Description: Record the change in the position of two naked eye planets over the course of the semester.
Materials needed: Two sheets of sketch paper, planisphere
Resources:
Instructions:
(1) Before you even go outside to observe, use the Monthly Sky Chart to identify which constellation each of your planets is in and devise a plan to find each of those constellations in the sky when you go outside (practice with your planisphere, Stellarium, etc.). If you can’t identify the constellation, you won’t know which “star” doesn’t belong. This is the planet!
(2) Go outside and find each of the two constellations and the planets within them. Note that the planet will be a bright object that is within the constellation but is NOT part of the constellation as it is drawn on your planisphere. It is not drawn in on your planisphere because its location changes with time, which is precisely what you will be trying to observe.
(3) For now, ignore the planet and carefully draw the sky as it appears for about 20 degrees (two fists at arm’s length) on either side of the planet. Make your drawing large – it should take up most of the paper! Draw all of the nearby stars that you can see and try to capture the relative distances between them as accurately as possible. You may even wish to write in the distances in degrees between some of the stars as it will help you later. You will use these two drawings (one for each planet) throughout the semester, so it is to your advantage to take some time and draw them carefully the first time. Use the size of the dot you draw to represent the how bright each star appears (larger dots for brighter stars, smaller for dimmer).
(4) The planets move slowly relative to background stars, so you do not need to make your observations at the same time or from the same location each time. The planet simply needs to be up in order for you to observe it. You should make your observations approximately once per week over the course of the entire semester, for at least 10 total observations spread over 2.5 months for each planet. Each time you make an observation, mark the position of each planet carefully on the sketches you made the first night (one for Mars, one for Jupiter). Mark the date next to each observation, and also note which of the other stars in the field is closest in brightness to the planet on that night.
Data:
(1) Sketch showing the changing location of Mars relative to background stars over the course of the semester.
(2) Sketch showing the changing location of Jupiter relative to background stars over the course of the semester.
Questions to Address in Your Poster’s Data Analysis Section:
(1) How far (in degrees, which you can estimate using your sketch and the fist and finger method) did each planet move over the course of the semester. If your planet didn’t follow a straight line, give the total straight line distance it moved and the approximate distance along the path it actually took.
(2) Which planet moved more and why?
(3) Did the brightness of either planet change over the course of the semester? Why or why not (what would cause it to change)?
(4) Calculate the rate of movement for each planet from one observation to the next (number of degrees moved divided by the number of days between each observation gives the rate of motion in degrees per day) and list it in a separate table on your poster. Did the planets always move in the same direction? Did they always move at the same speed?
(5) Were the patterns of motion (speed, total distance traveled, shape, etc.) different between Mars and Jupiter? Why or why not?
(6) If you were to have observed Venus or Mercury instead of an outer planet, how would their motions have been different over the course of the semester?
(7) Whether or not either of your planets showed a retrograde loop during the semester, explain the actual cause of retrograde motion in a heliocentric (sun-centered) solar system.