on the heels of yesterday’s total lunar eclipse, a partial solar eclipse will be visible from the UK on the morning of 4 January 2011. The next solar eclipse visible from the UK will not be until 20 March 2015.

The partially-eclipsed Sun will rise in the south-east a little after 08.00 and the eclipse will end around 09:30. The greatest eclipse will be seen from northern Sweden at 08.50.

The table below shows details of eclipse times and magnitudes for various UK cities:

Eclipse details courtesy of Fred Espinak (NASA)

The best viewing locations with longest viewing time, greatest obscuration and greatest magnitude are in southern and eastern UK, declining towards the north and west.

Viewing the eclipse

WARNING: never look at the Sun directly through an optical instrument such as telescope or binoculars – it can result in permanent blindness. It is also dangerous to look at a bright Sun with the naked eye. Do not use sunglasses, polaroid filters, smoked glass etc to look at the Sun.

The safest way to view an eclipse is via optical projection, such as a pinhole projector. The following links from Exploratorium explain how to make two kinds of projector and also how to obtain safe filters:

• Making a pinhole projector
• Other optical projection and filters

Image: Partial solar eclipse, 3 October 2005, taken through a solar
filter. Mike Dryland, Flamsteed Astronomy Society

21 December 2010 – UK viewers will be able to catch the start of a total lunar eclipse this morning, the first for three years, with totality starting at 07.41 GMT and lasting a little over an hour. Within the UK, Scotland and Northern Ireland will get the best views.

Lunar eclipses occur when the Moon passes through the Earth’s shadow. During eclipse, the Moon may turn blood red or pink, with indirect sunlight giving the Moon a ghostly hue. Find out more in our eclipses fact file.

The last time a total lunar eclipse occurred on the winter solstice was in 1638, and the next time will be in 2094.

20 December 2011 – At 23.38 UTC (GMT) tomorrow, 21 December, the solstice will occur when the poles of the Earth align with the Sun. In the Northern hemisphere, the North pole will point directly away from the Sun (the winter solstice), while in the Southern hemisphere, the South pole will point directly towards the Sun (the summer solstice).

At the solstices the Sun is at its furthest from the celestial equator (the projection of the Earth’s equator onto the sky). The world ‘solstice’ comes from the Latin solstitium meaning ‘Sun stands still’ because the apparent movement of the Sun’s path north or south stops before changing direction. At the winter solstice, the apparent position of the Sun reaches its most southerly point against the background stars.

Shortest day and sunrise/sunset times

The winter solstice also marks the shortest day (and longest night), but not the earliest sunrise or latest sunset. The earliest sunset occurred on around 12 December 2010 (15:51 in London) and the latest sunrise will occur around 30 December (08:06 in London).

The reason for this is the slight variation in the length of ‘natural’ days throughout the year, resulting from a combination of the Earth’s elliptical orbit around the Sun and the tilt of the planet’s rotation axis. For clocks to work all days need to have an equal length, which is therefore fixed at the average length of a natural day (hence the ‘mean’ in Greenwich Mean Time). This has a knock-on effect on sunrise/sunset times, and the earliest sunrise occurs several days before the longest day and the latest several days (about 9) after the shortest.

Opinion is divided over whether the solstice marks the start of winter or the middle of winter, or whether winter actually starts on 1 December (as reckoned by most meteorologists).

Marking the solstice

Under the early Julian Calendar, the winter solstice occurred on 25 December. When the more accurate Gregorian calendar was introduced in 1582, the solstice slipped to the 21st, but the Christian celebration of the birth of Christ has continued to be held on 25 December. This date is also associated with the Roman Saturnalia festival, and ‘Dies Natalis Solis Invicti’ (the birthday of the unconquered sun), as well as Nordic pagan festivals.

Solstice shorts: Yuletide stargazing

For an alternative way to celebrate the solstice, why not join us for our 25-minute Yuletide stargazing sessions, daily at 16.30 and 17.00 on 20-23 December? These offer a unique opportunity to look through our historic 28-inch diameter refracting telescope, and to view one of the more striking double stars.

Places are limited and tickets are £6 per person. You can book online or call 020 8312 6608 between 10.00-16.00. (Please note: If adverse weather conditions prevent viewing through the telescopes, an alternative programme will be offered. We are not able to offer refunds under such circumstances.)

Whichever way you choose to celebrate this time of year, we hope you will enjoy yourselves and have a very happy festive season!

