- Education and Science
Watching the skies - Hubble and James Webb Space Telescopes
In the fairly recent past, when the burning at the stake was still a good show for the public, we believed that the Earth is the center of the universe and the Sun and the other planets orbit it. Then we realized that we’re wrong, and the Sun is the center of the universe. Later on, when the technology allowed, we found that we are only a very small part of an entire crowd of stars and dust, which we called “Galaxy”, the Milky Way galaxy, our galaxy. And until Edwin Hubble (yes, the Hubble space telescope is named after him) the whole science community believed that our galaxy is the only galaxy in the universe. A few other unknown bodies were observed though, that were neither stars nor planets, and they were called “nebulae”, some lost gas and dust floating randomly into nowhere. Edwin Hubble turned the 100 inch telescope (a big one at that time) to one such nebula (named Andromeda) and he saw, well, another Milky Way. That nebula was a dense cluster of millions of separate stars and it looked more like another galaxy than a nebula. In one of the observations he saw that one of the stars pulsed. Edwin used that star to calculate the distance to it in order to see if the nebula was in fact located into Milky Way galaxy! Turned out that the nebula was nearly 900,000 light years away, which proved that Andromeda was a separate galaxy. Then he looked at every other known “nebulae” and saw the same: they were all galaxies just like our own, different in shape, color, size, but they were all galaxies.
Hubble Space Telescope
One hundred years later (in 1995), another similar breakthrough takes place when the Hubble Space Telescope takes the most important photo ever taken and reveals to us what really lies beyond a dark spot in the sky.
The resulting image was astonishing: called Hubble Deep Field (HDF), this photo shows more than 1,500 galaxies in different stages of evolution, most of them being nearly 30th magnitude (about four-billion times fainter than can be seen by the human eye). What makes this photo so famous, so important? Well, this photo truly tells us just how small we are as compared to this immense universe.
Since 1990 Hubble found lots of exoplanets of all kinds (planets that orbit other stars than our Sun) scattered all over our galaxy. Statistically, if only one star in ten has planets (and current knowledge indicates that at least that many do), if the average star with planets has at least three, and if only one in every hundred are rocky planets in life-sustaining orbits (and recent discoveries indicate that to be the case), then there are at least 300,000 planets capable of supporting life in our galaxy, and thanks to Hubble Space Telescope, we know that there are at least 125 billion galaxies out there, each one containing 200 – 400 billion stars or even more. If you can, you do the math :) Hubble estimated this number in 1999. Since that time, new space probes have been placed into orbit and this number increased significantly, especially considering the fact that a large number of galaxies aren’t visible to Hubble.
James Webb Space Telescope
In 2014 a new space telescope, named James Webb, will observe the sky, especially in infrared. The WMAP probe definitively determined the age of the universe to be 13.73 billion years old to within 1% (0.12 billion years). While Hubble can “see” 13,3 billion years old objects, JWST (James Webb Space Telescope) will be able to see 13,5 or even (hopefully) 13,7 billion years old objects, so its primary mission will be finding the young universe, only 200 – 300 million years old.
You can find a detailed comparison between Hubble and James Webb here, but the main differences are as follows:
- Hubble is no larger than a school bus, JWST is almost as large as a tennis court;
- Hubble looks at the universe in optical and ultra-violet wavelengths while JWST will study it in infrared. Webb also has a much bigger mirror than Hubble. This larger light collecting area means that Webb can peer farther back into time than Hubble is capable of doing;
- Hubble is in a very close orbit around Earth (570 km). Webb will be at the second Lagrange (L2) point, which is 1.5 million kilometers away from Earth.
Webb won’t even orbit Earth, basically it will orbit the Sun along with the Earth and the Moon and will use its solar shield to block the light coming from the three bodies in order to stay cool, which is very important for an infrared telescope.
Why study the universe in infrared?
Observing the universe at different wavelengths is essential because observations at different wavelength return different results, which combined, form a more complete image of what really lies out there. For example, stars and planets that are just forming lie hidden behind cocoons of dust and cannot be seen in visible light. The same is true for the very center of our galaxy. However, infrared light can penetrate this dusty shroud and reveal what is inside.
A similar process is astrophotography. Every astronomer wants his own telescope in order to see with his own eyes the celestial objects, but only few enthusiasts know that the number of objects that can be seen in true color is very small. More than 95% of the objects, especially the deep space objects, can be observed in black and white only. That’s because the human eye refreshes the image that it sees every 0.25 seconds, and that leaves a too small timeframe for the light particles coming from such a great distance to gather on the retina. This is why we use special cameras that don’t refresh the image; they capture and hold the light particles coming from the distant objects instead.
The process NASA uses to take those high-quality photos is a little more complicated. In order to surprise every detail of the targeted object, the telescopes used in the process photograph the object through three filters: red, green and blue (RGB). Then special software is used to combine the three or more photos into one, and the result is always spectacular.