Honestly, we love all the questions that we extract from Pandora's Jar. Some of them, we admit however, are particularly delicious. The query written on today's piece of parchment is just such a dainty confection. It pertains to some of the Universe's most beautiful things: stars, hobbits, and thoughts of verdant places. We needed to spend some time formulating what we hope is a coherent answer, so we're limiting ourselves to just one Pandora today.
"The other night I was looking at the stars and wondered. 'Can we see any of the same stars that those little people in Hobbit village in New Zealand can see?' I can't yet afford to visit the place myself -my birthday is August 11th- but I thought it would be nice to know if there are any stars I can see here that could also be seen in the night sky in Hobbit Village. Please use the pseudonym I wrote down, but you might not want to use just the first initials of each word. Thank you!"
The "Green Dragon Inn" in Matamata, New Zealand, the
location of the world renowned Hobbit Village. The coordinates
for this wonderland are about 38 degrees south, 175 degrees east.
The first value, the latitude, is necessary to answer today's question
Matamata, New Zealand, is located 38 degrees south of the Equator. We know that Portland, Maine, is about 43 degrees above the equator. These two pieces of information will help us determine which stars are visible from Portland and Hobbit Village. We know that the night sky changes dramatically with latitude because latitude determines which stars one can see. Here we need to introduce the term "declination," which measures a celestial body's angular distance from the celestial equator. (The celestial equator is the projection of Earth's equator onto the sky.
Declination measures a celestial body's angular distance
north or south of the celestial equator. The celestial equator's
angle relative to an observer's horizon depends on the observer's
latitude. Portland, Maine's latitude is about 43 degrees. Therefore,
the celestial equator is 90 - 43 = 47 degrees above the southern horizon.
Thus, we can see any star whose declination is greater than -47 degrees.
Let's pretend we're on the equator. (I know Portland residents are savouring the 7th straight day of drizzle and highs in the low 40s and are therefore loath to venture to warmer regions, but we'll come right back.) On the equator, the celestial equator would extend from due east to due west and would pass through the zenith, the point directly overhead. The celestial equator is 90 degrees above the southern horizon on the equator. Now, pretend that you travel to 10 degrees N latitude. At this location, the celestial equator is displaced from the zenith by 10 degrees. It would then be 80 degrees above the southern horizon. Continue northward to 20 degrees N latitude. Now, the celestial equator is 20 degrees south of the zenith and 70 degrees above the southern horizon. We have thus established a relation between the celestial equator's angle above the southern horizon and the observer's latitude. The angle will be 90 degrees minus your latitude.
Here in Portland, our latitude is 43 degrees and so the celestial equator passes 47 degrees above the southern horizon. The stars that are aligned along our southern horizon have a declination of -47 degrees. (They are 47 degrees south of the celestial equator.) We know that every northern hemisphere observer can see every star north of the celestial equator. So, any Portland observer can see any star that is north of -47 degrees declination.
Here in Portland, our latitude is 43 degrees and so the celestial equator passes 47 degrees above the southern horizon. The stars that are aligned along our southern horizon have a declination of -47 degrees. (They are 47 degrees south of the celestial equator.) We know that every northern hemisphere observer can see every star north of the celestial equator. So, any Portland observer can see any star that is north of -47 degrees declination.
We go next to Matamata. New Zealand. Its latitude is 38 degrees south. As it is in the southern hemisphere, the celestial equator draws closer to the northern horizon as an observer travels south. In Matamata, the celestial equator would be 90 - 38 = 52 degrees above the northern horizon. An observer at this location would see all stars south of the celestial equator and would also be able to see all stars that are less than 52 degrees north of it.
By these two calculations we have determined that all we and the hobbits share all stars that are within the region between 52 degrees north of the celestial equator and 47 degrees south of it. This area is a wide swath of the sky.
Orion the Hunter (called Menelvagor in Middle Earth), Scorpius the Scorpion, Hercules, Canis Major, Aquarius, Pisces, and the Summer Triangle constellations Lyra the Harp, Aquila the Eagle and Cygnus the Swan are examples of the constellations we share with the Hobbits.
This southern hemisphere planisphere shows some of the constellations that we can see
here, such as Aquarius the Water Bearer and Pisces the Fish.
So, when you look up in the sky tonight, realize that our sky shares many stars with the sky that the Hobbits admire.
Glow worms illuminating a cave in New Zealand, which resembles a
night sky. This has nothing whatsoever to do with the topic at hand, but
the photo was so gorgeous, we had to include it. (Courtesy: National Geographic)