--- title: "Locating the Cosmos" author: Jed Rembold date: January 14, 2025 slideNumber: true theme: tokyo-night-light highlightjs-theme: tokyo-night-light width: 1920 height: 1080 transition: slide hash: true history: false --- ## Announcements - Welcome to DATA-275: Data in the Cosmos! - Things to do: - Access the course webpage [here!](https://jrembold.github.io/Website_Backup/classes/data275/data275/) - This page is also linked from Canvas - Read over the full syllabus - Join the class Discord server for ease of communication and announcements - Invite information in an announcement on Canvas - If you don't already have a GitHub account, sign up for one - Homework 1 will be posted Thursday. Not due for two weeks from Friday. # An introduction ## Who Am I? ::::::cols ::::col Name : Jed Rembold Background : PhD in Physics with specialization in Astrophysics Office : Ford 214 :::: ::::col Office Hours : M, W 2:00 - 4:00 : T, Th 3:00 - 4:30 : Online or anytime my door is open Email : jjrembold at willamette.edu :::: :::::: ## Why This Course? - The amount of data that telescopes produce is growing...astronomically - LSST to collect 20 TB _per night_ starting **this year**! - First light is scheduled for July - Square Kilometre Array will generate 10 PB _compressed_ daily starting in 2028 - One of the largest sky surveys currently, SDSS, has collected 40 TB over **the past 20 years** - As such, the field of astronomy is becoming (or has become) a data science field - Astrophysicists adopting data science skills - Collaboration between astronomers and data scientists only going to build ## Course Objectives - Learn some science! How do astronomers and astrophysicists attempt to make sense of their data? - Learn some new data analysis techniques! - Learn scientific communication! The most brilliant analysis is worthless if not well communicated. - Learn teamwork! It is invaluable, and most of us are worse at it than we should be. ## Deliverables and Scoring ::::{.cols style='align-items: center'} :::col - Standard 90/80/70 etc grade cut-offs - Top 2% get +'s, bottom 2% get -'s ::: :::col ------------- ---------- Homework (6) 45% Checkins (14) 5% Quizzes (3) 25% Projects (1) 25% ------------- ---------- ::: :::: ## Homework - One assignment due after each unit, so approximately 1 every 2-3 weeks - Assignments will be done in pairs - Pseudo-randomly assigned (You won't be with the same person more than once) - 3-4 problems per assignment - Solutions should be written up as short computational essays, using a Jupyter Notebook, RMarkdown, or Quarto, and exported to HTML before being submitted - Distribution and submission of materials managed through GitHub Classroom - 3 cumulative late days over the semester without penalty, then a 20% loss of credit per 24 hours late - Late days count against **both** partners, so don't be that person who tanks your partner's grade because _you_ had the days ## Check-ins and Debriefings - A large portion of this course revolves around working with peers who may have very different skill sets to your own - Doing this well is difficult! - Each week an assignment is **not** due, you will have the weekend to complete a very short check-in - Asks about what you've accomplished that week, and how you and your partner have planned the upcoming week to finish the assignment - Each week an assignment **is** due, you will have a short debriefing reflection - Reflect on what you did well as a partner, where you dropped the ball, and how you could improve going forward. You can't improve what you don't realize needs improving. - You have the weekend to complete these. They can not use late days. ## Group Dissolution - You will likely have a mix of great groups, and less great groups over the course of the semester - You can learn from and improve your ability to work in groups from both - What is inexcusable is ghosting your fellow group members. Nobody learns anything in that case. - I will thus dissolve a group should one of the members ask and be able to show me the following: - A written communication to a group member that clearly requests a response, and which has not been responded to (in the same form) 48hrs after being sent - This is brought to my attention at least 48hrs before the assignment deadline ## Repercussions - Group dissolution is meant as a last resort, if things just really are not working - To incentivize you treating it as such, there are