Science Buddies: "Ask an Expert"

ET is the "Extraterrestrial constant" which is determined for your instrument by using the calibration procedure. Yes, I do think you need to measure the sun's angle as a part of the calibration procedure, and to determine the air mass, m.

Here is an explantion of how you calculate the air mass term, m.
http://hop.concord.org/lph/lph.concepts.html

"ln ET" is sometimes written as "ln(ET)", which in plain english is "the natural logarithm of ET". If you need more help with that, I would suggest making a post in the mathematics forum, where they will give you a very thorough explanation.

well today i went to a physics teacher and he gave me the average air mass so i might use that because i dont think i can measure the suns angle. and the ET, i dont realy understand all that well. its the constant of the monitor? is that the reading when i put a dark object over the hole that the sunlight goes through?

Gabby, there is no generic "average" air mass of the type that is needed for this equation. This air mass in the equation is normalized to 1 atmosphere thickness, so it will depend on the time of year, time of day, and latitude. More info is provided on those web pages that are linked in previous posts.

Yes, you can think of ET as a constant of the monitor. Here are three ways to calculate the value:
http://hop.concord.org/lph/lph.concepts ... chor967681

Hi,
I have now purchased everything I need for the project including one extra "op. amp" and an extra LED. I got these because "going forward" section suggested that I could measure some other wavelength using these extra components. Now, I am wondering where can I get instructions for adding these components into the haze monitor .... How do I get to measure another wavelength of light ? My project is due on first week of February.

Any suggestions/pointers would be much appreciated .
Thank you.

Hi,
I have now purchased everything I need for the project including one extra "op. amp" and an extra LED. I got these because "going forward" section suggested that I could measure some other wavelength using these extra components. Now, I am wondering where can I get instructions for adding these components into the haze monitor .... How do I get to measure another wavelength of light ? My project is due on first week of February.

Any suggestions/pointers would be much appreciated .
Thank you.

[quote="nxg"]Hi,
I have now purchased everything I need for the project including one extra "op. amp" and an extra LED. I got these because "going forward" section suggested that I could measure some other wavelength using these extra components. Now, I am wondering where can I get instructions for adding these components into the haze monitor .... How do I get to measure another wavelength of light ? My project is due on first week of February.

Any suggestions/pointers would be much appreciated .
Thank you.
[/quote]

I am very sorry, While trying to delete my first post [ which I could not finally] -- I ended up posting it thrice. Seems like there is no way to delete it.

Thanks.

I am unable to figure out where the 4 terminals are [referred to in step 4 of "Prepare the switch".
Please help ASAP.

Thanks.

Finally, I have built the first version of it and I think it is working. But would love to add another LED and op amp to add a new feature but I need help.
Can someone please point me to the right direction ?

Thanks,
nxg

Sorry - I'm not adept at electronics. I'll see if I can find somebody to help.

HELP!!!! i have all the sun angles now but i dont know where to go from there. what equation do i need for air mass because i need to air mass to find the 1n ET. my project will be late but i have just been stuck on this one thing and if there is an equation is there a place where i can just enter my data and it automatically give me the air mass.???

well while im here let me tell you how and where i got the angle of the sun. http://www.susdesign.com/sunangle. soooooo how do i get the air mass with the angle? all the places i went to want the pole height and shadow length and then put that in a formula and BAM you got your air mass. pleeeze im desperate![/url]

"The air mass m for each of your measurements is 1 divided by the sine of the Sun's angle."

http://hop.concord.org/lph/lph.concepts.html

The xls speadsheet refers to some year code, the year code for 2007 is not provided. Can someone please provide me that and let me know what is it ?

Thanks,
nxg

The year code for 2007 should be 2557. In this case, it is the number of days elapsed between 1/1/2000 and 1/1/2007.

what happens if my AOT is negative??? on one website it said if its negative i cant use it. is that true? im scared if that is so because what if i have too many negative AOTs and only a few positive ones??? i didnt think this project would be this hard and stressful.

Hang in there Gabby. You are dealing with the hardest part right now, and it will get easier.

Have you double checked your calculations to make sure there are no errors? If you like, you can post all your values and calculations here, and I (and/ or other experts) can double check them for you.

well i think i figured out what went wrong my calculator wasnt in the right setting so i'll redo them and post them up later tonight. and just for my knowlege what grade level is this project normally for??? it seems like an 11th grade project to me dealing with physics and all.

