NAME: DATE: INTRODUCTION This lab exercise introduces the arrangement and motions of the stars, constellations, and other objects of the night sky. LEARNING GOALS Describe the motions of stars during a single night. Describe the stars changing pattern of rise & set times during the year. Use a planisphere or planetarium program to identify bright stars and constellations. Use a star atlas to find an astronomical object using its celestial coordinates. Use a star atlas to find the celestial coordinates of an astronomical object. Southern & Dobson: Investigate the starry sky in the MCC Planetarium. EQUIPMENT scientific calculator planisphere (aka starwheel ) pocket star atlas computer with Starry Night software DAILY MOTIONS OF THE STARRY SKY All celestial objects (the Sun and Moon, stars, planets, the Milky Way, deep sky objects) move across the sky. These motions can be displayed by a physical device such as a starwheel (also known as a planisphere) or on a computer using a planetarium program. A starwheel displays the stars and constellations on a flat, round map with the days of the year printed along the edge of the map. A second panel labeled with the hours of the day is attached on top of the star map. By rotating the two panels relative to one another, you can match a specific date with a specific time. The transparent window of the top panel displays the visible starry sky for a chosen date and time. Brighter stars are indicated by larger dots in the starwheel s map. The constellations are labeled in all-capital letters ( ORION ) while the brighter star names are capitalized ( Rigel ). The edge of the transparent window represents the observer s horizon. The center of the window represents the location directly overhead (90 o from the horizon). The compass directions are labeled along the horizon. The metal pivot of the starwheel represents the point around which the starry sky appears to rotate. This location is known as the North Celestial Pole. 1) What is the name of the star located at the pivot point of the starwheel? Is this point directly overhead for a latitude of 30 o North (Mesa, Arizona)? THE STARRY SKY 1
2) Set a starwheel for 9:00PM tonight. Identify a large, prominent constellation and a bright star that is directly overhead at that date and time. Record both names below. 3) In the circle below, sketch and label 6 large, bright constellations and the bright, named stars within them. Be sure to orient the starwheel to the compass directions shown on the page before you start sketching. Also be careful to draw each constellation with their appropriate relative sizes. NORTH EAST WEST SOUTH THE STARRY SKY 2
4) Set the starwheel for 2:00AM later the same night. Locate the star and constellation you identified in Question 2. In which compass direction have the constellation and star moved since 9:00PM? Does this direction of motion make sense? Explain your reasoning. 5) Set the starwheel for 9:00PM for the date one month from today. Again sketch and label the same 6 constellations and their bright stars you used for Question 3. If a constellation is not visible at that date/time, write the constellation s name along the horizon to show its location. NORTH EAST WEST SOUTH THE STARRY SKY 3
THE ANNUAL CHANGE IN THE STARRY SKY You have now demonstrated that the starry sky changes over the course of a night and over the course of many nights. 6) Compare the sky from tonight (your sketch from Question 3) and the sky visible one month from now (Question 5). In which direction did the constellations and stars appear to shift? Continue to investigate this pattern of motion with the Starry Night computer program. On the astronomy lab computers, Starry Night is available in the Astronomy section of the Start Menu. Once the software begins, check that the viewing location is set to Mesa, Arizona. If Mesa is not set, choose Options, then Viewing Location from the menu. Next, choose Zip/Postal Code and then select United States and enter 85202 as the Zip/Postal Code. Click the Go To Location button. Next, click on the Find tab on the left side of the main window and type Altair in the search box. Click the check box next to Altair and then click the small down arrow to the left of the check box. Click Center. The program may prompt you to set the Best Time to view Altair. A. Click the small down arrow to reveal the menu again. B. Click Generate Ephemerides to display a table of astronomical data sorted by date and time called an ephemeris. C. In the window, set Start to January 1 at 12:00:00 AM and End to December 31 at 11:59:59 