

Observing the Night Sky: Tracking the Motion of Solar

System Objects in the Spring 2004 Semester

(An alternative to the Moon Orbit Project)

The goalofthissemester-long project is to get you outside observing the night sky. This includes tracking the phases of the Moon, identifying and observingthe planets, and finding constellations. For the Spring 2004 semester, you will be carefully monitoring the motion of the planet Jupiter throughthe constellation Leo. To perform this lab properly, you will have to record your work in an observing notebook, and learnhow to use the star charts at the back of the lab manual. So, obtain a small spiral notebook, or someother set-up thatallowsyoutowrite down your observationsand keep them organized (having a bound notebook is alsousefuldue to the windy conditions that frequentlyoccurduringthe springin Las Cruces!).This project is worth two regular lab grades, and should be taken very seriously!Notethat all of the observing projects must be startedas soon as possible to insure that bad weather does not eliminate the possibility of making your observations.This is especially true of Exercise #3, since you need to track the planet Jupiter for the entire semester to insure you detect its motion.

Setting Up Your "Observatory" To enable youtocomplete the exercises in thislab, youmustfind a site from which you can conduct your observations. This maybeyourbackyard,nearyourdorm, or somewhere else of your choosing. The key requirements for a good observingsite are clear views of the southern and western horizons (it would also be nice to have a clear view to the East, but it is not always possible to find such a perfectlocation).Youalsomust not have any bright lights at this site-no streetlights, etc. To conduct your observations it must be as darkas possible. One excellent location on campus to perform these observations is on the activity fields above the track, near the campus observatories. Mark your chosen location (mentally or otherwise) so that you can return to thesamespot each time you observe.

After choosingthesiteforyourobservatory,youmust then find the directions of the cardinal points (North,South,East and West).Tofindthedirection of West is probablythe easiest: simply note the point of sunset on one eveninginJanuary.ThisisWest. If you face due West, and stick out yourlefthandhorizontally,itwillbepointingSouth.Northis directly opposite South, and East is directly opposite West. Note these directions so that youcanorientyourself each time you observe. You then need to have a watch, a flashlight,a pencil and your notebook for all of your observing projects.

Observing Highlights Spring 2004 Here are some of the mostimportantsolar systemevents that occur during the Spring 2004 semester: January 4: Earth reaches perihelion (closest approach to the Sun) January 5: Latest sunrise January 7: Full Moon January11: Mars sets at midnight (about the same for aweekor two on either side of this date) January 14: Uranus can be found 1 due north of Venus (need binoculars)

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January 17: Mercury reaches greatest western elongation (24) [See lab #5.]

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January 21: New Moon February 1: Jupiter rises at 8 pm (about the same for a week or two on either side of this date) February 6: Full Moon February 20:New Moon March 3: Jupiter is at opposition (rises at sunset, transits at midnight, sets at sunrise) March 6: Full Moon March 19: Spring begins 11:49 pm MST March 20: New Moon March29: BothMercuryandVenusreachgreatesteasternelongation(19&46, respectively)

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April 5: Full Moon April 19: New Moon April20: Saturnsetsatmidnight(aboutthesameforaweekortwooneithersideofthis date) May 4: Full Moon May 19: New Moon May 14: Mercury reaches greatest western elongation (26)

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During the spring semester in 2004, several planets put on excellent shows: During the entire semester,Venus is above the westernhorizon. Venus is the brightest "star" in the nighttime sky. You caneasily locate Venus by looking towards the West after sunset (in fact, you might be able to see Venus before sunset!). Saturn is high in theskyallsemesterlong,andis locatedin the constellation Gemini. You will have an opportunity to look at Saturn during the observatory sessions this semester.Jupiter is also easilyseen thissemester.BeginningFebruary1, Jupiter rises in the East

