Reading the Sky

230 Pages·2014·18 MB·English

Digital Comprehensive Summaries of Uppsala Dissertations
from the Faculty of Science and Technology 1196
Reading the Sky
From Starspots to Spotting Stars
URBAN ERIKSSON
ACTA
UNIVERSITATIS
ISSN 1651-6214
UPSALIENSIS
ISBN 978-91-554-9086-7
UPPSALA
urn:nbn:se:uu:diva-234636
2014
Dissertation presented at Uppsala University to be publicly examined in Polhemsalen
(Å10134), Ångströmlaboratoriet, Uppsala, Thursday, 11 December 2014 at 09:00 for the
degree of Doctor of Philosophy. The examination will be conducted in English. Faculty
examiner: Associate Professor Edward E. Prather (University of Arizona).
Abstract
Eriksson, U. 2014. Reading the Sky. From Starspots to Spotting Stars. Digital Comprehensive
Summaries of Uppsala Dissertations from the Faculty of Science and Technology 1196.
229 pp. Uppsala: Acta Universitatis Upsaliensis. ISBN 978-91-554-9086-7.
This thesis encompasses two research fields in astronomy: astrometry and astronomy education
and they are discussed in two parts. These parts represent two sides of a coin; astrometry, which
is about constructing 3D representations of the Universe, and AER, where for this thesis, the
goal is to investigate university students’ and lecturers’ disciplinary discernment vis-à-vis the
structure of the Universe and extrapolating three-dimensionality.
Part I presents an investigation of stellar surface structures influence on ultra-high-
precision astrometry. The expected effects in different regions of the HR-diagram were
quantified. I also investigated the astrometric effect of exoplanets, since astrometric detection
will become possible with projects such as Gaia. Stellar surface structures produce small
brightness variations, influencing integrated properties such as the total flux, radial velocity
and photocenter position. These properties were modelled and statistical relations between the
variations of the different properties were derived. From the models it is clear that for most
stellar types the astrometric jitter due to stellar surface structures is expected to be of order 10
μAU or greater. This is more than the astrometric displacement typically caused by an Earth-
sized exoplanet in the habitable zone, which is about 1–4 μAU, making astrometric detection
difficult.
Part II presents an investigation of disciplinary discernment at the university level. Astronomy
education is a particularly challenging experience for students because discernment of the ‘real’
Universe is problematic, making interpretation of the many disciplinary-specific representations
used an important educational issue. The ability to ‘fluently’ discern the disciplinary affordances
of these representations becomes crucial for the effective learning of astronomy. To understand
the Universe I conclude that specific experiences are called. Simulations could offer these
experiences, where parallax motion is a crucial component. In a qualitative study, I have
analysed students’ and lecturers’ discernment while watching a simulation video, and found
hierarchies that characterize the discernment in terms of three-dimensionality extrapolation and
an Anatomy of Disciplinary Discernment. I combined these to define a new construct: Reading
the Sky. I conclude that this is a vital competency needed for learning astronomy and suggest
strategies for how to implement this in astronomy education.
Keywords: Astrometry, Astronomy Education Research, Disciplinary Discernment,
Extrapolating three-dimensionality, Reading the Sky
Urban Eriksson, , Department of Physics and Astronomy, Physics Didactics, 516, Uppsala
University, SE-751 20 Uppsala, Sweden.
© Urban Eriksson 2014
ISSN 1651-6214
ISBN 978-91-554-9086-7
urn:nbn:se:uu:diva-234636 (http://urn.kb.se/resolve?urn=urn:nbn:se:uu:diva-234636)
ToMariaandourchildrenfortheirpatience.

List of papers and conference presentations
Thisthesisisbasedonthefollowingpapers,whicharereferredtointhetext
bytheirRomannumerals.
Papers
I Limitsofultra-high-precisionopticalastrometry: Stellarsurface
structures. AstronomyandAstrophysics,476(3),1389-1400.
II Whoneeds3DwhentheUniverseisflat? ScienceEducation,98(3),31.
