Observations 4.2

Astronomy Cast

Episode 34 Discovering Another Earth
Astronomers have found three planets orbiting the red dwarf star Gliese 581. The smallest is roughly Earth size, with a radius of about 1.5 Earth radii, but it has more mass. Its gravitational acceleration is greater than Earth’s. It is a rocky planet, and it is the proper distance from Gliese for water to be liquid; it may actually be covered in oceans. It was detected by measuring changes in Gliese’s radial velocity caused by its satellites. The European Space Agency is currently planning to launch three 3m telescopes in a few years that would greatly help in terrestrial planet finding.

Episode 111 Nebulae
Giant molecular clouds are huge clouds of dust and gas that are cool and dark. They absorb light and block part of the sky from view. When light from another object passes through such a cloud, it scatters off particles and we see a Reflection Nebula. When there are bright objects inside the cloud, the gas may heat up and an Emission Nebula is seen. Our perspective determines whether we see absorption or emission lines from a star whose light passes through a cloud. Various causes can lead to the collapse of clouds; when they condense, stars are formed. Planetary nebula are created when a star dies and releases its material.

Episode 3 Hot Jupiters and Pulsar Planets
Our previous theoretical models of solar systems in general have proven inaccurate. Strange types of planets and systems have been discovered that we cannot explain. Astronomers have found large, gaseous planets like Jupiter, but very close to their parent stars, and orbiting incredibly quickly. It is strange that such planets can exist so close to stars, where the gas should evaporate, leaving rocky planets to be formed. Astronomers have also found at least two planets with the density of cork; in order to have such low densities, they are probably generating large amounts of heat, which is a process we can’t explain. It has been theorized that lone planets not orbiting a star were ejected from star systems, but a pair of apparently ejected planets have been found, barely bound together gravitationally. It is unlikely that they could have been ejected but still remain gravitationally bound, since the attraction is so small.

Episode 26 The Largest Structures in the Universe
Interactions between galaxies are common. The Magellanic Clouds may be being distorted by the Milky Way, or they could be being ripped apart by it. The impending collision with the Andromeda Galaxy is the next major interaction that the Milky Way will undergo; it will drastically alter both galaxies. Most stars won’t actually collide with each other, but their orbits and the structures of each galaxy will be transformed. New generations of stars will form, and the two supermassive black holes will eventually merge. The result will likely be an elliptical galaxy, which astronomers theorize is how elliptical galaxies usually form. Galaxies tend to be found in groups; galaxy clusters trace out the large-scale structure of the universe, which may be described as sponge-like.

Episode 76 Lagrange Points
Lagrange points are points between objects where the gravitational forces exactly balance. They are useful places for man-made satellites. Spacecraft at Lagrange points have their own engines making constant corrections in order to stay in place. There are five useful Lagrange points relating to the Sun and Earth: L1, L2, L3, L4, and L5. L1 is between them, but closer to Earth. Sun-observing objects are placed at L1; they have the same orbital period as Earth. L2 is beyond Earth, but objects there would still orbit the Sun. L3 is on the opposite side of the Sun as Earth; there are not any spacecraft there. L4 and L5 are in Earth’s orbit, but behind or ahead of Earth. They are the most stable points.