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at sunset, and is high in the sky by 10 pm.Jupiter spends 2004 in the constellation Leo. After its close approach last August, the Earth is rapidly leaving Mars behind and the planet grows dimmer (and smaller)daybyday. At the beginning of the semester, Mars can be found high in the Southwest sky at sunset. By the end of the semester, Mars will become difficult to find in the twilight sky after sunset. At the end of March, it should be easy to see the most elusive of the naked-eye planets: Mercury. Mercury and Venus reach "greatest elongation" on the same date (March 29). At this time,

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Mercuryhas itslargestangular separationfrom the Sun. To find Mercury, go out right after sunset-- allyouhave to doisdrawan imaginarylinefrom Venus, tothe point where the Sun just set. Mercury will be slightlymore than halfway down that line from Venus towards the western horizon. To see Mercury requiresyouto observe it within a few days of the 29 (on either side). Mercury moves

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quickly,and spends only a few days near its greatest elongations. Finding these planets will be part of this semester-long project.

Observing Project #1: The Ever-Changing Moon The goal of the first project is to get you familiar with the motion of the Moon, and the changing phasesoftheMoon.IntheObserving Highlights calendar just presented are listed the times of New and Full Moon. Forthis exercise,youwill trackthephasesoftheMoon as it progresses from New to Full. This exercise will require you to go outside for about eightdifferentnightsover a two week period,onetime duringthesemester--DONOTLEAVE THIS PROJECT UNTIL APRIL!!! If so, you might not have good enough weather to allow youtocomplete this exercise. You need to conduct this project from your observatory site.

Step #1: Find the date of the nextNew Moon. As you have found out in your lecture class, during New Moon, the Sun, the EarthandtheMoonareallonastraight line. Atthetime of New Moon, the un-illuminated side of the Moon is facing us, and the Moon is located close to the Sunin the sky. Thus we cannotsee the Moon during its New phase (unless there is a solar eclipse!). It is  usually not possible tosee the Moonuntiltwofulldaysafter New. Among amateur astronomers, there are contests on who can be thefirstto seetheMoonaftera New Moon. The record is 12.1 hours after New Moon. For most people though, it is difficult to see the Moon much less than 24 hours after New Moon. For people in theNorthernHemisphere,however,the days following the New Moons in February and March offer the best chances for seeing a "young Moon" because the tilt of the Earth's axiswithrespecttoitsorbitplacestheMoonvertically above the point of sunset during these months. Given a clear western horizon, and a pair of binoculars, you might be able to see a very young Moon yourself.

Step #2: Beginning (one or) two days after the chosen New Moon, go out about 20 minutes after sunset and look for a very thin crescent Moonnear the western horizon. Can you find the Moon? Either way, note the time of your observation in your logbook, and whether you were successful at seeing the Moon. If you saw the Moon, draw a sketch of its appearance. [For this sketch, it might be handy to find a bottle top or drinking glass that is about 1.5to 2 inches in diameter and use this to make a perfect circle for the Moon, and then shade in the part you cannot see torender a drawing of the phase of the Moon. Use the samecircle-maker for the entire exercise.] In your notebook note the time and date of this observation along with your drawing. Note whether there areany bright stars or planets near the Moon.

Step #3: You mustattempttoobservetheMoonthreedaysafterthetimeofNewMoon.Make a drawing of the phase of the Moon and note the time and date. Observethe Moon about 30 minutes after sunset so that it is fairly dark. Besides the bright crescent, can you see the other parts of the Moon glowing faintly? Within a few days after New Moon, it is often quite easy to see the "dark" portion of the Moon (the part not directly illuminated by the Sun). Thisphenomenon is called "Earthshine", or  "the old Moonin the New Moon's arms". For step #3, you need to research the natureof Earthshine. You can use the web (for example enter "Moon and Earthshine" on Yahoo or another search engine) or look in a booktofindoutthe cause of Earthshine. Write-up a paragraph or two in y our observatory logbook describing the phenomenon of  Earthshine, with a

drawing/diagram showing how it arises. Step #4: Continue to observe the Moon every other day until the Full Phase,and make sure you observe on the night of the Full Moon! Note the time and dates of your observations, and make drawings of the appearance of the Moon. Note the locations ofanynearbybright starsorplanets. Use the star charts at the back of the lab manual to see if you can identify which constellations the Moon happens to be passing through. Note that the star charts are different for each month, and that the positions of the constellations change throughout the night and month!

