Some Stars in Milky Way Could be Stolen

Assessment 15- Milky Way Galaxy


This article from talks about how two astrophysicists from Harvard have found that the Milky Way has stripped a few stars from the Sagittarius dwarf galaxy, which orbits the Milky Way. The Milky Way is a barred spiral galaxy. A barred spiral galaxy appears like a spiral, with a bar running through the middle, with a flat rotating disk made up of spiral arms around it. Our galaxy has four spiral arms. The size of the Milky way it also pretty huge, being 100,000 light years across. We saw this in a powerpoint slide in class that showed the massive size of the Milky Way.


I learned a lot from this conceptual objective given I knew little about the structure and size of the Milky Way Galaxy previously. I was surprised at how massive the Milky way really is. 100,000 light years is far greater than I expected.

New Type of Galaxy Discovered

Assessment 16- Other Galaxies

Article link from
Article link from

Scientists have recently discovered a new type of galaxy. PGC 1000714 appears to be a normal ring galaxy, consisting of a ring of stars around a galactic core. But this galaxy actually has two rings, the first time a galaxy like this has been observed.32894679-ring-galaxy-1.jpg

This galaxy is, in appearance, much different than our Milky Way, which is a barred spiral galaxy. A barred spiral galaxy appears like a spiral, with a bar running through the middle. This is different than PGC 1000714, which has uniform rings around it. This newly discovered type of galaxy is also much more rare, as only about 0.1 percent of galaxies, according to, are ring type galaxies. Spiral type galaxies are much more common, being the most common type of large galaxy.


I learned a lot about the Milky Way and other types of galaxies from this conceptual objective. I didn’t know much of anything about the structure of the Milky Way, and how it is similar and different than other types of galaxies. This article surprised me that we are still discovering new types of galaxies.


Assessment 17 – Size and Age of the Universe

Assessment 17 – Size and Age of the Universe

 I can explain how astronomers know that the universe is expanding and
how they determine the age of the universe.

An article from talks about a new study of  3 quasars that suggest the universe is expanding faster than we thought.

This relates to our conceptual objective, I can explain how astronomers know that the universe is expanding and ow they determine the age of the universe. In class we discussed Edwin Hubble, how measured the velocities of galaxies and found that almost all galaxies are moving away from us. This is evidence that the universe is expanding. Hubble’s Law can be expressed as  v = H0D, where v= velocity, H0= Hubble’s constant, and D= distance.

Here is a graph from our textbook that shows Hubble’s constant

The data from the quasars has found that Hubble’s constant is between 68.9 and 74.3 160 km/sec per mega-parsec, which could be higher than the current accepted value of Hubble’s law, which is about 71.

This article showed how hard it is to find Hubble’s constant. I had no idea that scientists are still trying to find the precise value for this constant. It is also interesting to find out that Hubble initially estimated that the constant was 160 km/sec.

F i n a l

This article is my favorite because it showed my how the sky will appear to change over time. Throughout our lifetimes the stars in the sky do not seem to change much. The article from that I wrote about shows that the stars in the sky will actually change pretty significantly, over the next 5 million years. Another cool thing about this post is that the ESA actually has a four minute video simulation that shows the gradual change of the sky over the next few million years. I quite enjoy these simulations as you are able to see massive amounts of information and data combined in a short amount of time.

The article from that I read for this post talks about the HR diagram, and links to a video simulation that shows an image of the Omega Centauri star cluster from the Hubble Space Telescope being converted into an HR diagram. I quite enjoy these simulations. This video is cool because it takes the HR diagram, a concept we covered thoroughly in class, and applies it to a star system in real life.

This article was interesting because I never knew before this that galaxies actually collide and interact with each other. It is amazing to think that our Milky Way will combine with Andromeda in the future to form a single giant elliptical galaxy. Also, there is a video simulation of this from NASA, and I quite enjoy these types of simulations.

Before taking this class, I thought astronomy was kind of interesting. Now I think astronomy is slightly more interesting than I did before. I was exposed to a lot of new information in this class that has increased my understanding of the universe. I particularly enjoyed learning about things that are connected in some way to the formation of Earth and humans. This includes but is not limited to: the formation of planets, the formation of solar systems, and the elements produced in stars, which we are composed of. Additionally, the video simulations I came across in various articles were great because they allowed me see a complex concept expressed in a way that is easy to comprehend, like the change in the night sky over 5 million years. All of these factors contributed to make me feel a little less apathetic toward astronomy.


