Telescope apertures to see all Messier objects

Galileans/Refractive: 142mm / 5.79" about 6 inches
Newtonians: 164mm / 6.46" about 7 inches (commercially 8 inches)
Maksutov/Catadioptrics: 174mm / 6.85" about 7 inches (commercially 8 inches)

Apparent magnitudes of stars are exponential. Each magnitude measures a light intensity 100^0.2 times less than the previous magnitude. The average human eye can perceive stars up to magnitude 6. Messier objects have a magnitude of up to 11.5. That means that a telescope must capture at least 100^1.1 = 158.5 the amount of light that human eyes capture. So, the relation between a telescope effective area and the human eye area must be about 158.5.

With perfectly efficient lenses, this implies that the minimum aperture for a telescope to help perceive all Messier objects would be (100^1.1)^0.5 = 12.6 times the aperture of the human eye. [ Because 158 = PI *R1^2/ (PI*R2^2) ]. If the average human eye diameter is 9.6mm (http://www.iovs.org/content/37/7/1396.full.pdf), then the minimum telescope aperture should be 121mm, or 4.76". However, telescopes lenses are not that efficient.

In fact, very good telescopes such as those produced by Meade or Celestron, have an efficiency of 85% in each lens.

Different types of telescopes have different numbers of transmissions (lenses/ or mirrors):

Galilean : 2 transmissions
Newtonian : 3 transmissions
Catadioptric: 4 transmissions

Newtonians and catadioptrics have obstructions of about 10%, so they have an additional factor of 90%.
So, the real efficiency of telescopes with transmissions with efficiencies of 0.85% is :

Galilean : 72%
Newtonian : 54%
Catadioptric: 48%

That is, a Galilean telescope effectively transmits 72% of the light that the primary lens concentrates.

The calculated apertures must take in account the efficiency and type of telescope.

[(158 / efficiency)^.5 * Reye = Rtelescope ]

So for the different types of telescopes, apertures are:

Galilean: 142mm / 5.79"
Newtonian: 164mm / 6.46"
Catadioptric: 174mm / 6.85"

That is, if they have very efficient lenses and obstructions of 10%.

Memory aid on redirecting ports

sysctl -w net.ipv4.ip_forward=1

iptables -t nat -A PREROUTING -d < DEST > -p tcp -m tcp --dport <original destport> -j DNAT --to-destination <new machine>:<new port>

iptables -t nat -A POSTROUTING -d <new machine> -p tcp -m tcp -j SNAT --to-source <this box ip>

iptables -A FORWARD -d <new machine> -j ACCEPT

Change the admin user password in drupal

UPDATE users SET pass = md5('The password!') where uid=1;

Enable pci parport in ubuntu 10.04

Applying (http://ubuntuforums.org/showthread.php?t=1233589) :

As root:

root$ lspci

02:00.0 Parallel controller: NetMos Technology PCI 9865 Multi-I/O Controller

root$ lspci -v

02:00.0 Parallel controller: NetMos Technology PCI 9865 Multi-I/O Controller (prog-if 03)
Subsystem: Device a000:2000
Flags: bus master, medium devsel, latency 32, IRQ 3
I/O ports at b010 [size=8] <<<<<<<<<<<<<<<<<<<<<<<< See here
I/O ports at b000 [size=8]
Memory at fe102000 (32-bit, non-prefetchable) [size=4K]
Memory at fe101000 (32-bit, non-prefetchable) [size=4K]
Capabilities:

root$ modprobe parport_pc io=0xb010
root$ ls /dev/parp*
/dev/parport0

Voilà

How to rename a vmware machine disk

After shutting down the machine and getting to the folder where the vmdk is located:

vmware-vmdiskmanager -n original_disk_name.vmdk destination_disk_name.vmdk

El reto del tiempo

Contemplando la vida se va y aquella que nace, veo como el tiempo avanza implacable poniéndonos el reto de no desaparecer en la historia. Solo nos queda la esperanza de estar a la altura de su desafío.

Debian utils for programming microchip microcontrollers

Utils:

apt-get install picasm picprog gputils gputils-doc gputils-common gpsim-dev gpsim\

Programmer:

http://www.jdm.homepage.dk/easypic.htm

For the picStartPlus:

apt-get install picp

Simulator:

apt-get install simulpic

C compiler and utils:

apt-get install sdcc sdcc-libraries sdcc-doc sdcc-ucsim