WO2021156581A1

WO2021156581A1 - Device for observing a star

Info

Publication number: WO2021156581A1
Application number: PCT/FR2021/050218
Authority: WO
Inventors: Arnaud MALVACHE
Original assignee: Unistellar
Priority date: 2020-02-07
Filing date: 2021-02-05
Publication date: 2021-08-12
Also published as: FR3107124A1; FR3107124B1

Abstract

The invention relates to an optical device (30) for observing a star, comprising: - a hollow body (31), the inside of which is penetrated, when in operation, by light rays (35) from the star, - a filtration means (33) which is positioned in the hollow body (31) and suitable for selecting at least one spectral line centred on a wavelength of light rays (35), - an optical system (32, 320) positioned in the hollow body (31) to make the light rays (35) converge in a focal plane (39), - a sensor (34) positioned in the focal plane (39) to generate data produced by acquiring the spectral line, - an electronic image processing unit (36) connected to the sensor (34), which unit is suitable for processing the data from the sensor (34) and generating an image of the star on a screen (40), characterised in that the filtration means (33) is suitable for simultaneously selecting at least a first spectral line (381) centred on a first wavelength of the light rays (35) and a second spectral line (382) centred on a second wavelength of the light rays and stopping the other wavelengths of the light rays, the first line and the second line being separated and/or not overlapping.

Description

Title: Apparatus for observing a star

Technical area.

[1] The invention relates to an apparatus for observing a star. It also relates to a method for generating an image of a star.

[2] The invention relates to the technical field of cameras and in particular to that of telescopes. The invention is particularly, but not exclusively, suitable for observing the sun.

State of the art.

[3] Astronomy is a discipline most often practiced at night since it is necessary to have as much darkness as possible to observe the stars correctly. And yet, the earth is close to the only star in our solar system, which might tempt an amateur astronomer.

[4] A user can observe dark areas or sunspots of the visible surface of the sun, or photosphere. It is also possible for the user to observe what are called solar protuberances, which make up the sun's chromosphere.

[5] Observing the sun is not trivial, however. The sun is extremely bright, so much so that it is impossible to stare at it with the naked eye without sustaining eye damage. However, the goal of a telescope is to collect as much light as possible, thus multiplying this extreme luminosity. Observing the sun through a telescope therefore requires adequate protection.

[6] Moreover if the light rays enter directly into the telescope, in a concentrated way, they could cause overheating resulting in deterioration of the telescope. The light rays could also cause irreversible damage to the user's retina if the telescope is not equipped with adequate solar protection or filtration.

[7] This is why it is important to protect both the telescope and the user's eyes. Most of the time, a special filter called a sun filter is used. [8] Document US 2008/0017784 describes an example of a device for observing the sun. This type of device is shown schematically in FIG. 1. The light rays 35 coming from the sun enter the hollow body 31, through a first end 310, and pass through a filtration means 33. The light rays 35 are reflected by a mirror. 32 to a sensor 34 centered on the optical axis 37. The sensor 34 transmits the electrical signals that it transfers to an electronic processing unit 36 which processes the image.

[9] There are several types of sun filters on the market today that could be divided into two categories:

- Broadband filters for the observation of sunspots in the photosphere: these are in particular Astrosolar ® solar filters or Mylar ® filters, very affordable in terms of cost for telescope users but very fragile and can easily be removed. damage and become unusable. Indeed, the slightest defect could allow light rays to pass through that could damage the eyes. Also in this category are glass filters, which do not allow viewing of the details of the structure of the sun. The sun is observed in white light, that is, all wavelengths are present. These filters are said to be reflective, that is, they attenuate the intensity (or brightness) of the rays entering the telescope.

- Band-pass filters for observing the characteristics of the chromosphere: this category includes solar filters made of glass, polymer, H-Alpha, Calcium-H and Calcium-K type filters. These filters allow a single, particular spectral line to pass, centered on a specific wavelength of light rays, corresponding to a chemical element of the sun. Usually you get a monochromatic image of the sun. For example, document US2016291311 describes a solar telescope incorporating a standard filter adapted to select only a single spectral line.

[10] The prior art telescopes used for the observation of the chromosphere generally include only one type of bandpass filter: an H-Alpha filter, or a Calcium-H filter, or a Calcium filter. -K. A user wishing to visualize the distribution of several chemical elements on the surface of the sun, must therefore have either several telescopes equipped each a specific bandpass filter, or a set of several bandpass filters. This considerably increases the costs and complicates the observation. In any case, it is not possible to simultaneously observe several chemical elements on the surface of the sun.

[11] In addition, night-time observation, especially for deep-sky stars such as nebulae, may be limited if this observation is performed under poor conditions. In particular, a user can suffer from the light pollution of a city which tends to greatly impair the observation. Indeed, the strong luminosity emitted by the city causes a reduction in the contrast in the telescope, not allowing to visualize correctly the stars of the deep sky.

[12] An objective of the invention is to remedy all or part of the aforementioned drawbacks.

Another objective of the invention is to provide an apparatus specially designed for simultaneously observing several characteristics of a star, of simple design, and inexpensive and easy to use.

Yet another object of the invention is to provide a new type of apparatus provided with a filter specially designed for the simultaneous observation and analysis of the distribution of several chemical elements of a star.

An additional objective of the invention is to provide a method for generating, in a simple and rapid manner, an image on which simultaneously appear the distributions of several chemical elements of a star. .

Presentation of the invention.

