Star Points for August, 2004; by Curtis Roelle Will it Be Clear Tonight? Observational amateur astronomy is a fair weather hobby. A telescope will not catch starlight in the rain. When planning an observing session one must pay attention to the forecast for the location the observing will be taking place. Weather reports are often ambiguous or misleading. A D.J. on the radio might report clear skies outside. Poking your head out you'll find that while the sun is shining, the sky isn't blue. Instead it's milky white and hazy due to humidity and possibly smog. It may be sunny out, but the sky is anything but clear. At night the weather man says, "clear skies outside." Rush out with your telescope you see the moon and high overhead only a couple of stars. What's wrong? The haze is having a debilitating effect on the transparency of the atmosphere. In addition, unshielded and misdirected outdoor light fixtures are spewing waste light into the sky. The haze is scattering the light and turning the sky orangish-grey instead of black making even fewer stars visible. So, how do you evaluate astronomical observing conditions and where can you obtain a timely and accurate forecast? In a nutshell, here are four primary sky factors given in no particular order: (1) cloud cover, (2) transparency, (3) steadiness or "seeing" and (4) light pollution effects. There are additional factors but they usually manifest themselves in the four given above. For example, humidity can increase cloud cover, improve seeing, and degrade transparency. Now, let's take a brief look at each. CLOUDS. This is the factor that most people are familiar with. Simply put, the thicker the clouds, the fewer stars that will be seen from the ground. Planets and a few stars may still be visible through thin clouds. However, faint telescopic objects such as galaxies and nebulae won't be seen. TRANSPARENCY. The clarity of the atmosphere between the observer and space. High humidity reduces transparency, and low humidity provides transparent star-studded skies. Measured by noting the magnitude (i.e. brightness) of the faintest stars visible to the unaided eye. Stars near the horizon are harder to see because you're peering through more atmosphere than when looking at stars straight up where the atmosphere is thinner. Thus, transparency is sometimes measured using stars overhead near the "zenith." But the stars overhead move during the night as Earth rotates causing them to rise and set. So instead stars near Polaris (a.k.a. the North Star) are used because they remain roughly at the same altitude above the horizon at all times. Transparent skies are important when seeking faint and fuzzy objects such as star clusters, nebulae, and galaxies. SEEING: The "steadiness" of the atmosphere. Twinkling stars is an indication of poor seeing. Churning cells of air and atmospheric turbulence causes stellar point light sources to scintillate and flicker. There are both objective and subjective methods for measuring seeing. An example of the latter is the Antoniadi Scale. A ranking of 1 means images are "perfectly steady without a quiver" whereas 5 indicates very bad seeing. Good seeing is important for viewing details such as surface features of planets, the moon, and on the sun. Next month we will continue the discussion on assessing observing conditions and learn about a scale for measuring light pollution. Now, we wrap up with some final bits. With the recent passage of the 35th anniversary of the first manned lunar landing in 1969 it is time to bring you up to date on plans by other nations who hope to someday come in second place. In May, Reuters reported that China had shelved its plan to put astronauts on the moon choosing instead to focus on building a manned space station in Earth orbit by 2020. The change in plans was being blamed on "financial reasons." But last month the BBC reported a flip-flop saying China announced plans for both building a space station and going to the moon starting with an unmanned lunar orbit mission as early as 2007. Seems China is anxious throw something at the moon before the 2008 Olympic games in Beijing. Meanwhile the U.S. is still contemplating its return to space even as the shuttle fleet remains grounded. Apollo 11 astronaut Michael Collins recently told CNN "Mars is the next logical step." In June I attended a lecture by John Glenn. Although he expressed disappointment that President Bush plans to scale back support for the International Space Station (ISS), Glenn said that it was up to NASA to remain focused and carry out the President's goal of returning men to the moon and pressing onward to Mars. The Perseid meteor shower peaks on the night of August 11-12. The next planetarium program and public star Party at Bear Branch Nature Center north of Westminster is scheduled for Saturday, August 21.