Assignment 6 - Modern Astronomy

The Hubble Space Telescope - above atmosphere 

      All astronomers have had and still have a single goal in mind - that is to see the entire universe at its deepest. However, in the past technology was an issue and the astronomers were very limited in what they can actually see. After many technological advances the Hubble Space Telescope was finally launched in 1990. It is known as one of the greatest advances in humanity to this day. This is no ordinary ground-telescope, for the Hubble orbits the Earth in outer space. Its ability to give a view of the universe is remarkable due to its position in the atmosphere - blocking and distorting the light headed directly below towards Earth. It was created by NASA (National Aeronautics and Space Administration) and enabled to unlock the greatest mysteries of astronomy.

Phase of Design

The Hubble Space Telescope with the it's science instruments.
This diagram also shows the direction light hits the telescope
and its pathway. 

     It was only due to Hubble's discoveries that changed the light of modern astronomy and how the world viewed the universe. Hubble allowed us to winnow down the numerous theories that have been proposed due to speculation, while also proposing new theories. The Hubble Space Telescope was created two avoid a twofold problem. Firstly, ground telescopes on Earth produce images that are distorted by the air pockets in the Earth's atmosphere. This problem is unavoidable no matter how technologically advanced the ground telescope is. An example of the distorted view from Earth is in the way the stars twinkle when you look up at them from Earth. The second situation is the fact that the atmosphere blocks and absorbs different wavelengths of radiation emitted by celestial objects (UV rays, gamma rays, x-rays). However, the only way to fully understand any object in space is to view all radioactive elements emitted by it. Therefore, one can understand that there is no way to create a ground telescope on Earth that views the wavelengths of celestial objects when the wavelengths of radiation do not even reach Earth in the first place. Hence, NASA came up with an effective solution to avoid the atmospheric distortion - placing a telescope beyond the atmosphere, 552 kilometers away from the surface of the Earth. The mission of the Hubble Space Telescope is "to serve the community of astronomers, journalists, teachers and laypeople with the best possible science communication products, as efficiently as possible, and adapt to our strategies to suit the needs of the target group whenever needed". Although the Hubble Telescope has endless amount of objectives, some of its key ones are to publish and distribute world-class news and photos, rapid response hotline to requests from media, scientists, educators and public.
   
     The way the Hubble Space Telescope works is that every ninety-seven minutes it completes a spin around the Earth - moving at 8 kilometers per second while doing so. This speed is incredibly fast and it was shown to compare it speed by stating that one would be able to travel across United States in ten minutes. While travelling, the Hubble captures light and directs it into the rest of its machinery. Once the light has entered the telescope it hits the primary mirror and reflects off to the secondary mirror. The secondary mirror's task is to essentially focus the light through a hole in the center of the primary mirror, which ultimately leads to the telescopes instruments inside. Each of these instruments are made to view the universe in a different way from each other, and either work together or independently creating clear images. The clarity of the images lies upon two factors; the ability of the telescope to capture light (length of mirror) and the fact that the telescope is placed beyond the atmosphere.

The Launch & Problems

The launch of the Hubble Space Telescope into space with a space shuttle. 

     After many delays, the Hubble was launched on April 24, 1990. The Hubble carried five instruments when it was launched; the Wide Field/Planetary Camera, the Goddard High Resolution Spectrograph, the Faint Object Camera, the Faint Object Spectrograph, and the Highspeed Photometer. However, right after the Hubble was launched, the crew detected some errors with the primary mirror. The telescope was in no doubt providing pictures of the universe, just not to the degree it was expected - the pictures were rather blurry and were not clear as expected. The flaw of the primary mirror was something called "spherical aberration". This means that the primary mirror was the wrong shape which caused the light that reflected off the centre to not focus on the same location as the light that reflected off the edge of the mirror. Regardless of the fact that the differences in location of focus was extremely small, it caused a huge difference in the pictures produced by the Hubble.

The making of the primary mirror which was later
found to be faulty. 

     Fortunately, NASA's scientists were able to quickly find a solution where they would use numerous small mirrors to direct the reflecting light to the correct location, allowing the light to reflect to the telescope's science instruments. These small mirrors were called The Corrective Optics Space Telescope Axial Replacement (COSTAR) and the scientists were required to replace another instrument within the Hubble with this. In order to precisely fix the telescope, the scientists spent almost a year training for the work required to correct the lens. Finally, on December 2, 1993 the crew of seven was ready to go out in space to the Hubble that required five days to repair. In order to repair the Hubble, they removed the High Speed Photometer and replaced it with COSTAR while also replacing the Wide Field/Planetary Camera with a newer version. A newer version was installed because it had small mirrors that would also compensate for the spherical aberration. By the time the crew was all finished with the Hubble it was December 9, 1993 and this allowed NASA to release exceptional high resolution pictures by January 13, 1994. The following years, many astronauts went back to the Hubble for routine check ups and to add new features.

