Transcript A Collaborative Variable Star Observing Project

A Collaborative Variable
Star Observing Project
for Introductory
Astronomy
R. Carey Woodward, Jr.
University of Wisconsin—Fond du Lac
Motivation
Astronomy students should observe
something in the sky…
 …preferably something that changes.
 Usual choices—Sun, Moon, planets—not
suitable for 2nd semester (stars & galaxies).
 Sunspot sketches? Not many sunspots this
solar cycle.
 Most stars constant…but not all.

Variable stars
Usually covered mid-semester.
 Several types; many periods.
 Period and type can be identified by light
curve: plot of brightness over time.

Eclipsing binary
Late-stage unstable stars
Cepheid: high mass; period > 1 day.
 RR Lyrae: medium mass; period < 1 day.
 Both have same light curve shape.

Advantages
Some change in timescale that fits in a
semester (hours or days).
 Some are naked-eye objects.
 Determining type and period challenging
but reasonable for intro astronomy.

Drawbacks and solutions

Many observations needed.
– Pool all class observations.
– Adds collaborative element to project.

Students could “google” star.
– Never mention star’s name!
– Choose star near others to defeat smartphone
apps.
The project: First year
Observations start after variable stars
covered; end week before end of class.
 Students given finder chart and
instructions to find star.
 “Field trips” after 2-3 classes to point out
star with laser pointer.
 Students estimate magnitude by
comparison with nearby stars.

Finder/estimator chart
The project: First year (cont’d)
Students e-mail me observations in
spreadsheet (CSV) I supply.
 I consolidate all data in Excel spreadsheet,
adding light curve and adjustable phase
diagram.
 Students determine which data are good,
what type of star it is, and its period.
 Short written report (results and
justification) due at final exam time.

First year light curve
Nobody got it, except by chance (or cheating)!
The project: Second year


Starts earlier (after magnitude system
covered in class).
Each observation entered in one-shot
“survey” in Desire2Learn:
1. Date, time, and location of observation
2. Magnitude (to nearest tenth)
3. Comments (seeing, etc.)

Must be entered within 24 hours!
The project: Second year (cont’d)
Three observation deadlines throughout
semester (for five required observations).
 Observations graded and feedback posted
(in D2L gradebook) after each deadline.

– Includes correct magnitude range for that
date/time
I monitor data, make observations myself
at key times if necessary.
 Deadlines flexed if/as weather dictates.

The project: Second year (cont’d)

I edit observations, consolidate good ones, post
data as before.
The project: Second year (cont’d)

Final report in (editable) survey in D2L:
1.
2.
3.
4.
5.

What is the period?
How did you determine the period?
What is the uncertainty in the period?
What is the type of variable star?
How did you determine the type?
Grade is 70% observation, 30% analysis
(with more detailed breakdown given)
Results
Only 64% did the analysis!
 Of those, 68% correctly determined the type…
 …and 35% found a correct or plausible period.

Conclusions
Variable star observing project works, but
requires frequent feedback and editing of
class data (and decent weather).
 I will probably do this again, but will…

– Start earlier and add another 1-2 observations
– Give range of possible periods
– Count analysis more and/or give 0 if omitted
– Probably pre-empt for strong solar max