Dictionary tag: U-V-W-X-Y-Z

Why the sky is sometimes red

If we understand why the sky is usually blue it’s easier to understand why it can be filled with reds and pinks at sunrise and sunset.

Let’s review why the sky is blue
  • In most weather conditions, the Sun and the area around it appear intensely white to an observer because vast numbers of photons of every wavelength make the journey from Sun to their eyes in an almost straight line.
  • The Sun, and the area around it, appears white because it contains a mixture of all wavelengths of light (white light).
  • In every other area of the sky, sunlight is striking billions of particles that make up the atmosphere and scattering in every possible direction.
  • If it were not for this scattering (deflection of light in all directions), the sky would be as black as night. In reality, an observer is bathed in light arriving from every direction and the sky, as a result, appears to be full of diffuse light.
  • Not all wavelengths of light behave in the same way when scattered by the small particles that make up the atmosphere.
  • Longer wavelengths of light (red, yellow, orange and green) are too big to be affected by tiny molecules of dust and water so scatter the least.
  • Shorter wavelengths (blue and violet) are just the right size and are affected by reflection, refraction and scattering as they strike successions of particles. It is these collisions that direct light in every possible direction including towards an observer.
  • Because human eyes are more sensitive to blue than violet, in most atmospheric conditions, and in the absence of the longer wavelengths, the sky appears blue.
  • A wide band of wavelengths corresponds with what we often describe as blue. As a result, the sky is filled with an enormous variety of distinctly different blues during the course of every day.
Why the sky is sometimes red
  • A red sky suggests an atmosphere loaded with dust or moisture and that the Sun is near the horizon.
  • In the morning and evening, photons must travel much further through the atmosphere than at mid-day.
  • Assuming the air above our heads is around 20 km, the total distance light travels increases fivefold to around 500 km when the Sun is on the horizon.
  • Remember that:
    • Longer wavelengths of light (red, yellow, orange and green) are too big to be affected by tiny molecules of dust and water so scatter the least.
    • Shorter wavelengths (blue and violet) are just the right size and are affected by reflection, refraction and scattering as they strike successions of particles.
  • In the right weather conditions, light travelling horizontally through the atmosphere undergoes so much scattering that no yellow, green, blue or violet wavelengths remain.
  • In these conditions, the light that reaches us, illuminating the sky and clouds and reflecting off every surface around us, is composed of wavelengths that bath the world in red and orange.

Work

In physics, work is defined as the transfer of energy that occurs when a force is applied to an object, causing it to move in the direction of the force. The amount of work done depends on the magnitude of the force, the distance the object moves, and the direction of the force relative to the movement.

  • Work is done when energy is transferred. For example, lifting a box transfers energy from your muscles to the box, giving it gravitational potential energy.
  • Work is measured in joules (J), where 1 joule is equivalent to 1 newton of force causing an object to move 1 meter.
  • Direction matters. If the force is in the same direction as the displacement, work is maximized (cos(0°) = 1). If the force is perpendicular, no work is done (cos(90°) = 0).
  • Examples related to work:
    • Pushing a car that rolls forward involves work because energy is transferred to the car, causing it to move.
    • Holding a heavy object stationary involves no work because, although force is applied, there’s no displacement.
  • The mathematical definition of work is:
    • Work=Force×Distance×cos⁡(θ)
    • Where:
      • Force is the applied force (in newtons, N).
      • Distance is the displacement of the object (in meters, m).
      • θ (theta) is the angle between the direction of the force and the direction of the displacement.

Workflow

A workflow is a series of tasks arranged in a specific order to achieve a goal effectively and efficiently. By planning and organizing a workflow, you can ensure no important steps are missed and that the process runs smoothly. This can save time, reduce errors, and lead to consistent results.

  • A successful workflow requires careful assembly and organization of all resources beforehand so that they can be structured into a step-by-step procedure.
    • A typical colour management workflow might begin by ensuring that colours viewed through a camera viewfinder are captured and digitally recorded.
    • Image editing software such as Adobe CC might then be used to work through a decision-making process to ensure an image is fit for purpose.
    • When the workflow requires it, monitor calibration might be used to ensure that information is accurately displayed when viewed on screen.
    • A successful outcome is achieved when the final image accurately represents all decisions made during the editing process.
Related diagrams

Each diagram below can be viewed on its own page with a full explanation.

References
  • A workflow is a series of tasks arranged in a specific order to achieve a goal effectively and efficiently.
  • By planning and organizing a workflow, you can ensure no important steps are missed and that the process runs smoothly.
  • This can save time, reduce errors, and lead to consistent results.
  • A successful workflow requires careful assembly and organization of all resources beforehand so that they can be structured into a step-by-step procedure.
    • A typical colour management workflow might begin by ensuring that colours viewed through a camera viewfinder are captured and digitally recorded.
    • Image editing software such as Adobe CC might then be used to work through a decision-making process to ensure an image is fit for purpose.
    • A successful outcome is achieved when the final image accurately represents all decisions made during the editing process.

Workflow

A workflow is a series of tasks arranged in a specific order to achieve a goal effectively and efficiently.

  • By planning and organizing a workflow, you can ensure no important steps are missed and that the process runs smoothly.
    This can save time, reduce errors, and lead to consistent results.
  • A successful workflow requires careful assembly and organization of all resources beforehand so that they can be structured into a step-by-step procedure.
  • A typical colour management workflow might begin by ensuring that colours viewed through a camera viewfinder are captured and digitally recorded.
  • Image editing software such as Adobe CC might then be used to work through a decision-making process to ensure an image is fit for purpose.
  • A successful outcome is achieved when the final image accurately represents all decisions made during the editing process.