Public Night Sky Observing

Physics & Astronomy Department at Western Washington University

What is the magnification of Western's telescope? This is a tricky question for many reasons. For one thing, the magnification changes depending on what eyepiece we use. For another, greater magnification does not necessarily mean a better view as one might assume. Sometimes, although an object has greater magnification, it can appear very blurry because the light is too spread out. A slightly better question might be what is the angular resolving power of the telescope. One way to consider this question involves considering detail that can be viewed through the scope but is not visible to the naked eye. The scope can bring into focus detail that is about 38 times smaller than the eye can see.

What is the brightest star in the sky? Sirius is the brightest star in the sky, with an apparent magnitude of -1.46. However, Sirius is a Southern star and never climbs much above the horizon in Bellingham. In our skies, Arcturus and Vega shine the brightest. In fact, Vega was chosen by astronomers as the standard against which all other stellar objects are compared. The apparent magnitude of Vega is 0. The magnitude scale is a logarithmic scale that ‘runs backward' with the brightest objects assigned either 0 or negative numbers and fainter objects assigned positive numbers. On average, the human eye can see out to sixth magnitude. Using Western's telescope, it is possible to see objects of magnitude 15 because the scope's mirrors are so much bigger than the pupil of your eye. That is, the scope can show you objects that are about 200 times dimmer than the dimmest objects visible to the naked eye. For comparison, Sirius is a magnitude -1.46, the North Star 3.7 and the Sun is about a -26.

Can we see the Milky Way? The Milky Way Galaxy is the one in which we live and it is all around us. So, in one sense, the Milky Way is most of what we see most of the time. Of course, because we are inside of it, we cannot see it the way we can other galaxies. However, astronomers have techniques that allow them to gather data and piece together a picture of the Milky Way as it would appear to an outside observer. To the naked eye, the disk of the Milky Way is like a murky band of starlight across the night sky. The center lies in the constellation Sagittarius and can be better viewed from the equator or southern hemisphere than in the northern latitudes.

Why do stars twinkle? Do planets twinkle? The light from stars must pass through the earth's turbulent atmosphere (after the journey through interstellar space) to reach our eyes. The churning of the atmosphere refracts this light in many directions, hence the twinkle. Planets do not twinkle the way that stars do. While stars are so far away they are basically point sources, planets have a finite size. This larger size means that the light is hitting your eye from more than one direction. So, while some bit of it may get refracted by the atmosphere, some other bit is likely to hit your eye and you will not notice a twinkle.

How many Stars are in the night sky? This is a tricky one. If you mean how many can we see the answer is that it depends. On a dark night, the average person can see a few thousand stars (about 2,500). If you mean how many stars are visible from the entire Earth, that would be about 8,400. If you mean how many are in the Milky Way Galaxy, the estimate is anywhere from 100 billion – 400 billion. If you mean how many stars are in the universe at large, the math gets even more muddied. One estimate, as of July 2003, puts the number at 70 sextillion stars (7 followed by 22 zeros). That is more stars than there are grains of sand on all of the beaches on Earth.

What paths do the stars and planets trace across the sky? The Earth rotates counter clockwise on its axis, causing the stars and the Sun and the Moon and everything else to appear to rise in the east and set in the west. The apparent path of the Sun across the sky is called the ecliptic. The planets and the moon trace more or less (plus or minus about eight degrees) the same path as the sun as they traverse the sky. This is because the solar system is like a disk with all of the planets rotating about the Sun in the same plane.

Can we see other galaxies with the naked eye? If it is dark enough, the Magellanic clouds, two galaxy companions of the Milky Way, can be seen from the Southern hemisphere. The Andromeda galaxy in the constellation Andromeda can be seen in the Northern Hemisphere. A telescope is necessary to view most other galaxies. Galaxies, unlike stars, are diffuse patches of light difficult to see with the naked eye unless the sky is very dark. So even these three relatively close galaxies can be very difficult to spot.

What is dark matter and how do we know it exists? All matter in the galaxy rotates about the galactic center. Astronomers know from observing rotation in the solar system that the speed of rotation about an object is proportional to both the mass of the object and the distance away from it one is. Because most of the luminous matter in the galaxy is close to the center this means that objects should be rotating slower the farther from this mass that they are. However, this is not the case. In fact, all objects in the galaxy share more or less the same orbital speed. One way to explain this is to theorize some sort of dark matter that we have not yet been able to observe. What is it? Well, no one really knows yet, except that it cannot be like mass as we know it composed of protons, electrons, or any other known particles. Are we the only galaxy with this dark matter problem? No, in fact most observed galaxies are thought to contain dark matter. Is it possible that there is no dark matter? Yes, it's possible. Other explanations include a misunderstanding of gravity or the existence of some as yet unknown force acting on galactic scales to speed up the rotation of the outer galaxy.

Do toilets drain counter clockwise in the Northern hemisphere and clockwise in the Southern due to the Coriolis effect? Nope! The Coriolis effect is due to the earth's rotation on its axis. It causes large scale weather systems like hurricanes to spin clockwise in one hemisphere and counterclockwise in the other as they take on the rotation of the earth beneath them. However, when it comes to the much smaller system of your sink or toilet, the Coriolis force is much too small to make any noticeable difference. Think about it, the earth rotates on its axis only once a day while the water in the sink may rotate once every few seconds. So the Coriolis effect is orders of magnitude smaller than factors like sink design and water pressure. Don't believe me? Check out the sinks in Bond hall and then try the ones in Carver gym.