Monday, July 22, 2013

Crab Nebula Expansion

Here are 4 images over 6 years showing the expansion of the crab nebula, a supernova remnant. 


Extrapolating the expansion back to time 0 gets close to the observed 1054 AD supernova.  Note the bluish pulsar wind lower left, seems to be moving faster than the red filaments

Saturday, July 6, 2013

4th of july supernova revisited-crab pulsar wind

On July 4th 1054 AD, astrologers observed a bright blue square in the sky near the sun at dawn. it was visible during the day for 3 weeks and at night for 2 years. 700 years later, the Crab Nebula became the first object in Charles Messier's famous catalog:
 What makes the crab nebula glow? The bluer of the two central stars is a dense neutron star,
the remnant of the original star that went supernova on the 4th, spinning at 30 revolutions per second. A strong magnetic field associated with the spinning star accelerates electrons in the surrounding space to relativistic speeds. Collisions between the electrons and surrounding matter give off very high energy photons. Rather than the central star, it is the photons from these collisions (EDIT: my physics buddies have informed me that it is the acceleration itself that causes the high energy photon emissions, no collisions needed)  that cause the gas in the surrounding filaments to glow like fluorescent lights.  
pulsar wind:
enamored with the concept of the pulsar wind, i attempted to capture it with a filter which blocks the emission line signal, giving only the broad band pulsar wind. a quick look at the crab nebula spectrum shows a wide region devoid of emission lines



after making a few calls, trying to get a nice wide filter in this region, i found a custom filter would cost more than my camera. so i went with a narrow filter in the region that was available in order to capture this broad band signal. i had hoped to capture some motion with the filter, but the broad band emissions were so weak with the narrow filter, that i was unable to get enough detail on any given night (or two) to convincingly demonstrate motion.

in any event, the combined stack gives a nice view of the pulsar wind without the pesky emission lines obscuring the view. i find the blink fascinating, tracing the swirls, wisps and arcs of broad band emission, and then following them into the combined image.

here's my 2011 crab nebula animation showing some motion in the broad band.

happy 4th

-bill w

Thursday, June 20, 2013

sun and moon for summer solstice

 this is the year of the solar maximum--maximum sunspot activity in the 11 year solar cycle.
10 pm pacific today 6/20/13 is the summer solstice.
what better time for solar images?


here are two images of the sun taken at about the same time with different filters. 

first up, the sun in "white light", using a filter that blocks out 99.999% of the sun's light
you can see a few dark sun spots (which are still blindingly bright without filters), a slightly granular appearance, and a few lighter areas.  this is the photosphere which is basically the surface of the sun.

the second image is the sun imaged with a hydrogen alpha filter that allows all of the sun's light at a specific frequency, which corresponds to absorption and emission of light due to hydrogen.  this shows the chromosphere, a thin layer above the photosphere dominated by hydrogen emissions.  it usually can't be seen as it is overwhelmed by bright emissions from the photosphere.  the hydrogen alpha filter allows us to see the chromosphere's wavy filaments and prominences.
you can still see hints of sunspots, but there's much more going on. 





next i colorized the image and then lightened it dramatically to show the faint prominences (things shooting off the disk around the rim).  since this overwhelmed the central detail, the original darker image was superimposed to maintain some of the surface detail.  bear in mind the prominences seen at the edge are much more faint than the central detail.  the dark line upper right across the face is called a filament.  it's basically the same phenomenon as a prominence, but coming off the surface towards the viewer rather than occurring at the edge. 





last up is the full moon, which happens to be the same size as the sun, which is convenient for things like eclipses
and finding something to do with your solar rig at night. 
this was taken with the same scope and camera as the first image, leaving off the filter. 
why do astrophotographers rarely image the full moon? 
the sunlight is shining straight down on the face which washes out the detail of landscape. 

the sharp eyed viewer will note better contrast at the extreme bottom portion of the image
where a few shadows are cast enhancing detail in this moon that was 6 hours away from full. 




have a good summer

whw

Monday, May 20, 2013

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

Tuesday, May 14, 2013

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

Wednesday, May 8, 2013

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 planet
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

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

Tuesday, May 7, 2013

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 mercurysmall, 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