PM. D. Choose 1 day as the Time Step and select Local Time, Rises, and Sets from the Show menu on the right. E. Click the Generate Values button at the bottom left to update the ephemeris for Altair. The table now displays the rise and set times for Altair for every day of the year. F. Use the ephemeris to record the Rise Time and Set Time for Altair on the first of each month (Jan 1, Feb 1, Mar 1, etc.) in Table 1 on the next page. G. To fill in the other columns, open the supplementary Excel file available on the lab webpage. Simply change the Rise Time and Set Time shown in red. H. Record the number of hours that the star is above the horizon during the night. Rise and set times must be entered with a space separating the number of minutes and AM or PM. For example, 12:34 PM. For this calculation, night is assumed to start at 6:00 PM and end at 6:00 AM. THE STARRY SKY 4
TABLE 1: Altair Rise and Set Times by Month Date Rise Time Set Time January 1 Hours Up At Night (6:00 PM 6:00 AM) February 1 March 1 April 1 May 1 June 1 July 1 August 1 September 1 October 1 November 1 December 1 7) During which months is Altair in the night sky longest? 8) Compare Altair s rise time on January 1 and January 2. By how much does the rise time change from one day to the next? Does the rise time get earlier or later? 9) Now compare Altair s set times on January 1 and January 2. By how much does the set time change from one day to the next? Does the set time get earlier or later? 10) Imagine you watched Altair rise today and recorded the time. How long would you have to wait to watch Altair rise again at exactly the same time? (Examine Table 1 if you are unsure.) THE STARRY SKY 5
Now collect the same measurements for the brightest star in the night sky Sirius. Then fill in the remaining columns to calculate the hours of nighttime visibility of Sirius during the year. TABLE 2: Sirius Rise and Set Times by Month Date Rise Time Set Time January 1 Hours Up At Night (6:00 PM 6:00 AM) February 1 March 1 April 1 May 1 June 1 July 1 August 1 September 1 October 1 November 1 December 1 11) During which months is Sirius in the night sky longest? 12) Which star (Altair or Sirius) would be considered a star of the summer sky? 13) Which star (Altair or Sirius) would be considered a star of the winter sky? 14) Imagine you watched Sirius rise today and recorded the time. How long would you have to wait to watch Sirius rise again at exactly the same time? (Examine Table 2 if you are unsure.) 15) To summarize: The daily rising and setting of celestial objects is due to Earth s. The seasonal change in the starry sky is due to Earth s. THE STARRY SKY 6
16) Explain why the rise and set times of stars change throughout the year. NAVIGATING THE STARRY SKY A starwheel displays the entire starry sky visible at a specific date and time. In contrast, a star atlas displays pieces of the starry sky in much greater detail. A typical star atlas will include many fainter stars as well as star clusters, nebulas, galaxies, and patches of Milky Way suitable for viewing through binoculars or a telescope. In a sky atlas, a small portion of the starry sky is displayed on a single page. Pages are numbered that reference a map of the entire sky at the atlas back or front. Numbers along page edges indicate which pages show neighboring portions of the starry sky. Turn to Page 14 of a Sky & Telescope Pocket Sky Atlas. This page includes portions of the constellations Auriga, Gemini, Orion, and Taurus labeled in CAPITAL LETTERS. Thin dotted lines marks the boundaries between these constellations. 17) Which constellation fills the lower half of Page 14? 18) Which constellation appears along the top of Page 14? 19) In which constellation is the Crab Nebula (M1), near the center of Page 14? 20) Set a star wheel to NOON on June 15. Rotate the star wheel so that NORTH is pointed up. Which side is the Eastern Horizon on the star wheel? Which side is the Western Horizon on the star wheel? 21) Locate Taurus and Orion on the star wheel. Rotate the star wheel to match the constellation s appearance on the star wheel with their appearance on Page 14-15 of the star atlas. In which direction is the top of Page 14? The bottom? Be careful with the next two questions! In which direction is the left side of Page 14? The right side? THE STARRY SKY 7
