Gravity – an accurate depiction of gravity?

Recently, Neil deGrasse Tyson posted a storm of tweets both criticizing and praising the new Sandra Bullock/ George Clooney movie ‘Gravity’.

Among his criticisms were:

“Mysteries of #Gravity: Satellite communications were disrupted at 230 mi up, but communications satellites orbit 100x higher.”

“Mysteries of #Gravity: How Hubble (350mi up) ISS (230mi up) & a Chinese Space Station are all in sight lines of one another.”

“Mysteries of #Gravity: Why Bullock, a medical Doctor, is servicing the Hubble Space Telescope.”

Let’s keep in mind that the movie gravity was meant to accurately convey the experience of astronauts during a catastrophic disaster while on a servicing mission to Hubble. This is why I’m allowed to pick it apart – if a movie sets out to portray a fictional reality set in some alternate universe’s space (ie Star Wars, Star Trek, etc) then it can do whatever it wants.

However, Gravity attempts to portray a present-day reality-based scenario. So its lack of accuracy is more concerning.

Let’s pick it apart.

Things it did wrong:

• The first thing that struck me as inaccurate was the fact that Sandra Bullock is servicing the Hubble Space Telescope, one of the most expensive science investments in human history. A medical doctor would not be sent into space to service the 2.5 billion dollar telescope. Instead, NASA would bring her in as an instrument specialist, and she in turn would train professional astronauts how to install her instrument.
• The debris – it was orbitting west to east when nearly all orbitting bodies orbit Earth east to west.
• Also, Bullock sets her watch to 90 minutes corresponding to the orbit time of the debris. Here’s a fun fact about how satellites work- communication, GPS, and spy. Satellites are put in highly elliptical orbits so that they can spend more time over a particular area of the Earth. This means that if the Russians destroy their satellite, they will destroy all the Russian satellites (and probably some US spy satellites orbitting over Russia), but this could of debris will not interact with orbit of Hubble or the ISS, or at least not very often. Keep in mind that space junk is a very real threat – just recently an Iridium satellite collided with a Russian defunct satellite and produced 2500 new pieces of space junk. 
• Satellite communication is disrupted – most of the communcations satellites orbit at 2500 mi above the Earth – the ISS has an altitude of 230 mi – so this catastropic disaster would not disrupt Hubble or the ISS.
• Btw, Hubble has an altitude of 350 mi, so Sandra and George would not be able to travel to the ISS from their original docking with the shuttle Endeavour because it would be in a completely different orbit.
• Sandra Bullock takes off her spacesuit and floats around in her spanx. It has the sex appeal of a Hollywood movie but totally lacks in accuracy. She would be wearing an adult diaper, sweating profusely, and covered in the Liquid Cooling and Ventilation Garment, which is a very ugly, tube-filled, full-body suit.

• George Clooney spends the opening 20 minutes of the movie horsing around in a jet pack. However, NASA would never allow an astronaut to blow through all this fuel. Additionally, the suits are not nearly that maneuverable.

Things it did right:

• Director Alfonso Cuarón handled the insides of the ISS beautifully – this is truly a feat of modern-day movie simulations.
• The maneuvering of the astronauts under zero g was mostly accurate. However, the space suits would not allow Bullock to so easily grab metal poles or grip objects – the gloves are notoriously immobile.
• The trails of the chinese space station upon re-entry were stunning and highly reminiscent of the Challenger disaster.
• The northern lights and view of the Earth from space were my favorite parts of this movie.

Overall, some major oversights and some chart-topping actors made for another Hollywood drama. I enjoy the attempt at realism, but I’m also just struck by the lack of universally popular non-fiction space movies.

I highly recommend Hubble 3D – see it in imax. It is a 2010 documentary about the astronauts on the mission to repair Hubble.  

 

Why is the sky blue?

This is really a two part answer. First, let’s talk about the physics of the atmosphere. Then, it’s time to consider the biology of the human eye.

Part 1: The physics

Light is a wave. It travels through a vacuum. However, it can be blocked by particles in the atmosphere. Why?

All light will travel in a straight line unless something blocks it – it could be reflected (off a mirror), bent (like through a prism), or scattered (by molecules). In the case of our atmosphere, molecules of air scatter the light.

