Hubble Space Telescope

Until the late twentieth century, astronomers could only observe the heavens with Earth-based instruments. Although many observatories across the globe contained some of the most advanced equipment with the farthest optical scope, a space-based telescope could capture images with far greater benefits. In space, noise interference and atmospheric blurriness have no distorting effect; in space, a telescope can capture farther and fainter objects than any telescope on Earth. [1] Above the Earth's atmosphere, light can be gathered at a much greater rate and accuracy, with much more detail and at significantly farther distances. Thus, even with a rather small 2.4-meter mirror, the Hubble Space Telescope revolutionised astronomical imaging upon its launch into the cosmos. [2]

The first space telescopes were imagined soon after the conclusion of the Second World War. It is believed that Lyman Spitzer's report in 1946 laid the foundations for the eventual launch of a space telescope. Almost half a century later, the Space Shuttle Discovery carried its precious cargo into space. Named after Edwin Hubble, the greatest American astronomer of the twentieth century, the Hubble Space Telescope left its earthly plane on 24 April 1990. [3]

Of course, the Hubble Space Telescope was not without severe faults prior to and following its launch. It was delayed at least half a decade by the tragic disaster of the Challenger explosion in 1986. However, the Challenger disaster proved to be a benefit for the preparation of the Hubble Space Telescope. Rather than rushing it into space, recalculations and upgrades could be made to its equipment. [4] One of the most pressing issues however concerned its main mirror which was erroneously grounded. Even an aberration of a thousandth of an inch disrupted the image-gathering capabilities of the telescope. Rather than focusing all of the light into its core, the off-mounted mirror cast a 'halo' of light around the core - enough to minimally distort the pictures being taken. [5] With other mechanical problems after its launch, NASA was forced to send a mission in 1993 (and another in 1997) to correct its issues. Though costly and rife with political antagonism, the missions proved successful and the Hubble Space Telescope has been able to capture the most incredible images from across the universe. [6] In its first eight years of operation alone, the Hubble Space Telescope had, in its orbit around Earth, travelled farther than the distance to Saturn, and transmitted billions of bytes of data. [7]

The Hubble Space Telescope is not designed much differently from its Earth-based counterparts. A large main mirror condenses light into a smaller secondary mirror, which is reflected back through a hole in the centre of the main mirror. The light gathered here is captured with the telescope's instruments, all of which are fitted with electronic cameras (CCDs) to transmit the information to Earth. Electric currents produce pixellated images on computers, which can also be manipulated with imaging techniques like colouring, contrast, and imposition. [8] There are some features of the Hubble Space telescope that are different from Earth-based telescopes, including panels to generate solar energy for the telescope's instruments and a magnetometer for detecting the Earth's magnetic field. [9]

The Hubble Space Telescope has done great things for astronomy. Just some of its many accomplishments include measuring star clusters to determine the age of the universe, observing supernovae to aid the theory of a rapidly-expanding universe, detecting the presence of other solar systems, and studying our own Solar System's planets and moons:

"The pictures sent back from Hubble have, really for the first time, brought home

to ordinary people the immensity of the forces at work in the heavens. We have

seen the effect of comets smashing into the surface of Jupiter with an explosive

power of 100 million megatons; watched storms brewing on the surface of

Saturn; witnessed doomed stars exploding amid brilliant fireworks displays, with

loops and rings of gas light-years across surging outwards into space; black holes,

white dwarfs, red giants... all have been revealed." [10]

Two of the Hubble Space Telescope's greatest observations are of a distant redshift 6.8 galaxy which, along with the Spitzer Space Telescope, could estimate its age and mass, and in 2002 and 2003, observations of the Andromeda galaxy determined that it had collided with one or more galaxies billions of years ago, distributing billions of stars into an awesome halo. [11]

Eventually, the Hubble Space Telescope will fail to serve its purpose. This can happen in at least two ways: either the instruments on the telescope are fatally damaged or cease to operate effectively, or it's image-capturing capabilities are deemed obsolete. Most likely, the the U.S. government will determine that its maintenance is too costly to continue servicing and will terminate the project. [12] One option is to simply shut the machine down, but the risk of it crashing down to Earth is far too great. Instead, NASA has discussed sending a satellite to either lift the Hubble Space Telescope to a safer orbit or bring it back down to Earth. The latter option seems to be a more desirable one, as the effect of space on a great machine could be studied and its body housed in a museum. [13]

No other instrument in the history of astronomy since Galileo's first telescopes has done more to advance scientist's understanding of the universe so quickly. [14] For over twenty years, the Hubble Space Telescope has generated millions of outstanding images and introduced astronomy to the greater public. Now, more than ever, the universe can be viewed by anyone with even a remote interest in space. Thus, he Hubble Space Telescope has proven to be one of the great moments in astronomy.