Late Phase

    It all sounds all good - man has created a telescope to observe far beyond what anyone can see from Earth, creating spectacular high resolution images and changing the scientific community. Nevertheless, at one point in the near future the Hubble telescope will eventually degrade to the point where it completely shuts down. However, even when the Hubble stops working it will still continue to orbit the Earth. It will continue to orbit the Earth until the Hubble's orbit also decays and when this occurs the Hubble will come falling towards the Earth. But not to fear, because NASA is still working on a robotics mission to aid in degrading the telescopes orbit and guiding its plunge down to Earth.

The degradation of the Hubble Space Telescope over time. 

Hubble's Great Moments

The change of the brightness of a star due to a planet's orbit. 

     The Hubble Space Telescope had made countless contributions to the astronomic community and will always be looked as one of humanities greatest moments. An example of a breakthrough because of Hubble occurred due to the discovery of extra-solar planets. These planets have been discovered by ground-telescopes by observing tiny wobbles in the motion of a star as a planet pulls at it or by the dimming of light when a planet passes by it's parent star. For this, the Hubble allows us to have a more depth view of these planets blocking light. The periods when the lights are blocked by a planet are called transits. Until this day, Hubble is the first to make observations about planets around stars other then the Sun. Through these observations the Hubble has discovered atmospheres with sodium, carbon and oxygen, as well as a planet with a tail that has hydrogen evaporating. Also, methane was found in an extra-solar planet that was the size of Jupiter - the first organic molecule found on any other planet. Hubble also was able to take a picture of an extra-solar planet that is now known as Fomalhaut b and they were also able to observe a disk of gas and dust surrounding this planet. Afternumerous observations, scientists strongly believe that this star has its own planets.

The Andromeda Galaxy - Milk Way
Galaxy's closest neighbor. 

     The Hubble Space Telescope also assisted in following the galactic histories. It was thought that galaxies in the earlier universe collided, causing the galaxies that we now see to arise - evolving. Our galaxy is called Milky Way Galaxy and the closest galaxy next to is called Andromeda Galaxy. In Andromeda's halo (perimeter region of the galaxy containing stars) the Hubble was able to distinguish individual stars. It is known that halos only develop during the early formations of galaxies and so astronomers predicted that the Andromeda Galaxy's stars would be extremely old. However, when observing from the telescope they were able to tell that the stars were in fact varying in age - some 13 billion years old and other 6 billion years old. The most plausible explanation for this is that Andromeda was created through collisions of various other galaxies, and the Hubble provided substantial evidence for this.
 
      Lastly, another great breakthrough by the Hubble Space Telescope is it's ability to observe the universe's rate of expansion. When trying to study how old the universe really is, astronomers look for Cepheids. Cepheids are a special type of stars that are pulsing and their cycles of intensity show their brightness. Astronomers use Cepheids by comparing how bright they actually are with how faint they appear, and then finally determine the distance of their galaxy. Before the Hubble was created, astronomers have predicted that the universe's age was approximately 20-30 million years old. Hubble was able to observe 31 Cepheid stars and narrowed the age of the universe to approximately 13.7 billion years old (plus or minus 100 million years). The Hubble was able to narrow down the large interval and we are now able to develop a time scale and predict how the universe actually formed.

The view of Cepheid from the Hubble Space Telescope and their variable brightness. 

     The reason why I chose these three specific great moments of the Hubble Space Telescope is because by finding extra-solar planets and their compositions we may be able to see if there is indeed life on other planets as well. Also the Hubble was able to show us that galaxies grow and evolve by colliding into each other, indicating that there is constant change within our universe. Lastly, by being able to understand the birth of cosmology, one is able to measure the rate of expansion of the universe, and ultimately unfold how the universe was made along with its compartments.

References

Historical Milestones of the Hubble Project. (2009). Retrieved from http://www.nasa.gov/mission_pages/hubble/story/timeline.html

ESA. (2014) The Hubble Space Telescope. Retrieved from http://www.spacetelescope.org/about

Space Telescope Science Institute. (2008). Hubble Space Telescope. Retrieved from http://www.stsci.edu/hst
All pictures are from public domain.