The fascinating and perilous journeys made by migrating birds has been a natural wonder for centuries with the first records of this phenomena made more than 3,000 years ago. The innate knowledge of migratory birds is mentioned in Job and Jeremiah and the ancient Greek writers Homer, Hesiod and Aristotle noted their passage.

Sensing the Earth’s magnetic field allows birds and other animals to determine their approximate position on the Earth. Research looking at how birds navigate over vast distances has shown many species are able to sense the compass direction of the Earth’s magnetic field and process this information. Non-migratory birds also have this ability using magnetoreception to orientate themselves in a local sense to map habitat.

There are two basic mechanisms involving magnetism used by animals; one method uses the iron based mineral magnetite found in the body’s cells and the other involves a protein found in the eye which is sensitive to light of different colours and intensities.

In plants and some animals, the light sensitive cryptochrome molecules are also involved in the control of the body’s circadian rhythms by tracking the difference between night and day. They can be found in cell nuclei of mammals and in the retina of several bird species. Ilia Solov’yov from the University of Southern Denmark has found the particular structure of cryptochrome Cry4 is unique and when light hits Cry4 cryptochromes in the eye of a migrating bird, they undergo chemical reactions that are influenced by the direction of Earth’s magnetic field, providing a signal of the bird’s orientation.

This light sensitive magnetic compass used by birds is affected by the polarisation direction of light. This was discovered by Rachel Muheim in a study where zebra finches were set the task of finding food in a maze. The birds were only able to use their magnetic compass when the direction of the polarised light was parallel to the magnetic field, when the polarised light was perpendicular to the magnetic field the birds became completely disorientated.

Researchers have put forward a theory that polarised light at sunrise and sunset accentuates the magnetic field at times when birds are ready to migrate or roost but in the middle of the day when the polarised light is approximately perpendicular to the magnetic field and less visible to them they can rely on sight to hunt and spot predators.

Magnetite is the most magnetic of Earth’s naturally-occurring minerals and microscopic particles are found in the cells of animals. Unlike the cryptochrome protein found in the eye and used by birds to perceive the Earth’s magnetic field, a magnetite-based magnetic sense does not need light to function.

Mole rats navigate their tunnels using this method which works like an internal compass. Birds also use this mechanism based on magnetite as an additional method to determine their position.

Sensing Earth’s geomagnetism is a functional ability seen in many creatures from bacteria and birds to turtles and bats. It is an evolutionary advantage to be able to orientate and navigate. Joseph Kirschvink and researchers at Caltech have completed experiments testing the human capacity to sense the magnetic field. Volunteers inside a chamber shielded from electromagnetic interference were subjected to an altered magnetic field while their brainwaves were monitored. The team found clear evidence that the subjects’ alpha brain waves were effected suggesting a rudimentary magnetic “sense”. The scientists believe that cells containing crystals of magnetite could register changes in magnetic fields and report this information to the brain. It is already known that magnetotactic bacteria have structures containing nanoscale magnetite crystals called magnetosomes that act as biological compasses, allowing the bacteria to navigate.

This research suggests that human alpha brainwaves react to a changing magnetic field. Alpha waves are always present, but are more prominent when in a relaxed and idle state of mind. Noticing a dip in the amplitude of the alpha waves would indicate the neurons in the brain becoming engaged in a task. The experiment was conducted to mimic how the Earth’s magnetic field would be experienced by the brain. The laboratory field was similar in strength to the Earth’s and the researchers moved it slowly to simulate how the field would change when turning one’s head. 

More experiments with iron filings, etchings and magnets.

Large etching on steel plate and small polymer etching.

Also some green screen filming towards the video work I am creating on this subject.

While back in the print studio I made some more prints of the mossy forest and added a little burst of colour.

A little progress with building the cosmic ray detector. I have drilled the holes in the plastic scintillator which was quite stressful as the project notes say it is easy to break. I did a test first in acrylic to gauge the size of the drill bit needed. The scintillator turned out to be much softer though and so I am hoping the holes are not too big now. I sent the Printed Circuit Board off to get the components soldered. I really wanted to do the soldering myself but am glad I went for help as there have been some issues with getting the voltage correct for the connection to the SiPM PCB.

I was lucky to grab a bargain box of Super 8 filming kit though haven’t had time yet to explore this fully and see if I can work out how to operate everything.

Out of studio

A visit to APT Gallery to see Periastra curated by Paul Malone looking at methodologies of curiosity within the fields of art and astrophysics.

I really like the presentation by Nicola Rae of a collection of fireball videos collected by the meteor watch group UKMON

I was excited to meet John Berman who was showing a muon detector he had built. He has used a Geiger Müller (GM) tube, for his detector which can be bought as a kit . A GM tube will detect alpha particles, beta particles, gamma rays and Cosmic Muons. It can be adapted to run in coincidence mode – this is when two or more tubes are connected and only when all tubes register a particle passing through at the same time can it be certain it is a cosmic particle and not background radiation. There is some downtime in a GM tube after each ionisation is recorded so it is possible not all particles are registered. When a particle passes through the tube the LED’s will flash.