FOR THE FAMILY OF: INVESTIGATING CONNECTIONS Investigating Stars The creation of the expanding nebula shown in this image was recorded by Chinese astronomers in 1054 AD... See story on page 2. INSIDE THIS ISSUE! Family Feature Decoding Life Cycles 2 Family Feature The Stellar Zoo 5 Star Witness 6 Sky Watch 7 Cultural Connections 9 Talk Like an Astronomer 9 2 Family Features Decoding Life Cycles Part 1 Your First Challenge: Decoding the stages in the life of some Pretend for the next few moments that Now that you have found this particu- living things can be challenging, espe- you are “aliens” visiting Earth for a very lar life form to be of special interest, cially if those stages are very different short while. You’ve observed a wide you are going to try to determine the — like an egg, tadpole, and frog; or an variety of life forms. One in particu- various stages of its life cycle. Unfortu- egg, caterpillar, cocoon, and butterfly. lar, whose activities seem to have an nately, you are not visiting Earth long But time is often on the biologist’s side. impact on all the others, interests you enough to follow a single specimen If a group of eggs is found, the eggs the most. Let’s call them “humans.” from birth to death, but you’ve been can be observed, and what comes out You’ve collected a number of images observing and collecting pictures and of them can be tracked through each of these humans as part of a research information on a variety of humans for stage. Time, however, is not so kind to project. Note: While collecting these sufficient time to form some ideas. Can astronomers. Stars live for millions or images, you [the aliens] recorded data you put the pictures in order from earli- billions of years — far longer than the (including size) and got a sense of what est life stage (youngest) to latest life astronomers who observe them. In this is truly the human body vs. the “acces- stage (oldest)? It would also be helpful two-part activity, you first play the role sories” and other material objects that to list the characteristics that you used of “aliens,” here on Earth for a short humans wear, touch, and operate (e.g., to determine your order. while, trying to decode the stages of clothing, tools and/or toys). In addition, the human life cycle from a set of pic- you made a number of observations of tures. Then you apply the same reason- how different types of humans interact. ing as you become astronomers, trying Make use of this knowledge as you to decode the stages in the life cycles of work. stars from a set of astronomical images. On the Cover Credit: Clipart.com Very massive stars die dramatic deaths called supernova explosions. The release of energy at the time of such an explosion can mean that a single star will outshine an entire galaxy. The nebula in this image resulted from just such an explosion. It was recorded as a “new star” by Chinese astronomers in 1054 AD. It outshone every star in the sky for months and was even visible in the daytime sky. (Credit: NASA) 3 Figure 1 Figure 4 Figure 7 Figure 2 Figure 5 Figure 8 Figure 6 Figure 3 Credit: ASP 4 Part 2 Now pretend that you are an astrono- mer. No astronomer has been alive long enough to witness a star’s birth, life, and death. We see a sky filled with stars, but how can you tell how old they are? Where did they come from, and will their light ever burn out? Astronomers have several ways of collecting clues to the answers to these questions about the lives of stars. They have telescopes and instruments like CCD cameras and spectroscopes that give them pieces to the puzzle in addition to the tools of math and physics. Figure 1 (Credit: NSO) Figure 4 (Credit: NASA) Your Second Challenge: Examine the images that follow and order them so that they demonstrate the life stages of a star. The clues that we have are: 1. Stars don’t seem to form by them- selves, but in groups. 2. Many stars seem to have planets in orbit around them. 3. As they age, stars expand and be- come unstable. 