Sunset observation project

Number of observations: 7 (seven)

(You may change the location you use for your observations from day to day)

The general explanations for the oblateness (flattening) and the redness of the low sun are well

understood. Oblateness is the direct result of the refractive (light bending) property of light: when light

travels through the Earth’s atmosphere it takes the fastest path (rather than the shortest), and as a

result, it angles downwards. The reddening of

the sun is the direct result of light’s scattering

property: the shorter wavelengths (violet,

blue, green) will scatter off water vapor

particles, ozone and nitrogen in the Earth’s

atmosphere. The more atmosphere the light

has to travel through, the more short-

wavelengths photons (blue) will be scattered

out on the way. This varying thickness of the

atmosphere also makes light to bend more

and thus gradually compresses the sun’s

appearance in the vertical direction. (More info:

http://www.atoptics.co.uk/atoptics/sunflat.htm and http://www.youtube.com/watch?v=c9y5nwok1to).

While in general we understand the phenomena, the influence of weather and sky conditions on the

intensification of these effects is not very well documented. For instance, it is known that volcanic

eruptions lead to very red sunsets. Thus, it appears as if the level of pollutions should play a role. Your

task is to conduct precise observations of the setting sun and record its color and color gradation (color

transition) and to connect the solar appearance to the atmospheric and/or meteorological conditions.

Every day throughout your observations look for the meteorological data on this website (make sure to

enter your zip code): http://www.wunderground.com/ and fill out your observational data tables (a

separate document).

What you should be able to see is the following: “The top of the Sun may look yellow when the middle is

orange and the bottom is red. Of course, usually it is different shades of the same color that are noticed –

IMPORTANT! Your observation must begin when the sun is low and very close to the

horizon. Never stare at the bright sun; you may permanently damage your eye sight! If the

sun is not dim enough and your eyes are even slightly dazzled by the light, DO NOT LOOK!

WAIT for a few more minutes. Take a quick glimpse at the sun first to make sure that it is

safe to conduct your observations.

the farther toward the red end of the spectrum, the lower on the solar disk.” (Fred Schaaf, Seeing the

Sky, 2012)

NOTE: it takes practice to see different colors and gradation of the sun. Your first observations may not

be precise but with more observations you will be able to easily detect redness on an absolute scale (1-

8, yellow – deep red). It is exciting to look for the least red and the reddest sunsets and then find out

how atmospheric and meteorological conditions correspond to these sunsets!

When you make your sketches, make them all for the exact same situation, namely when the bottom

of the Sun appears to touch the ground. Thus, you have to choose a location that has an open horizon.

Color scale for the observations: 1 – yellow, 2 – orangish yellow, 3 – yellowing orange, 4 – orange, 5

reddish orange, 6 - orangish red, 7 – red, 8 – deep red.

Throughout your observations you have to keep a journal log (description) in which you should note the

following:

 the change in color and gradation of color from the top to the bottom of the Sun;

 how rapidly the reddening increases as the sun is setting;

 how gradual or abrupt the transitions are;

 how many distinctly different shades you perceive;

 how big a total difference there is from the hue at the top to the one at the bottom.

 What the weather is the day after you conduct your observations

Include photos of the overall sky and sketches for each of your seven observations of the sun’s shape

and transitions of colors (one separate sketch for each observation). So you need to take a photo AND

make a sketch every day of observation.

Next, ascertain how a) the overall color and b) the oblateness of the sun correlates (if at all) with

atmospheric and meteorological conditions as written down in your data tables. For instance, you can

plot the oblateness on the vertical axis and the temperature on the horizontal axis. Do the points look

random or does it look like there is a correlation between them? Do this for other variables such as color

of the Sun versus humidity. So this takes a bit of effort since there are 2 x 5= 10 graphs you would have

to make.

Lastly, is it true that a red sunset imply that it will be a beautiful day tomorrow? We have sayings such as

“red sky at night, sailor’s delight” and we can even find it in the Bible (Matthew 16:2) “He answered and

said unto them, When it is evening, ye say, It will be fair weather: for the sky is red”. Scientifically this

makes sense since at sunset the Sun is low and sunlight has to travel through lots of atmosphere. Blue

light will be scattered out (hence the blue sky during the day), leaving only red rays. But if red rays can

reach us, then this means they were not absorbed by clouds to the West, where our weather comes

from the next day. So investigate this, make a graph of the color of the sky at sunset, and the weather

(clear or cloudy or in-between) the next day.

In conclusion,

You have to write a two paragraph summary of your observations. The first paragraph is about whether

there is a correlation between the color of the Sun and/or its shape and atmospheric conditions. Make

sure I can follow your reasoning.

The second paragraph details why you concluded that there is, or that there is not, a correlation

between the color of the sky at sunset and the weather the next day.

o NOTE: you will be analyzing a number of variables which may or may not show any

correlation, based your conclusion on the outcome of your data analysis. If you see no

correlation, state as such and support your conclusion with two graphs (one graph per

statement) that demonstrate your findings. If your data shows that there are more than

one variable affecting the appearance of the sun, create separate graphs to

demonstrate these correlations;

If you feel like you have found a correlation between the gradation and atmospheric conditions, write a

third paragraph showing this. This third paragraph is for bonus points.

Examples (Data table is posted as a separate document)

Data table of Observations and Atmospheric Conditions

Observa tions #

Date Time (hour :

minutes)

Location Sky condition

Shape of the Sun

Color of the sky

(overall, qualitative)

Color of the sun (overall,

scale)

Gradation (details of each distinguishable

band, scale)

1 June 18th

8:50 PM

Columb ia, a hill above Twin Lakes park

Clear with a couple of tiny white clouds in the North

Looked a bit flattened at the bottom, round at the top

Red 7 The top of the sun appeared to be bright yellow (1), closer to the middle it transitioned to 2 and then it abruptly looked as orangish-red (6)

2 --- --- ---

Data table of Observations and Meteorological Conditions

Observation #

Temperature (at the

sunset, °F)

Visibility (miles)

Humidity (%)

Pollen (out

of 12)

Tomorrow’s weather: clear or cloudy?

1 83 10.0 65 5.1

cloudy

2 --- --- --- ---

Sketch for Observation # 1

I copied this photo (overleaf), but you have to make your own sketch for each of your observations!

NOTE: if you are good in photography, you may attempt to take your own photographs of the sun but make sure that your photographs complement your observations and that your photographs correctly reflect the colors of the setting sun.

Grading rubrics (out of 50 points):

Table 1: 10 points

Table 2: 10 points

Photos of overall sky at sunset: 7 points (1 point per photo)

Sketches: 7 points (1 point per sketch)

Conclusion Paragraph 1: is there a correlation between the color and/or shape of the Sun and atmospheric conditions? 8 points

Conclusion Paragraph 2: does red sky mean good weather? 8 points