Why Aren't The Van Allen Belts A Barrier To Spaceflight?

I follow all kinds of information about space and the stars. My brother has only recently started paying attention to these issues, but has been reading some naysayer websites. Because of this, he says he has doubts about the ‘truth’ of the space shuttle, the flight to the moon and other missions, as some claim that they would be impossible because of the heated layers of atmosphere around the earth, which would destroy them—the Van Allen belts. I know that heat shields are used, and am assuming that the rarefied atmosphere might not conduct heat as well. But what is the real reason why these flights are possible and are not eliminated by the heat of the Van Allen belts or other layers?
In a very unique setting over Earth's colorful horizon, the silhouette of the space shuttle Endeavour is featured in this photo by an Expedition 22 crew member on board the International Space Station, as the shuttle approached for its docking on Feb. 9 during the STS-130 mission. Image credit: NASA

In a very unique setting over Earth's colorful horizon, the silhouette of the space shuttle Endeavour is featured in this photo by an Expedition 22 crew member on board the International Space Station, as the shuttle approached for its docking on Feb. 9 during the STS-130 mission. Image credit: NASA

So there are two questions mixed up in here - the first is about traversing the atmosphere without burning up, and the second about traversing the Van Allen belts.

It’s true that re-entering the atmosphere from space is a delicate business, and there are only a few...

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How Come The Oort Cloud Isn't Torn Away From Our Sun By Nearby Stars?

If the Oort Cloud is three light years away from our Sun, then it’s closer to Alpha Centauri than our Sun, right? So how can it stay around our Sun if the mass of Alpha Centauri is 1.1 times the mass of our Sun - wouldn’t the gravity of Alpha Centauri rip it away?
An illustration of the Kuiper Belt and Oort Cloud in relation to our solar system. Image credit: NASA

An illustration of the Kuiper Belt and Oort Cloud in relation to our solar system. Image credit: NASA

The Oort cloud is an interesting feature of our solar system; a nebulous, spherical cloud of comets which marks the very outer limit of our solar system. The Oort cloud is also the source of our long period comets - those icy fragments of the early solar system...

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Is Space Curved? Can We See The Milky Way In The Past?

Is it possible that space-time is curved in such a way that one (or many) of the galaxies we see in telescopes is actually our own Milky Way a few billion years earlier?
This infrared view reveals galaxies far, far away that existed long, long ago. Taken by the Near Infrared Camera and Multi-Object Spectrometer aboard the NASA/ESA Hubble Space Telescope, the image is part of the Hubble Ultra Deep Field survey, the deepest portrait ever taken of the universe. Image credit: NASA, ESA and R. Thompson (Univ. Arizona)

This infrared view reveals galaxies far, far away that existed long, long ago. Taken by the Near Infrared Camera and Multi-Object Spectrometer aboard the NASA/ESA Hubble Space Telescope, the image is part of the Hubble Ultra Deep Field survey, the deepest portrait ever taken of the universe. Image credit: NASAESA and R. Thompson (Univ. Arizona)

It is mathematically possible for a universe to be shaped this way, but not our Universe. Our Universe is as close to...

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When Was Dark Matter Formed?

Was dark matter created during the Big Bang?
This full-sky map from the Planck mission shows matter between Earth and the edge of the observable universe. Regions with more mass show up as lighter areas while regions with less mass are darker. The grayed-out areas are where light from our own galaxy was too bright, blocking Planck's ability to map the more distant matter. Image credit: ESA/NASA/JPL-Caltech

This full-sky map from the Planck mission shows matter between Earth and the edge of the observable universe. Regions with more mass show up as lighter areas while regions with less mass are darker. The grayed-out areas are where light from our own galaxy was too bright, blocking Planck's ability to map the more distant matter. Image credit: ESA/NASA/JPL-Caltech

Originally posted on Forbes!

Our current understanding of the event dubbed the Big Bang implies that all matter, and all energy, appeared in our Universe at that moment. Ever since then, the Universe has been changing, and those changes are reflected in the behavior of matter and energy.

Unfortunately, we can’t observe this event directly in order to get a better understanding of how the earliest stages of the Universe’s evolution unfolded. This isn’t something that can be fixed with a more powerful telescope, either; at an early point in time, the Universe was quite simply opaque to light. And much in the same way that I can’t see through furniture, even the best observatories can’t penetrate into the depths of time beyond this point.

To explain how we know that dark matter has been around since the very early Universe, I have to talk a bit about how we’ve managed to learn about the early Universe in general.

This map shows the oldest light in our universe, as detected with the greatest precision yet by the Planck mission. The ancient light, called the cosmic microwave background, was imprinted on the sky when the universe was 370,000 years old. Image credit: ESA and the Planck Collaboration

This map shows the oldest light in our universe, as detected with the greatest precision yet by the Planck mission. The ancient light, called the cosmic microwave background, was imprinted on the sky when the universe was 370,000 years old. Image credit: ESA and the Planck Collaboration

You may have seen this image before. The cosmic microwave background, which has the alternate name of the “oldest light in the Universe” is the surface of the cloudy Universe, just as it became transparent to light. There’s a lot of information about the early Universe embedded in this image, which tells us about the temperature of the Universe, and how the matter which later became clusters of galaxies was distributed around.