4. Unstable older stars may blow off outer layers (smaller stars—with a gentle burp, larger stars—as a Figure 2 (Credit: NASA) dramatic supernova) to try to regain Figure 5 (Credit: NSO) some stability. Figure 3 (Credit: NASA) Figure 6 (Credit: JPL/Caltech) The Stellar Zoo 5 Table of Star Diameters All stars, with the exception of our Star Name Type of Star Diameter (suns) sun, appear as pinpoints of light in the Sirius B white dwarf companion of Sirius 0.05 night sky. At first glance, all the stars Proxima Centauri red dwarf .25 seem to be about the same. A closer look reveals an amazing diversity of Sun yellow 1 star colors and brightnesses. The color Procyon yellow star in Winter Triangle 2 of stars is determined by their tem- Sirius white star in Winter Triangle 2 perature—hot stars are blue or white; Trapezium Stars very hot blue stars in Orion Nebula 10 cooler stars are yellow and red. Polaris (North Star) yellow giant star in the Little Dipper 30 Using our largest telescopes, Rigel hot white star in Orion 70 astronomers have only directly mea- sured the diameters of a handful of Betelgeuse red supergiant star in Winter Triangle 650 stars. But using principles of phys- ics, we can estimate stars’ sizes and Table of Common Object Sizes Compared to the Sun compare them. In this activity, we’ll Object Approximate Diameter (cm) compare of star sizes using a lemon to grain of sand 0.025 represent our sun. dot of an i 0.050 Our sun is a huge ball of hot gas, peppercorn 0.30 over one hundred times larger than Earth. Place a lemon on a table as a coffee bean 1.0 model of the sun. To represent Earth acorn 2.0 at this scale, you would need to cut cherry tomato 2.5 out the dot on top of an “i” and place it lemon (our sun) 5.0 next to the lemon. grapefruit 10 Use the diameters of the stars cantaloupe 15 listed to match the size of stars in the stellar zoo with some common volleyball/bowling ball 20 objects. In this model, the sun will be small car 350 the size of a lemon (5 cm in diameter). SUV 500 Place the objects that you have on House 1500 hand next to your model sun. high school football stadium 10,000 At this scale, the nearest star (Proximi Centauri) to our sun would be star. once-dynamic the of left be will carbon of chunk black 1451 km or 870 miles away! No mate- a only and years, of billions over energy their lose will stars these slowly, Cooling Earth. rial object of any size lies between of size the about stars dwarf white as lives their end will sun our like stars Small 1: Fig. 6) them. Space is truly vast and almost revealed. gradually is core central nebula around the star. By shedding its outer layers, the hot hot the layers, outer its shedding By star. the around nebula 5) Fig. 4: An older star throws off gas from its surface forming a a forming surface its from gas off throws star older An 4: Fig. 5) its outer layers to expand. to layers outer its internal fusion processes cause instability in the star, causing causing star, the in instability cause processes fusion internal 4) Fig. 2: Stars like our sun become bloated red giant stars as as stars giant red bloated become sun our like Stars 2: Fig. 4) billion years or so. or years billion continue to bathe Earth with its light and heat for another 4 4 another for heat and light its with Earth bathe to continue been shining steadily for the past 4.6 billion years. It should should It years. billion 4.6 past the for steadily shining been 3) Fig. 5: Our sun (image is taken in ultraviolet wavelengths) has has wavelengths) ultraviolet in taken is (image sun Our 5: Fig. 3) clumps of material—planets and moons. and material—planets of clumps hydrogen into helium. The left over material forms smaller smaller forms material over left The helium. into hydrogen the star is large enough and hot enough to begin fusing fusing begin to enough hot and enough large is star the 2) Fig. 6: Stars form by gravity drawing particles together until until together particles drawing gravity by form Stars 6: Fig. 2) white stars surrounded by wisps of gas. of wisps by surrounded stars white called nebulae. They form in clusters and usually appear as as appear usually and clusters in form They nebulae. called 1) Figure 3: Stars begin their lives in vast clouds of gas and dust dust and gas of clouds vast in lives their begin Stars 3: Figure 1) The correct sequence of images that describe the life of a star is: star a of life the describe that images of sequence correct The Answer Key for Challenge for Key Answer Two cool stars (left and right lower corners) with a cluster of hot stars. (Credit: NASA) 6 Star Witness Dr. Aparna Venkatesan, University of San Francisco Tackling physics and math, subjects that do not generally inspire passion, Aparna Venkatesan feels fortunate to specialize in a subject that inherently touches on topics that dazzle the imagination.