As summer approaches, many of us like to get in a car or plane and travel to new places or spend time with distant friends and family. I recently returned from a trip to Fort Collins, Col. for my niece’s college graduation. We ate huevos rancheros, tramped around in the Rockies and talked in the glow of a drier drum fire. My niece has repurposed an old dryer drum into a fire pit. Highly recommended.
When you travel east or west of your home it only affects the rising time of the stars. If you live in Iowa and fly to Baltimore the stars rise an hour earlier. It gets dark there an hour sooner. Fly to Utah, and it gets dark an hour later. Otherwise observers in both places see the identical stars. But if you travel north or south of your home, which stars you see changes. Even driving 1o0 miles (160 km) makes a difference but too subtle for most of us to notice.
But if you travel a couple thousand miles like I did, the difference becomes obvious. I live at 47°N latitude. Three hours and one pat-down later I arrived at 40°N, having flow 7° of latitude south of my Duluth, Minn. home. Right away, I noticed that the sun appeared higher in the sky, 7° to be exact or a little more than three fingers held together at arm’s length. The extra sunshine had advanced the season by about 2 weeks compared to home.
The nearly full moon also stood 7° higher in the sky, so I had to crank my neck back a little more than normal for a look. Like the sun, all the stars in the southern sky had moved upward (north) by 7°. The difference boosted the visibility of Corvus the crow, a little rhombus of stars located low in the southern sky from home. Contrariwise, when I faced north all the stars in the northern sky appeared 7° lower including the famous North Star.
When you travel south, stars otherwise hidden by your local southern horizon ascend above it. To “make room” for the newcomers every star south of the overhead point, called the zenith, also slides upward. Stars north of the zenith — in the northern sky — drop lower to make room for the pusher-uppers. I could easily tell that the North Star had descended in the north compared to the view in Duluth.
The really fun part of globe-trotting is seeing new stars that have always been hidden by your southern horizon. No new bright stars popped into view at 40°N, but a chunk of the southern constellation Centaurus invisible from Duluth rose high enough for me to make out. Had I traveled another 10° south, say to Houston or New Orleans (both at 30°N latitude), I would have seen the topmost star in the Southern Cross called Gacrux. Ten more degrees and the entire cross would have sailed into view. Meanwhile, the North Star would have sunk ever lower in the northern sky.
The summer Milky Way also gains visibility the farther south one travels. From the northern states one of its brightest sections, which billows from the southern sky constellation Sagittarius, has to compete with light-sucking haze and light pollution. Not so much from the southern U.S. where its increased altitude places it in a darker sky.
If you’re traveling north or south this summer, keep an a tourist’s eye on the sky. To find out if there’s a significant difference in latitude (north-south distance) between your home and your destination, use this latitude/longitude calculator. Regular skywatchers can easily discern differences of 5° or more with the naked eye. Polaris, the North Star, is a handy indicator. Shoot a line downward through the two Pointer Stars in the Big Dipper to the first star of similar brightness — that’s Polaris. If you know how high it is from home, you’ll see a difference.
The more familiar you are with the bright stars and constellations of the season the easier it will be to see their change in elevation when you travel. Download the free Star Chart app (iPhone / Android) and use it to find planets and constellations from your home. Then when you travel, it will pick up on your current latitude and show you new stars to look for. If you live in the mid-northern latitude belt and travel south, keep watch on the southern sky for new stars and increased visibility of constellations near the horizon.
Jet lag may be one of travels’ most familiar consequences, but the slipping of the stars makes one’s journey palpable in a more pleasant way.