Highlights of the Universe ASTR 111 – 003 Fall 2007 Lecture 02 Sep. 10, 2007 Highlights of the Universe This week’s highlight Tonight’s sky chart from Starry Night

Astronomy Picture of the Day (2007 Sep. 10) Building Galaxies in the Early Universe Credit: NASA, ESA, and N. Pirzkal (STScI/ESA) et al. Explanation: What was the very early universe like? To help find out, astronomers pointed the Hubble Space Telescope between bright nearby objects to create one of the deepest images ever -- the Hubble Ultra Deep Field (HUDF). The resulting HUDF is like a jewel box of strange and distant galaxies. A recent analysis of the HUDF focused on the smallest, faintest and most compact galaxies imaged. These small galaxies are thought to be the building blocks of modern galaxies. Analysis shows that these small galaxies are indeed themselves frequently merging to form large galaxies. An image of this field with the Spitzer Space Telescope shows a lack of infrared emission that would be expected from old stars, indicating that these small galaxies are very young, possibly only a few million years old. Therefore the young blue stars might be members of the first-ever generation of stars. Part of the HUDF is shown above, while one blue building-block galaxy, highly redshifted by the universe so as to appear more yellow, is shown in the upper left inset.

Astronomy Picture of the Day (2007 Sep. 2) Lunation Credit & Copyright: António Cidadão Explanation: Our Moon's appearance changes nightly. This time-lapse sequence shows what our Moon looks like during a lunation, a complete lunar cycle. As the Moon orbits the Earth, the half illuminated by the Sun first becomes increasingly visible, then decreasingly visible. The Moon always keeps the same face toward the Earth. The Moon's apparent size changes slightly, though, and a slight wobble called a libration is discernable as it progresses along its elliptical orbit. During the cycle, sunlight reflects from the Moon at different angles, and so illuminates different features differently. A full lunation takes about 29.5 days, just under a month (moon-th). Click on the picture to view the animated gif file.

Advanced Question Chap. 1, Q37 in P18 Suppose your telescope can give you a clear view of objects and features that subtend angles of at least 2 arcsec. What is the diameter in kilometers of the smallest craters you can see on the Moon?

Advanced Question Chap. 1, Q37 in P18 Answer: Using small angle formula: D = α d /206,265 α = 2 arcsec d = 384,400 km  D = 3.7 km This is the linear resolution of the telescope at the distance. The size of the smallest craters that can be seen is about 3.7 km