Astronomy connects all of us. While the sky looks slightly different based on your location, when put together it is our common heritage. Understanding the differences helps us to understand the connections. In this guest post, Megan Ray Nichols briefly explains those connections, thus underlining how local perspectives can contribute to a global one.
Not everyone has the same set of stars in their back yard. The constellations appear in different positions throughout the seasons, disappearing and reappearing, depending on where you live in the world.
The moon seems to be the one constant – apart from it appearing “upside down” in the northern hemisphere compared to the south – it’s visible to all in its phases. Yet similarly to constellations, lunar features and eclipses are only visible in certain hemispheres. What makes the night sky, its star formations and moon, so unique across different areas of the world?
The Moon’s Many Faces and Phases
The moon has orbited the Earth since before the dawn of humanity. Many ancient cultures associated the moon with different symbols. Some saw a woman or a man in the moon, while others saw a ewe or hare.
The moon was a measure of time for many cultures with its 29.5 day cycle. While the moon appears to be changing, it’s reflecting solar light. The part of the moon facing the sun will always be illuminated, similar to the daylight side of Earth. In your back yard, the moon appears to grow from a small sliver to half full, until it is fully illuminated.
Like a human face, the moon’s phases shift due to its orbits around the Earth. A new moon, appearing fully dark on Earth, begins the cycles anew when the moon is between the Earth and the Sun, meaning you won’t see the illuminated side from your back yard.
The moon grows to a thin waxing crescent to half full as a first quarter moon, until it’s mostly full as a waxing gibbous. Once it’s full, the moon decreases in size, from a waning gibbous to a last quarter, until its sliver of a waning crescent births a new moon.
The Changing Constellations Between Hemispheres
The constellations shift in the night sky, and many are unique to the northern or southern hemisphere. These are called circumpolar constellations and never set or rise. They make great reference points when locating seasonal constellations.
These stars and their patterns shift because of the Earth’s movement as it orbits around the sun. If you measured the shifting of the night sky, you may notice it shifts one degree per day, with 360 degrees in a circle and 365 days in a year.
This shift is due to “apparent motion,” such as watching one car leave yours behind, feeling as though you are moving backward. The Earth spins west to east, which is why constellations seem to rise from the east.
Some constellations shift seasonally, while others are unique to the northern hemisphere and southern hemisphere. Sky maps help you discover which constellations are visible and disappear as the seasons shift year-round. Constellations such as Orion may be seen in both hemispheres, depending on your distance from the equator and the time of year. If you can’t see the entire constellation, it’s likely too close to the horizon line and are too far north or south for complete viewing.
These constellations stretch across the celestial equator. If you subtract your latitude from 90 degrees, you’ll be able to judge how much of opposite hemisphere you may observe. Keep in mind — constellations readily seen in both hemispheres could appear upside down in one hemisphere versus the other.
There are many well-known constellations that stay put in your back yard, as circumpolar constellations. The northern circumpolar constellations you’ll find are Ursa Major, Ursa Minor, Perseus, Lynx, Draco, Cepheus, Cassiopeia, Camelopardalis and Auriga. Southern circumpolar constellations include Phoenix, Grus, Tucana, Eridanus, Hydrus, Lupus, Cruz, Centaurus and Carina, among others.
The changing sky has always fascinated mankind. So, humanity created myths and legends about the moon and stars. As explorers took to the seas, they used fixed circumpolar stars and Orion, close to the equator, to navigate.
Learning more about the universe is a wonderful way to feel connected to it. What constellations are visible in your back yard?
This blog post was written by Megan Ray Nichols, a Freelance Science Writer. Find her at www.schooledbyscience.com. Content in the blog post is copyright of the writer and does not necessarily represent the views of the Office of Astronomy for Development.