ASTR101, Spring 2021

This is a webpage for ASTR101 (Spring 2021), Sections 0109 and 0110, of whom I am the TA. I will post useful links, announcements, lab solutions, etc., here.

Table of contents

Links and Files



Meet time: Wed 2:00-2:50 pm
Place: online meeting via Zoom
Instructor: ChongChong He

Discussion #1 (Feb 3)

Discussion #2 (Feb 10)

Discussion #3 (Feb 17)

  • Tasks

    • Finish Lecture-Tutorials activity "Kepler’s laws" (pp. 21-28), focusing on the following activities:

    • Kepler's Second Law, part I: questions 3-7; Part II: questions 8, 9, 11; Part III: 12, 13

    • Kepler's Third Law: start with questions 5-11, then go back to questions 1-4.

    • Finish Discussion #3 Quiz

  • Answer key to the discussion activities

  • Formulary of the Kepler's third law:

$$ \frac{a^3}{P^2} = M $$ or, $$ \frac{\rm (semimajor \, axis \, in \, AU)^3}{\rm (period \, in \, years)^2} = {\rm mass \, of \, the \, star \, in \, solar \, mass} $$

Discussion #4 (Feb 24)

Discussion #5 (Mar 3)

  • Tasks

    1. Finish Lecture-Tutorials activity "Path of the Sun, ecliptic" (pp. 89-92, 13-17). Focus on the following questions: "Path of the Sun": 1-5, 7-13, 19, 20; "Ecliptic": 1-12

    2. Finish Discussion #5 Quiz

  • Photo copy of the LT activities: Path of the Sun Ecliptic.

  • Answer key to discussion activities

Discussion #6 (Mar 10)

Discussion #7 (Mar 24)

Discussion #8 (Mar 31)

Discussion #9 (Apr 7)

Discussion #10 (Apr 14)

Discussion #11 (Apr 21)

Discussion #12 (Apr 28)

  • Task 1: Finish LT activities: Hubble’s law, The Big Bang (pp. 155-160, 165-168) (note that we have swapped this week's discussion with next week in order to prepare for this week's lab)

  • Task 2: Finish Discussion #12 Quiz

  • Answer key

Discussion #13 (May 5)


Meet time: Thu 6:00-8:00 pm (0109) or Thu 3:30-5:30 pm (0110)
Place: online meeting via Zoom
Instructor: ChongChong He

Lab #0 (Jan 28)



  • For macOS users while installing Citrix Workspace:

    • If you see a window asking you to "Add Account", copy and paste this url into the box: , then you'll see a login window where you can login using you umd Directory ID and password.

    • If your computer runs an older version of macOS (<= 10.14), it might not be able to install the latest version of Citrix Workstation. You need to download an older version of Citrix. Go to and click "Workspace App for Mac", then "Earlier Versions of Workspace App for Mac". Find the latest version that supports your OS. For instance, if you have macOS 10.13/10.14, "Citrix Workspace app 2008" should work.

Lab #1 (Feb 4) - Mathematical Tools

Lab #2 (Feb 11) - Phases of the Moon

Lab #3 (Mar 11) - Moons of Jupiter

Lab #4 (Feb 25) - Planetary Surface Features

Lab #5 (Mar 4) - Sky Motions

  • Tasks

    • Finish Lab 5 - Sky Motions. You'll need to use the Stellarium software.

  • A short guide to help you to navigte through Stellarium.

  • Clarification of the lab questions:

    • For Question 5: Turn on meridian, and turn on azimuthal grid (5th icon at the bottom menu) instead of equatorial grid.

    • Question 11-17: to turn on constellation boundaries, navigate to Sky and View Options Window (F4), then Starlore. Make sure Western is sellected on the left, then check "Show boundaries". You may want to adjus the thick and/or color in order to have a clear view of the bondaries.

    • Question 21: first figure out what a Circumpolar circle is. Tip: keep the ground on and fast forward the time through a whole day.

  • Tips

    • When your setting is messed up, restart Stellarium and all settings will be reset to default.

  • Answers to selected questions.

Lab #6 - Spectroscopy

Lab #7 (Apr 1) - Exoplanets

Lab #8 (Apr 8) - Stellar Spectra

  • Tasks: Finish Lab 8 Quiz - Stellar Spectra

  • Make sure you have VIREO installed and working (for Mac, it will be in Citrix).

  • Make sure you have access to Word or Pages! you will need to be able to edit a Word document.

  • Answer key to selected questions.

    Additional Lab Instructions

  • Skip Questions 1-5 in the beginning and jump to 'Stellar Classifications'. Come back to these questions in the end of the lab.

  • Q10: you should be able to answer Q10 just by finding a reference spectrum that minimizes the difference. No need to refer to the reading material under 'Procedure 5'. Note that 'class' is the letter and type is the number, for instance, if you identify a star to be B0 V stars, its class is B and type is 0.

  • Procedure 6: please download all 5 SSP files from Target List A to your local computer, either Windows or macOS, to 1) on Windows, anywhere you like, (e.g. Downloads folder) 2) on Mac, to your home folder. You don't need to open them. Just store it in the home directory of your computer.

  • Procedure 7: MUST READ! Follow the instruction: Click File>Unknown Spectra>Saved Spectra (*.ssp). When selecting your saved .ssp files,

    • Windows Users: navigate to your Downloads folder.

    • Mac Users: click “Local Disk: H” from the left-hand menu. Your Home folder should now appear in Citrix and you should be able to see the SSP files. Click on it.

  • Procedure 7: You only need to classify 5 spectrum, no 10. Record the name of the star (e.g. List A TARGET 13) and its classification (e.g. O5) on somewhere (e.g. in the Word document you downloaded, or on a piece of paper).

Lab #9 (Apr 15) - Measuring Parallax

  • Lab of today

    • Lab 9 - Measuring Parallax.

  • Answer key to selected questions.

  • Q2: When you change to Preset B, the ship is hidden in the Map view although it is still in the lake.

  • Target List to choose at "Determining Distance to Stars 1":

    Your Group # 1-2 3-4 5-6 7-8 9-10
    Target List A B C D E
  • Q6: Skip the part 2 since we are using different target list this week.

  • Q8: you should be able to see your answers to Lab 8 by visiting Lab 8 in another tab. Let me know if there is any difficulty doing that.

  • Q9: Hint: estimate the difference between the distance (d) of the stars and the distance of the cluster center (your answer in Q7). This tells you how far away a star is from the cluster center.

  • Q11: Write your answer from Question 7 to the following Google Doc (choose one depending on your lab section/time): 0109 (6:00 pm) or 0110 (3:30 pm). Please only add your value and DO NOT edit anything else!

Lab #10 (Apr 22) - Galaxies

Additional Instructions

  • "Target Observing Procedure"

    • In this first step, record the 'Type' for all galaxies, plus the Maj. axis and Min. axis for spiral galaxies. Leave the rest of the table for later.

    • Measure the major and minor axes ONLY for spiral galaxies. If an object is not a spiral galaxy, leave all columns blanck except the 'Type'.

  • Question 8. Do the following:

    • Calculate the angular size of the spiral galaxies. Fill in the last column of the table.

    • Find the four spiral galaxies with the largest angular size (including the ones that are already done for you). Write them in the answer box.

  • A printable ruler

  • A Ruler App for Mac. Instructions

    • Install and open the app. Select 'Rulers' (the fourth icon).

    • Take the measurement. Convert 10 px to 1 mm.

Lab #11 (Apr 29) - Expansion of the Universe