image of the Day… Sunset Sequence in Mars…!!!

Sunset on Mars

NASA’s Curiosity Mars rover recorded this sequence of views of the sun setting at the close of the mission’s 956th Martian day, or sol (April 15, 2015), from the rover’s location in Gale Crater.

The four images shown in sequence here were taken over a span of 6 minutes, 51 seconds.

This was the first sunset observed in color by Curiosity.  The images come from the left-eye camera of the rover’s Mast Camera (Mastcam). The color has been calibrated and white-balanced to remove camera artifacts. Mastcam sees color very similarly to what human eyes see, although it is actually a little less sensitive to blue than people are.

Dust in the Martian atmosphere has fine particles that permit blue light to penetrate the atmosphere more efficiently than longer-wavelength colors.  That causes the blue colors in the mixed light coming from the sun to stay closer to sun’s part of the sky, compared to the wider scattering of yellow and red colors. The effect is most pronounced near sunset, when light from the sun passes through a longer path in the atmosphere than it does at mid-day.

Malin Space Science Systems, San Diego, built and operates the rover’s Mastcam. NASA’s Jet Propulsion Laboratory, a division of the California Institute of Technology, Pasadena, manages the Mars Science Laboratory Project for NASA’s Science Mission Directorate, Washington. JPL designed and built the project’s Curiosity rover.  For more information about Curiosity, visit and

Credit: NASA/JPL-Caltech/MSSS/Texas A&M Univ.


Why We Say ” O’ Clock ” ….?

The practice of saying “o’clock” is simply a remnant of simpler times when clocks weren’t very prevalent and people told time by a variety of means, depending on where they were and what references were available.


Generally, of course, the Sun was used as a reference point, with solar time being slightly different than clock time. Clocks divide the time evenly, whereas, by solar time, hour lengths vary somewhat based on a variety of factors, like what season it is.

Thus, to distinguish the fact that one was referencing a clock’s time, rather than something like a sundial, as early as the fourteenth century one would say something like, “It is six of the clock,” which later got slurred down to “six o’clock” sometime around the sixteenth or seventeenth centuries. In those centuries, it was also somewhat common to just drop the “o’” altogether and just say something like “six clock.”

Using the form of “o’clock” particularly increased in popularity around the eighteenth century when it became common to do a similar slurring in the names of many things such as “Will-o’-the wisp” from “Will of the wisp” (stemming from a legend of an evil blacksmith named Will Smith, with “wisp” meaning “torch”) and “Jack-o’-lantern” from “Jack of the lantern” (which originally just meant “man of the lantern” with “Jack,” at the time, being the generic “any man” name. Later, either this or the Irish legend of “Stingy Jack” got this name transferred to referring to carved pumpkins with lit candles inside).

While today with clocks being ubiquitous and few people, if anybody, telling direct time by the Sun, it isn’t necessary in most cases to specify we are referencing time from clocks, but the practice of saying “o’clock” has stuck around anyway.

Source… i