penalties - Dissolved groups incur the following: - Group members will be responsible for turning in and submitting their own independent work, to be graded separately - The member that asked for the group to be dissolved takes a 2.5% penalty on the assignment - The member that failed to communicate takes a 7.5% penalty on the assignment ## Quizzes - This course is a mix of science and data analysis techniques - Quizzes are about the science - After every 2 units, there will be a short quiz (30 min) at the end of class - A handful of multiple choice or short answer questions pertaining to the scientific topics we have discussed in the previous 2 topics - I'll have example questions and study materials for you a week before each quiz ## Projects - One final project at the end of the semester - Projects will be group based, most likely of 3-4 - Projects are a chance for you to dive deeper into a topic that has been discussed, or look to bring several topics together to look at something that interests you - Can also be an opportunity to introduce the class to a concept that we haven't discussed, if your topic of interest necessitates - Project deliverables will be an approximately 10-12 minute presentation to the class ## Outline - Core units this semester will focus on: - The Solar System - Stars - Exoplanets - Galaxies - MCMC - Dark Matter and Cosmology - Expect to spend about 4-5 classes, or about two weeks, on each unit - Class lectures will be a mix of background science, analysis techniques, and interactive tutorials - Plan to bring a laptop if possible to work on during class activities ## Remain Flexible! - This is the third time this class is being taught! - While I try immensely hard to be good at what I do, I can not (yet) see the future - I am _incredibly_ excited to teach this class again, and that somehow more people seem interested each time the class is taught. - I ask in return that you be patient and forgiving if some things do not go perfectly - I promise to engage you and solicit feedback about any changes or tweaks we need to make on the fly # Today's Content ## Topics for Today - Positions on the Sky - What can we tell about the position of an astronomical object? - How do we describe those positions? - What are the common methods? - How can we transition between those methods? ## Looking to the heavens ![](../images/night_sky.png){width=100%} ## Looks can be deceiving - Stars (or other bright objects) generally only _appear_ to be next to one another - In reality, they are almost certainly separated by massive distances - Stars are so far away that we lose essentially all depth perception - Comparable to looking at far away headlights on a dark road - Looking upward, we could not tell the difference between space (as we know it to be) and us living inside a huge dark bubble with holes poked in it to let in light - Embracing this analogy, we commonly refer to the _Celestial Sphere_, which could be envisioned as this giant dark bubble with holes poked in it ## The Celestial Sphere - Defined to align with Earth's sphere: - The celestial North pole is directly above Earth's North pole - The celestial South pole is directly below Earth's South pole - The celestial "equator" aligns with Earth's equator - The celestial equator does **not** align with the disk of the Solar System, because Earth is tilted - The _ecliptic_ traces the intersection of the celestial sphere and the disk of the Solar System, and is the path that the Sun and planets follow through our sky ## Orientation and Vocabulary \begin{tikzpicture}%%width=45% [draw=Black, every node/.style={black,font=\tiny\sf},scale=.9, rotate=-25] \draw (0,0) circle(3); \draw[help lines, dashed] (0,3) arc (90:-90:1.5cm and 3cm); \draw (0,3) arc (90:270:1.5cm and 3cm); \draw[help lines, dashed] (-3,0) arc (180:0:3cm and 1.5cm); \draw[Red!75,thick] (-3,0) arc (180:360:3cm and 1.5cm) node[pos=0.75,above,align=center,xshift=-3mm] {Celestial\\Equator} ; \draw (0,-.8) node[below,align=center] {Earth\\South Pole} -- (0,.8) node[above,align=center] {Earth\\North Pole}; \fill[ball color=Purple!50] (0,0) circle (0.75cm); \draw[Red!75] (-.75,0) arc (180:360:.75cm and .25cm); \draw (0,3) -- (0,3.2) node[above,align=center] {Celestial\\North\\Pole}; \draw (0,-3) -- (0,-3.2) node[below,align=center] {Celestial\\South\\Pole}; \draw[Green, rotate=25, very thick] (-3,0) arc (180:360:3cm and .8cm); \draw[Green, rotate=25, dashed,thick] (-3,0) arc (180:0:3cm and .8cm) node[left,Green] {Ecliptic}; \end{tikzpicture} ## From Our Perspective \begin{tikzpicture}%%width=50% [draw=Black, every node/.style={Black, font=\scriptsize\sf}] \draw (0,0) circle(3); \draw[Red,latex-,yscale=-1,rotate=-235, dashed] (-.5,1) arc (100:-80:3cm and 1cm); \fill[Green, opacity=0.6] (0,0) ellipse (1cm and 0.33cm); \draw[Green] (-3,0) arc (180:540:3cm and 1cm) node[Green, pos=.4,sloped,yshift=-3pt] {Horizon}; \draw (-3,0) node[left] {N} -- (3,0) node[right] {S}; \draw (-.5,1.0) node[above left] {E} -- (.5,-1) node[below right] {W}; \draw[Red,latex-,yscale=-1,rotate=-55] (-.5,1) arc (100:-80:3cm and 1cm) node[pos=.6, Red, right] {Celestial Equator}; \begin{scope}[rotate=45] \draw[fill=Black](0,3) circle(0.75mm) node[below right,align=center] {Celestial\\North}-- (0,4); \draw[-latex] (0.1,3.4) arc (70:-250:.30cm and .10cm); \draw[fill=Black] (0,-3) circle(0.75mm) node[above left, align=center] {Celestial\\South} -- (0,-4); \end{scope} \fill[Black] (0,3) circle(.75mm) node[above] {Zenith}; \draw (.6,1.6) -- (1,2) node[xshift=2pt,yshift=2pt] {$\star$}; \draw (.1,1.3) -- (.5,1.7) node[xshift=2pt,yshift=2pt] {$\star$}; \end{tikzpicture} ## {data-background-iframe="https://astro.unl.edu/naap/motion2/animations/ce_hc.html"} ## The Equatorial coordinate system - Coordinates on the Celestial Sphere are determine just like on Earth: with a latitude and longitude ::::::{.cols style='align-items: flex-start'} ::::col :::{.block name="Celestial latitude (Declination)"} - Varies from -90 to +90 degrees - High precision uses arc-minutes, where 60 arc-minute $=60^\prime = 1^\circ$ - Can also use arc-seconds, where 60 arc-second $=60^{\prime\prime} = 1^\prime$ $$\begin{aligned}15^\circ45^\prime30^{\prime\prime} &= (15 + 45/60 + 30/3600)^\circ\\ &= 15.75833^\circ \end{aligned}$$ ::: :::: ::::col :::{.block name="Celestial longitude (Right Ascension)"} - Varies from 0 to 360 degrees - Because the celestial sphere rotates about its poles once every 24 hours, Right ascension is also commonly indicated in units of hours, minutes, and seconds - 1 hr = 15 degrees $$\begin{aligned}14h32m14s &= (14 + 32/60 + 14/3600)h\\ &= 14.5372h\\ &= (14.5372 \times 15)^\circ\\ &= 218.0583^\circ\end{aligned}$$ ::: :::: :::::: ## Movement - The further away something is from us, the more it seems to be "locked" to the celestial sphere - Stars are essentially motionless, with basically fixed declination and right ascension - Solar system objects, like planets or the Sun, slowly traverse along the ecliptic - The Moon follows a curve quite close to the ecliptic, but not exactly, at a faster pace - Objects in orbit, like satellites, do not seem fixed to the celestial sphere at all - The Milky Way, being comprised of stars, is fixed to the celestial sphere - The galactic plane lines up with neither Earth's equator nor the disk of the Solar System, and thus stretches across the sky at an alternative angle ## The Local System - Determined by **where** and **when** you are looking at the sky - Still commonly uses two coordinates: - The direction you are looking (_Azimuth_) - Generally determined by something like a compass bearing - The angle above the horizon that the object appears (_Altitude_) - Generally determined with a sextant, possible with rough hand measurements ## Other Coordinate systems - Astronomy will frequently utilize other coordinate systems as well: - Solar barycentric coordinates: based on the center of mass of the Sun - Galactic coordinates: also centered on the Sun, but with different orientation - Even Equatorial coordinates can vary some owing to the precession of the Earth, and thus often specify an _epoch_ - All can be transformed between one another using geometry - Not always very nice geometry! - We won't need to convert between coordinates too often in this class, and we'll try to leverage existing libraries to do this wherever possible ## Celestial Sphere Demonstrations - How long is the Sun up today (not that you can see it...) here on the 45th parallel? - How long is the Sun up in Alaska (roughly on the 65th parallel)? - How long after sunset will the bright star Arcturus rise today in Salem? ## Plotting Coordinates Demonstration - The file [here](../demos/brightest_200.csv) is a CSV file containing the names and coordinates of the brightest 200 stars - Suppose we want to visualize this arrangement of stars to see if we could identify any constellations