A Brief Introduction to Constellations

Constellations are a group of stars that form patterns in the sky. Constellations played a significant role in navigation for explorers of the Earth; these navigators created extensive star charts to help them find their way around the planet. The word “constellation” comes from the Late Latin term cōnstellātiō, which can be translated as “set of stars”; it came into use in Middle English during the 14th century.

Ancient humans spent a lot of time observing star patterns in the sky. They identified clusters of stars as gods, goddesses, heroes, animals, and objects. They also created stories to go along with these star patterns, which became the basis for many of the myths passed through centuries by the Greeks, Romans, Polynesians, Indigenous Americans, and members of various African tribes and Asian cultures. Most of the constellation names we know came from the ancient Middle Eastern, Greek, and Roman culture. In some cases, the constellations may have had ceremonial or religious significance. In other cases, the star groupings helped to mark the passage of time between planting and harvesting.

In 1930 the International Astronomical Union (IAU) officially listed 88 modern and ancient constellations in the Northern and Southern Hemispheres of the sky. In 1928 adopted official constellation boundaries that together cover the entire celestial sphere. It is roughly based on the traditional Greek constellations listed by Ptolemy in his Almagest in the 2nd century and Aratus’ work Phenomena, with early modern modifications and additions by Petrus Plancius (1592, 1597/98 and 1613), Johannes Hevelius (1690) and Nicolas Louis de Lacaille (1763), who named fourteen constellations and renamed a fifteenth one.

36 modern constellations predominantly lie in the northern sky, while 52 are found in the southern celestial hemisphere. Most constellations (more than 40) represent animals. Many were named after humans or figures from mythology, while some depict inanimate objects.

Constellations are typically grouped around asterisms, which are patterns formed by bright stars that appear close to each other in the night sky. These asterisms are often the most conspicuous parts of constellations, which is why the term constellation is still colloquially (and incorrectly) used synonymously with asterism. The constellations themselves are much larger than asterisms and occupy considerably larger areas. For example, the Big Dipper, Little Dipper and Southern Cross are not constellations. They are asterisms formed by the brightest stars of the constellations Ursa Major, Ursa Minor, and Crux.

Zodiac Constellations are constellations that lie along the plane of the ecliptic. The ecliptic, or the apparent path of the Sun, is defined by the circular path of the Sun across the sky, as seen from Earth. In other words, the Sun appears to pass through these constellations over the course of a year.

There are 12 constellations in the zodiac family. They are: Aries, Taurus, Gemini, Cancer, Leo, Virgo, Libra, Scorpius, Sagittarius, Capricornus, Aquarius and Pisces.

The northern zodiac constellations – Pisces, Aries, Taurus, Gemini, Cancer and Leo – are located in the eastern celestial hemisphere, while the southern – Virgo, Libra, Scorpius, Sagittarius, Capricornus and Aquarius – are found in the west.

Some prominent constellations include:

Ursa Major constellation lies in the northern sky. Its name means “the great bear,” or “the larger bear,” in Latin. The smaller bear is represented by Ursa Minor. Ursa Major is the largest northern constellation and third largest constellation in the sky. Its brightest stars form the Big Dipper asterism, one of the most recognizable shapes in the sky, also known as the Plough. Ursa Major is well-known in most world cultures and associated with a number of myths. It was one of the constellations catalogued by the Greek astronomer Ptolemy in the 2nd century. In Greek mythology, it is associated with Callisto, a nymph who was turned into a bear by Zeus’ jealous wife Hera.

Cassiopeia is one of the most easily recognizable constellations in the northern night sky. Nicknamed the W constellation, Cassiopeia is easily recognizable for the prominent W asterism formed by its five brightest stars. The constellation is named after the vain queen Cassiopeia in Greek Mythology, wife of the King Cepheus of Aethiopia. Cassiopeia can be found high in the northeastern sky on October evenings, not far from Polaris, the North Star.

Andromeda constellation is located in the northern sky, between Cassiopeia’s W asterism and the Great Square of Pegasus. The constellation was named after the mythical princess Andromeda, the daughter of Queen Cassiopeia and wife of the Greek hero Perseus. It is also known as the Chained Maiden, Persea (wife of Perseus), or Cepheis (daughter of Cepheus).