Notes:

[1] Fischer, Daniel, and Hilmar W. Duerbeck. Hubble: A New Window to the Universe. New York: Copernicus, 1996, p. 26.

[2] Kanipe, Jeff. Chasing Hubble's Shadows: The Search for Galaxies at the Edge of Time. New York: Hill and Wang, 2006, p. 5.

[3] Clark, Stuart. Universe in Focus: The Story of the Hubble Telescope. London: Cassell, 1997, p. 12.

[4] Leverington, David. New Cosmic Horizons: Space Astronomy from the V2 to the Hubble Space Telescope. Cambridge, UK: Cambridge University Press, 2000, pp. 431-2.

[5] Petersen, Carolyn C, and John C. Brandt. Hubble Vision: Further Adeventures with the Hubble Space Telescope. Cambridge: Cambridge University Press, 1998, p. 9; Clark, Universe in Focus, p. 16.

[6] Petersen & Brandt, Hubble Vision, p. 9.

[7] Fischer, Daniel, and Hilmar W. Duerbeck. Hubble Revisited: New Images from the Discovery Machine. New York: Copernicus, 1998, p. 185.

[8] Clark, Universe in Focus, p. 14, 23-4.

[9] Petersen & Brandt, Hubble Vision, p. 14.

[10] Wilkie, Tom, and Mark Rosselli. Visions of Heaven: The Mysteries of the Universe Revealed by the Hubble Space Telescope. London: Hodder & Stoughton, 1998, p. 13-15.

[11] Kanipe, Chasing Hubble's Shadows, pp. 38, 148.

[12] Kanipe, Chasing Hubble's Shadows, p. 5.

[13] Fischer & Duerbeck, Hubble Revisited, p. 191.

[14] Kanipe, Chasing Hubble's Shadows, p. 5.

References:

Clark, Stuart. Universe in Focus: The Story of the Hubble Telescope. London: Cassell, 1997.

Fischer, Daniel, and Hilmar W. Duerbeck. Hubble: A New Window to the Universe. New York: Copernicus, 1996.

Fischer, Daniel, and Hilmar W. Duerbeck. Hubble Revisited: New Images from the Discovery Machine. New York: Copernicus, 1998.

Kanipe, Jeff. Chasing Hubble's Shadows: The Search for Galaxies at the Edge of Time. New York: Hill and Wang, 2006.

Leverington, David. New Cosmic Horizons: Space Astronomy from the V2 to the Hubble Space Telescope. Cambridge, UK: Cambridge University Press, 2000.

Petersen, Carolyn C, and John C. Brandt. Hubble Vision: Further Adventures with the Hubble Space Telescope. Cambridge: Cambridge University Press, 1998.

Wilkie, Tom, and Mark Rosselli. Visions of Heaven: The Mysteries of the Universe Revealed by the Hubble Space Telescope. London: Hodder & Stoughton, 1998.

Pluto

Pluto is one of several million objects lying in an outer layer of small icy rocks on the edge of our Solar System, in the Kuiper Belt region. Most of these Kuiper Belt Objects (KBOs) have solid silicate cores with several layers of ice near and at the surface. Pluto may contain ammonia and methane ice as well. [1] Recent observations of Pluto also suspect levels of nitrogen and carbon monoxide, and possibly a gaseous, albeit thin, atmospheric layer. [2]

Pluto and Mercury, as the smallest planets* and as the furthest and closest planets to the Sun, respectively, have orbits with the least approximate circular motion. As we have come to understand in class on the laws of motion pertaining to astronomical bodies, Pluto's revolutions are some of the slowest in the Solar System, being one of the furthest objects from the Sun, taking nearly 250 (Earth) years to complete a single orbit. [3] What is interesting about Pluto here is that it rotates sideways to other planets (as does Uranus). [4]

Pluto has three moons. The largest of these, Charon, was discovered in 1978 and is large enough (about half the size of Pluto) that Pluto-Charon was the first double planet in the Solar System. [5] 

The following table gives some basic information on Pluto's characteristics [6]:

	Pluto	Earth	Relativity (Pluto-Earth)
Diameter (mean)	2280 km	12 740 km	0.179
Distance from Sun	5.9 billion km	149.6 million km	39.5
Surface temperature (Kelvin)	50	260-310	N/A
Mass	0.078 x 10²⁴ kg	5.98 x 10²⁴ kg	0.013
Mean density	2048 kg m⁻³	5520 kg m⁻³	0.371

American astronomer Clyde Tombaugh discovered Pluto in 1930, basing his search for the ninth planet on previous predictions established by Percival Lowell. Lowell had assumed that the gravitational motions of Uranus and Neptune were being affected by a massive object that lay beyond the two planets. That 'massive object' was thought to be Pluto. It was only after its discovery about thirty years later at the observatory which bore his name - the Lowell Observatory in Arizona - that it was realised that due to its small size, Pluto could not have had such a dramatic effect on Uranus's and Neptune's motions. In retrospect, Lowell's prediction was baseless, and can best be explained by faulty measurements. [7] It did, however, establish the beginning of a search for what lay on the outer reaches of our Solar System.

