Royal Astronomical Society of Canada – Victoria Centre

Outline  Light Introduction  Light in our Eyes for Vision and Time-keeping (the Circadian Clock)  Examples: 1. Humans 2. Horseshoe crabs  Eyes: Windows to the World  Vision into the Ultra-Violet Direct Indirect (via fluorescence)  Eyes: Windows to the World of Night Royal Astronomical Society of Canada – Victoria Centre

Sources of light Sun Fire < 1 million years Bioluminescence Electricity 4.6 billion years

View of clouds & sky from inside human eye Light in our Eyes for Vision and Time-keeping 1 Visual Cortex 2 Circadian clock (SCN) 3 Pupillary reflex (OPN) Human Retina - How many types of photoreceptor? Signals to Three Centres in our Brain Answer: Three types of photoreceptor 1 2 3

Visible spectrum for humans Electromagnetic spectrum

Time-keeping – blue-sensitive ipRGCs (synchronize circadian clock with day/night cycle) The 3 photoreceptors “divide” the visible spectrum according to time of day Day – sunlight Night – star/moon lightDusk Vision – Rods & Cones Photoreceptor spectraFunctions

Circadian clock  internal time-keeper  present in all organisms  ~ 24hr cycle (period) – range ~23-25 hr  orchestrates our biorhythms  adjusts sensitivity of eye  stable, reliable through life span  synchronized with natural light/dark cycle Horseshoe crab Limulus polyphoemus “CrabCam” records movies Electrode records optic nerve activity Lateral eye Example: The circadian clock of Horseshoe Crabs

ERG circadian rhythm persist for a year in darkness or red light ERG circadian rhythms are driven by brain The circadian clock of Horseshoe Crabs drives electro-retinogram [ERG] rhythm for > year in dark Animal #1 Animal #2

Human Circadian Clock Journal of the RASC Dec 2012 RASC-Victoria Centre: victoria.rasc.ca/light  internal time-keeper (located in SCN)  ~ 24hr cycle (period) – range ~23-25 hr  adjusts light sensitivity of eye  orchestrates our biorhythms  stable, reliable through life span  synchronized with natural light/dark cycle by input from the ipRGCs (blue-sensitive) Melatonin

Some effects of de-regulating our circadian clock 1. Insomnia & sleep disorders 2. Reduced alertness 3. Poor cognitive and motor function 4. Depression & mental disorders 5. Cardio-vascular disease 6. Altered hormone levels 7. Obesity 8. Early-onset diabetes 9. Cancer – breast, prostate, colon Altered immune function.... Sources & more information at

Eyes: Windows to the World Fruit flies need their sleep – Vision into the UV Functions of UV vision  Mate selection  Foraging (herbivores & carnivores)  Communication  Other – defense, escape  Ancestral in vertebrates  Widespread among invertebrates UV cone Circadian clock

Eyes: Windows to the World Day and Night

Royal Astronomical Society of Canada – Victoria Centre Eyes: Windows to the World at night

Royal Astronomical Society of Canada – Victoria Centre

Eyes: Windows to the World at night – Steering by starlight Royal Astronomical Society of Canada – Victoria Centre Celestial navigators:  Humans  Birds  Seals  Humpback whales  Cricket frogs  Fish  Insects... * Dung beetles *

Eyes: Windows to the World at night Royal Astronomical Society of Canada – Victoria Centre For half the world, the Milky Way is a museum curiosity, the northern lights are mythical, and the Moon doesn't even brighten the sky. The Magic Canvas Bob Berman 2008

Our ability to wonder at the stars has led to vast, amazing progress in understanding our world, our universe, our existence. The night sky’s awe-inspiring majesty has inspired creativity in the arts, music, literature, poetry – - IN THE PAST! Lighting up the night artificially deprives us and future generations of this rich source of untold wonders waiting discovery. Royal Astronomical Society of Canada – Victoria Centre Eyes: Windows to the World at night

Royal Astronomical Society of Canada – Victoria Centre Eyes: Windows to the World day and night, route to understanding International Year of Light 2015