Have you ever wondered how far can you see to the horizon from an elevated position ? Using simple trigonometry the distance to the horizon along the Earth's surface can be easily determined. Two cases are considered: (i) light travels in a straight line and (ii) light travels along a curved path as a result of atmospheric refraction. In both cases it will be assumed that the Earth is a sphere resulting in a circular cross section when examining the problem in two dimensions.

- Read more about Distance to the horizon
- Log in to post comments

**core**files. This document describes the update procedure for a minor revision update, e.g. from Drupal 7.10 to 7.12. Prerequisites for this procedure include: (i) a familiarity with the command line, (ii) ssh connectivity to the target drupal website and (iii) the availability of existing backups of the website (including the drupal database)

## Directory structure

- Read more about Updating Drupal
- Log in to post comments

$\pi$ is a mathematical constant defined as the ratio of the circumference of a circle to its diameter. There are many other definitions including the ratio of the area of a circle to the square of its radius. It is a constant that also appears in many formulae used in mathematics, physics and engineering.

- Read more about Calculating $\pi$
- Log in to post comments

The linux shell command line interface is a powerful tool for performing system administration tasks. In comparison a graphical user interface (GUI) is easier to use but has limitations: (i) confined to perform specific tasks, (ii) required to navigate through menus and (iii) not easily configurable to perform batch jobs.

Some of the advantages in using the command line interface are:

- Read more about Linux shell commands
- Log in to post comments