2-Stars and Constellations

STARS & CONSTELLATIONS Objectives 1. Recognize the names and shapes of a few major constellations 2. Recognize the names of some of the brightest stars visible from the northern hemisphere and the constellations in which they lie. 3. Use star maps to identify stars and constellations and determine when they will be visible. Equipment 1. The star maps located at the back of the textbook 2. Stellarium – available on the computers in the physics lab a. Free download. To access this do the following: b. Go to http://www.stellarium.org c. Click on the correct operating system to down load the correct version for your computer. d. The host site Sourceforge.net will send you to another site. Download latest version of Stellarium. e. Once the file has downloaded, RUN the file to complete the installation. Follow the onscreen instructions. Introduction The sky is studded with stars of different brightness and stars of different colors. As ancient people looked at the night sky they noticed how this inverted hemisphere seemed to move. They recognized how certain stars were visible in all seasons while others were seen only at definite times. They related the celestial happenings with events on earth, like flooding of the river or the onset of winter. To entertain themselves they wove stories around the strange shapes they saw in the sky. Some stars were so bright, they gave them their own names, and some names have passed through many different civilizations, and are still in use. It was natural for the ancient people to weave stories around the stars, relating neighboring shapes, depicting cultural traditions and morals. Each civilization has its interesting star tales, and you may want to read some of them as you get familiar with the stars. It is easily noticed that stars do not move in a random manner. A group of stars seems to form a family and move together. This group of stars is called a constellation. It was natural to relate the constellation shape and name to some easily recognizable pattern. The ancient constellations are named after mythical heroes and heroines, animals and birds. Constellations in the southern hemisphere, which were recorded after it was possible to travel vast distances by sea, have been given names that reflect the technology of the times like a compass and an hourglass. In 1928 the International Astronomical Union divided the celestial sphere into 88 regions and named each region after the prominent constellation in it. In many cases the constellation boundaries were drawn to fit the available well-known constellations. Therefore, today when we talk of "Orion", we mean the easily recognizable star pattern that you can see and also the region surrounding this constellation. The brightest stars have distinctive proper names . (Some authors use the term common name). Many of the proper names in use today are of Arabic origin and signify some descriptive term for the star or its position in the constellation. Since there are many stars without proper names, astronomers have developed different methods to name stars. The Bayer system, formulated in the early 1600's, uses Greek letters with the constellation name. The first letter of the Greek alphabet, alpha (α), is used for the brightest star, beta (β) for the next brightest and so on. For example, the brightest star in Scorpius has a proper name Antares, and its Bayer name is α-Scorpii (star belonging to Scorpius). The abbreviation for this is Sco. The path of the Sun in the sky is called the ecliptic, and the constellations that lie along the ecliptic form the zodiac. Since stars are visible only from the night-time hemisphere of Earth, as Earth revolves around the Sun, its night-time hemisphere faces different sections of the celestial sphere, allowing us to see different constellations through the year. From our perspective on Earth, the Sun comes up over the eastern horizon every morning, called sunrise. Stars also rise and set, but their rising time and position depends on the date and location of the viewer. Astronomers are now adept at making star maps, which allow us to easily find and follow constellations for any date, time, and location. Star maps are printed in a circle, with the center representing the “zenith”. Since we see the 1 9/9/2015

sky as a 3-dimensional hemisphere, but print the star map on 2-dimensional paper, we have to hold the map above our head and bend it like a cap to visualize the 3-dimensional sky. These ideas will become clear as you do this lab. LAB EXERCISE IMPORTANT ! The steps you must do are in alphabetic order (A, B, C…). Questions to answer are in numeric order (1, 2, 3…). A. Your textbook has star charts in the appendix (Backmatter) at the end of the book. Take a few minutes to look at them. On the Jan – March map do you see Orion and Canis Major? On the July – Sept map find Scorpius and Sagittarius. B. Let’s learn to read these maps. If you hold the star map right side up, you can see N (north) at the top of the page and S (south) at the bottom of the page. To use the circular star maps you must ALWAYS HOLD THE PAGE SO THAT THE DIRECTION YOU ARE FACING IS AT THE BOTTOM OF THE PAGE. This means, you should face south while holding the page right side up. In this position you will be able to see the constellation Scorpius, close to the southern horizon on the July – Sept star map. If you face north, you must turn the page upside down, and the visible constellations will be Ursa Major, Ursa Minor, Cepheus and Cassiopeia. If you face west, turn the map so W is at the bottom, and Virgo, Coma Bernices and Bootes will be seen. The constellations in the middle of the map, like Lyra, will be visible at the zenith (overhead) on the map date. 1. Locate Scorpius, Sagittarius, and Capricornus on the July – Sept star map. Which direction will you face to see Capricornus? a. South b. East c. Southeast d. West C. On the star maps, the constellation names are in upper case letters and bright stars that have proper names are printed in lower case letters. On the July – Sept star map, look for the stars marked Deneb, Vega and Altair. These stars lie in the constellations Cygnus, Lyra and Aquila respectively. If you connect these stars, you can see the “summer triangle” they form. 2. Which star, Deneb, Vega or Altair will be closest to the zenith (almost overhead) at the time noted on the July – Sept star map? a. Deneb b. Vega c. Altair d. They will all be overhead. 3. Look at the summer triangle on the Oct – Dec star map. What do you notice compared to the July – Sept star map? Write at least one complete sentence. Due to Earth's rotation and revolution around the sun, the stars in the night sky appear to move across the sky over the course of the year. As a result, the position of the Summer Triangle in the sky will shift over the course of the year, appearing to move lower towards the western horizon as autumn turns into winter. 2 9/9/2015

