Determining the Temperature and Luminosity of a Star.

I’ve recently read an article titled, “What is the Biggest Star in the Universe” written by Fraser Cain. This article goes into great lengths of detail about how there is a certain organization of temperature that stars in our solar system abid by. This system that Cain tells us about is called the MK system. With the MK system, the operations of this go into a different arrangement of letters such as (O, B, A, F, G, K, M) meaning that the letter “O” represents the hottest form of a star and the letter “M” meaning the coolest form of a star. Just like how this system implements the determination of temperature this system also gives the vast variation of cumulative size and mass of a star. Stars that fall in the “O” range of the MK system are massive stars in our solar system, while any star that falls into the “K” through “M” range tend to be relatively smaller and a lot more cooler in temperature like for example the red dwarf star. Finally, the end of the article brings a new bit of information to our attention by stating that the star Eta Carinae is one of the biggest and most luminous stars in our solar system. This star tops off at 25,000 kalvins making this hot.

I found that this article relates to objective 8 by making a connection to our lesson that we learned in class that talked about the temperature and luminosity of a star. In our workbooks the area that covers this concept is titled “Luminosity, Temperature, and Size”, in which we learned that luminosity can be increased by either a temperature raise or the overall size and mass of a star. On page 55 of this chapter the example letter “D” shows that there are two hot plates, one being large with a higher temperature and the other being larger with a medium temperature rate. It is a fact that the larger plate was able to cook the spaghetti quicker than the smaller plate even though the smaller plate had a higher temperature. This proves that a star relative to its size has a much higher temperature rate if the star is larger. On page 57, question #9 of our workbooks it says that the more luminous star is usually the one with a higher temperature rate in the case of two stars being the same in size. Another good connection to this article is in question # 10 of this chapter. The stars U and V have the same temperature, however, star U is more luminous than the other meaning that star U is larger in size than star V. Eta Carinae is one of the largest stars in the universe and being one of the most luminous. This proves that bigger stars are higher in temperature and luminosity.

What I’ve learned from this objective is the knowledge to determine which stars are the hottest in temperature and which ones shine the brightest in luminosity. This article also gave me the clarification on how to determine temperature and luminosity of a celestial body by giving the example of the MK system and Eta Carinae. I also learned that size really does matter in the case of stars and their temp and luminosity.




Brightest Neutron Star Ever Discovered

The article, “Ultraluminous Object is Brightest and Farthest Neutron Star Ever Discovered,” explains that astronomers have discovered the brightest neutron star ever found. This extremely dense object 1,000 times brighter than researchers previously thought was possible for neutron stars. The extreme brightness of this neutron star can be explained only if it has a complex magnetic field with more than two poles. This neutron star was first identified as an ultraluminous X-ray source (ULX). Research has found that ULX’s can pump out far more X-rays than anything in the Milky Way galaxy. In the past three years astronomers have discovered neutron stars capable of giving off up to about 10 million times more energy in X-rays per second than the Sun does in all kinds of light, suggesting that some ULX’s may have neutron stars at their hearts. Neutron stars, like black holes, are remnants of stars that died in catastrophic explosions known as Supernovas. Although neutron stars are typically small, with diameters of about 12 miles (19 kilometers) or so, they are so dense that a neutron star’s mass may be about the same as that of the Sun. NGC 5907 X-1 is the brightest neutron star discovered yet, blasting out up to about 55 million times more energy than the Sun per second. In one second, it emits the same amount of energy released by the Sun in 3.5 years.

Our objective was to be able to explain how astronomers determine the luminosity, the temperature, and size of stars. In the lecture tutorial, “Luminosity, Temperature, and Size,” we learned that the rate at which energy is given off is called luminosity. A star’s luminosity can be increased by increasing its temperature and/or increasing its surface area (size). The relationship between luminosity, temperature, and size allows us to make comparisons between stars. In this case, a neutron star is extremely luminous; much more luminous than the Sun and likely has a smaller surface area than the Sun. However, even though the neutron star is smaller than the Sun it would have about the same mass because neutron stars are extremely dense. In order for the neutron star to be more luminous than the Sun, in this case, it would have to have a higher temperature than the Sun because a higher surface temperature gives off more energy. In addition, since neither the Sun nor the neutron star have the same luminosity or the same surface temperature, it is more difficult to accurately predict the size of the neutron star without performing some kind of calculation.

I really liked this article because it is fascinating to think that there are stars that produce such high amounts of energy compared to stars in our galaxy; especially ones that are tiny that one without any background knowledge would think could not be more luminous than a much larger star. I also learned a few new things about stars from this article like the fact that neutron stars are remnants of stars that died in catastrophic explosions known as Supernovas, which is also how black holes are formed.

New ‘Scope. Who ‘Dis?


