AS101 J.I. Night Lab #1 Write-up 6/15/07 Observing the Night Sky (or at least trying!) Abstract The first night lab is a jump into putting factual knowledge from class and the homework assignments to practical observations of the night sky. The use of the Celestial Pipes, binoculars, quadrants aid in making observations of the stars apparent to both the aided eye and the naked eye. Even with a bit of trouble from the weather we were able to observe prominent stars, Polaris, Venus, as well as a few constellations. There were also two telescopes that had been trained on celestial objects from the previous open house that night. Overall the lab trains the eye that is new to observing the night sky. Introduction Ancient astronomy takes us back to the concept of all objects in the sky to be in a fixed sphere around the Earth. This is how the movement of the Sun and stars and planets spinning around the sky was originally interpreted. Of course we know now that that is not the right idea. However, the ancient concept of a celestial sphere around the Earth provided an ideal method for navigation and location of your position on the Earth and still to this day provides us with a fairly accurate model for finding your location at any given point on the Earth just by using observations of the stars. By breaking down the celestial sphere into lines of declination and ascension we can easily break down the motions of the stars into an easily readable and predictable map. This lab introduced me to a variety of methods of observing the night sky and certain motions that are critical to understanding the movement of the sky. Procedure Some of the more major observations throughout the night made use of the celestial pipes. These are aligned so that the North-South pipe represents a star's declination and there is a tab at 90 degrees to mark the North celestial pole. Marked off in 10 degree increments this pipe allows you to estimate the declination of any star when you are standing directly in the center of the setup. The second pipe available is on the Southern side of the setup and is the representation of the celestial equator and is marked off in one hour increments, this allows the viewer to estimate the current right ascension of a given star in the sky. The only issue with the setup of the pipes and the nature of the celestial equator in our location is that is only fairly useful in the southern sky because otherwise it is difficult to measure the right ascension of a star in the northern sky using something that is behind you. It makes sense though that this is the case because the stars in the northern sky have less apparent movement as many of them are circumpolar. Using the celestial pipes we located at least three objects in the sky and measured their declination and right ascension both at the beginning of the lab period and at the end of the lab period noting the time for each observation.
The next task was to locate and measure Polaris using quadrants. Quadrants are sticks with string tied to the end aligned with a protractor. When aimed at an object the weighted string settles at a location on the protractor allowing you to measure declination of an object. This we had to try a few different times as it kept quickly coming in and out of cloud cover. The next observation was of constellations. It proved quite difficult through the advancing cloud cover to find complete constellations but we were able to observe and sketch the constellation Bootes, of which Arcturus is the alpha star, and the Big Dipper. We used naked eye observations and binocular aided observations in order to develop a rough sketch of the constellation. The final set of observations comes from the telescopes set up. There were two telescopes trained on two different objects in the sky. One was pointed at the surface of the Moon, and the other on a Gas Cloud somewhere near the local Zenith. I jotted down some observations from these views, and took with me some amazing images in my head. Analysis At the start of lab I was able to get some quadrant readings of Polaris before it was covered up by cloud cover. The first measurements were a bit rushed, I had arrived early for lab and it was a good thing too because if I had just been on time I wouldn't have had as good an opportunity later in the night to get a measurement of Polaris. It did however peek out behind cloud openings to allow others and myself to get a better chance to using the quadrant. I had used that kind of equipment before and knew how to use it. I used to measure the height of model rocket launches using that kind of trigonometry. I had attempted to measure Polaris many times. The general readings that I got were between 48 degrees and 49 degrees. Using Google Maps I got an estimate of latitude and longitude for Boston University on Commonwealth Ave.1 This was approximately 42.35 degrees latitude and 71.1 degrees longitude. So, my measurements were slightly off, it could have been the equipment, it could have been my ability to read the equipment in low light situation, also could have been the scramble to use the quadrant before Polaris dipped in and out of cloud cover. Next I used the celestial pipes to measure the location of stars. There was not a great deal of visible stars available to the naked eye. There in and out of clouds in the northern sky but I only observed two in the more southern sky. This was easier to work with using the pipes. Finding right ascension was more difficult on the stars in the northern sky so I opted to locate stars in the southern sky. I also took observations of the Moon in the celestial pipes. I also noted the time I took the observations. Generally I took a batch at the start of the lab a and batch at the end before leaving. But unfortunately by the time the lab was over most of the sky was covered in clouds and it was difficult to get even a second reading on the Moon. On the attached data sheets are my charts for the measurements taken. My major observations were on the binary star Spica. I was able to get three separate readings from the pipes. Following the idea of the celestial sphere rotating around us proved to be true using the measurements of right ascension lines to show how much time should have passed. My first reading of Spica was at 9:40 where I read Spica at 0hr RA. Then again at 10:08, 28 minutes later, I read Spica at +.6hr RA. Then finally at 10:42, 34 minutes after that, I read Spica at +.5hr RA. The measurements