Continuous exploration and scientific discoveries in this part of the Milky Way have led to changing theories and debates regarding Pluto's status. In 2006, the International Astronomical Union (IAU) recategorised Pluto as a dwarf-planet, demoting it from the other eight planets in the Solar System. This ruling deemed that a planet must be spherical and orbit the Sun - two classifications which Pluto fits - but also be in a space free of cosmic objects. As stated above, Pluto is within the Kuiper Belt - a large swath of objects similar to an asteroid belt. Therefore, Pluto was considered unfit to hold full planetary status. In 2014, a debate amongst three of the most established astronomers in the world, Owen Gingerich, Dimitar Sasselov, and Gareth Williams, showcased a public decision at the Harvard-Smithsonian Center, in which a popular majority 'voted' to re-instate Pluto's planetary status to full membership. [8]

"Found in the inner parts of the Kuiper Belt, plutinos are Kuiper Belt objects {KBOs) that have orbital periods very similar to that of Pluto. Their orbits are stabilised against gravitational perturbations by the 3:2 mean-motion resonance with Neptune, meaning that they orbit the Sun twice for every three orbits of Neptune." [9]

This summer, NASA's New Horizons mission will reach Pluto - the farthest any object from Earth has been - and is sure to teach us new things about what lies on the peripheries of our Solar System.


End Notes:

[1] Roger Smith (Editor). (1998). The Solar System (Vol. 3). Pasadena, CA: Salem Press, 887.

[2] "Pluto". (n.d.). In Royal Museums Greenwich - National Maritime Museum: http://www.nmm.ac.uk/explore/astronomy-and-time/astronomy-facts/solar-system/pluto.

*- The planetary nature of Pluto has been disputed, as will be examined further in this post. From this source, Pluto is still considered a planet in our Solar System.

[3] Keith Holliday. (1999). Introductory Astronomy. Chichester, England: John Wiley & Sons, 90-1.

[4] Holliday, Introductory Astronomy, 65-6.

[5] "New Horizons: The First Mission to Pluto and the Kuiper Belt: Exploring Frontier Worlds." (January 2006). NASA: http://www.nasa.gov/pdf/139889main_PressKit12_05.pdf.

[6] Holliday, Introductory Astronomy, 67 [Table 5.2; calculations for Pluto are my own].

[7] Blondel, Philippe, and John W. Mason (Editors). (2006). Solar System Update. Chichester, England: Praxis Publishing, 267; "Pluto", National Maritime Museum; "Celestial Mechanics - Planetary Perturbations." (n.d.). Retrieved from http://science.jrank.org/pages/1295/Celestial-Mechanics-Planetary-perturbations.html.

[8] "Pluto", National Maritime Museum; Jennifer Hackett. (February 13, 2015). "Pluto's ongoing identity crisis stirs planet definition debate." In Scienceline: http://scienceline.org/2015/02/plutos-ongoing-identity-crisis-stirs-planet-definition-debate/.

[9] "Plutinos." (n.d.). In Cosmos - The SAO Encyclopedia of Astronomy. Swinburne University of Technology: http://astronomy.swin.edu.au/cosmos/P/Plutinos.


References:

"Celestial Mechanics - Planetary Perturbations." {n.d.). Retrieved from http://science.jrank.org/pages/1295/Celestial-Mechanics-Planetary-perturbations.html.

"New Horizons: The First Mission to Pluto and the Kuiper Belt: Exploring Frontier Worlds." (January 2006). NASA: http://www.nasa.gov/pdf/139889main_PressKit12_05.pdf.

"Plutinos." (n.d.). In Cosmos - The SAO Encyclopedia of Astronomy. Swinburne University of Technology: http://astronomy.swin.edu.au/cosmos/P/Plutinos.

"Pluto". (n.d.). In Royal Museums Greenwich - National Maritime Museum: http://www.nmm.ac.uk/explore/astronomy-and-time/astronomy-facts/solar-system/pluto.

Blondel, P., & Mason, J.W. (Editors). (2006). Solar System Update. Chichester, England: Praxis Pubishing.

Hackett, Jennifer. (2015, February 13). "Pluto's ongoing identity crisis stirs planet definition debate." In Scienceline: http://scienceline.org/2015/02/plutos-ongoing-identity-crisis-stirs-planet-definition-debate.

Holliday, Keith. (1999). Introductory Astronomy. Chichester, England: John Wiley & Sons.

Smith, Roger (Editor). (1998). The Solar System (Vol. 3). Pasadena, CA: Salem Press.