Wonders of the Sky

Eclipses

Types of Eclipses

• Solar: Eclipses of the Sun– Partial– Total– Annular

• Lunar: Eclipses of the Moon– Partial– Total

Solar Eclipses

• Eclipses of the Sun• Alignment: Sun, Moon, Earth (new moon)• The moon’s shadow covers part of the earth’s

surface• Last for just a few minutes, total phase often 3-7

minutes• Types:

– Partial– Total– Annular

Eclipse Geometry

Eclipse Map

• Solar eclipses are only visible in specific areas of earth

• Total Eclipse: Visible in “Path of Totality”

• Partial Eclipses: Visible in red bands

• On average, any location will receive a total eclipse every 400 years

• [Animation]

Moon’s Shadow from Mir, 1999

Photosphere

• Photosphere: The sun’s visible “surface”

• A layer of heated gas• Sunspots are

sometimes visible on the photosphere

• [current sun]

SF Partial Eclipse

Partial Eclipse Phases

Eclipse Shadows

Above: View of eclipse through a telescope, note the corresponding shadows (right)

June 1994 Eclipse

Bailey’s Beads

• Bailey’s Beads resemble a string of pearls briefly visible along the edge of the eclipsed sun

• Represent sunlight shining through valleys on the edge of the moon’s disk

• Single bright “bead”, diamond ring effect

Diamond Ring EffectLast remaining bit of sun’s visible surface before totality

Totality

• At totality, the sun is entirely covered by the moon’s disk

• The corona, the sun’s outer atmosphere, becomes visible as a pearly crown

• The sky becomes dark during totality, bright stars and planets are visible

Totality, Awesome

Chromosphere

• The sun’s visible disk is the photosphere

• Photosphere visible through thick clouds or a filtered telescope

• Chromosphere is red atmospheric layer on the sun just above the chromosphere

• Chromosphere is only visible briefly during total eclipses of the sun or through expensive solar filters

Chromosphere and Prominences•Prominences represent large segments of the chromosphere that can become detached from the sun

•Most prominences are larger than the earth

Chromosphere & Inner Corona

Dark Noon

• Totality Sky– Bright stars and

planets visible– Horizon glows sunset

colors, “360-Degree sunset”

– Venus, left of eclipsed sun

360-Degree “Sunset”

An all-sky image during totality

Note, “sunset” colors surround entire horizon

Eclipse Montage

• Note partial phases before and after totality (center)

• Sun imaged with solar filter, unfiltered at totality

Shadow Bands

• Shimmery affect on ground noticed right before start of totality

• Resembles flickering bands of light

• Best seen on white surface (sheet)

• Most likely due to bright, point like light source (diamond ring) distorted by atmospheric air flow

Shadow bands, 1870 Italy

Shadow Band Animation

Shadow Band Still Image

Eclipse Safety

• Caution:– Partial solar eclipses

are not safe to observe with unaided eye

– Total phase of a solar eclipse can be directly observed

– Safe Sunwatching– Note: Eclipses of the

moon are always safe to observe

• Methods:– Eclipse glasses– Filtered telescopes– Projection

Safe-totality

NOT safe- partial

eclipses

Eclipse Glasses

• Made from reflective mylar, designed especially for viewing the sun

• Don’t use sunglasses, smoked glass, film negatives, etc. Not safe!

Solar Projection

• Use a telescope to project the sun’s image onto a flat sheet

• Don’t look into the eyepiece!

Again, Jones’s sneaky colleagues aimed the telescope at the sun…

Pinhole Projection

Eclipse Videos

• Total Solar Eclipse - Egypt 2006

• Totality Highlights: Total Solar Eclipse 2008: Live from China

• Perfect Eclipse – Mexico, 1991

Annular Eclipse

• “Ring Eclipse”• Occurs when moon near

apogee, smallest apparent disk

• Moon’s disk not large enough to cover the sun completely

• Unlike true total eclipses, not safe to observe without protection

Eclipse ‘94

Annular Geometry

Lunar Eclipses

• Eclipses of the moon• Alignment: Sun, Earth, Moon (full moon)• The earth’s shadow covers part or all of the

moon’s surface• About 4 hours for complete eclipse, totality can

last for nearly an hour• Unlike solar eclipses, entire night side of earth

can witness• Types:

– Total– Partial

Lunar Eclipse

Total Lunar Eclipses

• When eclipsed, the moon usually appears red

• The earth’s shadow has some light directed into it by the edge of earth’s atmosphere

• Similar to red sunset colors

• Video

Lunar Eclipse Partial Stages

Eclipse ’04 Diagram• Earth’s shadow

has two zones, umbra and penumbra

• Moon passed through dark center of earth’s shadow (umbra) during totality

• Partial eclipses when moon partly immersed in umbra

Eclipse ’04: Red Moon

Earth’s Shadow

Lunar Eclipses

• Total: Moon passes completely into the earth’s inner shadow (umbra)

• Partial: Moon passes partly into the umbra

• Penumbral: Moon passes only into the earth’s outer shadow (penumbra)

Partial Eclipses: Impossible Lunar “Phases”

• The moon’s regular phases never appear like this and the following photos

Partial Lunar Eclipse

Penumbral Eclipses

• Not as dramatic, more difficult to see effect

• Penumbra resembles a slightly darker shading on one half of the moon

• Again, moon passes only through earth’s outer shadow, not the darker umbra in center

Total Lunar Eclipse Dark Sky

• During a total eclipse of the moon, a bright, full moon-lit sky becomes much darker during totality

• Dimmer stars appear, even the Milky Way and dim celestial objects can be seen

Full Moon Night

Next Eclipses• Solar

– America, 2017

• Lunar– Dec, 2010