III IntroducingtheAnatomyofDisciplinaryDiscernment: Anexample
fromAstronomy. EuropeanJournalofScienceandMathematics
Education,2(3),167-182.
Reprintsweremadewithpermissionfromthepublishers.
Conference Presentations
ThefollowingConferencepresentationsalsocontributedtotheworkreported
oninthisthesis.
Airey, J., & Eriksson, U. (2014a). A semiotic analysis of the disciplinary
affordances of the hertzsprung-russell diagram in astronomy. Presentation at
The 5th International 360 Conference: Encompassing the Multimodality of
Knowledge. Aarhus,Denmark: AarhusUniversity. 8-10May.
Airey,J.,Eriksson,U.,Fredlund,T.,&Linder,C.(2014a). Theconceptof
disciplinaryaffordance. PresentationatThe5thInternational360Conference:
Encompassing the Multimodality of Knowledge. Aarhus, Denmark: Aarhus
University. 8-10May.
Airey, J., Eriksson, U., Fredlund, T., & Linder, C. (2014b). On the disci-
plinary affordances of semiotic resources. Presentation at The First Confer-
ence of the International Association for Cognitive Semiotics (IACS), Lund,
Sweden: LundUniversity. 25-27September.
Airey,J.,&Eriksson,U.(2014). Whatdoyouseehere? Usingananalysis
of the Hertzsprung-Russell diagram in astronomy to create a survey of disci-
plinarydiscernment. PresentationatTheFirstConferenceoftheInternational
AssociationforCognitiveSemiotics(IACS).Lund,Sweden: LundUniversity.
25-27September.
Eriksson, U., Linder, C., & Airey, J. (2011). Watching the sky: new real-
izations, new meanings, and surprizing aspects in university level astronomy.
InSciencelearningandcitizenship: ProceedingsoftheESERA2011Confer-
ence. Lyon,France. 5-8September.
Eriksson, U., Linder, C., & Airey, J. (2014). Tell me what you see. Dif-
ferences in what is discerned when professors and students view the same
disciplinarysemioticresource. PresentationatThe5thInternational360Con-
ference: Encompassing the Multimodality of Knowledge. Aarhus, Denmark:
AarhusUniversity. 8-10May.
Eriksson, U., Linder, C., Airey, J., & Redfors, A. (2011). Watching the
sky: Newrealizations,newmeaning,andsurprizingaspectsinuniversitylevel
astronomy. Poster presentation at The Foundations and Frontiers of Physics
Education Research (FFPER) conference, Bar Harbor, Maine, USA. 13-17
June.
Eriksson, U., Linder, C., Airey, J., & Redfors, A. (2012). Who needs 3D
when the universe is flat? Poster presentations at the Gordon Research Con-
ferenceAstronomy’sDiscoveriesandPhysicsEducation,ColbyCollege,Wa-
terville,ME,USA.17-22June.
Eriksson,U.,Linder,C.,Airey,J.,&Redfors,A.(2013a). Awarenessofthe
three dimensional structure of the Universe. Presentation at the 21st Annual
ConferenceoftheSouthernAfricanAssociationforResearchinMathematics,
Science and Technology Education (SAARMSTE), University of the Western
Cape,Bellville,SouthAfrica. 14-17January.
Eriksson,U.,Linder,C.,Airey,J.,&Redfors,A.(2013b). Theoverlooked
challengeoflearningtoextrapolatethree-dimensionality. PresentationatThe
InternationalConferenceonPhysicsEducation. Prague,CzechRepublic. 5-9
August.
Eriksson,U.,Linder,C.,Airey,J.,&Redfors,A.(2013c). Whatdoteachers
of astronomy need to think about? Presentation at the Nordic Physics Days,
Lund,Sweden. 12-14June.
Eriksson, U., Linder, C., Airey, J., & Redfors, A. (2014a). The anatomy
ofdisciplinarydiscernment–Anargumentforaspiraltrajectoryoflearningin
physics education. Presentation at The First Conference of the International
AssociationforCognitiveSemiotics(IACS),Lund,Sweden. 25-27September.

Contents
1 Prelude 21
........................................................................................................