I would recommend that future Astronomy 101 classes continue to do a class blog, because it is a great way to increase ones understanding of the conceptual objective of the particular article. When I was trying to connect the article I read to class, and demonstrate that I understood the conceptual objective, I had to actually know what I was talking about. This forced me with a few articles to do some outside research on the conceptual objectives that I did not fully understand. I feel I learned just as much doing these blog posts as I would have doing a conventional test because I actually had to apply my knowledge instead of memorizing things for a multiple choice test.

Images of Explosive Star Formation

Assessment 13 – Star lifetimes and energy production

Article link from

The Orion Molecular Cloud (OMC-1) is a stellar nursery about 1350 light years away. 500 years ago, two protostars stars bumped into one another, and according to, it created “[A] powerful eruption that released as much energy as produced by the sun in 10 million years.” The protostars were projected out of the cloud at high speeds, and it sent hundreds of ‘streamers’ of gas and dust into space. Analyzing the images of this event might provide information about the carbon monoxide distribution in the streamers. This could help scientists understand the effect of such events on star formation.

This article relates to our conceptual objective “I can describe how stars form and produce energy in their cores by nuclear fusion” because it discusses the formation of stars. As we learned in class a star forms from a cloud of gas and dust that form a clump due to gravity. The collapsing clump flattens into a disk like shape and begins to rotate. More material is gathered during the rotation, the core gets hotter, and a protostar forms. After this protostar becomes hot enough, hydrogen atoms fuse, which produces energy and helium. An illustration from the textbook of a star’s birth is shown below.


Video from the European Southern Observatory (ESO)

I thoroughly enjoyed this conceptual objective because I have always been a little curious to how our sun actually formed. Never curious enough to learn about it on my own time, but now because of this class I know have a basic idea of how stars form. I now know, for example that our sun was at one point a protostar, millions of years ago. As I gazed into the sun as a small child, I was filled with a sense of wonder. Now because of this conceptual objective I have a deeper understanding of the object in the sky I had been fascinated with as a youngster.

Star Cluster Omega Centauri converted into HR diagram

Assessment 12 – HR diagram


In this recent video from ESA/NASA, the stars in Omega Centauri are rearranged into a Hertzsprung-Russell diagram. A HR diagram consists of values for luminosity and absolute magnitude on the y-axis and spectral type and temperature on the x-axis.


HR diagrams reveal quite a lot of information about stars. According to astrophysicist Brian Koberlein “Since most stars lie along this line (known as the main sequence) they must spend most of their lives there” We also learned some things the HR diagram can tell us from our lecture-tutorial H-R diagram, as illustrated in the picture below. For instance, stars of the same spectral type have the same temperature, because spectral type and temperature are on the same axis. Also, stars with the same absolute magnitude have the same luminosity, as these align on the y-axis.

Lecture-tutorial H-R Diagram


Video below

I unfortunately did not find this conceptual objective as wonderfully intriguing as previous ones. The diagram does give us a lot of insight into stars, but it is just a graph, and I do not find the the relation between variables as exciting as, for example, the marvelous intricacies of telescopes.

The Sky in 5 Million Years

Assessment 11 – Distance and size of stars

The European Space Agency (ESA) has put out a video simulation showing how the stars in the sky will appear to move over the next 5 million years. A night sky in 5 million years looks quite different than it does now, as stars have moved quite significantly. ESA’s Gaia, in their words, [I]s an ambitious mission to chart a three-dimensional map of our Galaxy, the Milky Way, in the process revealing the composition, formation and evolution of the Galaxy.

The article I read from says that Gaia uses parallaxes to measure the position of stars so accurately. As we learned in class, a parallax is the apparent movement of a star due to a changing viewing angle. The equation used to approximate the distance to a star is D=1/P (P= parallax angle and D= distance in parsecs). We applied this in class in the lecture-tutorial titled Parallax and distance, as seen below.

A correct and specific connection to class lecture-tutorial


The ESA’s video can be watched below

This conceptual objective allowed me to acquire new knowledge. Before now, when people brought up parallaxes in conversation, I had no clue what they were talking about. Now, thanks to this class, this will no longer be an issue, as I have learned what a parallax is, as I have demonstrated above. This piece of acquired knowledge justifies my opinion that this conceptual objective allowed me to acquire new knowledge. Additionally, I am thankful for this conceptual objective, as it has enriched my life with some fundamental knowledge of how astronomy works.