Pegasus is one of the most prominent constellations in the northern sky. It was listed by the astronomer Ptolemy during the 2nd century and was named after a winged horse in Greek mythology. The brightest star in the constellation is Epsilon Pegasi, which forms the creature’s nose. Pegasus belonged to Poseidon, the god of the sea, earthquakes, and storms. In a battle between Perseus and Medusa, Perseus decapitated her and the winged horse “sprang” from her blood. In the Northern Hemisphere, the Pegasus constellation can be found high in the sky from the end of summer through autumn.

Orion is one of the brightest and best known constellations in the night sky and lies on the celestial equator. It is named after Orion the hunter in Greek mythology. In mythology, Orion was a supernaturally gifted hunter, and the son of Poseidon. He proclaimed himself as the greatest hunter in the world. This angered Zeus’s wife Hera, who had a scorpion kill him. Out of compassion, Zeus put Orion into the sky. Located on the celestial equator and made up of bright young blue giants or supergiants, it is one of the most prominent and recognizable constellations in the sky and can be seen throughout the world. Orion’s Belt includes the three most prominent stars in the constellation: Alnilam, Mintaka, and Alnitak. Orion is clearly visible in the night sky from November to February.

Each Latin constellation name has two forms: the nominative, for use, when talking about the constellation itself, and the genitive, or possessive, used in star names. For instance: Hamal, the brightest star in the constellation Aries (nominative form), is also called Alpha Arietis (genitive form), meaning literally “the alpha of Aries”. 

The 88 officially recognized constellations are visible at different times throughout the year. Each season has distinctive star patterns because the visibility of stars in the sky change as the Earth orbits the Sun. The Northern and Southern Hemisphere skies are very different from each other, and there are some patterns in each that cannot be viewed between hemispheres. In general, most people can see about 40-50 constellations over a year.

Most people can see more than half of them throughout the year, though it can depend on where they live. The best way to learn them all is to observe throughout the year and study the individual stars in each constellation. To identify the constellations, most observers use star charts found online and in astronomy books. Others use planetarium software such as Stellarium or an astronomy app. 

An Introduction to Halley’s Comet

Image Credit: NASA

Halley’s Comet, officially known as 1P/Halley, is a short-period comet visible from Earth every 75–76 years. It is the most famous known comet and is the only known short-period comet that is regularly visible to the naked eye from Earth and thus can be viewed twice in a human lifetime. The comet made its last appearance in 1986 and will next appear in mid-2061. 

Comet Halley was the first comet recognized as a periodic or short-period comet, with an orbit lasting 200 years or less. Its shape vaguely resembles that of a peanut shell, and its dimensions are about 9.3 by 5 miles (15 kilometres by 8 kilometres). It is one of the darkest or least reflective objects in the solar system, reflecting only 3% of the light that falls on it.  While it travels around the Sun, Halley leaves behind a trail of dust and ice particles that form the annual Orionid Meteor shower every October.

Origin:

Halley’s periodic returns have been subject to scientific investigation since the 16th century. Although it was around for centuries, it wasn’t until 1705 that Edmond Halley, an English astronomer and physicist, calculated its orbit and predicted its next appearance. He noted the three occurrences of the comet, used Isaac Newton’s recently developed Laws of Motion and some observational records and concluded that the comets which appeared in 1531, 1607, and 1682 were the same comet, and predicted that it would appear again in 1758. As foretold, the comet did reappear, but unfortunately, Edmond Halley wasn’t around to see its appearance. In 1759, Nicholas-Louis de Lacaille, a French astronomer, named the comet after Halley to honour him.

History of the Comet:

Some historians believe that the comet was sighted as early as 467 BCE by the ancient Greeks. A comet in ancient Greece, recorded between 468 and 466 BC with its timing, location, duration, and an associated meteor shower all suggest it was Halley.

The first official known sighting of this comet, according to historical records, occurred in the year 240 BC. The Chinese recorded this sighting in the Chinese chronicle ‘Records of the Grand Historian’ or ‘Shiji’, which describes a comet that appeared in the east and then moved north. 

