Ask Nathalie

An artist's depiction of the two Voyager spacecraft as they approach interstellar space. Image credit: NASA/JPL.

Hi Nathalie,

I do have a question about space-time. How is it that all the different stars can be connected to us…? They seem a lifetime away. Is there any relation between the history of space, and a spiderweb — like if you touch a spiderweb with a finger, it moves and affects the whole web…

From,
Whoa, It’s Like… Duuuuude 

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Dear Dude,

Okaaaay, err… Let me try and break this question into manageable parts I can actually answer. Alright, stars being connected to us. So I could argue that all these stars have a gravitational effect on us, since they are so massive, but gravity is a force that falls with radius squared. That means that, while we are basically controlled by the Sun’s gravitational field, the next closest star (Proxima Centauri) which is 4.24 lightyears away doesn’t have a whole lot of effect on us. Furthermore, lines of a gravitational field cannot “move” faster than the speed of light. That means that if Proxima Centauri were to suddenly vanish without a trace, whatever tiny amount of gravitational effect it has on Earth would not disappear until 4.24 years after the star’s disappearance. On a shorter distance scale, that means that we would not notice the Sun’s sudden disappearance until 8 minutes after the fact, since the Sun is about 8 lightminutes away from Earth.

The Universe is heavily interconnected. The Sun moves around the Milky Way based on the gravitational field created by the sum of all the other stars in the Galaxy. Our Milky Way moves around the Universe based on the gravitational field created by the sum of all the other galaxies in our Local Group of galaxies. Our Local Group as a whole is moving away from other clusters of galaxies based on the expansion of the Universe. These phenomena require the compounded effects of millions and billions of objects, though. Unless they’re very close to each other (like within a stellar system), single objects don’t really affect other objects.

As an example, the Voyager I probe which was launched in 1977 is on the cusp of exiting the Sun’s sphere of influence and entering interstellar space. Once it does, the magnetic and gravitational fields of the Sun will have a much weaker effect on the probe. It has travelled nearly 0.002 lightyears to get to this stage. Compare this distance to the diameter of our Galaxy, 120 000 lightyears, and we realize the Sun’s influence is short ranging. Add the Sun to all its stellar neighbours, though, and you create massive fields!

I feel there might be a really cute moral to this story along the lines of “If you work together, you can fling neutron stars out of the galaxy!”.

Enjoy!
Nathalie 

Ask Nathalie

This is not how I remember Contact....... Image credit: N. Ouellette.

Hi everyone! Welcome to the first (and maybe, but I hope not, last; please send me questions) edition of “Ask Nathalie” where you get to ask me random questions about astronomy, and I probably answer them! Nathalie is the person in the picture who hopes she doesn’t get sued by Jodie Foster, Carl Sagan’s living relative and whoever made the movie “Contact”. Also, I kind of hate the name “Ask Nathalie”, so please suggest other names. Alright, we have a triple header from a single reader, so here we go.

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Hi Nathalie!

1) Why does the Sun get hotter as you move outwards?

2) Which moon has a methane cycle? 

3) If all the material in the asteroid belt were to combine, how big would this object be?

Cheers, 
Knows Which Moon Has A Methane Cycle

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Dear Methane Cycle,

Yeah, that’s right. I’m also doing that thing where I’m giving the people who are writing in weird descriptive names. And yes, Methane Cycle, I really do believe you do actually know which moon has a methane cycle, because that sounds like an extremely pointed question for someone not in the know!!! Nevertheless, I will humour you and answer all your queries:

1) This isn’t quiiiiite true. On average, the hottest part of the sun is its core (about 15,000,000°C). As you move outwards from the core, the temperature drops until it reaches about 5,700°C at the surface, or photosphere. Temperature continues to drop once you enter the atmosphere, until you reach 500 km above the photosphere and hit the minimum temperature. Here, it’s a chilly 3,800°C. But then!… Now the weird stuff starts happening. A little higher up, you have the chromosphere that reaches 20,000°C. Further still is the corona where it’s 1,000,000°C to 2,000,000°C on average. Some hot spots can temporarily heat up to as high as 20,000,000°C, though! Toasty. Now why… Well, sadly we’re not sure (this column sucks!). In the Sun’s atmosphere, where it’s still very hot but the gravitational force is weaker, much of the gas is turned into plasma. And plasma is craaaaazy. By that I mean, of course, that it is heavily influenced by the Sun’s magnetic field. It may be that energy is transported from the cooler surface to the hotter corona (breaking the laws of thermodynamics, cringe) using a magnetic mechanism we don’t quite understand yet. So my advice to you is to become a physicist, figure this out and report back to me ASAP.

2) I think you already know this, but Saturn’s moon Titan has a methane cycle. By this, we simply mean it has a cycle very much like Earth’s water cycle (precipitation, evaporation, condensation, repeat), except with methane instead. The average temperature on Titan is about -180°C. Methane’s melting point is -182°C, and its boiling point is around -162°C. Oooh, look at that! That means Titan is covered in GIANT LAKES FILLED WITH COMBUSTIBLE FUEL. It’s thought that life may be harboured within these crazy fuel lakes, but if you’re interested in that topic, you should’ve asked that question specifically (aka send in this question).

3) It would be so easy for my to just answer “As big as your mama” here and call it a day, but I’m absolutely not that kind of a person. Instead, I will be extremely lazy and copy-paste the following from Wikipedia: “The total mass of the asteroid belt is estimated to be 2.8×10^21 to 3.2×10^21 kilograms, which is just 4% of the mass of the Moon”. I love you, Wikipedia.

SEND ME YOUR QUESTIONS!!!

Love,

Nathalie

P.S: OR ELSE.