22) How are the compass directions on a star atlas chart different from a map of Earth s surface? Plotted along the top of Pages 14 15 are the coordinates of right ascension: 6 h, 5 h, 4 h, 3 h. This coordinate is similar to longitude (east-west) on Earth s surface. 23) Does right ascension increase to the east or to the west? Notice the star cluster called the Pleiades (M45) on Page 15. An enlarged map of the Pleiades is displayed on Chart A near the back of the atlas. On this page (7 th from the back cover), the coordinates are labeled: 3 h 50 m, 3 h 48 m, 3 h 46 m, 3 h 44 m. The h stands for hours and m stands for minutes. Examine how right ascension changes on Page 78-79 of the atlas. 24) How many hours of right ascension sweep by overhead during one day? Plotted along the left side of Page 14 are the coordinates of declination: 0 o, +10 o, +20 o, +30 o. This coordinate is similar to latitude (north-south) on Earth s surface. 25) Does declination increase to the north or to the south? 26) What is the approximate declination of Mintaka, western-most star in Orion s Belt? 27) Turn to Page 16. How are declinations in the southern sky identified? 28) Find the south celestial pole in the star atlas. In which constellation is it? 29) Find the north celestial pole in the star atlas. In which constellation is it? Practice with the starwheel, Starry Night program, and sky atlas by answering the following questions. The back inside cover of the star atlas might be useful. THE STARRY SKY 8
30) What are the right ascension & declination of the Andromeda Galaxy shown on Page 3 of the star atlas? Report right ascension in hours and minutes and declination in degrees. In which constellation is the Andromeda Galaxy? 31) What kind of objects are M32 and M110? (The Chart Legend before Page 1 can help.) 32) Use a star wheel to find the Andromeda Galaxy (M31). In which 3 months would this object be seen high overhead at midnight? 33) Try a little treasure hunt: What is the name of the very bright star at right ascension 18 h 37 m and declination +39 o? In which constellation is this bright star located? 34) Use a star wheel to find this bright star. In which 3 months would this star be seen high overhead at midnight? 35) Use the Find function in Starry Night to find the Moon at midnight tonight. In which constellation is the Moon? Is the Moon visible in the sky at midnight tonight? If it is visible, where should you look to see it (compass direction and height above the horizon)? SOUTHERN & DOBSON: OBSERVING THE STARRY SKY IN THE PLANETARIUM Set a starwheel for 9PM on the date given by your instructor. Have a seat in the Planetarium. Find a few bright stars and prominent constellations in the part of the sky shown on the star wheel. Then try to locate those same stars and constellations on the planetarium dome. A few things to remember: The sky in the planetarium is oriented with south in front of you and north behind you. Hold the starwheel upside down above you and look up at the starwheel and the dome. Rotate the starwheel so north on the starwheel matches north on the dome (backward). THE STARRY SKY 9
I. There is a star located at the pivot of the star wheel (see Question 1). Where is this star on the planetarium dome? Describe its position and height on the dome. II. Use a starwheel to identify five of the brightest stars visible on the planetarium dome. Next, identify the constellations in which each of these stars is located. Finally, identify the compass direction and height above the horizon you should look to see each star in the sky. Record your findings below. For example, you might find the star Appletrix in the east and close to the horizon. Or you might find star Zipperooni in the northwest and high above the horizon. Star Constellation Direction in sky Practice with a starwheel until you can identify several other bright stars and constellations visible on the planetarium dome. Throughout the semester go outside and practice! Use a starwheel, a planetarium program, an astronomy magazine, or other resource to help you. Recognizing the stars and constellations takes practice, but it s a lot of fun and it s easy to do! You will be given time during lab periods throughout the semester to practice. Make use of this time. At the end of the semester, you will be given a Constellation Quiz to test your knowledge. A series of bright stars, prominent constellations, and bright planets will be displayed for you in the planetarium. You will be asked to identify 20 of them. The Constellation Quiz will also include 5 short-answer questions about the night-time sky. To help you study, your instructor will provide a handout of objects that will appear on the Quiz. If you have questions about the Constellation Quiz, be sure to ask your instructor! It is an important part of your astronomy lab grade. THE STARRY SKY 10