## The Chandler Wobble

Earth precesses around its axis every ~26000 years.

But in addition to this precession, there is an extra wobble that was observed by Kustner and later followed up by Seth Carlo Chandler, Jr called the Chandler Wobble that occurs at a much smaller time scale.

In 1888, Kustner found that the latitude of Berlin had changed slightly
during his observations of the night sky.

Therefore in 1891,Chandler. decided to conduct a 14 month study examining this change. The following is a plot of the spiral path taken by the earth’s axis over that 14 month  period.

The following plot shows the motion from 1909 – 2001.

Although many theories indicate that this is due to the fact that earth is not a perfect spherical rigid body, it is still not entirely clear on the mechanism that drives earth into this small wobbly motion.

If you took a closer look at the plots you would find that this wobble is of the order of a couple of meters which most certainly does not seem like a lot.

But if you are an astronomer if you do not account for this correction, you might just end up pointing your telescope at the wrong object

Have a great day!

## Shape of Earth is an oblate spheroid

As you can see from this dramatic demonstration, the consequence of imparting a rotational velocity to an object is the flattening of object at the poles.

The rotational velocity of Earth is a staggering 1,674.4 km/h
and as a result  bulges at the center by a tiny fraction, as is evident from the following image:

# If the earth is such round, then how come we don’t see the shadow of the mount Everest on the moon ?

Just to give a perspective on how tiny Mount Everest is compared to
Earth : Mount Everest is 8850m high and the radius of the earth ~6400km.
It is only 0.1% of the radius of the earth.

But surely it does cast a shadow on the moon no doubt about it, but you just can’t see it.

## Shadows cast by the moon on the other hand…

If you took a look at the recent solar eclipse animations by NASA, then you might have noticed the shadows cast by the moon during the eclipse were not circular (like yesteryears – see figure above).

But had an eerie irregular shape to it. Why is that ?

First thing to note is that if you take a circle and project it on a sphere, the shadow is no longer circles, but ellipses.* That’s why the image is elongated.

Importantly, the surface of the moon is interesting; It is irregular with lots of mountains and valleys. Hence you will not get a perfect little ellipse when you project it.

Based on whether it is a valley or a peak it would affect the shadow region during an eclipse.

As
mentioned in a previous post, eclipses on earth are too surreal to be
true
because if the size of the moon were any bigger then you would be
witnessing only perfect elliptic shadows and none of this complex mess.

But if the moon’s valley were any bigger, you might never achieve complete totality.

* Unless you project it face onto the source

# Understanding Pressure

Sometime back, I was asked to explain the concept of pressure to
someone who had a tough time understanding it. And here is an account of
how that went:

## The Books Analogy

Consider the layers of fluid stacked on top of each other to be represented by books instead of fluid.

Now, what does high pressure represent?
Well, it just means that there are many books on stacked on top of each other.

Suppose
you apply a force and try to move this stack of books. Velocity is
nothing but how much this stack has moved in 1 second.

What does low pressure represent according to the books analogy?
It
means that there are less books stacked on top of each other.

So, with
the same force you applied for the first case, you would be able to move
the books by a larger distance in one second. Hence it would have
higher velocity.

## Shock Waves

One could relate this analogy to last week’s posts on shock-waves as well.

You can think of shock waves as these set of big books hurtled at supersonic speeds. And when they crash into objects, they break.

Subtle eh ?

The nuance of life is that we are constantly subjected to atmospheric pressure and yet we are oblivious to it.

Its profound because 1 Bar is considerable ( for instance, it can crush containers  ). But yet here we are 🙂

## Gravity and Atmospheric pressure

Standard Atmospheric Pressure is a product of gravity and the density and thickness of the gas in the atmosphere.

On
Earth, at sea level, the weight of a one square inch column of air from
the surface to the top of the atmosphere, (the tropopause, about 36,000
feet) is  14.7 pounds, or one bar, which is standard air pressure.

If
gravity had a higher value the atmospheric pressure would be
correspondingly higher because that column of air would weigh heavier.

Atmospheric
pressure on the top of Everest is much lower due to the considerably
shorter column of air above the summit, (plus the fact of  slight

Atmospheric pressure on Venus is 33 bar or 33 times higher than on Earth.
This is due to the higher gravity and the depth and density of the atmospheric gas.

( Source Credit: Tony Vincent )

Hope you enjoyed this post . Have a great day!

The intricacies involved in launching a shuttle off the ground and successfully completing its mission is no doubt a meticulous task. Every move made during a launch is calculated and deliberate, nothing is left for chance.

On that note, having watched a couple of historic shuttle launches, this peculiar behavior caught my eye: the orbiter always faced the earth! ( The orbiter is the plane part of the shuttle)

## Why do shuttles orient belly up ?

Protection against space debris

Upon entering the atmosphere, most space debris burn up. But out in space, without the protective blanket of our atmosphere, the space shuttle is exposed to all sizes and shapes of space debris ( also man-made ).

The space shuttle’s belly is designed to take up intense heat and pressure so that the shuttle doesn’t fall apart when it re-enters the atmosphere, and therefore best suited for taking hits from flying space junk

The Sun

Do you remember the heat-resistant space shuttle tiles that I posted about a couple of weeks back?

Putting the spacecraft with it’s bottom to the Sun it is these heat-resistant tiles on the bottom that are most exposed
to the full power of the Sun.

This keeps the astronauts safer and
cooler than they would be otherwise.

