Answers to last issue's Do You Know?
1. What is the difference between a moth and a butterfly? 
ANSWER: Yes, it is often easy to get confused between a moth and a butterfly. They both belong to the same insect family (Lepidoptera). But there are a few differences to look for:
. Butterflies usually rest with their wings closed, while moths rest with their wings open.
. Butterflies have long, thin antenna, while moths have shorter feathery antennas.
. As a rule moths tend to be duller and less vibrant in colour, with less intricate and striking patterns. (But rules have exceptions! For instance, the Madagascan Sunset Moths are incredibly colourful and striking)
. Butterflies generally gather food during the day while moths are seen more at nighttime.
. Most moths make a silky cocoon, while butterflies usually make a shiny chrysalis.
. Moths have a frenulum, which is a wing coupling device that ensures the wings travel together during flight. Butterflies do not have this.
. Generally speaking, moths tend to be stockier and have furry bodies, whereas butterflies are smooth and lean. This difference in appearance is due to scale size: butterflies possess far smaller scales.
. Moths have "superposition eyes", which reflect light at the same angle that they take it in. This type of eye creates images up to 1000 times brighter than "acquisition eyes", but sacrifices image quality. On the other hand, butterflies have "apposition eyes", which work by gathering multiple images and combining them in the brain.
An interesting fact: the largest moth, the Atlas moth, can grow to be over 15 cm wide!

2. Which are the top 10 largest stars in the Milky Way galaxy? 
ANSWER: Some of these stars may be known to you, some may be new. The sizes of these stars is measured in a unit called solar radius (plural radii). One solar radius equals the Sun-Earth distance of 6.957x105 km. Astronomers also use the natural unit light year, to indicate distances to stars. One light year is (not a time but is) the distance travelled by light in one year. Since light travels at a veloity of 3x108 m/s, one light year is 9.46x1012 km. Conversely, one solar radius is 2.32 light seconds (distance travelled by light in so many seconds)! Light from the Sun takes about 8 minutes to reach the Earth.
1. V838 Monocerotis
It belongs to the the constellation Monoceros, is about 19,900 light-years away from the Earth. With a range of 380 to 1,970 solar radii, V838 Monocerotis is one of the biggest stars in the known Universe. It was noticed only in 2002 after a massive eruption. (Why the eruption occurred is still a mystery, much debated by astronomers.)
2. Betelgeuse
This one is part of the Orion constellation, well-known to all of us. It is a red supergiant "only" 640 lights years away from Earth. Its radius is roughly thousand times that of our Sun, ranging between 950 and 1200 solar radii. It is one of the biggest stars visible to the naked eye from the Earth.
3. KW Sagittarii
This is also a red supergiant on the boundary of the constellation Sagittarius. Lying 7800 light-years away from Earth, it is 1480 times the radius of the Sun.
4. VY Canis Majoris
A part of the Canis Major constellation, this is one of the most massive and luminous red hyper-giant stars known to us, with a radius of 1420 (plus-minus 120). The Earth is 3900 light-years away from VY Canis Majoris. 
5. V354 Cephei and VX Sagittarii
These are two different stars, their exact solar radii of 1520 (estimated diameter) put them on the same spot, making them two of the largest stars in the Universe. V354 Cephei is roughly 9000 light-years away and belongs to the Cepheus constellation. VX Sagittarii is closer to the earth with a distance of 1076 light-years between them.
6. HD 143183
6523 light years away from the earth, this star belongs to the constellation Norma, and has a radius between 1,480 and 1,830 solar radii.
7. Westerlund 1-26
Located around 11,500 light-years away from the planet Earth. its radius ranging from 1,530-2,550 solar radii makes it a huge supergiant.
8. RW Cephei
This is in the constellation Cepheus in the northern hemisphere sky. An orange hypergiant with the solar radii of 1535, RW Cephei is 11,400 lights years away from Earth's surface. If you replace the Sun with this star in the solar system, it would stretch even beyond Jupiter!
9. WOH G64
With a size of 1,540-1,730 solar radii, WOH G64 is the second-largest star in the Universe, located in a satellite galaxy of the Milky Way: the Large Magellanic Cloud. It is a red supergiant star, 1,63,000 light-years away from the Earth. Because of torus-shaped clouds of dust that obscures the light of the star, its brightness fluctuates over time. Astronomers believe that it was larger in 2004 with an estimate of 3000 solar radii.
10. UY Scuti 
A hypergiant with a radius 1700 times more than the Sun, it was first detected it 1860 by German astronomers. It is about 9500 light-years away from the Earth and lies near the core of the Milky Way. To really grasp how big UY Scuti is, here is a comparison for you: If the Sun were a ball with a diameter of 20 cm, UY Scuti would be a ball with a diameter of 20,1168 kilometers! 
This lists keep changing, as astronomers make newer discoveries. Stars erupt and shed their mass, and astronomers constantly recalculate their radius. Also remember that there may be bigger stars in space, hidden between dust and particles. 

