Introductory Astronomy Complete University Course - Spirals, Ellipticals, and Irregulars: Hubble’s Tuning Fork and Galaxy Classification Scheme

This video is part of a comprehensive series initially developed for William Paterson University and CUNY Hunter, aimed at supporting online classes and course materials for introductory astronomy. By engaging with all the videos within this series, you will effectively complete a full undergraduate course in astronomy, equipping yourself with the knowledge and skills necessary to navigate the night sky with confidence, learning all the basics and many advanced topics! Now we delve into the visual and structural characteristics of various galaxies. Our understanding of galaxies commenced with Edwin Hubble, who unveiled the existence of our Milky Way as one of numerous “island universes” within the vast cosmos. We will explore Hubble’s classification system, which categorizes galaxies into three primary types based on their morphologies. Initially, we will examine elliptical galaxies. These galaxies span a spectrum, ranging from diminutive dwarf galaxies with a mere few million stars to colossal giants that harbor trillions of stars. Notably, elliptical galaxies lack the distinct disks and spiral arms observed in other types. Instead, they manifest as smooth, featureless ellipses predominantly composed of older, red stars and devoid of the gas and dust essential for star formation. Subsequently, we will explore spiral galaxies. These galaxies are renowned for their captivating visual appeal, characterized by graceful, swirling arms emanating from a central bulge. According to Hubble’s Tuning Fork classification, spirals exhibit a range of characteristics, from tightly wound arms and substantial central bulges to more loosely defined arms and smaller bulges. Furthermore, we will examine barred spirals, which feature a prominent central bar structure. Spiral galaxies are characterized by their abundance of gas and dust, making them vibrant centers of ongoing star formation. Lastly, we will consider irregular galaxies. These galaxies lack a defined structure and often appear chaotic and turbulent. Examples such as the Large and Small Magellanic Clouds illustrate the prevalence of active star formation due to their disrupted and messy appearances. Throughout this video, we will be presented with stunning images sourced from various celestial bodies, including the Hubble Space Telescope and ground-based observatories, showcasing the diverse and intricate beauty of galaxies. Galaxies are fundamental units of luminous matter in the universe. They are the birthplace, residence, and final resting place of stars, providing us with profound insights into the processes that shape our cosmos. This is a component of my comprehensive introductory astronomy course, which I taught at William Paterson University and CUNY Hunter. All the images in this slide set come from these sources: NOAO: http://www.noao.edu/image_gallery/ AAO: http://203.15.109.22/images/ or http://www.aao.gov.au/images/ Gemini: http://www.gemini.edu/gallery/v/astronomical_images_and_illustrations/ ESO: http://www.eso.org/public/images/ Keck Observatory: http://www.keckobservatory.org/gallery/ Hubble Space Telescope: http://hubblesite.org/gallery/ Hubble Heritage: https://hubblesite.org/images/hubble-heritage SEDS: http://spider.seds.org/ngc/ngc.html NGC Project: http://www.ngcicproject.org NASA Database of Galaxies: https://ned.ipac.caltech.edu/forms/byname.html Johannes Schedler (Panther Observatory): http://panther-observatory.com/gallery/deepsky/doc/M81_M82_cass.htm Stéphane Guisard: http://sguisard.astrosurf.com/ #Galaxies #EdwinHubble #MilkyWay #HubbleTuningFork #EllipticalGalaxies #SpiralGalaxies #IrregularGalaxies #StarFormation #AstronomyEducation