Assignment 3 SPS 1010, Introductory Astronomy Dr. Ringwald 1999 September 13 Due as a hardcopy at the beginning of class, 2:00 p.m., Friday, September 24. Use other pages for this assignment. If you write everything on this page and hand it in, it'll be so crowded it'll look terrible! Also: Always show all work. Always write the units. Always do your best. Make attempts at everything. If you have trouble, please by all means come to office hours in S418 Crawford, MW 3-5, T 4-5, and by appointment other times (phone or better, e-mail first). 1) Hubble Deep Field (see the poster on the wall outside my office) is the deepest image yet taken of the Universe. It was made by Hubble Space Telescope, by staring at an apparently blank field in the sky for a week and a half. It found 1500 galaxies in three square fields, each 70'' on a side. (The notation 70'' means 70 arcseconds, not 70 inches: we don't like inches anymore, remember?) a) The number per area (also called the areal density) of galaxies in HDF is therefore 500 galaxies per square field, 70'' on a side. Calculate how many galaxies Hubble could see, if somehow enough telescope time were to become available to cover the whole sky. [Hints: There area of a sphere is 4*pi steradians; 1 steradian = 1 (radian)^2; 1 radian = 180 degrees/pi] b) With about 10^11 stars per galaxy, how many stars are there in the Universe observable by Hubble? This may be within a factor of 10 of the total---although we won't know until Hubble's successor, Next Generation Space Telescope, is launched in 2007. c) Now estimate the number of air molecules in our classroom, A106. [Hints: 1 mole = how many liters of gas, at STP? Air is about 70% N_2. Determine the volume of the room as best you can, and remember, this is only an order-of-magnitude estimate.] d) Compare the results of 1b and 1c. Which is much larger, and how many times larger? 2) Calculate a scale model of the Solar System, like the one presented in class. This time, scale it so that the equatorial diameter of Earth is 1.3 mm in diameter, the size of the head of a straight pin. Find: a) The Earth-Moon distance; b) The Earth-Sun distance; c) The Sun's diameter (it should be about the size of a grapefruit); d) The distance from Earth to Mars, when Mars is at opposition (closest to Earth); e) The distance from Earth to Jupiter, when Jupiter is at opposition; f) The diameter of Jupiter; g) The distance from Earth to Pluto; h) The distance from Earth to the nearest extrasolar star system, Alpha Centauri, which includes Proxima Centauri, the nearest extrasolar star -- although recent research suggests they might not be physically bound! 3) The Cosmic Calendar on three Number Lines: a) Take a ruler, turn a blank 8.5-inch x 11-inch piece of paper sideways, and draw a line 26 cm long down the piece of paper. You might want to try this in pencil the first time you draw it. Let this line represent the age of the Universe, which we'll for now assume to be 13 billion years. Draw tics down this line every 2 cm; they reprent each billion years. Now mark and label every event given in The Cosmic Calendar handout given in class---EXCEPT for those in the last 500 million years. (If you do this, it'll get crowded.) For the labels, it'll help to orient the lettering so it's perpendicular to the page, otherwise it'll get crowded. b) Repeat (a) on another piece of paper, only this time draw a line only 25 cm long. Let it represent the events of the past 500 million years. Draw tics down this line every cm; they represent 20 million years. Label all the events between 500 million years ago and 100,000 years ago. c) Repeat (b) on another piece of paper, only this time draw a line only 25 cm long. Let it represent the events of the past 100,000 years. Draw tics down this line every cm; they represent 4,000 years. Label all the events between 100,000 years ago and now. It still gets crowded at the end, doesn't it? d) In your own words, briefly write the punchlines and following ideas for the Cosmic Calendar. 4) The image (or spatial) resolution of the SARA telescope on Kitt Peak is 2''. In other words, it can discern detail as small as 2'' in angular diameter. a) How far away could the SARA telescope read a newspaper? [Get a newspaper and measure the text (not the headlines) with a ruler.] b) Could the SARA telescope discern any artifacts left behind on the Moon by the Apollo landings? [Estimate the size of an Apollo Lunar Module Descent Stage as best you can. Use the full-size model or the actual flight model at KSC, or look it up in the library, or on the Web.] c) Could Hubble Space Telescope? The resolution of its Planetary Camera is 0.0455''. d) What resolution, in arcseconds, would this require? Believe it or not, instruments are now being designed that would be capable of this---although they'll be used mainly for extrasolar planet detection, not for observing the Moon. This is partly because the Moon is too bright, but also because, by that time, perhaps there will be more spacecraft going there...