For this conceptual objective I was tasked with the challenge of explaining how astronomers use light to determine the chemical composition, speed, and direction of an astronomical objects motion. As per usual, I will start by explaining the science of this process that was discussed in class.

Using light to determine the chemical composition of an astronomical object is a simple place to start. With this we use color spectrums. Say a planet it orbiting a white star, we would point the telescope at the planet and when it passes in front of the stars  (or any other light sorce) we would then test the wavelengths of of visible light that reflect off the planet. The absorption method is used and tells us what chemicals are present. What this means is, specific atoms present in the planet/atmosphere will cause certain colors to be missing from the spectrum. Scientists can then accurately speculate what chemicals are present.

The speed of an object in space is also determines using wavelengths. The Doppler Effect is used specifically for this. The light waves emitted by an object will appear differently depending on where, or if, the object is moving. The wavelengths are shorter in the direction an object is moving, and longer in the opposite. With visible light this makes an object appear red as it moves away and blue as it moves closer. These phenomena are called redshift and blueshift respectively. It is with this that astronomers can detect the direction in which an object is moving in space. This method can also be used to determine the speed of an object. Still using the Doppler Effect, and the colorshifts, planets and objects will have a more intense hue depending on their speed. If it is moving away very rapidly then it will appear redder than if it was slowly moving away, and the same goes for the blueshift.

*image from The Essential Cosmic Perspective by Bennett, Donahue, Schneider, and Voit 

Now that was a bit of a lengthy explanation, but don’t worry, it ties into the article that I listed above. A brief summery of the article is that scientists are excited to use the new James Webb reflecting Telescope on the recently discovered Trappist-1 system. With this new telescope astronomers will have a much more powerful tool to use methods such as the Doppler Effect with greater accuracy. As mentioned in the article, scientists are planning to point the telescope at the three most hopeful candidates for harboring life. In the atmospheres they’re looking for chemicals such as Oxygen, Hydrogen, Nitrogen and water. If these chemicals are found in any concentration that could lead researchers to belive that the planet’s in the habitable zone of Trappist-1 have a great potential to harbor life. Unlike the method mentioned above, the speed of the planet’s orbiting the star in Trappist-1 has their speed estimated by their rate of orbit, but the scientists behind James Webb Telescope’s controls could easily use it to track the wavelengths emitted by the star, thus answering how fast and in what direction the system is traveling.

I enjoy articles like this one because because it covers two of my favorite topics of astronomy: new discoveries,  and technological feats. The new telescope will bring great opportunities to NASA and other astronomical corporations and I look forward to that with gusto.

Temperature and Luminosity of a Star

I read an article on by Frasier Cain called, “what is the biggest star in the universe?”, that I feel correlates with the conceptual objective #8, “I can explain how astronomers determine the luminosity, the temperature, and size of the stars”. The article goes over how the temperature of stars is organized into what is known as the MK system, which uses the letters, O, B, A, F, G, K, and M, making O the hottest and M the coolest. The article then states that stars in the O range are much larger and much more massive, making them much hotter, where as stars that are in the K and  M are usually a lot smaller, like a red dwarf, making them much cooler. The article also introduces the Eta Carinae, which is one of the biggest stars in the universe, but also one of the most luminous stars we know of, and to top it all off, its sits at 25,000 Kalvin, making it extremely hot.

This article relates to what we learned in class about the temperature and luminosity of a star. In the Lecture-Tutorial “Luminosity, Temperature, and Size”, We learned that Luminosity can be increased by either increasing the temperature or the size of a star. In the article, it was stated that the much larger stars were usually the hottest, indicating that size matters. This can be proven on page 55, letter D. There are two hot plates, one being smaller with a higher temperature, and the other being larger with a medium temperature. It was found that the Larger plate actually cooked the spaghetti faster, despite the smaller one having a higher temperature. Also on page 57, Question #9 states that the more luminous star is usually the one with the higher temperature in the case of 2 stars with the same size. Also, question #10 states that star U and star V have the same temperature, but star U is actually more luminous, this indicates that Star U is actually larger than star V. A perfect example of all of this is the Eta Carinae star. It is one of the largest stars in the universe, but also one of the most luminous, proving that the biggest stars are usually higher in both temperature and luminosity, and also proving how important a role size plays into this.

This conceptual objective helped me learn how to tell what stars are the hottest and which shine the brightest. The hot plate exercise on page 55 was my favorite because it helped put everything into perspective and also helped to distinguish confusion with a question like letter D, how just because the smaller plate was hotter, doesn’t mean It was going to cook the spaghetti faster. I learned again the role that size takes on, and how the big bad stars shine the brightest.

“They Say Size Is All Relative… And In This Case It Is Certainly True.”

