## Honolulu "Street Henge"? Find your alignment in the city!

### Introduction

OBJECTIVE: The objective of this exercise is to get you thinking about directions on Earth and Earth-Sun orientation. Your task is to photographically document one such sunset or sunrise on a Honolulu street this semester.

Background: There was a newspaper story not too long ago about the Sun setting and rising aligned with some street in Manhattan on a couple of days each year got me thinking... it's not some mystical emergence; just a little thought should convince you that any street oriented within about 23 1/2 degrees of true east-west should have the Sun rise and set aligned with the street a couple of times a year. You just have to watch for it. (Planning an astronomically timed Druid theme party might make this a group activity.)

Solar Ephemeris. At a href=http://www.esrl.noaa.gov/gmd/grad/solcalc/sunrise.html> www.esrl.noaa.gov/gmd/grad/solcalc/sunrise.html you will find a tool that calculates sunrise and sunset times Local and UTC) and direction (as solar declination). The solar declination tells you how far north or south of the east-west line the sun will rise or set. For example, if the solar declination is -13.00 degrees, (as in late October) the sun will both rise and set 13 degrees south (the minus in the declination) of the true East-West (270--90 degrees) line, so, you would be looking for a street that has a true heading (270 - 13 =) 257 degrees for the sunset or (90 + 12 =) 103 degrees for the sunrise.

Street headings. In Google Earth, the straight-line distance tool (ruler icon) gives you a length and a (true) heading for the line you are measuring. Try to superimpose a line of the desired orientation on the display, and then look for streets with that orinetation. Check the candidates more closely, and note that the direction will change by about 1/4 degree per day on average. Waiting (er... planning ahead) few days may bring a street into better alignment.

Practical Concerns: For fun and safety, you should be cognizant of traffic. Don't stand out in the middle of the street. You might work together in teams of 2 or 3 classmates or friends on this project. (Even though you work together to collect the data each person has to hand in their own report.) Be sure that your team can all meet for a few hours outside of class to survey the streets together. Don't trespass and don't go places that seem unsafe. Don't stare at the Sun. Watch out for traffic and any other hazards.

### Procedure...

Plan where to collect a photograph with the sun setting or rising framed down the length of the street. (You might want to find a specific day or a specific street.)

Look up the Sun's rising and setting directions for the next few days.

Find a street with that orientation.

Collect the photograph. (Be careful; don't stand in traffic.)

Write a brief (~1 page) report to accompany your photograph. At a minimum, you should include the street name, its orientation w.r.t. True North, the time and date that you took the photograph and the coordiantes of the place from which you took the photo. If you can find any history for the street and its development, include it.