Model of the SeasonsJosh Kratzer, Carly Reed, Feliciti Fredsti, Dr. Bruce Palmquist, Dr. Tim Sorey, Dan Durr*

Department of Physics, Central Washington University (*Entiat Public Schools)

IntroductionThis is a classroom model to show students the relationship between the earths tilt and the seasons at different latitudes. Light and temperature sensors were placed on the northern hemisphere of a small globe at different latitudes. The globe was built on a stand that allows it to tilt to the desired angle to simulate any time of the year.

The latitudes picked:•23.5 degrees (Tropic of Cancer)•45 degrees (Mid latitude)•66.5 degrees (Arctic Circle)•90 degrees (North Pole)

To set up this model each sensor can be connected to data collection device like the Vernier LabPro. A heat lamp is placed a distance away from the globe to simulate the Sun. Then adjust the globe to the desired tilt and collect the data.

ALLDATASHEET.COM . ALLDATASHEET.COM - Datasheet search site, Datasheet search site for Electronic Components and Semiconductors and other semiconductors.. Retrieved May 17, 2011, from http://www.alldatasheet.com

References

Figure 2. Is one of the light sensors. Using the SD 5443 phototransistor, 4 wire telephone cable, 9V battery terminal and a 1000 ohm resistor to measure the voltage across.

Figure 3. Is one of the temperature sensors. Using the LM35 transistor, 4 wire telephone cable and 9V battery terminal. The voltage is taken across the transistor itself.

Data

Figure 4. This is data taken with no tilt (Spring or Autumn equinox) at the latitudes of 45 degrees and 66.5 degrees. The globe was rotated to simulate a 24 hour period (1 full day).

As expected the mid latitude sensor received more intense light as it turned toward the heat lamp (Sun). The difference in temperature is also seen showing it is much colder at the arctic circle. The thermal variation doesn’t change as the globe rotates. That is because of the high thermal resistance of the LM35 sensor. We let it sit before rotating the globe so the LM35 sensors could heat up from the heat light (Sun), this is why they are not both at room temperature.

Figure 1. This is a picture of the model we have built. It shows the two types of sensors and their relative location on the globe. The wires coming from the globe go to each sensor and can be connected to your data collection device.

The Sensors Used

The light curve of SV Cam with the I filter shows a much more significant drop in magnitude than the V filter. The stars in SV Cam have a peak in the red to infrared part of the visual spectrum. The I filter would therefore be more sensitive than the V filter.

ConclusionFigure 2

Figure 3

LM35 sensor SD5443 Phototransistor

The two sensors used in this model are the LM35 (temperature) and the SD5443 phototransistor (light).

The LM35 temperature sensors voltage difference has a direct relationship with the Fahrenheit scale making it easy to read. The main downside is its high thermal resistance. Meaning it takes time to heat up and cool down. Which is hard to show temperature variations in the classroom setting.

The SD5443 phototransistor works well except it has a small convex lens on it. This can have a tendency to refract the light and not give a accurate reading of how much light is hitting the area. The SD3443 phototransistor would be a better choice because it has a flat lens on the front of it and would refract the light much less.

Ongoing WorkThere is still more to refine with this model and others can build off this prototype. One thing is using thermistors for the temperature sensors. They have low thermal resistance allowing for a more rapid change in the temperature. Also the SD5443 phototransistor could be replaced with the SD3443 phototransistor. A stepper motor and a turn table could be set up so it could rotate at a more consistent rate.

Modifying the telescope has highlighted additional work that will benefit using the observatory to produce high quality astronomical data, several of which we have already begun work on:

•Polar aligning the telescope more precisely•Repairing the dome mechanism•Refining the periodic error correction table•Developing focus methods for the new filter set•Troubleshooting flat fielding issues

Flat fieldingMarginal rays have been shown to introduce image calibration errors in differential photometry measurements with the CWU observatory. We have begun investigating this issue and we have found that the flat field images that are used for calibrating images can have a significant marginal ray contribution, thus “over-correcting” in an important step of image reduction.

CWU OBSERVATORY MODIFICATIONSColby Neal, Andrew Lawler, Gregory Lyman, Dr. Michael Braunstein

Department of Physics, Central Washington University

AcknowledgmentsThis work has been supported in part by the Washington Space Grant Consortium

(NASA grant NNX10AK64H).

Figure 3. Light curves of a secondary eclipse of SV Cam on 5/9/2011 obtained by collecting 190 sequential 30 second exposures alternating V and I filters. Images were reduced as described in the Figure 2 caption, and the light curve was obtained by the differential photometry component of MaxIm DL 5.

IntroductionLind Hall houses a telescope originally equipped with a manually operated filter wheel using 1¼" diameter filters. While this filter wheel produced satisfactory images, there was a substantial problem of vignetting (attenuation of light signal at the edges of the image), due to the small diameter of the filters and the flip mirror couplings. In order to reduce this vignetting and to address other optical aspects of the telescope the system was modified. The final observatory system consists of:

• 0.3 m Cassegrain reflecting telescope• Large custom-built flip mirror• Apogee AFW50-9R computer-operated filter wheel, equipped

with high quality astronomical 2” diameter Kron-Cousins UBVRI filters

• Apogee Alta U47 Charge Coupled Device (CCD) camera• ACE observatory control system (hardware and software)• Upgraded MaxIM DL 5 camera control and image analysis

software

Key design parameters for the improved observatory system and filter upgrade included structural integrity and an increase in the aperture in the optical path through couplings with an increased inner diameter and a flip mirror with larger area.

An important component of the of the work included design and construction of a flip mirror :

SV Camelopardalis ephemeris from: J.M. Kreiner, 2004, Acta Astronomica, vol. 54, pp 207-210.

References

Figure 5. Schematic representation of the flat-field-marginal-ray issue in a Cassegrain telescope.

Figure 2. Star field for the eclipsing binary star system, SV Cam. The image is 5 stacked 30 second V filter exposures of the field of SV Cam obtained using the modified system on 5/9//2011. The images were reduced using MaxIm DL 5 by subtracting bias and dark and flat fielding. The dimmest stars visible in the image are less than 15th magnitude.

Ongoing Work

Figure 4. A marginal ray flat field image obtained on 5/3/2011 by covering the secondary mirror during a flat field exposure.

-0.06 -0.04 -0.02 0 0.02 0.04 0.06 0.08 0.1

-3.925

-3.875

-3.825

-3.775

-3.725

-3.675

-3.625

-3.575

-3.525

SV Cam, Secondary EclipseKron-Cousin I and V Filters

(V Filter and C3V data offset in magnitude for comparison)

I Filter

C3V

V Filter

Time (Epoch-5381.5)

Diff

eren

tial M

agni

tude

Figure 1. The schematic depicts the flip mirror we designed and constructed for this project. It consists of a hollow aluminum box with an internal mirror that is manually flipped up or down and two cylindrical brass couplings bored out to 2” that slip fits into the telescope and screws into the filter wheel housing. The entire structure acts as a coupling between telescope and the filter wheel/CCD camera.

First Data

The light curve of SV Cam with the I filter shows a much more significant drop in magnitude than the V filter. The stars in SV Cam have a peak in the red to infrared part of the visual spectrum. The I filter would therefore be more sensitive than the V filter.

Conclusion