HOU Project: Parallax of Mars

Welcome to http://sunra.lbl.gov/~vhoette/Explorations/MarsParallax/

How Far is Mars?
Parallax Project

Challenge: Estimate the distance of Mars using parallax.
Use observations taken from the same location when Mars is close to east and west horizon positions.

Nature of Project: This project is an exploratory parallax project by HOU teachers. We are not guaranteeing the correctness of our methods or reasoning. :) This web page is for information and data links so that teachers and students can explore and debate this problem.

Method: Use the baseline of Earth's size to calculate the distance to Mars using parallax. Take images of Mars on the same night as close to rising and setting positions as possible. Mars images must also contain stars.

Reasoning: As Earth rotates, the baseline of the observations is represented by the time difference which can be related to a segment of Earth, depending on the location on Earth and the portion of rotation. How to measure this dimension on Earth is one challenge; it is not simply a portion of the Earth's diameter. If we were on the equator it might be easier, but Yerkes is at latitude 42° 34.2', longitude -88° 33.4'.

Complication of orbital motion: Earth and Mars are also moving in their orbits during the time delay. To account for this motion, images of Mars are taken at the same azimuth (angle around the horizon) each night for three nights, two of the nights on either side of the parallax data collecting night. This motion of Mars against the stars at the same azimuth is then calculated and averaged. This motion can be subtracted from the positions on the parallax data night to eliminate the motions of the planets in orbit.

Images: Click here for HOU fts images of Mars of the nights of September 4, 5, 6, 2003. The first set of images near rising and setting of Mars were taken on September 5, 2003. The sets taken on Sep. 4th and 6th are for determining apparent motion due to the orbital motions. See explanation below. The images have a pixel scale of 2.90 arcseconds/pixel. The size of the field is about a half a degree. North is up and East is to the right when the images are opened in HOU-IP. Images are named by "object date-time filter exposuretime telescope".

About the images: In most of the images, Mars is overexposed in order to see the starfield clearly. In other images the stars are faint or not detectable but Mars is seen as a disk if you increase the max scale. Blooming means that the CCD is saturated and the photons 'spill over' especially in a vertical or horizontal direction. (Counts have been divided on the images so you can shift and add them without getting black centers... to see motion... if you choose to analyze this way.)

Observatory, Telescope, CCD: These images of Mars were taken with the Yerkes Rooftop Telescope (yrt8). The telescope is an 8 inch F/6.3 LX200. The CCD is an SBIG ST8e with 2x2 binning for 18 micron pixels. This telescope can be operated by HOU teachers remotely, so new observations by teachers and students taking the images remotely are possible.

Documents related to this project are linked here. One is an illustration of Earth with an idea of how to figure out the baseline of the Earth distance for Yerkes latitude by Harlan DeVore, HOU Teacher Resource Agent. Rich Kron, Univ.of Chicago Astronomer, provides an excel file of Earth's moon positions and the graph showing the parallax depending on time of observation; a similar phenomenon occurs with Mars. Other documents may be added as teachers and students work on this challenge.

Resources (how to use these resources is not so complicated but you may need some coaching to be added to this page soon):

Ephemeris Generator: http://ssd.jpl.nasa.gov/cgi-bin/eph Use this excellent resource from NASA's Jet Propulsion Laboratory for determining the position of Mars on the dates of observation, times, elevation, azimuth, etc. The location of Yerkes is Observatory Code 754.

Skyview Advanced: http://skyview.gsfc.nasa.gov/cgi-bin/skvadvanced.pl Use this excellent database operated by NASA's Goddard Space Flight Center to find the starfield in the images.

Credits: Thanks to Kevin McCarron, HOU teacher of Oak Park and River Forest HS for his work in building this remote observatory. Thanks to Jerry Gunn for his work in making the Robot software to run the observatory, telescope and camera systems. Thanks also to the Univ. of Chicago astronomers who inspire / challenge us and the engineers and staff at the observatory who help us maintain the telescopes, servers, etc.

Comments, Suggestions, Questions? Email. Vivian L. Hoette
University of Chicago Yerkes Observatory, 373 West Geneva St., Williams Bay, WI 53191