Answers to last issue's Do You Know?
1. Does Venus really spin backwards?

Ans: Yes, Venus spins backwards compared to most of the other planets. It spins or rotates in the opposite direction that Earth rotates. This means that on Venus the Sun rises in the west and sets in the east. On Earth the Sun rises in the east and sets in the west. Venus also spins very slowly - only once every 243 Earth days. Venus is the slowest spinning planet in the Solar System. Actually, a day on Venus is longer than a year on Venus! A year on Venus (the time it takes for it to orbit the Sun) is 225 Earth days.
No one really knows why this is so. Also, for instance, Uranus’ spin axis is tilted perpendicular to most of the other planets (its spin axis is in the plane of the solar system) and many other planets in the solar system have a variety of different spin axis angles (for example, Earth’s spin axis is tilted about 23 degrees from the plane of the solar system). All these could be due to the same reason.
Another theory is that any planet has to conserve its total angular momentum, which is directly related to its net spin axis. The net spin axis is made up of the spin axis of its core (the iron part of the planet) plus its mantle (the rocky part of the planet) plus its atmosphere. Because Venus is believed to have a liquid core (like the Earth does) and it has a thick atmosphere, it's possible for friction forces to exchange angular momentum between the core and the mantle or between the atmosphere and the mantle. This can result in changing the spin axis of the mantle by changing the spin axes of the core and/or atmosphere. So it might be that interactions between the different layers of Venus have resulted in tilting the planet’s mantle so that the mantle is spinning retrograde (or backwards). It's the mantle spin axis that we equate with the planet’s spin axis since that is the part that we see rotating. In order for this theory to work, it helps that Venus is a slow rotator (a day on Venus is 117 Earth days!).

2. We forget so many things that we learn, but we never forget how to
ride a bicycle. Why is this?
Ans: Most of us learn how to ride a bike during childhood. But as we grow older, many of us stop riding and put those once-beloved bikes in storage. Years later, when we discover these relics and hop on, it’s as if we never stopped biking.
This is surprising because our memories let us down in so many other instances, such as remembering the name of a place or a person we once knew or where we put our keys. So how is it that we can ride a bicycle when we haven’t done so in years?
As it turns out, different types of memories are stored in distinct regions of our brains. Long-term memory is divided into two types: declarative and procedural
There are two types of declarative memory: Recollections of experiences such as the day we started school are called episodic memory. This type of recall is our interpretation of an episode or event that occurred. Factual knowledge, on the other hand, such as the capital of France, is part of semantic memory. These two types of declarative memory content have one thing in common—you are aware of the knowledge and can communicate the memories to others.
Skills such as playing an instrument or riding a bicycle are, however, anchored in a separate system, called procedural memory. As its name implies, this type of memory is responsible for performance.
One of the most famous studies showing the separate memory systems was that of an epileptic named Henry Gustav Molaison (aka H. M.). In the 1950s he underwent the removal of portions of his brain, including large parts of his hippocampus. After the operation doctors found that although the number of seizures had decreased, H. M. was unable to form new memories. Many of his memories of the time before the operation were also erased.
To learn more about his amnesia, neuropsychologists carried out various tests with H. M. In one, they asked him to trace a five-pointed star on a sheet of paper while only looking at it and his hand in a mirror—meaning the image was reversed. Although H. M.’s hand–eye coordination skills improved over the several days he performed this task, he never remembered performing it. This meant that he could develop new procedural, but not declarative, memories.
Is procedural knowledge then fundamentally more stable than explicit knowledge? As it turns out, the former is more resistant to both loss and trauma.
Even with traumatic brain injury the procedural memory system is hardly ever compromised. That’s because the basal ganglia, structures responsible for processing nondeclarative memory, are relatively protected in the brain’s center, below the cerebral cortex. However, it’s not clear, beyond brain damage, why procedural memory contents are not as easily forgotten as declarative ones are. According to one idea, in the regions where movement patterns are anchored fewer new nerve cells may be formed in adults. Without this neurogenesis, or continuous remodeling in those regions, it’s less likely for those memories to get erased.
One thing we know for sure, however, is simple sequences of movements we internalize, even far in the past, are typically preserved for a lifetime. Or as the saying goes, it’s “just like riding a bicycle.”

3. Smells seem to vanish after some time. Where do smells go?
If you are smelling something, you are inhaling gases, particles, or a combination of the two. They don't normally build up in the atmosphere because of three reasons: transport/dilution, chemistry, and deposition. Yes there is plenty of fresh air out there, but over billions of years there would be a lot of accumulation of odorous compounds if it weren't going somewhere. Though, stinky air does get trapped near the ground sometimes during stagnation events, caused by a temperature inversion close to the surface which prevents mixing with the upper air.
Atmospheric chemistry usually involves the hydroxyl radical (OH) in some way. Rapid chemical conversions of gases often depends on OH, which is cycling and replenished thanks to the abundance of oxygen and water vapor in the atmosphere. Many gaseous pollutants will go through a series of chemical reactions with OH, other chemicals, and/or sunlight. They are then converted to simpler chemicals that we don't really smell. Most odorous pollutants are chemically converted quickly (e.g. hours, days). Some pollutants do take years to convert (e.g. methane) and so accumulate in the atmosphere. We don't smell them, though, because our ability to "smell" things is limited to organic compounds and other molecules like hydrogen sulfide and ammonia.

4. Why are lemons yellow and limes green?
All citrus fruits are green while they are still growing on the tree. Lemons lose their green colour as they ripen because the chlorophyll pigment is replaced with a chemical called anthocyanin.
Many lime species would also turn yellow if you left them on the tree long enough, but they never get a chance. This is because ripe citrus fruits are too soft to travel well, so farmers always pick the fruits while they are green and under-ripe.
Oranges and lemons will continue to ripen on their way to the supermarket, but a quirk of biology means that limes stop ripening once they are picked.

5. When we start uploading our brains to computers, will our sense of self be uploaded too?
Our sense of self emerges from the activity of a poorly understood network of neurons, glial cells and blood vessels in the brain, which together produce the electrical and chemical processes that give us our thoughts and consciousness.
One day, it might be possible to scan all of this activity with perfect fidelity – this would be a hugely intensive process, involving recording the activity of every cell and chemical at an atomic level. This digital scan could be turned into a computer simulation, essentially allowing you to go on living after death. In theory, the simulated version of your brain would believe that its sense of self had been successfully uploaded, transferred from a biological body to an artificial one.
However, it’s not quite as simple as that. If scientists can develop a way to perfectly scan the brain without destroying it (which isn’t a given), then your original brain (and sense of self) would still exist, trapped in a body that will eventually fail. Your digital self might come to the realisation that it’s a copy, triggering an existential crisis.
And what if someone decides to make a hundred copies of this digital self? Now there are a hundred digital versions of ‘you’, each with its own sense of self. Is each of these selves equally valid? Does the second sense of self know that it’s the original copy, and thus expect a higher status? Could the separate selves decide to share their experiences and become a super-intelligent ‘hive mind’?
We don’t yet know the answers, but one way to limit any potential complications might be to become immortal piece by piece. We naturally change as we age, so if you slowly replaced failing biological tissue with computerised prostheses, then by the time all of your body and brain had been replaced, your sense of self will have been transferred without leaving behind a biological remnant.
Just watch out for the delete key… a digital brain is much easier to wipe than an organic one!
--From many sources