The predecessor of "James Webb" is 40 years old: how was the mission of the first IR telescope

From the earliest times, mankind has been interested in the stars and explored the surrounding space. But long

time, both amateur and professional astronomers were limited only to visible light: what can be seen with the naked eye or with simple optical telescopes.

Only in the 20th century did the situation begin to change andthe space of opportunity for scientists has expanded. At this time, first radio telescopes were created, and later, as astronautics developed and the first satellites were launched, space telescopes operating in different parts of the spectrum: infrared, ultraviolet, x-rays and gamma radiation. One of the first among them and the first IR telescope was the IRAS observatory.

What can be seen in infrared?

Infrared is part ofelectromagnetic spectrum, located between the waves of visible light and radio emission. The length of such waves varies from 0.74 µm to 1 mm. It is interesting that this part of the spectrum accounts for most of the thermal radiation - the transfer of part of the internal energy by heated objects in the form of electromagnetic waves.

The infrared range is largeinterest for space explorers. Many objects in the universe are too cold and faint to see in visible light, but they can be found in infrared. For example, planets, cool stars, nebulae, and many other space objects can be studied using the thermal radiation that they propagate with infrared waves.

In addition, due to the longer wavelengthinfrared waves, unlike visible light, travel through dense regions of gas and dust in space with less scattering and absorption. This feature allows you to look beyond the veil of gas and dust and study hidden objects, galaxy formation, star formation centers and protoplanetary systems. This, for example, is used by the James Webb telescope.

Unfortunately, the Earth's atmosphere blocks most infrared wavelengths. Therefore, the only way out is to launch a specialized space observatory.

How is IRAS organized?

IRAS telescope. Photo during assembly (left) and artistic image (right): NASA

IR waves are associated, among other things, with thermalradiation. This means that an infrared telescope must be cooled to extremely low temperatures, close to absolute zero, so that the device's instruments do not interfere. Not surprisingly, the world's first ultraviolet and gamma-ray telescopes went into space in the late 1960s, and the first infrared telescope, IRAS, only in 1983.

IRAS - joint mission of space agenciesthree countries: the USA, the Netherlands and the UK. It was built by Ball Aerospace in collaboration with Fokker Space and Hollandse Signaal. The dimensions of the satellite were 3.6 x 3.24 x 2.05 m, and the mass (filled and with refrigerant) was a little more than a ton.

The satellite was equipped with a 57 cma Ritchey-Chrétien telescope with a beryllium mirror. And 73 kg of liquid helium was used as a coolant. The telescope devices carried out a complete survey of the entire sky at wavelengths from 8 to 120 microns using four broadband photometric channels centered at 12, 25, 60, and 100 microns. This covered part of the mid and far infrared range. Additional data were collected by spectrometers.

IRAS operated on a sun-synchronous circumpolaran orbit that precessed by about a degree each day. The celestial sphere was divided into "zones" bounded by the meridians of the ecliptic, spaced 30° apart. To survey the entire sky, the satellite scanned space at a speed of 1.1 m/s along arcs of constant solar elongation close to 90°. In addition, if necessary, the devices could be fixed at a given point for up to 12 minutes in order to obtain more detailed images of individual areas.

What did IRAS discover?

IRAS was launched on January 25, 1983 and beganactive observations already on February 9th. The telescope surveyed outer space for almost 10 months. Having exhausted all the cooling helium, on November 21, 1983, the satellite stopped working.

During its operation, IRAS has surveyed 96% of the celestialspheres, identifying 350,000 sources of infrared radiation, 250,000 of which were previously unknown. After analyzing the data collected by the telescope, taking into account refinement and confirmation by other scientific instruments, about 130,000 stars, 75,000 star-forming galaxies, 40,000 various objects located in the Milky Way were entered into the IRAS catalog. They are complemented by tens of thousands of regions of active star formation and nebulae. Even after 40 years, some objects observed by the observatory are still awaiting classification.

An infrared survey of the sky taken by the IRAS telescope. Image: NASA/JPL-Caltech

In addition to the study of individual objects, IRAS madea series of observations that have changed and refined the ideas of astronomers about the structure of stars and galaxies. For example, the telescope has discovered excess infrared radiation from a number of stars such as Vega, indicating that they are surrounded by dust disks.

In addition, with the help of a telescope, it was discoveredsix new solar system comets, very strong infrared radiation from interacting galaxies, and warm dust tufts called infrared cirrus clouds that are found in all directions in space. Finally, IRAS first attempted to peer into the center of our galaxy and showed the Milky Way's active galactic nucleus.

From the point of view of modern analogues,it seems that the IRAS telescope was too weak, too simple and worked for a very short time and did not leave such an impressive archive as, for example, Hubble. But it is worth remembering that it was the success of this mission that sparked interest in space observations in the infrared and, several generations later, in powerful giants such as James Webb.

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