OK, I'm glad to hear that you might have found the problem.
Yes, this is a fairly complicated project. Good for you for sticking with it!

ok well i still got some negatives but not as many hope you're ready for all my data!

1. Home-1
· Date= Jan. 13, 2007
· Time= 11:50 am
· Temperature= 56° F
· Pressure= 30.24"
· Weather= mostly cloudy
· Dark signal= 0.306v
· Sun signal= 1.05v
· Altitude angle= 26.38°
· Relative air mass= 2.251
· Ln signal= -.296
· AOT= .724

2. School- 1
· Date= Jan. 15, 2007
· Time= 10:11 am
· Temperature= 60° F
· Pressure= 29.99"
· Weather= cloudy
· Dark signal= 0.306v
· Sun signal= 0.967v
· Altitude angle= 15.76°
· Relative air mass= 3.682
· Ln signal= -.414
· AOT= .43

3. School- 2
· Date= Jan. 17, 2007
· Time= 9:11 am
· Temperature= 26° F
· Pressure= 30.74"
· Weather= clear
· Dark signal= 0.3v
· Sun signal= 3.17v
· Altitude angle= 6.90°
· Relative air mass= 8.324
· Ln signal= 1.054
· AOT= -0.055

4. School- 3
· Date= Jan. 17, 2007
· Time= 10:07 am
· Temperature= 28° F
· Pressure= 30.76"
· Weather= clear
· Dark signal= 0.305v
· Sun signal= 3.91v
· Altitude angle= 15.41°
· Relative air mass= 3.763
· Ln signal= 1.282
· AOT= -0.036

5. School- 4
· Date= Jan. 17, 2007
· Time= 12:03 pm
· Temperature= 31° F
· Pressure= 30.75"
· Weather= clear
· Dark signal= 0.306v
· Sun signal= 4.41v
· Altitude angle= 27.88°
· Relative air mass= 2.138
· Ln signal= 1.412
· AOT= -0.032

6. School- 5
· Date= Jan 17, 2007
· Time= 12:25 pm
· Temperature= 31° F
· Pressure= 30.75"
· Weather= clear
· Dark signal= 0.307v
· Sun signal= 4.76v
· Altitude angle= 29.16°
· Relative air mass= 2.052
· Ln signal= 1.494
· AOT= -0.069


7. Home- 2
· Date= Jan. 17, 2007
· Time= 2:54 pm
· Temperature= 33° F
· Pressure= 30.72"
· Weather= clear
· Dark signal= 0.288v
· Sun signal= 3.74v
· Altitude angle= 26.47°
· Relative air mass= 2.244
· Ln signal= 1.239
· AOT= 0.041

8. Home- 3
· Date= Jan, 17, 2007
· Time= 3:31 pm
· Temperature= 33° F
· Pressure= 30.72"
· Weather= clear
· Dark signal= 0.302v
· Sun signal= 0.748v
· Altitude angle= 22.94°
· Relative air mass= 2.566
· Ln signal= -.807
· AOT= 0.818

9. Home- 4
· Date= Jan, 17, 2007
· Time= 4:01 pm
· Temperature= 33° F
· Pressure= 30.72"
· Weather= clear
· Dark signal= 0.31v
· Sun signal= 1.586v
· Altitude angle= 19.44°
· Relative air mass= 3.005
· Ln signal= .244
· AOT= 0.331

10. Home- 5
· Date= Jan. 19, 2007
· Time= 3:05 pm
· Temperature= 46° F
· Pressure= 29.95"
· Weather= partly cloudy
· Dark signal= 0.628v
· Sun Signal= 2.24v
· Altitude angle= 25.96°
· Relative air mass= 2.284
· Ln signal= .477
· AOT= 0.375

11. Home- 6
· Date= Jan. 19, 2007
· Time= 4:01 pm
· Temperature= 43° F
· Pressure= 29.98"
· Weather= partly cloudy
· Dark signal= .632v
· Sun Signal= .956v
· Altitude angle= 19.86°
· Relative air mass= 2.944
· Ln signal= -1.127
· AOT= 0.809

12. Home- 7
· Date= Jan 20, 2007
· Time= 10:20 am
· Temperature= 30° F
· Pressure= 30.21"
· Weather= sunny
· Dark signal= .639v
· Sun Signal= 4.21v
· Altitude angle= 17.63°
· Relative air mass= 3.302
· Ln signal= 1.273
· AOT= -0.019