To maneuver

Wait, space shuttles maneuver in flight ? Yup ! For each mission the shuttle must be launched at a certain angle in order to accomplish the prescribed task.

Since the launch pad is fixed i.e you cannot change its angular orientation, the shuttle must perform the maneuver during the ascent in order to orient itself with the trajectory.

This maneuver is known as the Roll maneuver and is performed at a point about one minute or so after the launch.

The Atlantis performing a roll maneuver

Communication

The belly down position assists in communication with the ground and
allows instruments within the cargo bay to be pointed back towards
Earth, which is required for many of the experiments carried within the
bay.

Home, Sweet Home !

The reason why the shuttle’s cargo bay faces towards the earth has some psychological benefit as well.

The crew of the crew are given the spectacular views of our home planet glorifying the magnificence of its existence, rather than staring at the cold, dark void of space that lies afar.

## A colorful Rayleigh Background

The Space Shuttle Endeavour is featured in a very unique setting over the Earth’s colorful horizon in this Photo. And beholding this photograph instills a great deal of serendipity.

The light from the sun interacts with the different layers of atmosphere in this distinct fashion and this is attributed to a phenomenon known as Rayleigh Scattering.

In the lower thresholds of the atmosphere, the blue light and its variants are scattered away, leaving behind only red,orange and yellow shades to dazzle us, whereas in the upper atmosphere this scattering phenomenon of blue light is considerably lesser.

This produces the hypnotizing display of colors that you marvel. Amazing isn’t it?

## Reflections

Oh art nature,

How i wish everyone would truly appreciate

The beauty in you that is never to hate.

Image Credit: NASA

## The Tale of Earth and it’s sister Theia.

Have you found it weird that the earth’s axis is tilted by 23.5 degrees and wondered what led to this? Wait, Where did the moon come from?

Well, Here’s what scientists have theorized.

## The Giant Impact Hypothesis

Theia, a mars sized planet collided ( it glanced and thankfully did not collide head on, else it would have destroyed earth ) with the Earth around 4.553 billion years ago.

Theia’s debris gathered together around Earth to form what we now call- The Moon.

The collision between the early earth and Theia was so immense that
it tilted the axis of rotation of the early earth by 23.5 degrees.

And
it remains tilted so that way even today!!

## Why do they believe in this hypothesis ?

Scientists have a very good reason to believe in the Giant Impact Hypothesis:

• Earth’s spin and the Moon’s orbit have similar orientations.
• Moon samples indicate that the Moon once had a molten surface.
• The Moon has a relatively small iron core.
• The Moon has a lower density than Earth.
• Evidence exists of similar collisions in other star systems (that result in debris disks).
• Giant collisions are consistent with the leading theories of the formation of the solar system.
• The stable-isotope ratios of lunar and terrestrial rock are identical, implying a common origin

Have a good day !

PC: sarice,

# ISS is the third brightest object in the night sky!

It often comes as a surprise to people when i tell them that the space station can be seen with the naked eye! Flying at 400 km above your head, the ISS looks like a really fast moving airplane in the sky.

The ISS isn’t brighter than the day sky and hence cannot be seen during the day. But in the night, it’s the third brightest object in the sky! It reflects the sunlight off the solar panels on its surface.

## Spot the station!

If you would like to see the ISS for yourself, NASA ‘s Spot the station! is at your disposal. Register with your email address/mobile number and every time the ISS passes by your town/city, you will get a notification with the time, duration and inclination.

Have fun!

(Extras: There are mobile phone apps which you could use too, like the ISS detector satellite detector for android. At the end of the day all that matters is what is convenient to you.

ISS tracker– Real time tracking of the ISS)

# The Miura Fold

.

The Miura fold is a method of folding a flat surface such as a sheet of paper into a smaller area. The fold is named for its inventor, Japanese astrophysicist Koryo Miura.

## Why it is awesome?

The Miura fold is a form of rigid origami, meaning that the fold can be carried out by a continuous motion in which, at each step, each parallelogram is completely flat.

This property allows it to be used to fold surfaces made of rigid materials; for instance, it has been used to simulate large solar panel arrays for space satellites in the Japanese space program.

The fold can also be unpacked in just one motion by pulling on opposite ends of the folded material, and likewise folded again by pushing the two ends back together.

In the application to solar arrays, this property reduces the number of motors required to unfold this shape, reducing the overall weight and complexity of the mechanism.

## Other cool stuff.

Miura folded maps. Snug it into your pocket when not in need and open it up in style when you are lost !

# Mars: Red Planet, Blue sunset?

Mars has always been an interesting planet to us earthlings. The possibility of life, rovers leaving no stone unturned(literally), it’s demanding reddish appearance and now those breathtaking sunsets.Mesmerizing isn’t it ? But,

## Why are martian sunsets blue?

Here on earth, sunsets are bright with Yellow, Orange and Red colors dazzling in the sky. During sunsets, the light from the sun has to travel a longer distance in our atmosphere to reach the earth.

Consequently, all the blue and violet light is scattered( thrown in various directions) by the particles in our atmosphere leaving behind only shades of yellow, orange and red, which is what you see. This phenomenon is known as Rayleigh scattering.

On mars, the reverse effect occurs. The martian dust is smaller and more abundant than on earth and it incidentally happens to be just the right size that it absorbs the blue light whilst scattering the red ones across the sky. This makes martian sunsets blue :).

Stay tuned, there is more space stuff coming your way.