1.1 Introductionandresearchquestions 21
..............................................
1.2 Whoshouldreadthisthesisandwhy? 25
..........................................
1.3 Anoteonthelanguageusedinthisthesis 25
....................................
PartI:Stellarsurfacestructuresandtheastrometricsearchforexoplanets 27
.
2 Introduction 29
................................................................................................
3 OpticalAstrometry 31
....................................................................................
3.1 Sciencedriversforastrometry 31
.......................................................
3.1.1 Stellarastrophysics 32
..........................................................
3.1.2 Kinematicsanddynamicsofstellargroups 32
...................
3.1.3 Exoplanets 33
........................................................................
3.1.4 Solarsystembodies 33
.........................................................
3.1.5 Referenceframes 34
.............................................................
3.2 Classificationofastrometrictechniques 34
.......................................
3.3 Basicastrometricdata 35
....................................................................
3.3.1 Position 35
.............................................................................
3.3.2 Propermotion 36
..................................................................
3.3.3 Parallax 37
.............................................................................
3.4 Noiseandstatistics 38
.........................................................................
3.4.1 Randomerrorsintheastrometricdata 38
...........................
3.4.2 Statisticalbiasesintheuseofastrometricdata 41
.............
3.5 Astrometricdetectionofexoplanets 43
.............................................
3.5.1 Methodsfordetectingexoplanets 44
...................................
3.5.2 Expectedastrometriceffectofexoplanets 47
.....................
3.6 Thefuture: Frommasto μas 51
.........................................................
3.6.1 Gaia: TheBillionStarsSurveyor 52
...................................
3.7 Astrophysicallimitations 55
...............................................................
3.7.1 Circumstellardisks 55
..........................................................
3.7.2 Surfacestructures 56
............................................................
3.7.3 Multiplicity 58
......................................................................
3.7.4 Weakmicrolensingordistortionbygravitationalfields 59
4 Astrometriceffectsofsurfacestructures 62
..................................................
4.1 Methodsofmodellingstellarsurfacestructures 62
..........................
4.2 TheEquivalentAReaSpot(EARS)model 63
..................................
4.2.1 Propertiesofasinglespot 63
...............................................
4.2.2 Multiplespotsonarotatingstar 64
.....................................
4.2.3 Theoreticalrelationsusedinthemodel 67
.........................
4.2.4 Calculationofthemoments 69
............................................
4.2.5 Radialvelocity 72
.................................................................
4.2.6 Summaryofthemoments 73
...............................................
4.3 MonteCarlosimulations 73
...............................................................
4.3.1 Therotatingmodel 74
..........................................................
4.3.2 Thestaticmodel 76
...............................................................
4.3.3 Resultsfromthesimulations 76
..........................................
4.4 Summaryofnumericalresults 79
.......................................................
5 Impactonastrometricexoplanetsearches 80
...............................................
5.1 Predictedeffectsofstellarsurfacestructures 80
...............................
5.2 Comparisonwiththeeffectsofexoplanets 84
...................................
6 Conclusions 87
................................................................................................
6.1 Inreflection 88
.....................................................................................
PartII:AstronomyEducationResearch 89
.........................................................
7 Introduction 91
................................................................................................
7.1 Astronomyasascience–challengesforlearningand
understanding 92
.................................................................................
7.2 AimandjustificationforPartIIofthethesis 94
...............................
7.3 Researchquestions 94
.........................................................................
7.4 HowshouldPartIIofthethesisberead? 95
.....................................
8 Situatingthestudy–AReview 96
................................................................
8.1 PhysicsEducationResearch 96
..........................................................
8.1.1 PERandRepresentationResearch 98
................................
8.2 AstronomyEducationResearch 100
..................................................
8.2.1 HistoricaldevelopmentofAER 100
...................................
8.2.2 FocalpointsinAstronomyEducationResearch 101
.........
8.2.3 Alternativeconceptions 104
.................................................
8.3 VirtualLearningEnvironments–potenttoolsforlearning
astronomy 109
.....................................................................................
8.3.1 3DVirtualLearningEnvironmentsanddisplays 109
........