Shadows & Time of Year

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SWBAT identify the relationship between shadow length and direction to the time of day and year

Big Idea

Both daylight and time have an effect on shadow length and appearance, and this changes as a result of season, time of day, and location of the Earth and Sun

Lesson Introduction

This lesson introduces a deceptively simple concept - the idea of shadow placement as the function of the Sun's positioning during the sky. Due to the Sun changing position over both the course of the day and year, it's necessary for students to approach this lesson from disparate angles (no pun intended) and think carefully about how shadows point in the opposite direction of the Sun's position. We use a couple in-class examples, some videos, and a lot of practice to help cement this idea for students. 

Materials Needed:

  • Flashlight, floodlight, or thermal lamp

[Note: For embedded comments, checks for understanding (CFUs), and key additional information on transitions and key parts of the lesson not necessarily included in the below narrative, please go to the comments in the following document: 4.5 - Shadows & Time of Year (Whole Lesson w/comments). Additionally, if you would like all of the resources together in a PDF document, that can be accessed as a complete resource here: 4.5 - Shadows & Time of Year [Entire Lesson]. Finally, students may need their Earth Science Reference Tables [ESRT] for parts of the lesson (a document used widely in the New York State Earth Science Regents course) as well.]

Do Now & Objective(s)

10 minutes

Students come in silently and complete the (attached) Do Now. In this case, the Do Now is a review of material from Unit 3 (Geologic History), in preparation for the upcoming interim assessment. After time expires (anywhere from 2-4 minutes depending on the type of Do Now and number of questions), we collectively go over the responses (usually involving a series of cold calls and/or volunteers), before I call on a student and ask them to read the objective out loud to start the lesson.

As a general note, the Do Now serves a few purposes:

  1. It serves as a general review of the previous day's material; (again, this is a bit different, as they are reviewing for the quarterly Interim Assessment)
  2. It is a re-activation of student knowledge to get them back into "student mode" and get them thinking about science after transitioning from another content area or alternate class;
  3. as a strategy for reviewing material students have struggled with (for example, using this as a focused review for material that they have struggled with on unit assessments or recent quizzes); and,
  4. It is an efficient and established routine for entering the classroom that is repeated each day with fidelity (I never let students enter the classroom talking. While it may seem potentially severe to have students enter silently each day, this is both a school wide expectation and a key component of my classroom. In many respects, I find that students readily enjoy the focus that starting with a quiet classrooms brings each day).


15 minutes

After the Do Now, the lesson begins by have students view an animated picture of the University of Nebraska Memorial Plaza, where they can see the same photo snapped at the same time over the course of the year (link). I then have them connect what they've seen in the time-lapse photography to the data table at the top of the first page of the Introduction. This gives them appropriate scope to discern when and how shadows change throughout the year (the answer being that shadow length is inversely related with angle of insolation, so the longest shadows generally occur in the winter, while the shortest occur in the summer).

I also do a very brief demonstration to show this at the front of the room, using a powerful flashlight (I like this one from Amazon), and object (a ruler or piece of paper will work fine, but you can also have someone stand in front of the whiteboard too - literally anything will work here) and the whiteboard. I turn off the lights and switch on the flashlight at a 90 degree and have someone either hold an object against the board or stand in front of it. When the ray of light is perpendicular to the board, there is little to now shadow. But when you keep the light on the object but change the angle (as the Sun's angle changes in the sky), the shadow length gets longer and longer. When the light is practically parallel with the board, the shadow length is quite large. This matches up with what we notice happening outside. Shadows are longest at sunrise and sunset (with low angles of the Sun), and highest at solar noon (when the Sun reaches its greatest angle throughout the day). 

We then begin to extrapolate that data a bit by looking at a bar graph detailing the change in shadow length as the time of day changes. In addition to looking over the graph, we also utilize a clip from Youtube (embedded below) to illustrate this change:

I then take the time, post-video, to explain the overarching rationale, and to help students identify the relationship between shadow length and the time of day and year.

Following this on page two of the Introduction resource, students take the time to think that through and put their thoughts down on paper, and then we do some final notes before they jump into some group/independent practice work [Note: The Word document with embedded comments is particularly helpful in this section, as that very explicitly details a lot of what's happening behind the text you see in the resource, and what you see via the narrative in this section].


25 minutes

The Practice section in this lesson is, like the vast majority of questions found in all of my classwork and homework, is 100% Regents-based. All of the questions come from prior Regents examinations. Likewise, as I try to generally do with all of my lessons, the questions are mostly organized to get increasingly more difficult and increase in complexity, which is why the harder questions tend to come toward the end. For whatever reason, I've found that many students struggle with this content - they mix up the shadow lengths, the inverse relationships, all that stuff. The best way I've found to combat this is to give them the chance to identify and correct their mistakes in questions of this type, which is why this section is a little extended as per my usual lessons. 

In terms of student work habits, I tend to sometimes make this decision in the moment, and as a response of what I know about the students and how they're processing the material on, but I'll either ask them to work independently, in partners, or (sometimes) give them the option. Usually, before starting practice, we tend to go over some steps for self-help ("What should you do if you're stuck?"), and I might reference a previously used multiple-choice or free response strategy in order to build their skills while simultaneously learning content (as an example - one popular one we always use - "If you aren't sure what the right answer is, see if you can eliminate some wrong answer choices"). I tend to circulate for compliance and then hone in on specific students while they're doing this. 

After about 10 minutes, we go over their responses. Students who finish early are encouraged to work on the exit ticket (resource below) and double-check their responses. We use a combination of strategies (active voting, cold calling, popsicle sticks, volunteers) to go over the responses, where students correct their work and ask any clarifying questions. 

Exit Ticket & Closing

5 minutes

In the last few minutes of class, I have students complete the daily Exit Ticket. For the sake of time, I have students grade them communally, with a key emphasis on particular questions and items that hit on the key ideas of the lesson (Note: This usually manifests as students self-grading, or having students do a "trade and grade" with their table partners). After students grade their exit tickets, they usually pass them in (so that I can analyze them) and track their exit ticket scores on a unit Exit Ticket Tracker. 

After students take a few seconds to track their scores, we usually wrap up in a similar way. I give students time to pack up their belongings, and I end the class at the objective, which is posted on the whiteboard, and ask students two questions:

  1. Do you feel that you mastered the objective for the day?
  2. Can you reiterate one thing you learned about (in this case, information on where the vertical ray falls on the respective Equinoxes/Solstices, etc.)?

Once I take 2-3 individual responses (sometimes I'll ask for a binary "thumbs up/thumbs down" or something similar), I have students leave once the bell rings.