APOD 2.1

Enceladus Ice GeysersThe Cassini discovered this very thin atmosphere. Ionized vapor on Enceladus is the main component and these ice geysers are found in the south pole. This gives the idea what Enceladus is supplying the particles of Saturn's e-ring. I only wish I could be able to work with these kinds of things. They are so fascinating.

James Bradley Report

James Bradley was an astronomer born at Gloucestershire in March of 1963. He was most famously known for his discovery of the aberration of light. The aberration of light is known as an astronomical phenomenon which produces an apparent motion of celestial objects such as stars and planets. Bradley decided the cause was from the finite speed of light and the motion of the Earth around the Sun. The true position of an object depends on the velocity of the observer. The velocity will vary for people on Earth though seeing as the rotation of the Earth around the Sun will affect the velocity at which a celestial object is seen.

The maximum amount of the aberrational displacement of a star is approximately twenty arc seconds in right ascension or declination. People often confuse aberration with stellar parallax. The parallax is determined based on the distance between the observer and the object being observed. With stellar aberration, however, the distance really has nothing to do with what is being observed. It only depends on the observer's velocity with respect to the incoming light beam at that particular point in time. The beam of light must basically shoot straight at the observer for it to be seen and have no transverse velocity otherwise the light beam would never be seen. Light-time correction is another term that is mixed up with aberration. This is actually due to the motion of an observed object. It depends on velocity and the distance of the emitting object. Light-time correction has absolutely no relation to the motion of the Earth with respect to the Sun.

With the help of Samuel Molyneux, Bradley discovered this apparent motion of the stars. Molyneux had noted no change in position to a particular star which was being observed. When Bradley started to observe it, however, he noticed the slight change in position of the star. They thought at first that maybe the telescope had made an error, but there were no apparent problems with it. Bradley and his colleague observed the motion of the star for the next year and attempted to explain it. They figured that the motion was not due to parallax and it was not due to observational errors. The two worked out several different explanations for what might have gone wrong or in hopes of finding out what was really going on. The first idea thrown out was that the star's declination varied because of short-term changes in the orientation of the Earth's axis relative to the celestial sphere. Because this is a change to the observer's frame of reference, it would therefore affect all star equally.

Bradley made his own telescope a year or so into the study. This telescope had the advantage of a larger field of view and he was able to obtain precise positions of a large number of stars that transited close to the zenith over the course of about two years. Due to the observations that Bradley was able to make, he was able to formulate a set of rules that would allow the calculation of the effect of any given star at any specified date. No one really knows if Bradley really ever discovered a true reasoning for the cause of aberration. A few years before he died, Bradley discovered the existence of the nutation of the Earth's axis which he has originally believed was the cause of aberration but he had nothing to support his beliefs at that point in time.

APOD 1.7

Aurora, Stars, Meteor, Lake, Alaska

This is such a cool picture and is one of the many reasons why I would love to travel to Alaska or anywhere else where auroras can be seen. I also think that being able to study these when I go off to college or something would be pretty interesting. The variety of colors that auroras can be is amazing. They just look so not real in pictures and I think it would be cooler to be able to witness this amazing event in person.

APOD 1.6

Starburst Cluster in NGC 3603 I was thinking how amazing it must be to be able to travel up into space and be able to see this by looking out the window from some space aircraft. Stars are amazing to me in general and are always really fun to look at when going outside and just laying on the ground staring up at the sky. Just to think that millions of stars are formed every day is amazing. To be able to see them this in depth though would be even cooler.