In 1066, the comet was seen in England and was considered an omen. Later that year, King Harold II of England was overthrown and killed at the Battle of Hastings by William the Conqueror, who then claimed the throne.  The battle depicted on the Bayeux Tapestry chronicles those events and prominently displays the comet as a star. 

In 1456, on a return passage, Pope Calixtus III determined that the comet was an agent of the devil, attempted to excommunicate this natural phenomenon, and ordered special prayers for the city’s protection. His misguided attempt to frame it as a religious issue failed because the comet came back 76 years later. 

He wasn’t the only person of the time to misinterpret what the comet was. Around the same time, while Turkish forces laid siege to Belgrade, the comet was described as a fearsome celestial apparition “with a long tail like that of a dragon.”

Modern Observations:

The comet’s reappearance in 1986 sparked great interest in scientists around the world, who planned extensive plans to observe it closely. It marked the first time scientists were able to study it with sophisticated and developed technology. The high-quality images returned by the probes were the first of their kind, providing a fascinating insight into Halley and proving that its core is a solid mass primarily composed of dust and ice. Five spacecraft from the USSR, Japan, and the European Space Agency journeyed to Comet Halley. ESA’s Giotto obtained close-up photos of the comet’s nucleus. Halley being large and active, with a well-defined and regular orbit, was a relatively easy target for Giotto and the other probes. 

Telescopes

Telescopes are to astronomers what weapons to defense personnel and the lens size are comparable to ammo size. Larger the telescope better is the capability to capture light and make images. Galileo used the telescope which was small but still was able to spot the phases of the moon, moons of Jupiter, as those were the days, without digital imaging; therefore he drew whatever he saw. But today telescopes store whatever they capture and as the sizes of lenses grow, amount of data also increases posing a threat to the storage of data as no data can be marked bogus since the universe is not known to us, thus we can’t discard or forget whatever we see cause they are pieces of a bigger puzzle. Galileo made the first telescope just 400 years earlier. Galileo’s telescope had a major drawback that it was small thus images were not clear due to low angular resolution (low clarity). Increasing the size of the lens increased the size of the telescope and thus the possibility of bending due to self-load. The greatest Galilean telescope is Palomar 200inch, in fact, it was the biggest for 6 or so decades. But with the advancement in technology and the constraint that manufacturing, transporting, installation, maintenance of too big lenses would be cumbersome or near impossible and also would be uneconomical, innovative ideas were thought about like making clusters of lenses that would act as one. It is still expensive but easy to manage. Ground-based telescopes have seen drastic advancements in the last 2-3 decades but Larger telescopes have good resolution capacity as well as range. Owing to the large lens they are able to capture more light and produce more clear images. But ground-based telescopes aren’t feasible to install due to their large size and heavy maintenance. A slight error could lead millions of taxpayer’s money to go down the drain. Space-based telescopes have seen further fewer advancements since putting a telescope in space is a too risky and expensive task, thus one needs a good reason to do so despite all these astronomers to want to put telescopes in space despite their budgets being humongous because ground-based telescopes have some major drawbacks that no amount of money or technology can overcome. One is the blurring or twinkling of starlight due to turbulent motions in the atmosphere high above. The turbulence in the atmosphere leads to a distorted view of the objects, this turbulence is the reason for the twinkling of lights. Although this twinkling can be reduced by installing a secondary mirror that can fluctuate dozens time per second but still this doesn’t lead to that much clarification that can be observed through space telescopes. The primary mirror can’t be fluctuated due to its enormous size and money invested. And another is the opaqueness of the earth’s atmosphere to many of the wavelengths. Only some wavelengths like visible spectrum and a large part of radio waves and some of the infrared radiation are able to penetrate the earth’s environment. And since the light coming from distant heavenly bodies does not necessarily fall in one of the spectrums due to doppler’s effect that can penetrate the earth’s atmosphere, therefore, it is possible that much of the data we are just losing due the opaque atmosphere present. Also installing a large telescope on the ground requires structure to contain it, and those structures also have initial cost and maintenance cost thus resulting in the cost curve. The universe at every moment leaks loads of data in the form of X-rays, Gamma rays, and Infrared rays just we have to study it that is only possible through space-based telescopes. Thus the curiosity to understand how the universe works, the curiosity to know our origin leads to astronomers putting heavy telescopes in space.