Tuesday, March 6, 2012

Asteroids Missing Earth: What Means “Close Call”?

Every now and then you read about asteroids passing Earth in a certain distance but nobody gives you a feeling of how close such an encounter is. Allow me to fill in this gap.

Say an asteroid passes in a distance x from Earth, the radius of which we will call r. We now can ask how likely it is that an object that hits a disk of radius r+x also hits a disk of radius r provided that it any point on the larger disk is hit with equal likelihood.

The likelihood then is p = A(r)/A(r+x) where A is the area of a disk of the given radius, In other words p = πr²/π(r+x)² = 1/(1+x/r)². If we now define ξ=x/r (which is the distance in units of Earth's radius we get a quite simple formula: p = 1/(1+ξ)².

Using ξ is advantageous as it is a value you actually find in tables. Let’s try a couple of values; LD means Lunar distance and is the distance in terms of the average distance between Earth and Moon:

Distance inξp in %
1.65614636619.77100 0.098
0.49684190985.93 30 0.104
0.16561 63661.98 10 0.826
0.04968 19098.59  3 6.250
0.01656  6366.20  125.000
0.00497  1909.86  0.359.172
0.00166   636.62  0.182.645
0.00050   190.99  0.0394.260
0.00017    63.66  0.0198.030

Please note that the closer an encounter is the less meaningless this rough estimate becomes as the asteroid by no means randomly hits the disk of radius r+x but follows a clearly determined path.

Sunday, March 4, 2012

Termtter, a terminal-based Twitter client

Termtter is a terminal-based Twitter client written in Ruby that can be installed as a Ruby gem. In the easiest case you simply type in
gem install termtter
and you are done with installing the program, otherwise see How to Install.

Once termtter has been installed you can simply  run it provided that you do not need to use a proxy; in that case see Configuration. However, like any other Twitter application, termtter needs to be authorised in order to function properly.

Therefore, at the initial run, termtter will provide you with an authorisation URL.

First launch of termtter

Once you visit this URL, you will be asked whether you want to authorise termtter to use your Twitter account.

Visiting authorization URL

If you choose to authorise the application (i.e. termtter) you will provided with a PIN.

Obtaining PIN

After having obtained the PIN you need to enter it in termtter. Copy and paste will not work because the PIN is shown as an image.

Entering PIN

Now that termtter has been authorised you can use it at your liking.

Termtter at work

Michael Geist at INTA Workshop

If you want a brief explanation what is wrong with ACTA this video is an absolute must.

The full text of the report can be found at http://www.michaelgeist.ca/content/view/6350/125/

Friday, March 2, 2012

Easily Brighten Underexposed Areas of a Photo

In Overlay an Inverted Layer Onto a Photo to Brighten Underexposed Areas, PetaPixel shows how to do precisely that. I applied the method to a quite arbitrary underexposed photo and this is what I got:

Original image

Lit up using overlay method

Lit up, white balance applied

White balance only

A nice method indeed and it should work with any image processing program that's worth being used – in the article it's Photoshop while I have been using the Gimp.