Exploring Pleiades Star Cluster, Magellanic Cloud Galaxies, and Cat's Eye Nebula

Observatory / Course Archives / ASTR 110 Fall 2019 / Peter

Ceres

There are many star clusters in our universe and galaxy to observe, yet one in particular I thought would catch your interest; it is called, the Seven Sisters (or the Pleiades).This star cluster has, as you must know, seven main stars, or “sisters”. Their names are Maia, Electra, Alcyone, Taygete, Asterope, Celaeno, and Merope, and this constellation can be seen from anywhere in the world. The way to locate this intrigue is by finding ‘Orion’s Belt’ and following the belt to the top of his bow, then by using that line, you will be led to ‘Aldebaran’, a reddish star located between ‘Orion’s Belt’ and ‘the Seven Sisters’. Continuing from Aldebaran will lead to in the direction of the Pleiades. Aldebaran and the Pleiades have a long history with one another. You see, the word Aldebaran means ‘follower’ in Arabic. It is said that Aldebaran is forever chasing or following the Pleiades through the heavens.

The Pleiades has a way of making you think there are only six stars when you and I both know there are seven. When looked at from a dark country sky, this constellation seems to only hold six stars in view, this is the Legend of the Lost Pleiad. Modern astronomy has found the brightest star in this constellation, the Pleione, to be a ‘shell star’. This means that it has a varying amount of light it emits due to numerous permutations of gas; these variations cause the star seekers to see less than are physically there. On the same note, this cluster of stars tends to disappear during a certain time and re-appear causing this phenomenon to be titled “the seed planting season”. The Pleiades is known by Zuni of New Mexico as the “Seed Stars” due to this effect.

The Seven Sisters constellation is contained within Taurus, a well-known constellation used in human superstition as zodiac signs. It is the closest star cluster to Earth and is most visible to the naked eye during the night. In Greek mythology, the Seven Sisters are the daughters of Atlas and Pleione, the latter of the two who was an Oceanid (a sea nymph) and who the former was a titan who waged war against the gods, and who afterwards was condemned by Zeus to carry the heavens on his shoulders. Together, this star cluster represents a side to astronomy that is interesting and every changing.

The Magellanic Cloud Galaxies

Galaxies are any of the large groups of stars and associated matter that are found throughout the universe. The Magellanic Clouds is one of the Milky Way’s neighbors and large enough to be seen from Earth’s southern hemisphere without using a telescope. It is closer than most but still a whopping 180,000 light-years away from the Milky Way. Ferdinand Magellan first sighted this galaxy between 1519 and 1522 during his first voyage around the world. Although Ferdinand and his crew discovered the galaxy, it wasn’t recognized until the 20th century when astronomer Edwin Hubble discovered the nature of a galaxy and decided that The Magellanic Clouds were indeed a separate system entirely.

Within the Magellanic Clouds, there are two parts; the Large Magellanic Cloud (LMC) and the Small Magellanic Cloud (SMC). Both important but slightly differentiating in degrees. LMC is 5° while the SMC is only 2°, this does not pose any other difference besides them being slightly different angles, yet it does alter their appearance ever so minutely, making one more visible than the other. The Large Magellanic Cloud created the younger stars in its galaxy when it drew closer to the Small Magellanic Cloud. These young stars were created as a result of the LMC and SMC’s distance stirring up gas and triggering the birth of new stars.

One of the star clusters within the Magellanic Clouds contains the largest known star (R136a1) with a mass of 265 times that of the Sun, now that’s a big star! The Magellanic Clouds and our Milky Way formed roughly around the same time, but the former is stuck within orbit of our galaxy which contains many star clusters, young stars along with some much older stars. These orbits cause the Magellanic Clouds to experience many tidal encounters with the Milky Way Galaxy. These tidal encounters are when two masses in orbit with each other produce a force that are both produced towards each other. There is an attraction which keeps them together, and therefore, must be an equal and opposite reaction to keep them from colliding. In keeping them from colliding, the force they produce towards each other causes other things to happen in the midst, such as black holes. These tidal experiences don’t always cause something negative like a black hole, they have temperature effects on galaxies along with shape distortion as well, that’s an amazing side of astronomical events.

Cat's Eye Nebula

A Nebula is a cloud of gas and dust in outer space, it is visible in the night sky either as a bright patch or as a dark shadow that’s silhouetted off of luminous matter. One nebula in particular is named the ‘Cat’s Eye’ nebula, for the reason of which you’re thinking, it is shaped like a cat’s eye (as seen in the image above). This nebula has some interesting characteristics attached to it, the rings that you see surrounding the nebula are actually a result of the star releasing mass as it dies, this happens every 1,500 years. These mass convulsions result in dust shells which end up looking like the rings of an onion, yet each ring contains more mass than all of our solar system’s planets combined. The explanation behind the release of this nebula’s mass every 1,500 years is thought to be something similar to our own sun’s magnetic cycle of activity, or sunspot cycle.

Nebulae (plural of nebula) also carry stars within their vast expanse of dust and gas, mostly hydrogen and helium, and they’re formed through a process of gravitational pull. See gravity starts to pull together the very spread out dust and gases, forming clumps which become bigger and bigger. At a certain point, these clumps become so big that they collapse under the pressure of their own mass and form a superheated center which is the beginning of a new star. Dark Nebulae or Reflection Nebulae are opaque clouds which do not emit visible light radiation and are also not illuminated by any stars, hence their name. They do, however, block light from luminous objects behind them, these used to be considered ‘holes’ in the sky but are now called by astronomers as dark molecular clouds. Interestingly, these Dark Nebulae tend to absorb nearly all the visible light from background stars causing them to become one of the most cold and isolated places in the universe.

The home of nebulae is the space between stars, also known as interstellar space and the nebula which is closest to Earth is called the ‘Helix’ nebula. This nebula is only 700 light years away from Earth and is the remanence of a dying star, most likely like our sun. Let me explain light years for a second, one light year means that even if you travelled at the speed of light, it would take you a year to get to your destination. So, 700 light years, well, that’s a lot of snacks and road trip music!