Our sun is so large that is accounts for 99.86% of all the mass in our solar system. Even with that being said, the sun is just a spec compared to the star VY Canis Majoris. The article, “Can you spot EARTH in this stunning image? If you think you can, prepare to be ASTONISHED” explains just exactly how small our sun really is in comparison to other stars.

Red hyper giant VY Canis Majoris and our sun

This picture represents VY Canis Majoris, while that tiny white spec is the sun. Our earth in comparison on the picture would only be portrayed as one thousandth of a pixel on the computer screen. Our sun is about 93 million miles away from Earth, being classified as a yellow dwarf star and has a circumference of nearly 2.7 million miles. The sun is so large that one could fit 109 Earths could line up side by side, and can fit 1.3 million Earths inside it. This makes the Sun seems extraordinarily large, but unfortunately the sun is almost nothing compared to VY Canis Majoris. VY Canis Majoris is classified as a red hyper giant. It is 4,892 light years away from Earth with a circumference of 5.6 billion miles, almost 2000 times larger than the sun’s. The circumference is so large that is would take a jet plane 1,100 years to fly one lap around it. Although VY Canis Majoris is much larger than the sun, it is also much cooler as well. Because its surface is so far from the core, It’s surface temperature is around 3,000 degrees Celsius whereas our sun is 5,600 degrees. VY Canis Majoris is nearing the end of its life span where it is expected to explode into a super nova while our sun still has an estimated 5 billion years left before it burns out.  VY Canis Majoris, being as large as it is, will most likely create a black hole once it explodes.  Even though VY Canis Majoris is the largest star known, it is only a spec in the milky way, and their are many other galaxies with stars many times larger.

This article really gave a sense of how small we really are. The sun has always been portrayed as being this huge star and that it is some unbelievable size. After comparing it to VY Canis Majoris, we really need to be more careful when calling the sun “large,” even though it is large enough that it accounts for 99.86% of the mass in our solar system. The Earth and sun are more comparable in size rather than the sun and VY Canis Majoris would be. Because the star is so large, I am curious to what its gravitational pull is like if it pulls in any planets that get too close or if they are still able to orbit it like any other star. I am curious how old the star is if its only got about 100,000 years left until it forms a super nova, as compared to the sun’s 5 billion more years. Even though it is many times larger than our sun, I was very surprised to find out that its temperature is much less than our sun’s temperature: Although this could also be due to that it is burning out and at the end of its life span. I find it unbelievable that scientists are able to figure out the temperature of stars that are several light years away. To help them calculate temperatures of distant stars, scientists can using black-body radiation diagram, as we learned in class and our 8th conceptual objective. Scientists use the light waves that are given off from the star, and take the peak frequency, which determines the temperature.



For instance, as we did in our lecture-tutorial notes “Blackbody Radiation”  we learned that bluer light is hotter whereas redder light is cooler. Star E in the graph has a peak at a lower wavelength closer to violet, meaning that it is going to be a hot planet, such as its at 8000 degrees. Star F on the other hand has a peak at the red wavelength meaning that it is going to be a cooler star, as shown at 4000 degrees. Scientists can then use stars Temperatures to estimate the size of stars, as in “Luminosity, temperature, and size” in our lecture-tutorial notes using a H-R diagram.


If comparing star U and star X together, then an estimated size can be concluded. Star U has a higher Temperature than star X does. However, they are both just as luminous. Because they have the same luminosity, star X must be a bigger size than star U to make up for the lower temperature with a greater surface area. Unfortunately it would be much more difficult to compare the size of star U to star W because they both have different temperatures and luminosity so there is nothing to get a basis off of and comparison. After reading this article, I have an entire new outlook on our sun and especially the Earth. It really shown how small we are in the universe and that our galaxy alone is just a small spec within the universe.

