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.

APOD 4.8

Rho Ophiuchi Wide Field
http://antwrp.gsfc.nasa.gov/apod/ap100524.html

Rho Ophiuchi is a binary star system in Ophiuchus, but it has a nearby cloud complex that is one of closest star-forming regions to us. Antares and the globular cluster M4 are visible in this picture, along with the notable red emission nebula and Blue Horsehead Nebula. To the top-left is Sharpless 1, yet another reflection nebula. Throughout the image are dark dust lanes.

APOD 4.7

Panorama of the Whale Galaxy
http://antwrp.gsfc.nasa.gov/apod/ap100517.html

NGC 4631, also known as the Whale Galaxy, is a large spiral galaxy that is seen edge-on from our perspective. This pictures shows the high diameter-to-height ratio characteristic of spiral galaxies. It is similar to the Milky Way in size. The Whale Galaxy is seen in the direction of Canes Venatici and is about 30 million light years away. The blue stars are evidence of star formation; also notable in this picture are the dark streaks of instellar dust clouds.

APOD 4.6

Iguaçu Starry Night
http://apod.nasa.gov/apod/ap100514.html

This is a picture of the night sky taken on May 4 near the Iguaçu Falls and National Park in Argentina. Many prominent objects are visible in this picture. The brightest star in the sky, Sirius, is to the right of the photo. It has an apparent magnitude of 1.46 and is 8.6 light years from Earth. Canopus, the second brightest star, is to the left of Sirius. Its apparent magnitude is -.72, and it is located about 310 light years away. The Large and Small Magellanic Clouds are to the left of Canopus. They are irregular dwarf galaxies that orbit the Milky Way. Alpha Centauri and Beta Centauri are above the Magellanic Clouds in the picture. Alpha Centauri is a binary star with a red dwarf companion, Proxima Centauri, which is the closest star to the Sun at 4.2 light years away.

APOD 4.5

Northern and Southern Owls
http://apod.nasa.gov/apod/ap100506.html

This is a comparison between two planetary nebulae, M97, called the Owl Nebula, and PLN283+25.1, also called the Southern Owl Nebula. M97 is in Ursa Major and PLN 283+25.1 is in Hydra. These nebulae are approximately the same size (two light-years in diameter), and have a similar round shape. The Owl Nebula was discovered in 1781 and received its name because it appears to have owl-like eyes that are visible when viewed through a telescope. Planetary nebulae form when a Sun-sized star exhausts its nuclear fuel, expands, and eventually releases gas and plasma in an expanding shell.

Interacting Galaxies

http://upload.wikimedia.org/wikipedia/commons/8/81/Whirlpool_%28M51%29.jpg
http://upload.wikimedia.org/wikipedia/commons/d/db/NGC4676.jpg
http://imgsrc.hubblesite.org/hu/db/images/hs-2008-37-a-large_web.jpg
http://maludan.3dtoast.com/outerspaced/NGC%201531,%201532%20Interacting%20Galaxies.jpg
http://www.cartachronicles.com/uploads/Interacting_Galaxies_Group_Arp_194_800__x_600.jpg
http://www.daviddarling.info/images/interacting_spiral_galaxies.jpg
http://www.sciencecodex.com/files/sciencecodex-ed6v2QEeT0lv1EqD.jpg
http://imgsrc.hubblesite.org/hu/db/images/hs-2010-08-a-web.jpg
http://www.astro.uni-bonn.de/~maltmann/stephan4.gif
http://geology.com/nasa/galaxy-collisions/galaxy-eso-593-8.jpg
http://geology.com/nasa/galaxy-collisions/galaxy-ngc-5754.jpg
http://images.astronet.ru/pubd/2004/03/25/0001197280/ngc1531_keel.gif
http://www.nasa.gov/images/content/166908main_galex-20070110-516.jpg
http://www.starteachastronomy.com/pictures/galaxies_collide.jpg
http://www.astr.ua.edu/gifimages/ngc6621hst.jpg