In order to delve deeper into this remarkable astronomical event, we spoke with Christian Gigault, Assistant Professor in the Department of Physics at the Faculty of Science.
Q1: What is the occurrence of solar eclipses? And why don't we have a solar eclipse every New Moon?
Professor Gigault: At this point in time, we have the coincidence that the apparent size of the Sun is approximately the same as the apparent size of the Moon (about 0.5 degrees). A solar eclipse happens on the rare occasions when the Moon passes in front of the Sun. This can only happen during the so-call 'New Moon' (i.e. moonless night), but does not happen on every New Moon, far from it. It turns out that the orbit of the Moon is inclined about 5 degrees with respect to the path that the Sun takes in the sky (which is, aptly named, the 'ecliptic'). Since the Moon apparent size has been always about 0.5 degree no matter where it is in the sky, that 5-degree inclination means that most times the Moon misses the Sun, passing as high as 10 X its diameter above or below the center of the Sun. It's only when the relative orientation of the two orbits allows the Moon to pass directly in front of the Sun that we can have a solar eclipse.
Since the Moon is much smaller than the Earth, its shadow here is also much smaller, and if you happen to live too far north or south of the path that this shadow takes on the surface of the Earth (the 'path of totality'), you will not see a full eclipse or none at all even. This is not the case for lunar eclipses that occur at night at Full Moon, since the shadow of the Earth is larger than the Moon, and those are thus more frequent.
To complicate matters, the orbit of the Moon is slightly elongated, and you can expect +/-5% variations in apparent diameter from the smallest full Moon to the largest. This phenomenon causes what journalists call a 'supermoon' (no astronomer uses that term.), although nobody can realistically remember the size of a full Moon from one month to the next. So sometimes, even if otherwise the conditions are fulfilled for an eclipse, the Moon might a bit too far from Earth to cover the whole Sun, we then have an annular eclipse.
These days, the apparent size of the Moon from here is approximately the same as the apparent size of the Sun. However, the Moon's orbit is slowly becoming larger (a few cm per year) because of gravitational interactions with ocean and land tides. At the same time, the Sun is slowly becoming larger, as part of its natural stellar evolution. So, in about 600 million years from now, the Moon will appear too small to cover the Sun, and only annular eclipses will be seen (if there is still life on the planet, the Sun’s expansion will certainly affect climate!).
Q2: How to view a solar eclipse safely?
Professor Gigault: One should never ever stare directly at the Sun, and especially during an eclipse. Although on a normal clear day, looking at the Sun will usually trigger pupil constriction, squinting, crying and other protection mechanisms, doing the same during an eclipse can be especially dangerous because the relative darkness may not trigger those protection mechanisms, and permanent damage to vision can result. Remember that the Sun's luminosity does not change. Other than that, it is perfectly safe to be outside, as long as one does not look at the Sun—which can be very tempting unfortunately. Use official eclipse glasses or other official solar filters! An arc-welding mask works fine too. Do not use homemade filters, which can allow too much light to enter the eye. Projecting the light coming out of a telescope or binoculars onto a piece of white paper, and only looking at the paper, is also safe.
Apart from the novelty, and perhaps old superstitions, eclipses have little effect, if at all, on life. During the last partial eclipse, the sky was cloudy and if nobody told you, you would not have guessed anything special was happening.
Q3: Are there any impacts on the structure and dynamics of Earth's upper atmosphere?
Professor Gigault: Basically none. Remember, the shadow of the Moon is much smaller than the Earth, and the shadow sweeps across the land during the event. If you are not near the path of totality, there won't be much effect.
Q4: Can an eclipse cause mood swings or anxiety?
Professor Gigault: There is no scientific evidence linking eclipses to mood swings or anxiety. Any perceived effects are likely due to superstitions or individual beliefs rather than direct physical impacts.
“One should never ever stare directly at the Sun, and especially during an eclipse”
Christian Gigault
— Assistant Professor in the Department of Physics at the Faculty of Science
Q5: Can an eclipse impact weather or cause earthquakes?
Professor Gigault:Eclipses do not have measurable effects on weather patterns or seismic activity. The shadow cast by the Moon is too small and brief to significantly influence these natural phenomena.
Q6: How does an eclipse affect solar energy production?
Professor Gigault:Eclipses do not have a significant impact on solar energy production. The temporary reduction in sunlight during an eclipse is too short-lived to affect overall energy generation from solar panels.
Q7: Will we then be able to witness a total eclipse in Ottawa?
Professor Gigault: For the April 8 eclipse, the city of Ottawa is to the North of the path of totality, and we will observe a partial eclipse where the Moon will cover only about 96% of the Sun. Residents of Prescott and Brockville, however, will be much luckier!
Members of the media may directly contact:
Christian Gigault (English & French)
Assistant Professor, Department of Physics, Faculty of Science