3. When and where did people start having cake for birthdays? 
ANSWER: For us in India, these practices are recent. Cakes were brought to us by the Europeans and the custom of eating cake or blowing out candles on birthdays has become popular in India only recently.
Celebrations with cakes are thought to have originated from Greece. The Greek goddess Artemis was the goddess of the moon. The Greeks had celebrations in her name, in which they would make round cakes and light candles on them to symbolize the moon. The round shape would obviously represent the full moon, while the candles would represent the soft mooonlight. 
Birthdays of prominent persons have been celebrated in many civilizations. but celebrating birthdays with cakes is recent, and is have originated in Germany, around 1400-1500 AD.
In Germany the, "Kinderfest" was a celebration for children. The Germans used to believe that children were highly susceptible to any harm that might arise from evil spirits on their birthdays. Hence, on children's birthdays, cakes were baked in the morning and the tradition of putting as many candles as the child's age (plus one!) was invented there. The additional candle represented the parents' hope that their child would live through one more year.
The cakes with the candles were readied in the morning and, as soon as one candle would go out, it would immediately be replaced by another. This process would go on until the night, when the child was finally told to blow out all the candles at once. This was done because it was believed that the candles helped transfer the child's wishes to god, while blowing them out all at once makes both the wish and the child's connection to god stronger!
With Europeans colonizing much of the world, in the 17th century, the custom of cakes made its way in to many continents. But baking a cake was not easy those days, it was a long and laborious process relying on yeast.
The breakthough came in the 1800s, when a British chemist by the name of Alfred Bird was working on a series of food products. His wife, Elizabeth Bird, was allergic to yeast and eggs. He wanted to come up with a way of baking that was easy for her. Instead of using hydrochloric acid (which was used to initiate baking those days), he combined tartaric acid, cornstarch and sodium bicarbonate to make "baking powder".
This recipe came at the time when the Industrial Revolution was gaining momentum. Hence, with baking powder able to reduce baking time, and with mass production made possible by the industrial revolution, bakeries and cakes became a booming industry where everyone could celebrate their birthdays with cake.
 
4. Which is the oldest living creature on earth?
ANSWER: Before we get to the answer to this question, try to guess how old such a creature might be. Surely more than 100 years. 200 years? The oldest Bowhead Whale is recorded to be 211 years. 400 years? The oldest Greenland Shark is recorded to be more than 400 years. 600 years? The oldest creature on earth is older than that. 1000 years? Guess again.
How about "immortal"? Ah, you say, that is impossible! Yet, the oldest living creature in the world comes close to being immortal!
It is a jellyfish from the family Turritopsis Dohrnii, and hails from a class of small animals that live mainly in saltwater. It has never died.
The Dohrnii start their life as small larvae with a diameter of less than 4 millimeters. The larvae have a tiny vase-like body with a mouth surrounded by tentacles. They come together and attach themselves to the ocean floor. Soon, they mature into jellyfish, and travel great distances and hunt other fish for food. They are now found all over the world, and travel by sticking on to the underside of ships! 
How can the Dohrnii jellyfish achieve immortality? Imagine that you keep getting older, and at a certain age, you start becoming younger, say until you become 25 again, then again you start getting older. As you can see, you can keep oscillating between 25 and 50 for ever. This is what the Dohrnii jellyfish have managed to do.
When a Dohrnii jellyfish is exposed to shock, it reverses its aging process and slowly turns back into larvae, to be reborn again when the danger has passed. It is the only biological example of true immortality. The process by which Turritopsis Dohrnii achieves this is quite remarkable. The cells of the larvae get assigned roles before maturing. The roles are assigned by a tiny strand of genetic material called MiRNA. MiRNA decides which jobs a mature cell receives. When the jellyfish receives a shock, MiRNA begins converting the jellyfish cells back into larvae. Scientists are studying this to see if it can be used to reverse the aging process in other species as well.
The biggest danger to these immortal jellyfish comes from sea plankton, which eats them for survival. The Dohrnii jellyfish provides the only known method for a living being to cheat death and its secrets are yet to be fully uncovered.

Sources: ScienceABC, ScienceFocus, Australian Butterfly Sanctuary.