Different colors of light have different wavelengths – blue light is more energetic and thus has a shorter wavelength:

This part is intuitive – because blue has a shorter wavelength, it is more likely to interact with particles in the upper atmosphere, so it scatters. This is why we perceive the sky to be blue.

Okay, that is all very well. But why does the sun look yellow when we look directly at it? – Please don’t look directly at it. But the answer is that the yellow light from the sun is not scattered so it travels directly to us. Blue light is scattered away from that line of sight, so we don’t see as much along that path to the sun.

Why are sunsets red?

When the sun is setting, it is low in our sky, meaning we are looking through more atmosphere. This means even more blue light is scattered – and a lot of green light as well. The red light is the only remaining visible color that we can see. Also, when we’re looking close to the horizon, we see a lot more pollution, which ironically makes the sunset prettier.

Part 2: Our Eye

 People are limited. We have three eye cones in our eye, meaning we can see red, green, and blue colors. This means we see a full range of visible color – from very red things to very purple things. 

However, although the atmosphere in reality is most efficient at scattering purple light, we have very ineffective eye cones at this wavelength, so we see it as blue.

Just think, we are missing out on a purple sky.

-Becky

 

Giant Impact Theory

How did we get our moon? Why is it so much bigger than the other inner solar system moons? These questions can be explained by giant impact theory.

The definition of a scientific theory is a well-understood and accepted explanation of nature in the scientific community. For instance, the Big Bang Theory is a theory; likewise, evolution is a theory. Thus, we can conclude that it is generally accepted in the planetary science community that the moon formed as the result of a giant collision between proto-Earth and a large planetesimal/ protoplanet 4.5 billion years ago. Scientists are still debating the exact dimensions and symmetry of the collision.

Previously, giant impact theory described the formation of the moon this way: A mysterious Mars-sized object impacted the proto-Earth and the moon formed out of the disintegrated Mars-sized object’s material. However, studies of the lunar rocks has shown that the Earth and moon have the same composition.

Two recent studies attempt to cover up this hole in the theory.

Cuk and Stewart propose through simulations that if the proto-Earth had a rotation period of 2 to 3 hours, it would have had the angular spin momentum necessary to throw off the material to form the moon when impacted with a Mars-sized impactor.

Then, they explain the current 24-day rotation rate of the Earth by the subsequent gravitational interactions between the newly formed Earth-moon system.

Canup of the Southwest Research Institute in Boulder proposed that the moon can be produced through a collision between like-sized impactors.

Her simulation:

The yellow material surrounding Earth on the bottom right represents material amounting to the mass of three moons – this material will later accrete into the present-day moon.

The jury is still out about what actually occurred 4.5 billion years ago, but this is the nature of science – always open for new interpretations of data and simulations.

 

The Dinosaur Moon

The moon moves away from Earth about 3-4 cm/year. Why?

The differential force of the moon on the Earth raises tides in Earth’s ocean. The tides also have a significant effect on the moon – the mass of the water exerts a force on the moon. The bulges will move ahead of the moon since the Earth rotates once a day and the moon orbits once a month – this causes the bulges to get ahead of the moon and to pull it forward in its orbit.

Angular momentum is conserved. The force of the bulges on the moon actually adds angular momentum to the moon’s orbit.

This next idea may seem counter-intuitive, so you’ll have to take my word for it.

When an orbiting object gains angular momentum, it begins to move faster in its orbit, so it moves farther away from the object it is orbiting. The same is true for satellites and space shuttles orbitting Earth. If they want to increase their distance from Earth, they just fire their thrusters to jump into a higher orbit. Cool, right?

You may argue that angular momentum has to be conserved. Don’t worry – it is. As the moon gains orbital angular momentum, the Earth loses its rotational angular momentum. This means the Earth is rotating slower now than it did billions of years ago.

A dinosaur day was only 23.5 hours long!

So the moon is moving away from Earth right now. What did it look like when dinosaurs roamed?

Looks pretty similar! That’s because although the moon is moving away every year, in 85 million years it will have moved 2000 miles away. But this is only 0.8% of the total distance of the moon. So it won’t look different.

Do not believe those sci-fi movies that show the moon to be super huge during the time of the dinosaurs. It would look the same.

Pretty cool.