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Sharpen Your General Knowledge
Shamim Ansary:
Why Does Black Tea Lighten or Change Color When You Add Lemon Juice and What Causes the Chemical Change?
The simple answer to why black tea changes color is that adding lemon juice alters the acidity of the tea and the color change is an indication of this.
The color change is the same way that litmus paper changes color.
A similar effect can be observed by substituting the tea with some cooked red cabbage juice.
Tea leaves are rich in a group of chemicals known as polyphenols that amazingly account for almost one-third of the weight of the dried leaf.
Both the color of the tea and much of its taste are due to these compounds.
One group of polyphenols, the thearubigins, are the red-brown pigments found in black tea and constitute between 7 percent and 20 percent of the weight of dried black tea.
The color of black tea is also influenced by the concentration of hydrogen ions in the water.
Thearubigins in tea are weakly ionizing acids and the anions, or negatively charged ions, they produce are highly colored. If the water used to brew tea is alkaline, the color of the tea will be deeper due to greater ionization of the thearubigins.
If lemon juice, which is an acid, is added to the tea, the hydrogen ions suppress the ionization of thearubigins, and that makes the tea lighter.
Interestingly, the theaflavins, the yellow-colored poly-phenols in black tea, are not involved in the change in color that is associated with a change in acidity.
Shamim Ansary:
Why Are Traffic Lights Red, Yellow, and Green and What Do the Different Colors Mean for Signaling?
Red, green, and yellow traffic lights developed directly from the trial and error of controlling railways during the nineteenth century.
Trains needed advance warning to prevent fatal accidents and collisions.
The first choice was red for stop, which was logical because red had symbolized danger for thousands of years.
During the 1830s, engineers tried using green for caution and clear for go, but sunlight reflecting off clear lights gave false signals.
So engineers solved the problem by introducing yellow for caution and making green stand for go.
The very first traffic light using this system was introduced in Cleveland, Ohio, in 1914.
Shamim Ansary:
What Airline Is the World’s Largest?
The national airline of the Soviet Union, Aeroflot, which is owned by the Russian government, is now the largest airline in the world. Aeroflot has 1,300 planes and 400,000 workers, and carries about 90 million passengers a year to 65 different countries.
The largest airline in the U.S., and the world’s largest airline not owned by a government, is United Airlines, which has 365 planes carrying about 30 million passengers a year.
Shamim Ansary:
How Does the Earth’s Rotation Around the Sun Cause the Stars to Rise and Set at Different Times Every Night?
You may notice that when you are stargazing in your yard at 10:00 every night, the stars appear slightly to the west of where they were the night before.
Stars rise 4 minutes earlier every night, and set 4 minutes earlier.
Therefore, over the months, the starry night changes.
Over the period of a year, those minutes add up to 24 hours, so that every 12 months, the same stars show up at the same positions in the sky.
The difference in the stars’ rising and setting times results from Earth’s rotation around the Sun.
The celestial sphere remains relatively still, but Earth moves around the Sun.
The stars appear to be in a different place at the same time each night because, in fact, you are in a different place in space every night.
Because it takes 365 days for Earth to rotate around the Sun, you have 365 slightly different night skies to study.
Shamim Ansary:
When Was the Hubble Space Telescope Launched Into Orbit and Who Is the Hubble Telescope Named After?
Two months after the Hubble Space Telescope’s launch in 1990, it was discovered that the primary mirror had not been ground properly, among other problems.
The telescope could not be focused.
While this was a major embarrassment, the dangerous and complex repair mission was a coup.
The space shuttle Endeavor was launched in December 1993.
Its crew captured the Hubble Space Telescope, fixed it, and released it successfully.
The images and data returned since have more than outweighed the early difficulties, promising that the Hubble Space Telescope will be remembered for its scientific achievements rather than its flaws.
Many Hubble observations have led to breakthroughs in astrophysics, such as accurately determining the rate of expansion of the universe.
The Hubble Space Telescope is named after the astronomer Edwin Hubble.
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