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 

A Patchwork of Galaxies - Halfway to the Edge of our Universe

In this image we see more than halfway to the edge of the observable Universe. This image is the result of 14 hour exposure of the Hubble Space telescope. Many of the objects are galaxies within this image are clusters about 5 billion light years away. The light from quasar QSO-160913+653228 took nine billion years to reach us and allows us to observe time on a truly cosmic scale. 

Credit: NASA,ESA,Hubble

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. 

From Superbubbles to Galactic Fountains

Nebula NGC 1929 contains just the kind of superbubble that Astrophysicists think could cause a Galactic Fountain. Even though this nebula is not causing a fountain, it is theorized that similar nebula are causing Galactic Fountains within our Milky way galaxy. The illustration bellow shows how massive Galactic Fountains spew hot ionized gas away from our galactic disk to form Galactic Corona:

Supernova explosions within the galactic disc drive hot gas out of the disc, creating so-called galactic fountains that contribute to the formation of a halo of hot gas around the Milky Way. As the gas rises above and below the disc, reaching heights of a few kiloparsecs (more than 6,000 light-years!), it emits radiation and thus becomes cooler, condensing into clouds which then fall back into the disc, in a fashion that resembles a fountain.

Credit: ESO VLT/ESA/Fountains and Pumps

In the latest episode of the web series Shelf Life, How To Time Travel To A Star, Museum astrophysicist Ashley Pagnotta introduces one of her areas of interest: Cepheid variable stars. In 1912 Henrietta Leavitt discovered a way for these stars to be used as distance markers in the cosmos while identifying and studying variable stars at the Harvard Observatory.

Cepheid variables can be used to map objects in space because they pulsate between dim and bright phases over a regular span of time, usually between one and 70 days. The period between the star’s consecutive brightest points can be used to determine the star’s luminosity, or brightness compared to the Sun. The brighter the star is, the longer it takes to swing between its brightest and dimmest points. With this information in hand, astronomers can reliably calculate how far from the Earth the star is.

Learn more about cepheid variables and Henrietta Leavitt on the Museum blog. 

Image: The Cepheid variable star RS Puppis, in an image captured by the Hubble Space Telescope, is one of the brightest in the Milky Way Galaxy.

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)