Determining Characteristics of Stars

The eight conceptual objective, I can explain how astronomers determine the luminosity, the temperature and size of stars, has been discussed recently in class. Determining these certain characteristics of distant stars involves an in depth, precise process. In class, we discussed some ways that astronomers determine these specific characteristics of stars. In class, we exercised this concept in the Lecture-Tutorial book. The section of the Lecture-Tutorial book that relates to the eighth conceptual objective is titled, “Luminosity, Temperature, and Size”. This is pertaining to distant stars. In order for an astronomer to determine the luminosity or brightness of a star, they must first know the distance of the star. A star could be less bright because it is far away from us or because it is simply less luminous. Astronomers must measure the rate of the energy of the star. Ultimately, the distance of the star plays a big role in the luminosity it appears to emit. In order for astronomers to determine the temperature of a star, they must take in consideration the stars’ color. For instance, a star that is blue or white would suggest that it is really hot and that it gives off a lot of energy. Whereas a red star would suggest that the surface temperature is less of that of a blue star. The wavelength of a stars’ light can indicate its surface temperature. The size of a star can be determined by understanding the stars’ brightness and temperature. Once these characteristics are known, an idea of how big the star is can become more clear. This was carefully looked at in class as well as discussed in the Lecture-Tutorial book. The article I chose, “Are These the Most Distant Stars Ever Seen?”, relates closely to the eight conceptual objective. Astronomers have used gravitational lensing to observe ancient stars. These stars are located in a galaxy that is nearly 13 billion light-years away from Earth. This galaxy is one of the most distant galaxies from Earth that have ever been studied. In the process of studying this specific galaxy, astronomers have determined the luminosity, temperature and size of many stars in this distant galaxy. Because this galaxy is massive, it can bend light substantially. This allows astronomers to see and study these stars more carefully. This article relates to our eighth conceptual objective because it demonstrates how astronomers characterize stars. Even if the stars are billions of light-years away from Earth. The brightness, temperature, and size of a star is unique to each one, and may seem like a complex process to categorize them. With today’s technology and telescopes, astronomers have found precise processes that allows them to characterize a star. The technology used, such as telescopes, leads to our ninth conceptual objective. This article clearly demonstrates this concept and applies it to a real-world situation. This article was very interesting to me and proved to be very informative. The article has furthered my understanding of how stars are characterized by astronomers.


Why so Sirius?

If someone were to ask you how bright is the Sun, how would you respond? Pretty bright, right? I mean, the Sun is certainly brighter than the highest brightness setting on your phone and it’s brighter than any man-made light source. In fact, it so bright that it’s dangerous for us to stare at it for too long! It’s one of the brightest objects that we see in our daily lives, however, being a space object and all, is the Sun really that bright? Is there anything in the expanses of the universe that can top the Sun’s brightness? Surprise, surprise, there are and plenty of them too.

In scientific terms, brightness is luminosity. We learned from the previous conceptual objective that light is a form of energy and all light comes from accelerated charged particles. Space objects, like the Sun, are able to burn brightly because the heated particles radiate light. Incandescent objects emit light when the temperature gets too high, or when the photons become too energetic. How luminous an object becomes depend on how energetic the photons are, in other words, how hot the object is. Everything in the universe, above Absolute 0 produces some sort of light, including humans. Humans radiate energy as well, however, the energy level is fairly low which is why we aren’t able to detect it with our eyes. The wavelengths that radiate from our beings can be sense with thermal infrared technology (infrared is lower on the electromagnetic spectrum than visible light).


So back to the question, how bright is the Sun? Still pretty bright, in comparison to things on Earth. But if the question was rephrased to say, how bright is the Sun in comparison to other stars, the answer isn’t quite as obvious.


Meet Sirus.

In “Sirius is Dog Star and brightest star,” it mentions that Sirius is one of our brightest stars in the night sky. Knowing that a star is a distant Sun and our Sun is a close star, how is Sirius’ brightness than in comparison to our Sun? According to the article, astronomers have classified Sirius as an ‘A-type’ star, which is two grades hotter than our Sun (which is a ‘G type’ star) and it burns a white-to-blue-to-white color.

These are the different classifications for stars based off of temperatures. O is the hottest and M is the coolest. The Sun sits are Class G while Sirius is Class A. Sirius is much hotter than the Sun.

Because it emits white/bluish color, it means that its wavelengths are on the higher end of the electromagnetic spectrum. The higher it is on the spectrum, the higher state of energy, the higher the temperature and the more luminous the object will appear to be. So even though Sirius is 8.6 light years away, by comparing its luminosity with the Sun, we’re able to calculate that it’s “much hotter than our sun, with about surface about 17,000 degrees F (the sun is about 10,000 degrees F)” and produces 26x more energy.

In reference back to a lecture tutorial that we completed in class, ‘Luminosity, Temperature, and Size,’ we learned that a star’s luminosity can be increased by increasing its temperature and/or surface area (size). By identifying that Sirius is more luminous and is hotter than our Sun, we can also conclude that it is a lot larger than the Sun, at about “slightly more than twice the mass” and “just less than twice its diameter.”

At first, it was a little confusing for me to understand the relationship between luminosity, temperature, and size. But through time and by taking a look at other stars in our galaxy so I can compare them with our Sun. I was able to recognize the relationships and clear my confusion. Upon reading this article, I also learned more about Sirius and its properties-how it’s able to shine so bright in our night sky in comparison to other stars.

Humans have never physically reached Sirius and even with modern day technology we’re probably not going to anytime soon (it takes us 9 years just to get to Pluto, who is 4.67 billion miles away, and Sirius is again, 8.6 lightyears away). However, by understanding the relationship between luminosity, temperature, and size,  we can make fairly accurate estimations about distant celestial objects, such as stars.