James Webb vs Hubble, images and features compared

Although we are talking about two technologies practically divided by 30 years of history, the arrival of the first scientific images of the James Webb space telescope has opened a new and exciting chapter in astronomical observation and, inevitably, there has been no lack of comparisons with the observations of same areas of the cosmos made by the telescopes that preceded it. One above all, the legendary Hubble Space Telescope, which since 1990, the year it entered service after being placed in Earth’s orbit, has been operating continuously despite having suffered from some problems in recent years.

In this special we want to analyze the main differences between the two telescopes and then show you a comparison between the same images captured by Hubble first and then by James Webb. We tell you in no uncertain terms: even without any competence in astronomy, the results are quite eloquent in terms of sharpness and richness of details, but it is good to understand at least partially the differences between the two technologies to get a more precise idea.

The idea of ​​creating the James Webb was actually born following the vision of the first results obtained by Hubble, and from this point of view it could be defined as his successor, even if, as we will see later, it is very different in terms of operation. The basic idea at the beginning of his design was to create an even more refined vehicle capable of scanning the universe at even more extreme wavelengths, to get where Hubble could never have gone. So let’s see what unites them and what differentiates them, then we will compare the first images released by NASA and you will discover that the results are definitely astounding!

We have said this several times, even in articles prior to the launch of the Webb: the most significant constructive data that differentiates it from Hubble is relative to the dimensions. The most important element concerns the primary mirror, which with the James Webb’s 6.5 meters in diameter against the 2.4 meters of Hubble, actually offers a much larger light-gathering area. Doing a couple of maths, Hubble reaches an area of ​​4 m² compared to the 25 m² of the James Webb, which it turns out in fact dimensionally higher than 6.25 times.

The field of view is consequently wider and the spatial resolution significantly better even than any other previous generation infrared telescope. The James Webb Space Telescope also mounts a fundamental component (due to its orbital position) which is the parasol. We could define it as vital for an infrared telescope like the Webb, which requires optimal thermal insulation of each single component. The James Webb parasol consists of 5 layers of kapton and is huge! It measures 22 x 12 meters, reaching an area similar to that of a tennis court. Hubble is not equipped with a parasol and we will understand better why below.

Speaking of orbits, in fact, the differences are more palpable and if Hubble is located around the Earth at about 570 km high, for the James Webb the situation is very different. What makes it special is its fixed positioning about 1.5 million km away from Earth in what is called the second Lagrange point, or L2.

The choice of the term ‘fixed’ is not accidental, in fact, in that position the Webb solar shield will block the light coming from the Sun, the Earth and the Moon. This will help Webb stay cool and free of interference, which as mentioned above is very important for an infrared telescope. Given the particular position, while the Earth orbits the Sun the James Webb will orbit with it but will remain fixed in the same point with respect to the Earth and the Sun.

Finally, let’s talk about the different wavelengths that the two telescopes observe, starting with James Webb. The new space telescope operates mainly in the infrared and has four scientific instruments capable of capturing images at different spectra. On balance, the wavelength coverage ranges from 0.6 to 28 microns, thus covering a large part of the infrared spectrum, which starts at 0.75 microns. This means that the James Webb partially overshoots the range of the visible spectrum, particularly in the red and yellow component.

As for Hubble, the portion of infrared it is able to observe is actually very small and ranges from 0.8 to 2.5 microns, but that’s not its primary feature. Hubble, in fact, was developed to study light especially in the ultraviolet and visible parts of the spectrumi.e. from 0.1 to 0.8 microns.

One of the reasons Webb will be able to see early galaxies is that it is an infrared telescope and as such will be able to penetrate through the drier regions of space, where Hubble is unable to peer. But that’s not the only reason. We know from various evidences that the universe is expanding along with the galaxies it contains.

When we talk about distances of the order of billions of light years, Einstein’s General Relativity can only come into play. Along with the expansion of the universe it happens that the space between cosmic objects increases, and along with it the light in that space also lengthens, shifting the wavelength from a shorter to a longer one. This can make the observation of distant galaxies very complicated because the visible wavelength of light becomes increasingly weaker until it is invisible beyond certain distances, so the only wavelength to reach us in extreme cases is that infrared.

This is why the James Webb is currently the ideal way to observe primordial galaxies and the first cosmic objects born immediately after the Big Bang. But finally, let’s move on to the comparisons between the Hubble images (left) and the first ones captured by James Webb (right).

We are observing cosmic objects and galaxies that are up to 13 billion light years away from us, many of which have never been observed before. The cluster of galaxies in the foreground is called SMACS 0723, but the distortion of light caused by its gravity creates an effect of amplification of the objects positioned behind, which allows the observation of extremely distant galaxies otherwise impossible to identify. The effect is called ‘gravitational lens’.

The clarity of James Webb’s counterpart is astounding! It is as if we are standing in front of a time machine showing SMACS 0723 as it looked 4.6 billion years ago.

The Carina nebula is one of the largest and brightest in the sky and is located about 7,600 light-years away in the center of the southern Milky Way. It measures an average of 260 light years and is one of the most interesting stellar nurseries to observe from our point of view, inside which there are stars of various sizes, even much larger than our Sun.

The latest of the images revealed by NASA is certainly the most spectacular capture of the James Webb Telescope and makes us understand the potential of this new medium, especially when compared with the previous ones immortalized by Hubble. One of the most famous dates back to 2008 and we can see it on the left. Although it is clearly spectacular to the eye, it is impossible not to notice the lower amount of detail and the absence of the numerous areas rich in stars and cosmic objects, well present in the James Webb version.

Also called the “Eight-Burst” nebula or NGC 3132, it is composed of an expanding cloud of gas surrounding a dying star. It has a diameter of almost half a light year and is about 2,000 light years from Earth. The dimmer star in the center of this scene has been emitting rings of gas and dust for thousands of years in all directions, and NASA’s James Webb Space Telescope revealed for the first time that this star is cloaked in dust.

Hubble’s version is easily identifiable and, when compared to James Webb’s, appears considerably less detailed.

It is a group of five compact galaxies located about 290 million light years away from Earth, located in the vicinity of the constellation of Pegasus. It was first discovered in 1877 and is in fact the first such grouping ever observed. Although our line of observation may be misleading, it appears that only some of the five galaxies are really close to each other and have occasional interactions.

The Hubble vision of the Stephan Quintet dates back to 2009 and similar to those shown above, it appears much more blurry, moreover the number of cosmic objects is also considerably lower.

credits tested image: ESA / M. Kornmesser