Transcript evening star

VENUS
VENUS
Venus, the jewel of the sky, was once know by
ancient astronomers as the morning star and evening
star. Early astronomers once thought Venus to be
two separate bodies. Venus, which is named after the
Roman goddess of love and beauty, is veiled by thick
swirling cloud cover.
Astronomers
refer to Venus as
Earth's sister
planet. Both are
similar in size,
mass, density and
volume.
Both formed about the same time
and condensed out of the same
nebula
Venus is very different from the Earth. It has no oceans and is
surrounded by a heavy atmosphere composed mainly of carbon
dioxide with virtually no water vapor. Its clouds are composed of
sulfuric acid droplets. At the surface, the atmospheric pressure is
92 times that of the Earth's at sea-level.
Venus is scorched with a surface temperature of about 482° C
(900° F). This high temperature is primarily due to a runaway
greenhouse effect caused by the heavy atmosphere of carbon
dioxide. Sunlight passes through the atmosphere to heat the
surface of the planet. Heat is radiated out, but is trapped by
the dense atmosphere and not allowed to escape into space
A Venusian day is 243 Earth days and is longer than its year of 225
days. Oddly, Venus rotates from east to west. To an observer on
Venus, the Sun would rise in the west and set in the east.
Venus spins retrograde (opposite) relative to the earth's movement
Venus is never seen more than 47° from the Sun.
Given Earth’s rotation rate of 15° per hour, this
means that Venus is visible above the horizon for at
most three hours before the Sun rises or after it
sets.
On a moonless night away from city lights,
Venus casts a faint shadow. The planet’s
brightness stems from the fact that Venus is
highly reflective. Nearly 70 percent of the
sunlight reaching Venus is reflected back
into space
Venus’s maximum brightness, as seen from Earth,
actually occurs about 36 days before or after
closest approach to our planet. At that time,
Venus is about 39° from the Sun and 0.47 A.U.
from Earth, and we see it as a rather fat
crescent.
Until just recently, Venus' dense cloud cover has prevented
scientists from uncovering the geological nature of the
surface. Developments in radar telescopes and radar
imaging systems orbiting the planet have made it possible to
see through the cloud deck to the surface below. Four of
the most successful missions in revealing the Venusian
surface are NASA's Pioneer Venus mission (1978), the
Soviet Union's Venera 15 and 16 missions (1983-1984), and
NASA's Magellan radar mapping mission (1990-1994). As
these spacecraft began mapping the planet a new picture of
Venus emerged.
Venus' surface is relatively young geologically speaking
The Venusian topography consists of vast
plains covered by lava flows and mountain or
highland regions deformed by geological
activity. Maxwell Montes in Ishtar Terra is
the highest peak on Venus.
Sif Mons Venus
Venus has more volcanoes than any other planet in the solar system
Volcanoes and volcanic features are numerous. At least 85% of
the Venusian surface is covered with volcanic rock. Hugh lava
flows, extending for hundreds of kilometers, have flooded the
lowlands creating vast plains. More than 100,000 small shield
volcanoes dot the surface along with hundreds of large
volcanos. Flows from volcanos have produced long sinuous
channels extending for hundreds of kilometers, with one
extending nearly 7,000 kilometers (4,300 miles).
Over 1600 major
volcanoes or
volcanic features
are known to
exist
the total number may be
over 100,000 or even over
1,000,000
Large Shield Volcanoes
Venus has over 150 large shield volcanoes
One of the highest mountains on
Venus is Maats Mons which
reaches to 8 km (5 miles) above
the mean venusian elevation:
This rendition of Sif Mons,
about 2 km (1.2 miles) high and
covering an area of nearly 300
km (200 miles) in diameter,
Sif and Gula Mons
Sif and Gula seem to be hotspot volcanoes like those in Hawaii
Sapas Mons
Sapas is 1.5 km high and is about 120 km across
Unlike many large shields on
Venus, Sapas does not lie on
a major rift structure
Radar is brightest over rough, blocky
surfaces; thus, this range of color
suggests a change in volcanism over
time. Namely, the youngest lavas are
fairly bright, but the older lavas
seem to be much smoother, especially
in the band of dark lavas along the
lower right edge of the volcano
Ushas Mons
Ushas Mons lies in the southern
hemisphere on the northern part of
Dione Regio
It is surrounded by volcanic plains
with many small shields (especially in
the upper left and lower right). Also
note the clear north-south faults
running unde r the volcano. These
seem to have formed with the
volcano, and may contain volcanic
dikes
Ushas is over 500 km across,
and is about 2 km high
Theia Mons/Devana Chasma
Theia Mons is the largest volcano on Venus
It is over 4 km high, and its
lava flows cover an area more
than 800 km wide. It has an
oval central caldera roughly
75 km long and 50 km w ide.
The volcano also lies at the junction of 3 major rifts, one of which
is seen here running off the top of the image. This rift, Devana
Chasma, is over 200 km wide, but it narrows down to ~50 km as it
climbs
Venus is scarred by numerous impact craters distrubuted randomly over its
surface. Small craters less that 2 kilometers (1.2 miles) are almost non-existent
due to the heavy Venusian atmosphere. The exception occurs when large
meteorites shatter just before impact, creating crater clusters.
Danilova Crater
-26.4° Latitude, 337.2° Longitude; 49
kilometers (30 miles) diameter; central peak
crater
The first image shows the Venusian impact
crater Danilova as seen by the Magellan
spacecraft. The crater has a central peak, a
crater wall, a crater floor, an ejecta blanket, and
crater outflow deposits. The second image is a
geologic sketch map of the crater. (Copyright
Calvin J. Hamilton)
Mead Crater
Yablochkina Crater
Phases of Venus:
Are just like the phases of
the moon, but observed
differently