It’s a seasonal staple of carols, Christmas cards and nativity plays but what was the Star of Bethlehem? Astronomical fact or pious fiction, theological symbolism or astrological sign, or simply an inexplicable supernatural event?

The truth is of course that nobody knows for sure, but there are some more and less convincing theories.

The star according to Matthew

Only Matthew’s gospel mentions the star and the Magi or wise men, in the following passage:

After Jesus was born in Bethlehem in Judea, during the time of King Herod, Magi from the east came to Jerusalem and asked, “Where is the one who has been born king of the Jews? We saw his star in the east [or at its rising] and have come to worship him.”… Then Herod called the Magi secretly and found out from them the exact time the star had appeared… After they had heard the king, they went on their way, and the star they had seen in the east [or at its rising] went ahead of them until it stopped over the place where the child was. When they saw the star, they were overjoyed.
(Matthew chapter 2, verses 1-2, 7, 9-10, New International Version)

From this we gather that the star first appeared or rose at a particular time, that it apparently moved (‘went ahead of them’) and stopped, and that to the Magi at least it signified the birth of a ‘king of the Jews’.

Astronomical explanations

Astronomically, it’s been suggested that the star may have been a nova or supernova explosion; a comet; a triple conjunction of Jupiter and Saturn; a close grouping of the three planets Jupiter, Saturn and Mars; a stationary point of Jupiter; or a variable star (one whose brightness changes over time).

Chinese records mention a possible nova or comet in 5BC – an unusually bright star which appeared in the eastern sky for 70 days, and which may have been a nova outburst from the variable star DO Aquilae. This occurred at about the same time as a triple conjunction of Jupiter and Saturn in the constellation of Pisces. The rare combination of these two events may well have been seen by the Magi as a religious sign.

Astrological aspects

It’s likely that the Magi studied astrology, so the star’s astrological aspects are probably at least as important as its astronomical explanation. Rutgers astronomer Michael Molnar has suggested that a double
occultation of Jupiter by the Moon in Aries in 6BC could have astrologically
signified the birth of a divine ‘king of the Jews’.

Theological significance

Others of couse think that the writer of Matthew’s gospel simply invented the star, perhaps to fulfil the Old Testament prophecy that ‘A star will come out of Jacob; a sceptre will rise out of Israel’ (Numbers chapter 24, verse 17). More likely is that Matthew’s star is simply an example of ‘Midrash’ – an established Judaic tradition of theological writing in which non-factual elements can be used to bring out the religious meaning of the factual account. So whether or not there actually was a star is less important than the spiritual message Matthew is trying to convey.

We can’t know for sure whether, what or when the star was. But perhaps the answer is not either/or out of the alternative strands of explanation – astronomical, astrological, theological, supernatural – but both/and. It’s plausible that the Star of Bethlehem was a genuine astronomical event – perhaps a nova associated with a variable star – that had astrological significance to the Magi and theological significance to Matthew.

Whatever the truth is, we wish you a very happy Christmas!

Note: this post is an edited re-posting from last Christmas, based on our fact file about the Star of Bethlehem.

13 December 2010 – Clouds permitting, don’t forget to look out tonight and tomorrow for the last major meteor shower of the year. The Geminids are due to reach their peak at 16.45 UT on 14 December, as the Earth ploughs through a stream of debris left behind by asteroid 3200 Phaethon. The fragments burn up as they hit the Earth’s atmosphere causing the shooting stars, some reaching the size of big fireballs.

The Geminids shower seems to be intensifying each year, and an average of about 100 meteors per hour are expected to radiate from near the bright star Castor.

For the first time scientists have used data analysed by the public to make a real-time prediction of a significant solar storm that should hit Earth on Monday 13 December, thanks to the Solar Stormwatch web project.

The initiative, launched in February by the Royal Observatory, Greenwich (ROG), in partnership with the STFC Rutherford Appleton Laboratory and the Zooniverse Citizen Science Project, makes it possible for anyone with internet access to get involved in the latest solar research by helping to spot and track storms as they erupt from the Sun. These collective measurements enable scientists to forecast the arrival of storms far enough in advance to issue effective pre-emptive warnings for the first time.

Solar storms, power grids and aurora

The Sun is much more dynamic than it appears to the naked eye. Intense magnetic fields churn and pummel the Sun’s atmosphere, storing enormous amounts of energy that, when released, can hurl billions of tons of material out into space in eruptions called Coronal Mass Ejections (CMEs) – or solar storms.

