Science Buddies: "Ask an Expert"

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!

Congratulations! I'm happy for you.

Hi Chris,
I do not understand this data that Gaby posted:
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

It should be negative AOT, right ?

In any case, I am getting all AOTs negative, please help me understand this:

few examples:
Sun angle : 16.89,
Pressure (in inches): 30.33
Sun signal : 2.2v [ dark - sun ]
Airmass calculated : 3.44
MY ET : 1.78
AOT as -0.180.
=============
Sun angle : 29.85
Pressure (in inches): 30.30
Sun signal : 3.02v [ dark - sun ]
Airmass calculated : 2.01
MY ET : 1.78
AOT as -0.280
=============


Is it wrong ?

Thanks,
nxg

Hi nxg,
I also got different AOT values from Gabby's measurements.

For your first set of measurements, I calculated the same AOT as you. On the second set, I calculated an AOT of -0.38.

As far as an explanation for why your values are all negative, one possibility is that there is a problem with your ET value. For the first set of measurements, you would need an ET > 3.4 to bring your AOT into the positive range. I would suggest calibrating the instrument again, which is never a bad idea, even if your results seem reasonable. I do not think the m values are the culprit here - no matter how I change those, the AOT remains negative.

I hope that helps.

Chris

Hi Chris,
I think I know where the problem is. The graphical method of finding out ET gives me ln(ET), not ET, right ? If that is the case, then I am getting AOT as about 0.16 all the time. So, my ln(ET) was 1.78. Not ET.

I have to turn in the project in two days. I am assuming that anyways.

Thank you very much for your help. I really appreciate it.

nxg,
I believe you are correct. Congrats on figuring that out, and good luck with the final work on your project. It sounds like it will be very impressive.

Glad to help,
Chris

Finally I am ready with the project [ tomorrow] presentation and stuck with the following question. If AOT is the measurement of Haze why is this supposed to be fixed ?

Thanks,
NxG

Hi nxg,
I'm not sure I understand your question. Does it say somewhere that AOT should be constant?
Chris

Hi Chris,
While reading some part from haze101 -- I came across somewhere that AOT will be same, that's what confused me. Now, I did little more research and my confusion is clear.

Thanks,
NxG

OK. Good luck with your presentation!

now that i think about it i wanted to talk to you about the results i got when i measured the haze and did the formula. i was jsut wondering if i did everything right.

Hi Chris,
Thank you very much for your help. It went well, waiting for my grades.

Thanks,
NxG

Nxg, I'm glad to hear it! I hope you will get the grades that you want.

Gabby,
I think that you did your calculations correctly. I believe that nxg and I were originally getting different results from you because there was some confusion about ln(ET) versus ET. Now that the confusion is cleared up, I rechecked one of your calculations and got the same result. Good for you for following up on the work!

YAY!!! thankyou soooo much! ok well ill do the project again next year so i can get more data sooo until then BYE!!!

That's a good idea - now that you've done the hard work of building the equipment and figuring out the calculations, you'll be able to spend more time planning the experiment and collecting data.
See you next year.