J. Go to DATE & TIME (2 nd icon from the top). Enter the date as September 1 of the current year and the time as 10 pm (22:00:00). Close the window by clicking the “X” in the upper right corner. Notice the time is continuing to increase as seconds are ticking along. To stop the time, type 7 on your keyboard. To start the time, type L on your keyboard. To make time go faster you can type L repeatedly; to make it go backwards type J; to return to normal rate type K. Type 7 again to stop the time, and ensure it is still 22 hours on Sept 1. K. Some of the following features may not be available on your version of the software, do not worry it would not affect your lab work and you would not lose any points on the lab. Click on the SKY AND VIEWING OPTIONS icon (3 rd from the top) which allows you to set the details in the sky. At the top of the window click on the SKY tab. The following items should have a check mark in the box next to them: SHOW PLANETS, SHOW PLANET MARKERS, SHOW ATMOSPHERE, SHOOTING STARS RATE 10. Click on the MARKINGS tab at the top of the window. Make sure that CARDINAL POINTS, SHOW LINES, SHOW LABELS, and SHOW BOUNDARIES are checked. Click on the LANDSCAPE tab at the top of the window and choose OCEAN. Close the window by clicking on the “X” in the upper right corner. L. You are now ready to look at the screen! It shows the view from Dallas facing south (there should be an S on the horizon line). You can read some of the star names on the screen. M. The two left most icons on the bottom of the screen toggle on and off to show or hide the lines “connecting the dots” and the constellation names. Do you see some familiar patterns? Constellation Art (3 rd icon from the left) allows you to view pictures superimposed on the constellations. It is preferable to keep Constellation Art turned off while answering questions, but you can turn it on every time you are looking at something new, since it helps you visualize the pattern. N. Left-click on Antares and you will get information about it in the upper left of the screen. Note that Antares is also called α Sco. Take a moment to read the data about Antares, but don’t be concerned if you don’t understand it all! You will know what all the terms mean by the end of the course. O. Note the distance to Antares. It is 553.75 light years. P. Note the magnitude of Antares, which is 1.05. Magnitude is a number that tells you how bright a star appears to be. The magnitude scale was developed hundreds of years ago by Hipparchus, and he assigned the number 6 to stars barely visible to the naked eye. A star with magnitude 5 is BRIGHTER than a mag 6 star, and a mag 4 is brighter than mag 5 etc. Therefore, remember that the smaller the magnitude, the brighter the star. The brightest stars have magnitude values that are numbers less than 1, like 0 or -1. Q. Click on the two stars on either side of Antares and find the one named Al Niyat. 8. The magnitude of Al Niyat is a. 1.12 b. 2.15 c. 2.50 d. 3.05 9. In which constellation do the stars Nunki and Kaus Australis lie? a. Scorpius b. Sagittarius c. Corona Australis d. Telescopium R. Click on the magnifying glass (4 th icon from the top) which pops up a SEARCH box. Type in Arcturus and press enter. The screen will pan to the west and show you Arcturus in the constellation of Bootes. Click on all the stars in the “kite” of Bootes and find the distance of the second-brightest star (β-Boo). 10. β-Boo is at a distance of a. 120 light years 4 9/9/2015

