Galactic Tides - The Whirlpool Galaxy And Its Companion 

Astrophysicists were able to determine that the Whirlpool Galaxy (M51) and its small companion galaxy (NGC 5195) are tidally entwined by analyzing the light emitted from Supernova within M51. These Supernova have provided important clues about the structure and composition of these galaxies.

Credit: Cornell Astrophysics/NASA Hubble/IPAC 

Celestial Spheres.

In the ancient world, the Circle was seen as the ideal form, so it influenced the view of the Solar System and the vision of heavens.
Ptolemy’s geocentric model, which was the prevailing view of the Solar System and Earth’s place in it for over 1400 years (until debunked by Copernicus), held that the Earth was static at the centre of the Universe, with all other bodies revolving around it in perfect circles. In the Ptolemaic system, the planets are assumed to move in a small circle called an epicycle, while epicycles rotated along a larger circle called a deferent, which in turn rotated around the Earth. The Earth then was like as the central hub of the Cosmos, everything else orbiting it eastward in uniform motion. This allowed Ptolemy to explain planetoids retrograde motion - the point at which planets seem to double back on their orbits at certain points in the year. 
With circles turning on circles at somepoint they seem to double back on themselves, which creates the idea of the spirograph like pattern in the design. 

The Faint Young Sun Paradox

In the early days of the solar system the power of the Sun was about 75% or so of what it is now.

Observations of similar stars far away confirm similar behavior amongst other young stars.

The temperature on an Earth with a Sun blasting out 75% of what it does now would only be around 270 Kelvin (greenhouse equilibrium included).

Ice melts at 273 Kelvin.

The evidence of sedimentary rocks from this period however, shows that Earth was a water world even then. According to our established mathematical models… Earth should’ve been covered in nothing but ice.

Mars, a planet half again farther from the Sun than Earth, would only have been around 201 Kelvin - a staggering 70 Kelvin below the freezing point of water!

Yet both worlds clearly were covered in liquid water according to evidence at a time when they should’ve been balls of ice.

The potential habitability therefore of worlds seems to be something we have trouble still understanding.

Some potential solutions to these problems are that since the planets were younger, their interiors would’ve been much hotter and more radioactive still. This could’ve caused volcanic activity and an even heavier release of greenhouse gases than either are thought to have done.

Furthermore, something commonly thought to reduce average temperatures, cloud coverage, would’ve acted exactly the opposite in this situation.

Clouds today are reflective to lots of the solar energy, scattering it back into space. If the heat were coming from below the clouds however it’s possible they trapped significant amounts of greenhouse gases, exacerbating the situation enough to melt ice.

On one hand our ability to accurately determine a world’s habitability remains humble. On the other, these conditions seem to exist in many more places than we ever could’ve guessed. This is the faint young Sun paradox.

(Image credit: NASA)

NASA’s Hubble, Chandra Find Clues that May Help Identify Dark Matter

By Felicia Chou

Using observations from NASA’s Hubble Space Telescope and Chandra X-ray Observatory, astronomers have found that dark matter does not slow down when colliding with itself, meaning it interacts with itself less than previously thought. Researchers say this finding narrows down the options for what this mysterious substance might be.

Dark matter is an invisible matter that makes up most of the mass of the universe. Because dark matter does not reflect, absorb or emit light, it can only be traced indirectly by, such as by measuring how it warps space through gravitational lensing, during which the light from a distant source is magnified and distorted by the gravity of dark matter.

To learn more about dark matter and test such theories, researchers study it in a way similar to experiments on visible matter — by watching what happens when it bumps into other objects. In this case, the colliding objects under observation are galaxy clusters.

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