Mother of a Prom

interrupting the planetary overview.

lot's of solar activity on mother's day

here's a close up with the bright disk blocked out to emphasize the faint prominence:

still working on full disk versions

Mars

will skip earth and the moon for now
and move on to the 4th planet from the sun
Mars aka the red planet

mars is a small planet, about half the size of the earth
with mass equivalent to mercury

Mars is the only planet who's surface detail can be seen from the earth
(detail seen on other planets is related to clouds)

The red-orange appearance of the Martian surface is caused by iron oxide (basically rust) in the soil
as well as a reddening effect due to dust in the atmosphere.
many areas have blue tinted rocks altering the surface color.

the squiggly line upper right of center is a giant dust storm on the surface.
the white dot upper left is a melting polar cap
made of carbon dioxide and some water ice.

the polar caps change with the martian season
and can be followed in the telescope when mars is in view:

the orbit of mars is relatively close to the earth's
as a result detail in mars is only visible through telescopes
as the earth approaches mars in it's orbit
this occurs every 20 months (approximately)
and lasts for 4 to 6 weeks, with the best viewing for only 2 weeks
so folks get excited when this occurs
the next will be in april 2014 :(

this of course is the time when mars goes into retrograde motion
as the earth passes mars
(which we all learned about in earth science and promptly forgot)
http://en.wikipedia.org/wiki/Mars#Astronomy_on_Mars

more stuff

mars has two moons
Phobos and Deimos
Phobos is in a decaying orbit, slowly falling to the surface
which brings up an interesting tangent

classic example of the Roche limit:
as Phobos descends to the surface of mars, the gravitational force acting on it will increase.
gravitational strength varies with distance.
so at some point during the descent the gravitational pull on the near side of the moon will by *much* greater than the pull on the far side.
stronger than the force holding the moon together.
the net result is that the moon will break apart, potentially leaving a ring on the way down.
this point is known as the Roche limit

an extreme example of this occurs near black holes where matter is torn apart in strings pointing towards the black hole
a process known as spaghettification
which is fun to say
https://en.wikipedia.org/wiki/Spaghettification

lastly, the sci-fi book red mars

http://www.amazon.com/Red-Mars-Trilogy-Stanley-Robinson/dp/0553560735
considered "hard" sci-fi
gives what seems like a very real depiction of how mars could be colonized
has a feel similar to 50's sci fi accurately predicting space flight and moon walks
with lots of detail on martian planetology, whether, etc
warning:
very dark book, heavy on planetology, weak on biology

whw

Venus

Venus, about the same size as earth

the second planet from the sun

rocky, but covered with white clouds
which make it one the brightest planets
appearing brighter than any star

like mercury, it's close to the sun
and never strays far from it
it can only be seen in the evening just after sunset
or in the morning before sunrise
but get's much higher in the sky than mercury
as a result it's know as the dawn star
and the dusk star
depending on where it is in it's orbit
some have suggested that it took the ancients quite some time
to figure out that the dawn and dusk star were the same thing

gallileo was the first to view venus through a telescope
and note it has phases like the moon (see below)
the phases convinced him that the sun was the center of the solar system
not the earth
which was correct
but got him in trouble with the church

the cloud layer on venus
is rich in carbon dioxide causing a greenhouse effect
making venus the hottest planet in the solar system
far hotter than mercury although further away from the sun

the similarity in size and carbon dioxide content between earth and venus
lead many to conclude that earth will eventually become like venus
with no water due to the run away greenhouse effect

here are a few images at the "half moon" phase
viewers looking through a telescope for the first time
mistake it for the moon

and here's a shot of venus as it crosses in front of the sun

Mercury

continuing with the planet tour

mercury
closest planet to the sun
fastest in orbit circling the sun in 88 days
named after the fleet footed messenger god mercury
small, rocky, hot, no atmosphere
surface covered with craters
even though extremely hot, some craters near the poles cast shadows creating areas never touched by sunlight.  there appears to be water--ice in these areas

since it's so close to the sun it can only be seen just before sunrise or just after sunset
as a reddish dot near the horizon seen through turbulent atmosphere:

it has phases like the moon
a bit of imagination suggests a dark shadow upper left similar to a gibbous moon

on rare occasions mercury can pass directly in front of the sun, leaving a dark spot where the sun's rays are blocked:

note the sun spot lower left is much bigger than the planet mercury


whw