Chasing the Stars that Never Set: Exploring Circumpolar Stars & Constellations. Ursa Major, Ursa Minor, Canis Major

“Chasing the Stars that Never Set: Exploring Circumpolar Stars Constellations.”  By Meet Panchal

In the night sky, we frequently marvel at the beauty and wonder of the stars. But have you ever wondered if all the stars are circumpolar? Do they all revolve around the celestial poles, or are there exceptions? In this blog post, we will explore the concept in-depth and learn about the fascinating world of circumpolar stars.

What are circumpolar stars?

To understand circumpolar stars, let’s define them. When viewed from a specific location on Earth, the circumpolar stars never dip below the horizon. Depending on whether the observer is in the northern or southern hemisphere, they appear to rotate around the celestial poles. Unlike other stars, these ones remain visible all night, moving in circles around the celestial poles.

How are circumpolar stars different from other stars?

The original question: Are all stars circumpolar? Not all stars are circumpolar, and this depends on the observer’s latitude and the star’s declination. Declination is the angular distance a celestial object has above or below the celestial equator. A circumpolar star has a declination greater than the observer’s latitude, whereas rising and setting stars have a declination less than the observer’s latitude.

In order to better understand this, let us look at an observer at the North Pole, whose latitude is 90°. A circumpolar star is one whose declination is greater than 90° (including the entire celestial sphere), since it never dips below the horizon from the observer’s perspective. As a result, all stars are circumpolar for an observer at the North Pole.

circumpolar star
Circumpolar Star

For an observer at the equator at a latitude of 0°, no stars are circumpolar. For observers at the equator, the celestial equator passes directly overhead since it is a projection of the Earth’s equator onto the celestial sphere. Due to this, all stars, regardless of their declination, will rise and set as the Earth rotates, and none will remain circumpolar as it rotates.

At latitudes between the equator and the North or South Poles, some stars are circumpolar, but others are not. As an observer’s latitude approaches the poles, the number of circumpolar stars increases. At latitudes slightly above or below the equator, only a few stars near the celestial poles are circumpolar, whereas, at higher latitudes, many stars become circumpolar.

Can circumpolar stars change into non-circumpolar stars?

In addition, it is important to note that the concept of circumpolar stars does not remain constant over time. Due to gravitational forces from the Moon and the Sun, the Earth’s axis precesses over a period of about 26,000 years, moving in a circular motion. Because of this, the celestial poles slowly change position over time, causing stars that are circumpolar today to become non-circumpolar in the future.

Altitude can be a major influencing factor in the visibility of stars. For those standing on mountaintops or flying high above in planes, the closer proximity to the celestial poles may allow for more circumpolar stars to be seen than those observing from ground level. The smaller circle of rotation of stars around these poles when viewed from higher elevations means more stars can remain in view rather than disappear over the horizon.

What happens in each hemisphere?

It’s important to recognize that circumpolar stars exist in the northern and southern hemispheres, but the individual stars that are circumpolar depend on which hemisphere they appear in. For example, Polaris – otherwise known as the North Star or Pole Star – is markedly visible in the northern sky, and its proximity to the North Celestial Pole has made it a notable navigational reference point for centuries. Although this star is considered circumpolar, other stars with declinations lower than the observer’s latitude will still rise and set, although they may appear over a longer period of time than those located near the celestial equator.

World Atlas

In the southern hemisphere, there is no South Star or South Celestial Pole, making it more challenging to identify circumpolar stars. Still, certain latitudes offer a few options. For instance, the constellation Crux, commonly known as the Southern Cross, is visible to observers south of 25° S. This bright formation appears in the night sky and is used as a navigational tool similar to Polaris in the northern hemisphere.

It’s important to take other factors into account, such as light pollution, atmospheric conditions, and time of year, when considering the visibility of circumpolar stars. Light pollution can make it hard to spot these stars in cities with high levels, while haze or clouds can also block their visibility. Also, due to the Earth’s changing position in its orbit throughout the year, some stars may be hidden from view by the Sun’s radiance or behind the horizon.

What are the circumpolar constellations?

In addition to Polaris and Crux, various other stars are commonly circumpolar for observers at certain latitudes. Those in the northern hemisphere may recognize Ursa Major, Ursa Minor, and Cassiopeia, as they are readily visible at mid-northern latitudes. These constellations are often used as a guide in the night sky. On the other hand, near the South Pole, other well-known constellations such as Orion, Canis Major, and Centaurus also have circumpolar stars.

Circumpolar stars have been used as navigational and timekeeping tools throughout human history. Early sailors, explorers, and travelers relied on them as a reliable reference point to determine latitude, direction, hours, and seasons. For instance, Polaris has been a well-known navigational aid for individuals in the northern hemisphere for centuries.

Circumpolar Constellations
Circumpolar Constellations

How have circumpolar stars aided humanity?

Circumpolar stars have also been of great significance in mythology, culture, and symbolism. Ancient Egyptians, Greeks, and Native Americans had their own tales and myths related to these celestial bodies. A classic example is the Greek myth of Callisto and her son Arcas, who were transformed into bears and placed in the sky by the gods. Likewise, Native Americans used circumpolar stars in rituals, ceremonies, and calendars.

Circumpolar stars are important for space exploration by agencies such as NASA and ESA. The Hubble Space Telescope uses them to calibrate its instruments, enabling it to accurately observe celestial bodies. Satellite positions and orientations are also based on these stars, especially when taking part in deep space missions – such as the Voyager probes.

Circumpolar stars have been, and still are, integral to our daily lives and culture. In remote areas where modern navigation tools may not be accessible or reliable, they continue to be used for direction and location – hikers, campers, and explorers still use them on outdoor adventures. Beyond practical purposes, circumpolar stars have tremendous symbolic meaning in art, literature, and music – throughout the world, they are associated with cultural beliefs, traditions, and rituals. A perfect example of this is the Pleiades star cluster (or ‘Seven Sisters’), which is venerated by many indigenous people as a sign of fertility, guidance, and protection.

In conclusion, circumpolar stars have been of great importance throughout human history due to their significance in navigation, timekeeping, mythology, culture, and science. Not all stars appear to rotate around the celestial poles in this way, but for those located in the northern hemisphere, it is Polaris that stands out most prominently as a circumpolar star. Observers of the southern hemisphere will be familiar with Crux, known as the Southern Cross. Whether it’s Polaris or Crux inspiring us with its beauty and motion in the night sky or being used as reference points for determining location and time, circumpolar stars continue to captivate our imaginations and give us a greater appreciation for the universe.

Leave a comment