Wonders of the Sky

Wonders of theDarkening Sky

(The Twilight Period)

Twilight

• The period of darkening sky is also termed twilight

• Twilight is an effect created by the atmosphere

• If we had no atmosphere, the sky would be instantly black at sunset

Earthshine

http://www.spaceweather.com/swpod2006/03jan06/laveder.jpg

Crescent Moon, Earthshine“Old moon in the new moon’s arms”

Earthshine Explanation

• Earthshine: When the dark surface of the moon glows faintly from light reflected from earth

• Earthshine resembles a faint full moon held by the thin crescent moon

• “Old moon in the new moon’s arms”

At C, an observer would see light from the sun, reflected by the

earth, and then reflected back by the moon!

Ultimate Earthshine

March 2006 Total Eclipse

Young, Old Moons

• The thin crescent moon, just after new moon, is often known as a young moon

• A morning crescent, just before new moon, is an old moon

• Young moons-early evening; OId moons, early morning

• Young moons are easiest to seen in the spring

Young Moon, Old Moon

Young crescent moon in evening sky

Old crescent moon in morning sky

Dickens: Barnaby Rudge, 1841

• “It was a fine dry night, and the light of a young moon, which was then just rising, shed around that peace and tranquillity which gives to evening time its most delicious charm.”

• Barnaby Rudge, published 1841

Young Moon & Pleiades

Inferior Planets

• Mercury & Venus• Inferior planets: Between earth and sun• Visible:

– After sunset, or before sunrise– Twilight and early evening only, or twilight and late

morning

• Mercury is visible for about two weeks at a time, Venus is visible for about 9 months at a time

• An appearance of Mercury or Venus is termed an apparition

Where’s Mercury?

http://www.spaceweather.com/swpod2006/25feb06/vsoske.jpg

Moon and Venus

Moon and Venus Conjunction

Venus Corona

Venus is so bright, it can form a corona similar to the moon

and sun

June 1991 Conjunction of Mars, Venus, and Jupiter

http://www.stargazing.net/drsmith/vmj91a.jpg

Planets can often be seen to form groups or conjunctions

April 23, 1998: Moon, Venus, Jupiter

•Venus & Jupiter often appear close together creating impressive conjunctions

Conjunction of Naked-Eye Planets

Venus, not “UFO”

• The planet Venus resembles a very bright star when seen in the evening sky

• Venus has often been reported as a “UFO” (President Jimmy Carter in 1969)

Venus over San Francisco

Satellites: “Moving Stars”

• Since the 1957 launch of Sputnik, the sky is full of satellites

• Satellites resemble moving stars

• Most seen up to 90 minutes before or after sunset

http://satobs.org/image/trail.jpg

Satellite Visibility

A: Daylight, satellite not visible

B: Twilight, satellite visible

C: Night, satellite within earth’s shadow and not visible

Satellite Tracking

This view of the International Space Station was taken through a telescope equipped with a tracking computer

http://www.heavenscape.com/iss.gif

Noctilucent Clouds

• Noctilucent clouds are clouds that remain visible in a dark sky, resemble silvery cirrus clouds

• They are the highest visible clouds in the atmosphere, located above the stratosphere

• Noctilucent means “night glowing”• Only visible from high latitudes (45-60° north)

around the summer solstice (June 21)• Animation: http://svs.gsfc.nasa.gov/goto?10002

Noctilucent Clouds

http://antwrp.gsfc.nasa.gov/apod/image/0306/noctilucent_pp_big.gif

NLCs

NLCs in London

London, June 23, 1996

NLCs from ISS