13. Home- 8
· Date= Jan. 20, 2007
· Time= 1:03 pm
· Temperature= 37° F
· Pressure= 30.21"
· Weather= sunny
· Dark signal= .641v
· Sun Signal= 5.10v
· Altitude angle= 30.99°
· Relative air mass= 1.942
· Ln signal= 1.495
· AOT= -0.064

14. School- 6
· Date= Jan 23, 2007
· Time= 9:55 am
· Temperature= 35° F
· Pressure= 30.02"
· Weather= partly cloudy
· Dark signal= .61v
· Sun Signal= 3.94v
· Altitude angle= 14.44°
· Relative air mass= 4.01
· Ln signal= 1.203
· AOT= -0.018

15. School- 7
· Date= Jan. 23, 2007
· Time= 11:27 am
· Temperature= 39° F
· Pressure= 30"
· Weather= partly cloudy
· Dark signal= .606v
· Sun Signal= 4.41v
· Altitude angle= 25.97°
· Relative air mass= 2.284
· Ln signal= 1.336
· AOT= -0.002

16. School- 8
· Date= Jan. 23, 2007
· Time= 11:57 am
· Temperature= 39° F
· Pressure= 30"
· Weather= partly cloudy
· Dark signal= .577v
· Sun Signal= 4.36v
· Altitude angle= 28.56°
· Relative air mass= 2.092
· Ln signal= 1.331
· AOT= 0.011

17. Home- 9
· Date= Jan. 23, 2007
· Time= 3:16 pm
· Temperature= 41° F
· Pressure= 29.95"
· Weather= partly cloudy
· Dark signal= .569v
· Sun Signal= 2.26v
· Altitude angle= 25.85°
· Relative air mass= 2.293
· Ln signal= .525
· AOT= 0.352

18. Home- 10
· Date=Jan. 23, 2007
· Time=3:43 pm
· Temperature= 41° F
· Pressure= 29.95"
· Weather= partly cloudy
· Dark signal= .57v
· Sun Signal= 1.147v
· Altitude angle=22.95°
· Relative air mass= 2.565
· Ln signal= -.55
· AOT= 0.721

19. Home- 11

· Date= Jan. 25, 2007
· Time= 3:21 pm
· Temperature=37° F
· Pressure=29.86"
· Weather=partly cloudy
· Dark signal= .576v
· Sun Signal= 1.112v
· Altitude angle=25.83°
· Relative air mass= 2.295
· Ln signal= -.624
· AOT= 0.852

Hi Gabby,
What is your ET value?

I did put 122.01 west longitude, 37.23 latitude, time GMT -8, time 30th Jan 4 PM in sundesign.com/sunangle. It is giving me :

altitude angle 14.88, azimuth angle -53.58, hour angle -54.66.

Which one of these in my sun angle ?

I am yet to measure my sun angle with the manual method. I do not have the level -- thats why.

Thanks.

nxg,
According to this web page, the altitude angle (angle between the sun and the horizontal plane) is the one to use to calculate m.

oops. here is the web page
http://hop.concord.org/lph/lph.concepts ... chor967681

Hi ChrisG,
Thanks much for your help. Could you please help me to figure out where can I buy a bubble vial ? I am yet to get a clear and sunny day, so not able to find out the ET .

Thanks,
NxG

NxG - No problem. I'm glad to help.
Is a "bubble vial" the same as a "level"? You can buy those at most hardware stores. Also, many people have one in their toolbox, so you could just ask around.

my ET constant is 1.6

well my science fair is tommorrow so wish me luck! and in my lab report you are down in my ackknowledgements so KUDOS TO YOU!!!! thank you sooo much for all the help you have given me i realy do apreciate it and i will be sure to write beack and tell you how everything went and if i won an award or anything. well... awards are announced a week later so i write about it a week from tommorrow. THANKS AGAIN!!!!

hi again i need to know your full last name for my acknowledgements. i want it to be propper and G, Chris is not all that propper. i promise ill keep it a secret!!! if i dont know what it is then i cant list you down on my acknowledgements and i rele want to so message back ASAP!!!!

Hi Gabby,
Thanks very much for the acknowledgment, and congratulations on a well done project. You stuck with it through some difficult challenges.

Sorry we didn't get to compare calculations. I did run the numbers, so if you are interested, we can discuss more when you are done with the science fair.

I hope everything goes great for you at the science fair tomorrow.

Chris

YAY!!!!! i got 3rd place in my category!!!! woop woop hehe ok well thanx again and ill hopefully repeat the project again now that i know what to do soooo... until then, BYE!