In this first part of the project, you will be doing some observations of the constellation you have chosen. You'll find out what is located in your constellation aside from the pattern of stars you may be accustomed to associating with the constellation. You'll also see how its change in position during the year can be used to determine the length of the year.
Note: as you follow these instructions, please fill in your answers on the answer sheet.
Before opening Stellarium, make sure your computer's time zone is set to Central Time for the US and Canada.
| Windows users: Newer computers have 64-bit processors, but you can check using instructions found here. |
| Mac users: If your computer isn’t letting you install third-party software, please consult these instructions. |
The shortcuts given the first lab can also be in the PDF found here. You may have to hold "Function" with some of these keys. http://natsci.parkland.edu/ast/101/shortcuts2.pdf
Open the Configuration window and select the Information tab. Check only the following boxes in the "Displayed fields": Name, Catalog number(s), Altitude/Azimuth, Distance, Type, and Additional Information. Close the Configuration window.
Make sure your location is set to Champaign or Urbana. Remove the atmosphere and the ground, and turn on the azimuthal grid, the meridian, and constellation boundaries and labels. Find your constellation, either by scrolling around the sky and changing the time as necessary or by opening the search window.
In order to proceed, it is important to know what it is we are talking about.
1) Consult the textbook for the definition of the terms "constellation" and "asterism". Describe the difference between the terms in your own words.
Within every constellation is an enormous number of stars. Clearly, I can't expect you to analyze them all for this project. I've compiled a list of stars that you need to consider for your constellation. That list was linked from the main project page, but you can also access it here.
Note that several stars have Greek letters in their names. This is because the brightest stars have a Bayer designation listing their relative brightness in a constellation. For example, Antares is the brightest star in Scorpius, so its Bayer designation is alpha Scorpii or α Sco. Check here for a description of the Greek alphabet.
2) Fill in the table on the answer sheet with the list of the ten stars that you will need to analyze in your constellation. Write out each Greek letter in Latin script, e.g. "alpha" instead of ?. Check each star on Stellarium to see if it has a common name listed above the Bayer designation. If the star has a common name, write it in the "Common name" column.
You will now find the time when the constellation is most visible roughly an hour after sunset. Use the settings described at the beginning of this assignment. When the constellation is centered on the meridian your constellation is at the highest point in the sky. (Make sure the altitude is positive. For circumpolar constellations, make sure the stars are above Polaris.)
Change the time so the stars in your constellation appear to be centered on the meridian.
Change the date by sidereal days (Alt+= or Alt+-) until the time is in the evening.
Move the sky to the western horizon, turn off the ground and turn on the azimuthal grid. Adjust the time until the Sun has roughly a -10° altitude.
3) Use the procedure above to find the month of the year and the time that your constellation is the highest in the sky an hour after sunset.
A large portion of the stars in the night sky are in systems containing two (binary) or more (multiple) stars. Stellarium will usually tell you if a star is actually a multiple star system. Select each star in the list you used earlier and see if the type says "star", "double star", "eclipsing binary system", etc. If the type is "variable" or "pulsating", that doesn't mean there are multiple stars, so don't include them.
4) List which of the ten stars you are analyzing in your constellation which are in double, binary, or multiple star systems.
Okay, now it is time to consider what else resides within the boundaries of your constellation. In the late 1700s, a French comet hunter by the name of Charles Messier was becoming frustrated in his efforts to find comets. Comets are balls of rock and ice that are normally found in the outer reaches of our solar system. Some of them will dip in close to the sun and when they do, parts of the comet will be melted. The net result is the comet will develop a cloud of gas and dust around its central core (the nucleus) and the solar wind will interact with its icy and dusty components to produce tails. When observed in the night sky, the comet will be a fuzzy object, which makes it distinguishable from the planets and stars.
However, we know that there are many "cloudy" objects in the night sky, many of which are now called nebulae, others which are now called star clusters, and even others which are now called galaxies. In searching for comets, Messier invariably came upon these fuzzy objects. To ensure that he didn't mistake one for a comet, he began to make a catalog of all of these fuzzy objects that he could see with his telescope. For him, it was a list of objects to avoid since he was interested in looking for comets. Today, the Messier Catalog is a set of objects visible through a modest sized telescope and is heavily prized by amateur astronomers worldwide.
In Stellarium, many deep-sky objects including the Messier objects will be displayed by typing "N" or clicking the spiral-shaped button on the bottom menu. The Messier objects will be classified with "M" and a number. However, this can include dozens of objects in some cases. Please consult this list of Messier objects to find which of them are in your constellation. I recommend searching through the list using "F3" or "Ctrl-F".
5) List two deep-sky objects which are located within the boundaries of your constellation. They can be star clusters, nebulae, or galaxies, but try to pick two different types of objects. I recommend using Messier objects, but if your constellation has fewer than two of them, please look for them on Stellarium. You can also find them on the Astronomy Picture of the Day website or you can consult a list of objects in each constellation on this website.
6) Find one of the deep-sky objects from the previous question in Stellarium. If you can't find it, use the search window. Zoom in on the object. Write down the common name (if it has one) and describe the object as you see it on the screen. If it doesn't look any different from the surroundings, the image didn't display correctly. In that case, please find an image of the object on the internet. and cite the source.