Step #5:Describe/summarizeyourobservations of theMoon.When did the Moon reach a phase of "First Quarter" (when exactly one half of the Moonwas illuminated)?Was it possible for you to tell on which date the Moon was perfectly Full, or did it look Full to you for several days? Which direction did the Moon move over the course of this two week period? Did it come close to any planets (see Exercise #2 to make sure you know where the planets actually are)? Any other interesting observations?

Observing Project #2: Locating the Naked-Eye Planets As described in the Observing Highlightssection, several bright planets are easy to observe this semester. Your goal is to observe as many of them as possible. Note that Mercury will be the hardest of the planets to observe. It is only easily seen near the times ofgreatest elongation. Even then, you have to observe rightbefore sunrise (greatest western elongations), or right after sunset (greatest eastern elongations). Mercury is fairly bright at these times, so it can be seen easily with the naked eye, but you must have a clear horizon tohave anychance of seeing it. There are several methods to identifying the planets. Perhapsthe easiest istohave one of the TA's at the observatory session point them out to you.Butwewouldlikeyouto beableto searchfor and find them on your own. One way is to use the sky charts in the back of the lab manual.Read about how to use those charts, and then orient yourself by identifying someof the constellations in the nighttime sky using the sky charts. But there are two other good sources: online, or in a magazine. "Sky & Telescope" and "Astronomy" are magazines for the amateurastronomycommunity.Sky&Telescopeis a more advanced magazine than Astronomy. Both magazines can befound in the library, or at a book store (such as that  in the Mall).Insidethesemagazinesaremonthlycolumnsthattalkaboutwhich planets are visible, and where they can be found (including sky charts). In addition, however, both magazines have websites (www.astronomy.com and www.skypub.com). Both websites have interactive sky chartsthatshowwheretheplanetsareinthesky.AttheSky&Telescopewebsite,hit the "InteractiveSkyChart"link. At theAstronomymagazinewebsite,afteryouregister(its free), you can access theskychart by clicking on the link "The SkyOnline for Beginners" found on the lefthand side of the main webpage (note that it reads your zipcode to figure out your latitude tomake a chart just foryou!).Theyellowlinethatrunsacross theresultingskymapis the"ecliptic"(the plane of the Earth's orbit), and all of the planets will be found close to this line. Note where these planets are withrespecttothestars,andfindthesameconstellationsonyourskychartsand make a little note on the chart so that you can find the planet when you go observing.

Step #1: During the semester identify as manyplanetsin thenighttimeskyaspossible. Write down the details of the time, date of your observations, and constellation in which youfound the planet. Mark the location of the planet on the appropriate sky chart (make suretoturn-in this chart, or a handmade version of this chart,with the rest of your materials at the end of the semester). Note that the planets are just about always the brightest "stars" in eachconstellation,andthus are very hard to miss! You should conduct this exercise from your observingsite(unlessyourwestern horizon is not good enough to allow you to see Mercury-if so, youcanobserve Mercury from the campus observatory, or some other site with a good western horizon).

Observing Project #3: Tracking the Motion of the Planet Jupiter in 2004 For this exercise you will be plotting the position of Jupiter about once per week during the entire semester. You need to make at leasttenobservations of Jupiter spread out over the entire semester-you must start this bythesecond or third week of lab to insure that you have enough time and observations to complete this exercise. Jupiter spends all of 2004 in the constellation Leo. This constellation rises in the East about 8 pm in February. It can be seen on the February sky chart on thelefthandside(northeastofOrion).Itisalmost in the center of the sky chart for April. The Big Dipper can be found due North of Leo. This is the hardest of the three observing exercises. If you need some help,askyourTA,oroneof the TAs at the observatory. You can conduct this exercise from any location that works best for you.