1
http://tinyurl.com/34ahzu
do not coincide perfectly with the concept of the objects in the celestial sphere spinning around their declination at a rate of 1 hour per every +1hr of RA. The second reading at 10:08 is fairly close to the difference of the original reading. My observation claimed that 36 minutes had passed since the first reading at 0hr RA. My watched said that in fact 28 minutes had passed. This data is fairly close for a naked eye observation using the celestial pipes. The third reading was a bit of a failure there is quite a bit of error in that measurement. This may have been caused by not being exactly on the mark to get the reading. If I had been just a bit off of the mark in the center of the pipes, my reading would be significantly skewed due to the change in viewing angle. My RA readings for Arcturus prove to be similar to my observations of Spica. Sadly, I did not get a chance to get a second reading of the Moon so I can't use the Moon for the RA calculations. The next portion of the lab regarded using binoculars to aid in viewing and sketching constellations. Using the binoculars I was able to get a better look at the stars surrounding some of the major stars out in the sky at the time. Again it was fairly difficult to catch these stars with light pollution problems as well as cloud cover. While I did have a clear section in the sky I was able to sketch the constellation of Botes, the constellation where Arcturus is the brightest star. After later looking up the constellation and viewing the stars that make it up as well as its shape I was able to compare it to my sketch. On my drawing I marked 5 stars that I saw up around Arcturus. Looking up on Wikipedia images of the constellation map there are actually 7 stars that make up the constellation. 2 The ones that I was missing is a lower magnitude of brightness that may have not been visible due to light pollution conditions, this is the in between Arcturus and the triple tip. The last I may have overlooked as I may have thought that Arcturus was the start of the constellation and I might have missed the star at the tail end of the constellation, or it may not have been visible again it is on a lower magnitude. Arcturus was most certainly the brightest star of the system and I neglected to record the magnitudes of the other stars as I had a limited amount of time and visible light to work with in my notebook. The second constellation I mapped was the Big Dipper. It was visible for a good while and I was able again to peer through the binoculars and come up with a sketch of the pattern of stars visible around. The star Mizar was pointed out and identified as the middle star on the handle. My observation mapped the constellation fairly accurately and contained all the stars that make up the constellation. The final quick observation was a peek into the telescopes that had been set up and were left peering at images from the open house previous to our lab. The first was setup at the Moon. I concluded straight away that since much time had passed between the end of the open house and the end of our lab period, when I was looking through the telescope, that the Moon must have originally been focused centered on the Moon. When I looked through the Moon had moved through most of the shot but I was still able to take a peek at the edge of the surface of the Moon. The detail was very crisp and I could make out much of the details of the craters and varying depths of craters based on the shadows cast on them. The shadows were not severe and that was most likely because at the time of the lab the Moon was just past Full Moon phase so the sunlight was almost directly cast on the surface. The most intriguing clarity of the focus through the telescope was being able to make out the ridges of the craters on the very edge of the moon and being able to view those peaks pop out against the night sky. The other telescope had been
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http://en.wikipedia.org/wiki/Bo%C3%B6tes
trained on a very distant gas cloud / nebulae. The image was very small but you could make out distinct bright red, orange, and purple colors from the formation. It was something I had never been able to see in person before. That kind of power in a telescope is something I had never experienced before and it gave me a new outlook on the power that we have for peering into the great distances of space. Conclusion Overall the lab gave me a tiny slice of what it's like to build an understanding of the night sky and the difficulties in using just the naked eye to get accurate data. It is incredible that ancient astronomers were able to get the kind of data that they got without using technologically advanced equipment that we have available today. It helped me understand that it is leaps and bounds between ancient astronomy and the leap to much of the known facts we can compile about the universe with our technology. It has got me really looking at the night sky with a new outlook.