The latest storm identified by the project is predicted to hit Earth at 07.32 GMT on Monday 13 December. Solar storms have the potential to interfere with communication satellites, upset GPS navigation systems and also pose a health risk to astronauts on the International Space Station. In severe cases they can even knock out entire power grids causing widespread disruption here on Earth.

On a gentler note, the particles making up a solar storm can produce beautiful displays of the Northern and Southern Lights as they collide with the Earth’s upper atmosphere. Scientists are not overly concerned about the effects of the current storm, but the early warning provided by Solar Stormwatch will allow precautionary measures to be put in place.

Predicting storms

In the past solar scientists were only certain an approaching storm was directed towards Earth a few hours ahead of impact, but data from the NASA STEREO mission used by the Solar Stormwatch project allows Earth-directed storms to be identified up to three days in advance, enabling space agencies and power companies to take steps to limit any damage. In order to identify hazardous solar activity, the solar wind needs to be monitored constantly – a task that is too much for scientists to deal with on their own – so the Solar Stormwatch website utilises the spotting skills of the public to alert them to incoming storms.

Dr Marek Kukula, Public Astronomer at the ROG, says, ‘Solar Stormwatch is special in that it harnesses public interest in astronomy to provide data that is invaluable to scientists. The more people that take part in “stormwatching” the more we will learn, and the fact that the volunteers’ work has now enabled us to predict when a storm will hit the Earth is a significant milestone, not just for the project, but for science as a whole’.

Solar Stormwatch is the latest chapter in a long history of solar research at the Royal Observatory, Greenwich, dating back to the 1870s when the Observatory housed a photoheliograph – a telescope that took daily photos of the Sun to track sunspots. Visitors to the Royal Observatory today can see this telescope housed in the Altazimuth Pavilion.

Take part

Join the hunt for solar storms at the Solar Stormwatch website. Help scientists spot explosions on the Sun and track them across space to Earth.

Image: Composite image of a coronal mass ejection taken by the SOHO spacecraft, 2002 © SOHO, NASA and ESA

Earlier this month we launched a new blog and website. This will bring you the latest news on a five-year research project on the British Board of Longitude, which oversaw the successful introduction of effective methods for position-finding at sea (among other things, as we will show).

The project is a collaboration between the National Maritime Museum and the Department of History and Philosophy of Science at the University of Cambridge and is supported by a grant from the Arts and Humanities Research Council. We’ll be updating the blog regularly, so keep checking for the latest progress and news of events and activities.

Three recent discoveries with implications for the search for other Earth-like planets and for life in the Universe.

Red dwarfs increase possibility of other Earths

The universe may contain three times more stars than has been previously thought. New observations using the Keck telescope in Hawaii showed that galaxies older than ours may contain 20 times as many red dwarfs, which are older and less bright than the Sun.

This also greatly increases the estimated number of planets in the universe and therefore the likelihood of other ‘Earth-like’ worlds. Red dwarfs tend to be at least 10 billion years old, allowing plenty of time for complex life to evolve on planets in their system.

The discovery, led by a team from Yale University, also reduces the amount of ‘dark matter’ needed to explain the ‘missing mass’ of the universe.

First known atmosphere round ‘Super-Earth’ exoplanet measured

Scientists at the Harvard-Smithsonian University Centre for Astrophysics have been able to measure the atmosphere of a ‘Super-Earth’ exoplanet for the first time. The planet – GJ1214b – is 40 light years distant, is about three times the size of Earth and seven times the mass, and is the first of its kind around which an atmosphere has been detected. Measurements using the ‘transit method’ seem to show that it does not have a hydrogen or helium atmosphere, but further work will be needed to determine whether it has a thinner and steamier atmosphere or a thicker, cloudier one.

See related post New exoplanet may be habitable (1 Oct 2010)

‘Extremophile’ bacteria break the mould for life

Up till now, it’s been thought that all life on Earth must contain the six elements carbon, oxygen, hydrogen, nitrogen, sulphur and phosphorus. But an Arizona State University and NASA team have found a bacterium in a California lake that is able to substitute the usually-poisonous element arsenic for phosphorus.

The discovery of a separate ‘tree of life’ would have major implications in the hunt for alien life in the Universe. However, the researchers found that the bacterium still thrives best in a phosphorus environment, meaning that it is probably simply an unusual branch of the known tree of life rather than a member of an entirely different one.