Phenomena to watch out for during a total solar eclipse

During a solar eclipse, and especially as we approach totality, curious phenomena follow one another and overlap in rapid succession around us. To make the most of this event where everything seems to be rushing, you need to be adequately prepared. Here is a list of phenomena to watch out for during a total solar eclipse, many of which can also be observed during a partial eclipse.

(Time indications are approximate)

During partial phases (up to T – 5 minutes = 5 minutes before the start of totality)

• Observe the changing shape of the Sun as the Moon moves in front of it — SAFE EYE PROTECTION (“ECLIPES GLASSES”) MANDATORY TO DO THIS WITH THE NAKED EYE
• Observe the projection of the solar crescent through pinholes (natural or not)
• Ambient temperature (air) drops or reaches a plateau (keep thermometer in shade)
• What happens to the wind?
• Convective clouds dissipate
  • Convective clouds (fed by the warming of the ground by the Sun) will tend to dissipate as the solar heating decreases and the temperature drops
  • Unfortunately, does not work on all clouds...
  • Most effective on land, but little effect on the ocean

Approaching totality (from T – 20 minutes)

• Drop in brightness becomes noticeable (T – 15-20 minutes)
  • Visible fraction of the Sun’s photosphere decreases as the Moon hides it
  • Gradual decrease in ambient light
  • But the human eye adapts to changes in ambient light, especially when gradual
  • At T – 15-20 minutes, still sunlight + shadows, but dimming becomes noticeable
• Strange lighting
  • Takes on a strange hue
• Bright planets become visible (Venus, Jupiter)
  • Prepare in advance to know which bright planets and stars will be visible during totality, and in what position with respect to the eclipsed Sun
  • Use planetarium software (e.g. Stellarium.org or Stellarium-web.org, both free)
  • Venus visible very early-on (already visible to the naked eye in full daylight under good conditions, even outside of eclipse)
  • Depends on atmospheric transparency, but dimming in brightness helps to decrease the brightness of the sky and allows planets to punch through
• Strange shadows
  • Shadows getting sharper in one direction but still fuzzy in the perpendicular direction (Sun takes the form of a slit, becoming narrower and narrower as the Moon covers it)
• Notice the behaviour of animals and plants
  • Birds (easier to observe) get ready for the night
  • Flowers close (in season...)
• Look for the umbral shadow approaching from upstream of the path of totality (T – 3 minutes)
  • Locate the precise direction on maps (southwest on Apr 8, 2024, in Southern Quebec)
  • Arrives at +/– 4300 km/h!! (~1200 m/s) (on Apr 8, 2024, in Southern Quebec)
  • Darkening of the atmosphere above places a few tens of km away, already in totality
  • Noticeable on distant clouds
• Look for “shadow bands” (T – 30-90 seconds)
  • Manifestation of atmospheric turbulence
  • Same cause as the twinkling of stars, but for a long, narrow, and very bright source of light
  • Faint "waves" of light a few tens of cm apart, parallel to the thin sliver of the Sun
  • Analogy: luminous patterns at the bottom of a swimming pool in the Sun, but much fainter
  • Best seen on surfaces that are pale and as uniform as possible
  • White sheet, light-coloured auto body, uniform ground or walls

On the brink of totality, events unfold faster and faster... (from T – 1 minute)

• The inner corona!
  • A furtive glance, without filter, allows us to catch a glimpse of the brightest part of the solar corona surrounding the black disk of the Moon
• "Baily's beads" at 2^nd contact!
  • The last visible sliver of the solar photosphere begins to break up in smaller sections due to the mountains and valleys that poke along the lunar limb
  • Baily’s beads transform and disappear in just a few seconds!
• "Diamond ring" at 2^nd contact!
  • Brilliant glow of last Baily's bead, complements the fainter luminous ring of the inner corona

During totality — REMOVE ECLIPSE GLASSES

• Who turned off the lights??
  • As the photosphere disappears completely (2^nd contact and the beginning of totality) what remains of ambient daylight drops rapidly
  • It's a strange night in the middle of the day
  • Choose a site without automatic lighting!!!
• The pinkish chromosphere and prominences!
  • Thin lower layer of the solar atmosphere, just above the dazzling photosphere
  • Visible only for a few seconds after the 2nd contact
  • Visibility depends on the relative size of the Moon to the Sun
  • Hydrogen-alpha emission
  • Bright pink colour, almost neon, that the photos fail to adequately represent
  • Prominences rise from the chromosphere and are visible longer
• The middle and outer corona!
  • The Sun's outer atmosphere extends several solar radii to the naked eye
  • "Pirate patch" trick: protect one eye from light in the hours leading up to the eclipse, and uncover it during totality to better see the fainter parts of the solar corona
  • Examine structure, shape and details with binoculars
  • Pearl white, with streamers and volutes
  • Shaped by the complex lines of force of the solar magnetic field
  • General shape depends on the period in the solar activity cycle: Streamers extend mostly east and west near the Sun’s equator during periods of low solar activity but emerge all the way around the Sun during periods of high activity
• Bright stars and planets!
  • The actual degree of darkness depends on the size of the shadow and where you are located
  • Bright planets become clearly visible, if high enough in the sky
  • The same goes for the brightest stars (mag. < +1.5)
  • Use our finding chart
• The colours of twilight on 360 degrees!
  • 360-degree "sunset": daylight that arrives from regions outside the shadow
  • Fully immersive show

After totality, everything repeats itself in reverse order

• Chromosphere emerges a few seconds before the 3^rd contact (possibly preceded by prominences)
• Diamond ring + Baily's beads at 3^rd contact!  PUT THE ECLIPSE GLASSES BACK ON
• Daylight returns surprisingly quickly, almost abruptly
• Watch for shadow bands
• The umbral shadow moves away downstream along the path of totality (towards the east)
• What do animals do? Plants?
• How much longer can you see the planets?
• Partial phases take place in reverse