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Where did the solar system
come from?
Also:
Sun – Moon -Eclipses
Astr 221
2015
NW Chs. 8&9
Evidence from Other Gas
Clouds
• We can see
stars forming in
other
interstellar gas
clouds, lending
support to the
nebular theory.
Was our solar system destined to
be?
•
•
Formation of
planets in the
solar nebula
seems inevitable.
But details of
individual planets
could have been
different.
Earth
Earth and Moon with
sizes shown to scale
• An oasis of life
• The only surface liquid water in the solar system
• A surprisingly large moon
Giant Impact
First Quarter
Second Quarter
Formation of Lunar Maria
Early surface Large impact
is covered
crater
with craters. weakens
crust.
Heat buildup allows
lava to well
up to surface.
Cooled lava is
smoother and
darker than
surroundings.
Radius:
6.9  108 m
(109 times Earth)
Mass:
2  1030 kg
(300,000 Earths)
Luminosity:
3.8  1026 watts
Gravitational
equilibrium:
Energy supplied
by fusion
maintains the
pressure that
balances the
inward crush of
gravity.
What is the Sun’s structure?
Insert TCP 6e Figure 14.3
The proton–proton chain is how hydrogen fuses into helium in Sun.
Sunspots
Are cooler
than other
parts of the
Sun’s
surface
(4000 K)
Are regions
with strong
magnetic
fields
Loops of bright gas often connect sunspot pairs.
Insert TCP 6e Figure 14.21a unannotated
The number of sunspots rises and falls in an 11-year cycle.
Insert TCP 6e Figure 14.21b unannotated
The sunspot cycle has something to do with winding and twisting of
the Sun’s magnetic field.
Magnetic activity
also causes solar
prominences that
erupt high above
the Sun’s surface.
Charged particles streaming from the Sun can disrupt electrical power
grids and can disable communications satellites.
Aurora
Borealis
What causes eclipses?
• The Earth and Moon cast shadows.
• When either passes through the other’s
shadow, we have an eclipse.
Lunar Eclipse
When can eclipses
occur?
• Lunar eclipses
can occur only
at full moon.
• Lunar eclipses
can be
penumbral,
partial, or total.
Solar Eclipse
When can eclipses
occur?
• Solar eclipses can occur only at new moon.
• Solar eclipses can be partial, total, or annular.
Why don’t we have an eclipse at every new and full moon?
– The Moon’s orbit is tilted 5° to ecliptic plane.
– So we have about two eclipse seasons each year, with a lunar
eclipse at new moon and solar eclipse at full moon.
Summary: Two conditions must be
met to have an eclipse:
1.
It must be full moon (for a lunar eclipse) or new moon (for a solar
eclipse).
AND
2. The Moon must be at or near one of the two points in its orbit where it
crosses the ecliptic plane (its nodes).
Predicting Eclipses
• Eclipses recur with the 18-year, 11 1/3-day
saros cycle, but type (e.g., partial, total) and
location may vary.