Wonders of the Sky

Light & Color Classic

• M. Minnaert’s classic Light and Color in the Outdoors work is a comprehensive discussion of atmospheric optical phenomena

• Inspiration for these lessons

http://www.amazon.com/Light-Color-Outdoors/dp/0387979352

Wonders of the Day Sky

Blue Sky

Blue Sky Factors

• Factors effecting how blue the sky is– Cleanliness of air, amount of dust or pollution– Observer’s altitude– Water vapor content of air (humidity)

• The bluest sky would be under dry, clean, unpolluted air on a high mountain

• The air is bluest at an angle of 90° (right angle) from the sun-termed polarization band

• The sky at night is also blue, revealed by photography

Blue Sky at Night

http://hiidenkontti.net/hpl/photos/misc/0101-a02.jpg

Night Moves

Grand Canyon in Moonlight

Van Gogh, The Starry Night, 1889

Rainbow and Antisolar Point

• Rainbows are visible in a band opposite the sun’s position (antisolar point)

• The sun must be at most 42° above the horizon for a rainbow to be visible

• Created by reflection of sunlight by water droplets

Rainbow Phenomena

http://www.hmi.de/bereiche/info/dualismus/images/Hawaii_Rainbow.jpg

Primary rainbow

Secondary rainbow

Alexander’s dark band

Note that the color order of

each rainbow is reversed, red faces

each other

Rainbows

Missouri Rainbow

http://www.missouriskies.org/rainbow/february_rainbow_2006.html

Supernumerary Bands

• Supernumerary arcs are purple and green bands on the inside of the primary rainbow

• These are colors beyond the regular ROYGBV colors

The arrow indicates supernumerary colors

Rare Moonbow

http://homepage3.nifty.com/justin/diary/img_diary/Moonbow.JPG

Moonbow and Dipper

Fogbow

http://www.jimcline.com/whales/fogbow001_std.jpg

End of the Rainbow?

Halos

• The most common halo is a ring of light 22° from the sun or moon, the 22° halo

• Sundogs, or parhelia, appear as bright spots near the 22° halo on either side of the sun

• Created by ice crystals high overhead Caution: Never look directly

at the sun!

22° Halo

Halo and Sundogs

http://www2.und.edu/our/photo/images/campusscenes/campusscenes1107789753_large.jpg

Sundogs are bright patches on either side of the halo

22° halo

http://www.spaceweather.com/swpod2006/10feb06/levesque1.jpg

Lunar Halo

http://www.spaceweather.com/swpod2006/11jan06/bush.jpg

Click

Lunar Halo Movie

Circumzenithal Arc

• The circumzenithal arc is a rainbow-like arc that partially circles the overhead point (zenith)

• Compared to the rainbow, the CA resembles a smile

Have a nice day!

Circumzenithal Arc

http://www.livingwilderness.com/patterns/czarc.jpg

Smile in the Sky

Parhelic Circle

• The parhelic circle is a horizontal arc passing through the sun and running parallel to the horizon around the sky

• This photo shows the entire sky in one view

Parhelic circle

Panorama

Parhelic circle

22-Degree Halo

Halo Phenomena

http://hyperphysics.phy-astr.gsu.edu/hbase/atmos/imgatm/halo.gif

Pillars

• A low sun often shows a pillar of light reflected from ice crystals—a sun pillar

• Pillars are also visible above streetlights

http://www.acme.com/jef/photos/04nov2003_sun_pillar/mvc-6382r.jpg

Streetlight Pillars

http://www.spaceweather.com/swpod2006/20feb06/Gavan1.jpg

Bremen Sun Pillar

• Katie Laudeman

• Winter, 2008

Coronas

• The corona is a small, circular glow that appears to surround the moon (right) or sun

• Can be white or colored rings

• Created by water droplets, ice crystals, or pollen grains

Pollen Corona

Iridescent Clouds

http://cimss.ssec.wisc.edu/wxwise/class/iredsnce.html

•The colors of iridescent clouds are similar to the corona

•Iridescence is often visible in clouds positioned near the sun

•Use sunglasses

Iridescent Cloud

http://cimss.ssec.wisc.edu/wxwise/class/iredsnce.html

Glory

• The glory is an effect similar to a corona

• The glory resembles colored rings that surround the point opposite of the sun (antisolar)

• Glories are best seen from aircraft flying over clouds

• The shadow of the plane can be surrounded by colored rings

• When a person’s shadow displays a glory, it is termed the spectre of the brocken

Look for a glory when flying

Glory on Cloudtops

http://www.eurastro.de/missions/anta03/GIS50A.JPG

Glory

Specter of the Brocken

http://www.walkingbritain.co.uk/gallery/visitors/images/p043.jpg

Heiligenschein

• A form of glory named the heiligenschein can be often seen as a glow of light around the shadow of an observer’s head

• The heiligenschein is visible in wet or dewy grass (and even on the moon!)

http://home.arcor.de/alexander.wuensche/media/astro/tau_opp/heiligenschein_2004apr21.jpg

Apollo 14 Heiligenschein

Bishop’s Ring

• The Bishop’s Ring is a rare corona that is visible after a large volcanic eruptions

• Volcanic gas and dust injected into the atmosphere creates the Bishop’s Ring

Bishop’s Ring following the Mt. Pinatubo eruption, 1992

Concentric Rings•Concentric rings are produced by wet or icy branches

•The rings can be viewed with a light source shining from behind (sun, streetlight) the branches

Dappled Light• Dappled light is visible

beneath trees• The tiny spaces between

leaves form pinhole cameras producing thousands of overlapping images of the sun’s disk upon the ground beneath the tree

Camera Halos

• Visible often in movies, camera halos are created by light scattered from the individual lenses inside a camera

• Decorative, but not natural

Daytime Sightings

• The moon is often visible during the day

• Most of the moon’s waxing phases (between new and full moon) can be seen in daylight

• Venus is visible during the day when it is positioned away from the sun

• Computerized telescopes can be used to find bright stars and planets during the day The First Quarter moon is

visible in daylight and rises around noon

Daytime Moon, Venus

http://www.labteq.net/darkfire_observatory/images/sso/slides/Daytime%20Moon%20and%20Venus.jpg

Venus lies below the moon in this image

Venus by Day, Telescope

http://hea-www.harvard.edu/hrc.ARCHIVE/2004/2004104.000000-2004104.240000/SpaceWeather/index.html

Late-Day Moon

The moon’s phase in this

image is waxing

gibbous

Contrails

• Contrails: Short for “condensation trails”

• An artificial cloud produced by aircraft exhaust

• Exhaust provides water vapor condensation nuclei for water droplet formation

• Useful for judging humidity

• Contrails are short-lived in dry air, long-lived in humid air

Jet & Crescent Moon

Contrail Clutter

•NASA satellite image, Oct 2004

Contrail Shadow

Odd Clouds: Mammatus

• Sagging, pouchlike structure

• Represents a cloud that formed in sinking air

Mammatus Clouds

Virga

• Virga represents a streaklike form of precipitation that evaporates before reaching the ground

Clouds Trailing Virga