by James Peck

I teach electives to 8^th graders at Link Community Charter School in Newark. Ten students are lucky enough to be going to the Island School in the Bahamas for a week of enrichment at the end of April and I am working with them on various topics so they will be better prepared for the trip.

One thing I have done with them is to compare the sky in Newark versus the Bahamas to show them the differences they will see if they look up in the day or night. I used Stellarium software as it can be adjusted for the school’s location and view any part of the sky on any day or time.

The first thing we discussed is the apparent altitude of the north star at both locations, which is equal to your latitude. I rounded Newark to 40 degrees north and the Island School to 25 degrees north, which is a 15 degree difference. If you set Stellarium to a time at night and then jump between Newark and the Bahamas you can easily see the north star move up and down on the screen between 25 and 40 degrees.

Another thing we discussed is the difference is constellations you can see in both locations. Since the north star is lower in the Bahamas, as the stars circle it, some of the constellations that are always visible in Newark, like Cassiopeia, will dip below the northern horizon in the Bahamas. If you look south the constellations are about 15 degrees higher than in Newark, so some will be visible that you can’t see in Newark, like Telescopium.

I gave the students two low tech planisheres, one manufactured for each location, which are excellent for showing what I just discussed. These are dual plastic disks that can be spun and set to any date and time and show the stars that are overhead at that setting. The north star is the central rivet that everything twirls about and you can quickly compare how far above the horizon it is at both locations by holding the two planispheres next to each other; the 15 degree difference is immediately visible.

Also, an interesting thing about a planisphere is that if you turn the outer disk one full revolution you can see all the stars that will ever be visible for its range of latitudes at any time of the year, at any time of day. Of course if the time you set is when the sun is out its light overwhelms the stars and they are not visible, while a nighttime setting will show visible stars.

This is interesting because I have worked with a lot people from the general population who don’t truly understand why we see different stars at different seasons. The truth is that the earth is always pointing to the same place in space and the exact same stars are circling across the sky every day, all year long at any one location. It is only the fact that at different seasons the dark night hours occur when different stars are overhead and again this is easily seen and understood by looking at the planishpere. Of course there are many stars that are visible all year round.

The other thing I wanted to explain to the students is the difference in the sun’s path across the sky in Newark versus the Bahamas, specifically its maximum sun angle. The sun is highest in the sky each day at solar noon when its azimuth is 180 degrees (toward the south). The highest maximum solar angle occurs around June 21^st and the lowest maximum around December 21^st.

The formula for finding the highest altitude on these two dates is 90 minus your latitude plus or minus 23.5. So in Newark the sun will reach an altitude of 72 degrees (90 minus 40 plus 23) on June 21^st, which is the highest you will ever see it in there. In the Bahamas the highest the sun will ever get is 88 degrees (90-25+23), which is almost directly overhead. That formula (subtracting 23 degrees) shows that the highest the sun gets on December 21^st is 27 degrees in Newark and 42 degrees in the Bahamas.

Using Stellarium software we found the highest the sun will get on April 30th, when the students will be at the Island School, is 79 degrees, and if they were home in Newark it would be 64 degrees, which is a noticeable amount.

The other things we discussed are what planets and artificial satellites will be visible at the Island School when they will be there (April 30 – May 6^th). We looked on web sites and found that the Hubble Telescope will be visible along with some planets, notably Venus. The beauty of Stellarium is that in our class we could set the date and location to where they will be there and see exactly what the sky will look like then, including the planets and the Hubble moving quickly across the sky. If they bring a laptop running Stellarium outside during the actual viewing they can use it to zoom in on what they are looking at (like Venus) and see a simulated telescopic view.

When the students return May 7^th, I’ll get a report from them as to what they actually saw.

As a final thought, when I was 10 in 1957 and living in Albuquerque my father brought me outside to watch Sputnik I travel across the sky. At the time it was the only artificial satellite and now there are many thousands so that on any given night you will probably see at least one.