Posts: 2
Joined: Thu Jun 25, 2020 7:18 pm
Occupation: Student

What am I calculating?!?

Postby JeremyBelpois » Sat Jul 04, 2020 7:58 pm


I recently joined Science Buddies because I needed ideas for a science project for school. I have been working on to prove that it is possible to calculate distance using the parallax method, and I referred to the topic idea Similar Triangles- calculating stellar distances using parallax. I've got all the necessary equipment already, I just have a few questions about setting up the apparatus to gathering all the necessary data.

1. According to the procedure, it instructs us to use 2 small objects for the experiment. Can this be done using one object only too? or should I have 2 objects in from of the grid on the easel? also, why is it necessary to have 2 objects? I've attached 3 pictures taken from the telescope of the object I used, one taken from the centre and the other from the left and right positions. Is this what I should be seeing? I used a Christmas bauble as the object. Is this object too big or should I
use a much smaller object?
P3 pics of the object taken from different positions
(607.18 KiB) Downloaded 22 times

2. Should the distance between the telescope and the easel with objects attached be strictly 100m away from each other or can I use another distance since I cannot get 100 m in my ground? and does it have to be strictly 1m that I should move the telescope or is this also flexible? or would any distance be suitable, by also adjusting the distance moving the telescope from centre to left to right according to the chosen distance from the telescope to the easel?

3. If I take a photograph of the object/s from the centre position and the left and right positions (3 pics total) using the telescope and the camera, should I be measuring the distance the objects moved from the centre of the grid to the left and right? I'm not really sure if I have to mark the new locations in each instance on the grid or should I measure the distance moved ON the picture with a ruler?

4. I also noticed that according to your procedure, you do not use a camera to capture the data, if so, will using a camera to take a picture of the movement of the objects be easier? also, how was it supposed to be done without the use of the camera?

5. Is the left-right movement of the object on the graph/ picture, the only measurement I need to take or is there anything else I need to measure?

6. Do you have any suggestions as to what exactly I must do next after I have all the data?

I would really appreciate if you could help me out with these problems :)

Thank You in advance!

Kind regards

Posts: 37
Joined: Thu Apr 18, 2019 7:51 am
Occupation: Other Adult

Re: What am I calculating?!?

Postby charlesg » Sun Jul 05, 2020 11:25 am

Hi Jeremy,

Thanks for your question. I understand that you're working on the project described here: ... e-distance . I'll answer each of your questions separately:

1. The motivation behind this experiment is measuring distance to a star, and one might want to measure the distance between 2 stars that seem aligned (at times). Performing this experiment with 2 objects allows you to compare the distance between them to your calculations, although you can perform most of this experiment with a single object.

The Christmas bauble seems to work for this experiment. The main constraint is that the object gives you a good reference point for "how far did it move on the grid?" This can be the center-to-center distance or the bottom-to-bottom distance. Just make sure it's the same point. As the procedure points out, it is best to have this reference point on the grid-paper center-line.

2. The exact distances are flexible. Just be sure to measure the exact distances ("d" and "b" in ... #procedure), so you can use those values for your calculation.

3. Yes, you should measure the distance the objects moved from the center of the grid to the left and right. The diagram is a bit confusing, but b' is just one side of these measurements. Since you took photos, you don't have to mark out the movement physically, but you can calculate it from counting the grid marks and multiplying for the spacing. For example, if your grid-paper spacing was 10 cm and the movement was 4.5 grid lines, then b' = 0.1 m/line * 4.5 lines = 0.45m . (Replace those numbers with your actual measurements/grid paper.

4. A camera is a good use of technology here. Nice work. It is good to have those photos as "raw data." However, the use of grid-paper with known-spacing means that students without a camera can count the number of grid-lines the object appears to move, then compute a distance from the known grid spacing.

5. You should also measure the distance from the objects to the grid (step 1), the distance you move your telescope left and right, and the distance from the telescope (center-position) to the object (step 8), so you can compare your calculation with a true measurement.

6. The motivation behind this experiment is to measure the distance to a distant star (your object), if you weren't able to make a "direct measurement" with your tape measure. Use similar triangles and the formula in the procedure to estimate the distance to your object.
Once you complete the experiment, you might consider what limits your measurement accuracy and how this can be improved.

Great work so far. This is a challenging project. Hope you are having fun.


Posts: 2
Joined: Thu Jun 25, 2020 7:18 pm
Occupation: Student

What am I calculating 2

Postby JeremyBelpois » Sat Jul 18, 2020 6:47 pm

Hello again!

Charlesg, thank you for your comprehensive advice that you gave on the earlier topic (What am I calculating?!?), I just had a few last questions that I wanted to clarify for my project Stellar Parallax (referring to the project Similar Triangles: Using Parallax to Measure Distance), which I previously mentioned in the last topic,

1. What is S and S' in the diagram? because it is not shown. Are S and S' the hypotenuse of the triangles?

2. How do we calculate S' ? can we do it by using the Pythagoras theorem for the smaller triangle?

3. Once we find S' using Pythagoras, do we find S by using S'/b' = S/b ?

4. Once we know S', do we use the Pythagoras theorem again for the large trianlge to find d (distance from telescope in the center point to the object) ?

5. Do we measure this distance d using a tape measure and see wether the distance d that we got from the parallax calculation is the same value?

6. By doing the above steps and calculations what exactly am I trying to find and prove? is It that the distance d (distance from telescope in the center point to the object) the same value or close to the value I got from my direct measurements using the tape measure?

7. Lastly, are we trying to say that using this concept of parallax which we demonstrate in this ground based experiment, we can measure the stellar distance to stars using the same concepts?

Again, thank you very much for your great help. I really appreciate it! :D :D :D


Return to “Grades 9-12: Physical Science”