It’s this latter point which points to the existence of dark matter in the very early Universe.

One of the ways this image is analysed is by looking at the characteristic spacing between bright and cool patches. If this were 100% randomly distributed, you wouldn’t expect to find things at any particular distance more frequently than any other distance. And that could have been the way our Universe was arranged, but it isn’t. Our Universe has a few preferred spacings.

One of these sets of spacings is formally termed Baryon Acoustic Oscillations. Baryons are simply any matter, the protons and neutrons and electrons that make up humans and stars and dogs. Acoustic oscillations should sound like a musical term more than a physics one, and it’s not without reason. The early Universe was much like a fluid in many ways, and information travelled through it like sound through water. The Baryon Acoustic Oscillations, therefore, refers to the way that the stuff of atoms rippled through the early Universe.

Astronomers using NASA's Hubble Space Telescope took advantage of a giant cosmic magnifying glass to create a detailed map of dark matter in the universe. Image credit: NASA, ESA, and D. Coe (NASA JPL/Caltech and STScI)

Astronomers using NASA's Hubble Space Telescope took advantage of a giant cosmic magnifying glass to create a detailed map of dark matter in the universe. Image credit: NASA, ESA, and D. Coe (NASA JPL/Caltech and STScI)

The cause of those ripples? A pressure from dark matter. When the Universe became less fluid, the protons, electrons and neutrons were frozen into place, wherever their ripple had left them. There’s a huge number of these ripples in the Universe, so rather than a single stone thrown into a lake, our image is more like a water surface pummeled by a tropical rainstorm. The spacing between where the dark matter sat, and where some of the baryons in our Universe had rippled outwards to, is reflected in the statistics of the cosmic microwave image. Without the presence of dark matter, we wouldn’t expect to see this exact spacing. And if dark matter was present so early in the Universe, it probably was formed in the big bang. At the very least, it couldn’t have been formed later, the way the heavy elements in our Universe were formed by stars, many years after this snapshot of our early Universe.

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Is Dark Energy Pushing Our Galaxy Somewhere?

If dark energy is pushing our Galaxy in a known and straight line, then where is it pushing us to? What kind of force is driving the dark energy and where is it taking us to? Or is there a force that is drawing dark energy to it, and we are just trapped within it?
Still from an animation illustrating the accelerating expansion of the universe due to dark energy. Image credit: NASA's Goddard Space Flight Center Conceptual Image Lab

Still from an animation illustrating the accelerating expansion of the universe due to dark energy. Image credit: NASA's Goddard Space Flight Center Conceptual Image Lab

Originally posted on Forbes!

Dark energy isn't pushing our Galaxy in a specific direction; it's responsible for the expansion of the space between all objects in space which are not tied to each other by gravity.

So, for instance, dark energy doesn't influence the distance between the Sun and the Earth, because our gravitational ties are much stronger than the gentle stretching that space is doing. Similarly, our Sun isn't being moved relative to the center of our Galaxy, because the force of gravity binding us to the Galaxy is much stronger than what dark energy can exert.

Dark energy can't even shear apart the gravitational ties which attach our Milky Way to the Andromeda Galaxy and the numerous, tiny dwarf galaxies which hover around our Galaxy in their own orbits. The distances here are enormous; Andromeda is 2.5 million light years away. Light arriving to us from Andromeda now will have left that galaxy when our planet Earth had only just seen its first humans.

Dark energy is a force to reckon with only for galaxies much more distant from us, where the gravitational force between our Milky Way Galaxy and that faraway galaxy plays no role. It's often phrased as a gravitational counter-force, but that's only partially correct. It is true that dark energy seems to have a repellent influence on the space surrounding it, but unlike gravity, which is strongest around concentrations of mass in the Universe, dark energy seems to be evenly spread throughout the universe, with not a care for the presence of a galaxy, planet, or supercluster . It's this evenhandedness of dark energy that means that gravity can overpower it in densely populated regions of the Universe.

In this artist's conception, dark energy is represented by the purple grid above, and gravity by the green grid below. Gravity emanates from all matter in the universe, but its effects are localized and drop off quickly over large distances. Image credit: NASA/JPL-Caltech

In this artist's conception, dark energy is represented by the purple grid above, and gravity by the green grid below. Gravity emanates from all matter in the universe, but its effects are localized and drop off quickly over large distances. Image credit: NASA/JPL-Caltech

Dark energy is not a directional force - there's no bulk motion to the left, right, or an arbitrarily defined up that this expansion leans towards. So there's no point to which the universe is being drawn, and equally there's no origin point from which the expansion is unspooling. Any given point in space is simply, and very gradually, becoming more distant from most other points in the universe. It's not that our Galaxy is being pushed around- dark energy is instead ballooning out the space within which our Galaxy sits.

Where does dark energy come from? So far that's a mystery; we can measure its influence to a great degree of confidence, but if we knew the exact nature of why it behaves the way we observe it to, we'd probably rename it something less vague than 'dark energy'.

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