Step #1: Identify the constellation Leo. Go out after 9 pm in late January or early February (dress warmly!!),and look to the East to identify Leo. Use the February or March sky charts to find Leo. The brightest star in Leo is named "Regulus" ("Heart of the Lion"). Of course,the brightest "star" in Leo this year is Jupiter! Regulus forms the bottom of a backwards question mark ("?"). Jupiter is to the southeast of Regulus. Onthenext pageis aclose-upmapofthe constellation Leo. The stars have their names and numbers located nexttothem(includingsome Greek letters). The bigger the star symbol, the brighter the star. Note where Regulus is on this chart to orient yourself.We have drawn-in the lines that define the main stars in Leo (including the backwards question mark). The underlined namesfound on thischartare the neighboring constellations. Note in your logbook the time and date when you finally identified the constellation Leo.

Step #2:IdentifyJupiter.This is easy-in fact,it might beeasierforyouto first find Jupiter than the constellation Leo! Jupiter will bethebrightestobjectin thenighttimesky after Venus and the Moon. Look for the brightest starintheeasternskyafter9pminJanuary/February. Note the time and date when you first found Jupiter.

Step #3: FindingF (Sigma),D (Rho), and P (Chi) Leo. Over the last two thousand years, astronomers have usedGreeklettersto labelthebrighterstarsin aconstellation(see the introduction to theSkyCharts).Thebrighteststarin aconstellationwas usually given the designation" (Alpha),

thefirstletterin theGreekalphabet. This progresses all the way to the last Greek letter T (Omega). After that, the fainter stars were given numbers. Regulus is known as" Leo. On the close-up sky chart ofLeo,wehavedrawnablackarrowto identifythe star D Leo. This is a fairly faint star. It has several other stars (45, 44, 43, 48 and 49)located near it. You need to locate this star, and the two stars calledF and P Leo.F and PLeo are located tothe East (left) of D Leo.P Leo has another star numbered "59" close to it.F, 59 and PLeo makeasmall littletriangle, with the side of the triangle defined by 59 and F being the longest side. P Leo is the faintest of these three stars. Jupiter will spendtheentiresemesterin this small region of sky (betweenF and D Leo).  If you have too many bright lights near your observatory, you might have to do this exercise at a location where the sky is a bit darker. Ifyouarestillhaving trouble seeing these three stars, see if you can borrow a pair of binoculars to help you identify these three stars. Write down in your logbookhowsuccessful you were at finding these three stars. Note any tricks you used to identify them so that you can use that technique in the future.

Step #4: Tracking the motion of Jupiter.Onthepagefollowing the Leo sky chart is another sky chart that only shows the small regionofskythat includesF Leo on the bottom left (southeastern) edge of the chart, andD Leo on the righthandside.Thedotted line that goes through this chart is the ecliptic,theapparentpathoftheSun throughthesky(theprojection oftheEarth'sorbital plane). Mostplanetsare found close to the ecliptic. This ultra-close up map of the sky will be your worksheet for plotting the position of Jupiter. Using the twoskymaps,locate the position of Jupiter in the constellation Leo. Mark itspositiononthe "Jupiter Worksheet" with the date of observation. Note in your logbook the time of this observation. Every week or ten days, go outand observe Jupiter, and plot itspositionon your worksheet. You should have ten observations spanning the semester to complete this project.

Step #5: Summarize themotion of Jupiter during the semester. How far did Jupiter move? To do this, note that the little squares formed by the grid lines in the close-up sky chart are exactly one degreeonaside.Howmanydegreesdid Jupiter move?Which direction did Jupiter move during the semester? Did Jupiter follow the ecliptic, or did it move north/south of the ecliptic?Why do you think it did this?