7) Write the object type of the deep-sky object in the previous question. The type is listed below the name on the upper left or by checking the Messier list. "Galaxy" is not specific enough; state what type of galaxy it is, such a spiral, elliptical, irregular, interacting, lenticular, active, or radio galaxy. Go into your textbook or search online and write a 2–3 sentence description of this class of object (e.g. if your object is a spiral galaxy, define what a spiral galaxy is). Do not copy your definitions verbatim from your source. Define it in your own words.
8) Find the other deep-sky object from question #5 in Stellarium. Center on it and magnify it. Write down the common name (if it has one) and describe the object as you see it on the screen. Again, please find an image of the object on the internet if it didn't display correctly and cite the source.
9) Write the object type of the deep-sky object in the previous question. If it is a different type of object than the first one, write a 2–3 sentence description of this class of objects.
Now, we know that stars will rise earlier with each passing night. That is the reason there are some constellations we see at night during the summer months and some we see at night during the winter months. We expect that over the course of a year, the stars will make one complete circle around the sky and will return to their original position. If we were to make careful measurements of the rise or set times of the stars day after day, we could use this information to determine the length of the year. We'll finish part 1 of the project by performing such a calculation.
Begin by choosing one of the stars in your constellation. Please write the name of the star in the table at #10 of the answer sheet. Select that star in Stellarium and center on it. Make sure you adjusted the settings as described at the beginning of the assignment. This allows you to have access to the whole sky and you don't need to worry about your star going below the horizon. Set the date to 5/23 (May 23) of the current year.
The altitude of the star will tell us the rise time for the star. Adjust the time until the altitude is 0° and the azimuth is between 0° and 180°. (If the azimuth is greater than 180°, you found the set time instead.) You can do that using the Rewind, Play, and Fast Forward buttons, but the keyboard shortcuts are much better for this. I also recommend changing the time by an hour as you did in the first lab. If you chose a circumpolar star, it will not rise or set. Find a time when it crosses the meridian, i.e. when the azimuth is 0°. Record the rise time as the first entry in the table on the answer sheet (Make sure the date is still 5/23).
Advance time by seven sidereal days by typing Alt+"=". Note that the time has changed, but the positions of the stars relative to the horizon have not. Record the rise time of the star for 5/30. In some cases, the rise time will move from after midnight until before midnight. You have moved seven sidereal days ahead, but not seven calendar days, so you would record the rise time on 5/29 instead of 5/30.
10) Repeat the procedure from the last paragraph until you have filled in this table on the answer sheet.
Next, we'll need to find the change in the rise times. You'll find that the change in rise time over the seven-day period is less than one hour, so we won't include an "hours" column. While working through your calculations, remember that there are 60 minutes in an hour and 60 seconds in a minute.
To make your life easier, you can do the change in rise time calculation using the Javascript calculator included below. Note the format required for the calculator: two digits each for hours, minutes, and seconds. It may prompt you about using 12-hour time (AM/PM) or 24-hour time. Press Cancel to use 24-hour time. The calculator may tell you that your rise time values are incorrect, so it helps you check your work.
Once you have your change in rise time in minutes and seconds, convert the seconds to decimal minutes by taking (number of seconds) ÷ 60 + (number of minutes). For example, if the change in rise time is 25 minutes, 47 seconds, the change in rise time in decimal minutes is 47 ÷ 60 + 25 = 25.78 minutes. It is fine to round your answers to two decimal places in your calculations. Record these values in the second to last column of the table.
In the last column in the table on the answer sheet, you need to find the change in rise time per day. You already found the change in rise time in decimal minutes and we know that our time step was seven days, so divide the change in rise times in decimal minutes by seven to get your answer. In our example above, we found that the change in rise time was 25.78 minutes. Therefore, the change in rise time per day is 25.78 minutes ÷ 7 days = 3.68 minutes/day.
11) Follow the above procedure to complete the table.
Calculate the average change in rise time per day. Since you have four values for the change in rise time per day, add the four values together and divide the sum by 4. For example, let's say that we found that the changes in rise time per day were 3.16, 4.02, 2.78, and 3.74. The average would be (3.16 + 4.02 + 2.78 + 3.74) ÷ 4 = 13.7 ÷ 4 = 3.43 minutes/day.
12) Average change in rise time per day: ____________________
We know that the change in rise time per day should add up to one circle around the sky (24 hours) as one year goes by. There are 1,440 minutes per day. Therefore, taking 1,440 and dividing it by your average change in rise time per day will give you the number of days in one year. To complete our example: 1,440 minutes ÷ 3.43 minutes/day = 419.83 days in a year.
13) Calculated number of days in a year: ___________________
Obviously, the values that I chose were not the best for this part of the project, since a year has 365.2422 days. Calculate a percent error for the year length you determined using the following equation. Note: subtract before dividing, and the vertical bars mean you calculate the absolute value by dropping any negative signs.
14) Calculated percent error: ___________________
If your error is more than 2%, please check your work. Please let me know if you can't find where you made a mistake.
15) Evaluate the method you used to obtain the length of the year. What are some possible sources of error in the method? Do you think it was a good method or a poor method? Briefly explain your opinion.
You can find a complete and more accurate example by clicking here.