b. 250 light years c. 225 light years d. 560 light years S. Let’s look north. Click on the magnifying glass and enter POLARIS in the SEARCH box. The screen will pan to show the northern horizon. Ursa Minor and Polaris are at the tail end of the “Little Dipper”. Click on Polaris and note the Az/Alt information about it. Az stands for Azimuth and it represents the angle away from the north. Since Polaris is north, its azimuth is zero. The screen shows 0º 44’34” (or close to it) the numbers after the zero represent the arc minutes and arc seconds. We can ignore the arc minutes and arc seconds in our lab and round off the degrees. Alt stands for Altitude and it represents the angle above the horizon. Polaris’ altitude on Sept 1 at 10 p.m. is 32º. T. The “Big Dipper” is a part of Ursa Major, with seven stars forming the dipper. The Big Dipper is not a constellation, but an asterism. The stars Merak and Dubhe are known as “pointer stars” since they point to Polaris. 11. What is the altitude of Dubhe on Sept 1 at 10 p.m.? a. 15º b. 8º c. 27º d. 45º 12. Which other star of the Big Dipper has the approximately the same altitude as Dubhe on Sept 1 at 10 p.m.? a. Merak b. Phad c. Alioth d. Alkaid U. Mizar is an interesting star in the middle of the handle of the Big Dipper. If you look carefully you see another star very close to it; clicking on it will show you a star called Alcor. Mizar and Alcor are called “binary stars.” The Native Americans used these stars as an eyesight test. If you could see two separate stars you had good eyesight! 13. Alcor is further away than Mizar. a. True b. False V. Cassiopeia is another good sign-post for the north. 14. Looking north at 10 p.m. on Sept 1, Cassiopeia looks like a. M b. W c. E d. 3 W. Let’s fast-forward the sky. Click on L three or four times and watch the time change. If it moves too fast, click on J (to move backwards), K (normal speed) or 7 to stop. Notice how the Big Dipper, Cassiopeia, and Ursa Minor move around Polaris. Stop the time at 7 a.m. Notice where the Big Dipper and Cassiopeia lie compared to 10 p.m. 15. Summarize in one or two sentences what you have learned about the motion of the Big Dipper, Cassiopeia and Ursa Minor in one night. The Big Dipper and Cassiopeia revolve around Polaris, the North Star, in opposite directions, with the Big Dipper sweeping to Polaris’ east and Cassiopeia circling directly west of Polaris. Ursa Minor, also known as the Little Dipper, is located near Polaris and appears to remain stationary throughout the night. 5 9/9/2015

16. Taurus and Auriga share a common star whose name is Alnath (also called Elnath). The Bayer name for this star is a. α Aur b. αTau c. βAur d. βTau 17. This means Alnath is a. The brightest star in Auriga b. The brightest star in Taurus c. The second brightest star in Auriga d. The second brightest star in Taurus Y. Click on a smudgy collection of points above Aldebaran called the Pleaides. Or use the Search icon (magnifying glass) to find it. The Pleaides is a relatively young star cluster, only a few million years old. Click on the individual stars and determine which one is brightest. To zoom the image in or out use the “page up” and “page down” buttons. 18. The brightest star in the Pleaides star cluster is a. Atlas b. Alcyone c. Electra d. Taygeta Z. Notice that at 10 p.m. only Bellatrix in the constellation of Orion is visible. Press L a few times to fast forward the time and stop (press7) when the entire constellation of Orion (including the star Saiph) is above the horizon. What time is it? 19. The star Saiph rises about ________ after Bellatrix. a. 15 minutes b. 30 minutes c. 1 hour d. 2 hours 20. It is fun to see how the ancients saw figures in the sky. Click on Constellation Art (3 rd icon from the left). What do you think about the imagination of the ancients? It is ingrained in humans to perceive patterns. Seeing the stars in the sky and without the luxury of modern technology we have today, they were imaginative in forming patterns out of a random collection of stars. Although, it did significantly contribute to the field of navigation and astronomy. 21. Look at Gemini and the two stars Castor and Pollux. Which star is closer to us? a. Castor is closer b. Pollux is closer 22. What is the azimuth of Rigel at 11 p.m. on January 1? a. 180º b. 90º c. 220º 7 9/9/2015

d. 49º 23. Click on Sirius in Canis Major, and note its data a. Sirius has a magnitude of -1.45 b. Sirius is 8.6 light years away c. Sirius is brighter than Polaris d. All statements are true 24. Look for Leo on Jan 1 at 11 p.m. Leo is supposed to represent a lion. The brightest star is called Regulus. Using the J key to run time backwards, estimate the rising time of Regulus in January. The rising time is a. After 11 p.m. b. Between 8 p.m. and 10 p.m. c. Between 6 p.m. and 8 p.m. d. Before 7 p.m. 25. Which was your favorite constellation? Why did you choose it? Answer in complete sentences. My favorite is Orion. First off, because to the characteristic pattern of three brilliant stars that make up Orion's belt, this constellation is among the easiest to identify in the night sky. Because of this, it serves as a fantastic beginning place for newcomers to the art of stargazing. Several additional prominent stars and features may be seen in Orion, including the red supergiant star Betelgeuse and the blue-white supergiant star Rigel. Another well-liked object for telescope users is the Orion Nebula, a star-forming area close to Orion's belt. Grading Rubric Ques 1-25: 4 points each 8 9/9/2015