[13] The solution proposed by the invention is an optical device for observing a star, comprising:

- a hollow body inside which, in use, light rays from the star penetrate,

- filtration means, positioned in the hollow body, suitable for selecting at least one spectral line centered on a wavelength of light rays,

- an optical system positioned in the hollow body, to make the light rays converge in a focal plane, - a sensor positioned in the focal plane, to generate data resulting from the acquisition of the spectral line,

- an electronic image processing unit connected to the sensor, which unit is suitable for processing sensor data and generating an image of the star on a screen.

The apparatus is remarkable in that the filtration means is adapted to simultaneously select at least a first spectral line centered on a first wavelength of light rays and a second spectral line centered on a second wavelength of said light rays. and stopping the other wavelengths of said light rays, said first line and said second line being distant and / or not overlapping.

[14] The use of this specific filtration means allows the user to visualize simultaneously, and easily, the arrangement of several chemical elements of the star, with a single device. Manufacturing, purchasing, maintenance and handling costs are thus greatly reduced. This filtration means also makes it possible to easily visualize stars in all circumstances, including stars in the deep sky. In addition, this filtration means avoids any post processing of the image.

[15] Other advantageous features of the invention are listed below. Each of these characteristics can be considered alone or in combination with the outstanding characteristics defined above. Each of these characteristics contributes, where appropriate, to the resolution of specific technical problems defined above in the description and in which the remarkable characteristics defined above do not necessarily participate. These may be the subject, where appropriate, of one or more divisional patent applications:

[16] Advantageously, the sensor is suitable for transmitting, to the electronic unit: first data resulting from the acquisition of the first spectral line and, second data resulting from the acquisition of the second spectral line and the unit electronics is adapted to process the first data and the second data and combine the results of said processing in order to generate a single image combining the results of the first processed data and the second processed data. [17] Advantageously, the filtration means is adapted to select, simultaneously with the first spectral line and the second spectral line, a third spectral line centered on a third wavelength of light rays, said first line, said second line and said third line being distant and / or not overlapping.

[18] Advantageously, the sensor is further adapted to transmit, to the electronic unit, third data resulting from the acquisition of the third spectral line and, the electronic unit is adapted to process the first data, the second data. and the third data and combine the results of said processing in order to display a single image combining the results of the first processed data, the second processed data and the third processed data.

[19] Advantageously, the filtration means is configured so that the first spectral line, the second spectral line and the third spectral line are spectral lines belonging to the Fraunhofer spectrum.

[20] Advantageously, the filtration means is configured so that the first spectral line corresponds to the spectral line K of Fraunhofer.

[21] Advantageously, the filtration means is configured so that the second spectral line corresponds to the spectral line Di of Fraunhofer.

[22] Advantageously, the filtration means is configured so that the third spectral line corresponds to the spectral line C of Fraunhofer.

[23] Advantageously, the filtration means comprises a common support on which are installed an integer number n of filters distinct from each other, n corresponding to the number of spectral lines to be selected.

[24] Advantageously, the optical system comprises at least one mirror adapted to make the light rays converge towards the sensor, the filtration means being arranged between said mirror and said sensor.

[25] Advantageously, the optical system comprises at least one lens adapted to make the light rays converge towards the sensor, the filtration means being arranged between said lens and said sensor. [26] Advantageously, the sensor is a matrix color sensor formed by a mosaic of colored filters and the spectral lines selected by the filtration means have wavelengths included in the spectrum of the color filters of the sensor.

[27] Advantageously, the filtration means is positioned before the optical system.

[28] Advantageously, the filtration means is positioned between the optical system and the sensor.

[29] Advantageously, the filtration means is placed at a distance of at least 1 cm from the sensor.

[30] Another aspect of the invention relates to a method for generating an image of a star, comprising the steps of:

- filter the light rays coming from the star so as to select at least one spectral line centered on a wavelength of said light rays,

- make the light rays converge in a focal plane,

- generate data from an acquisition of the spectral line,

- process said data to generate an image of the star on a screen.

The method is remarkable in that the step of filtering the light rays consists in simultaneously selecting at least a first spectral line centered on a first wavelength of light rays and a second spectral line centered on a second wavelength of said wavelengths. light rays and stop the other wavelengths of said light rays, said first line and said second line being distant and / or not overlapping.

[31] Advantageously, the method also comprises the steps of generating first data resulting from the acquisition of the first spectral line and of the second data resulting from the acquisition of the second spectral line and in processing the first data and the second. data and combine the results of said processing to generate a single image combining the results of the first processed data and the second processed data. [32] According to an alternative embodiment, the method also comprises the steps of selecting, simultaneously with the first spectral line, and with the second spectral line, a third spectral line centered on a third wavelength of light rays, said first line, said second line and said third line being distant and / or not overlapping.

[33] Advantageously, the method also comprises the steps of generating third data resulting from the acquisition of the third spectral line and in processing the first data, the second data and the third data and combining the results of said processing in order to visualize a single image combining the results of the first processed data, the second processed data and the third processed data.

Brief description of the figures.

[34] Other advantages and characteristics of the invention will appear better on reading the description of a preferred embodiment which follows, with reference to the appended drawings, produced by way of indicative and non-limiting examples and on which :

[Fig. 1] above schematizes an apparatus for observing the sun according to the prior art.

[Fig. 2a] shows schematically an apparatus according to the invention according to a first embodiment.

[Fig. 2b] shows schematically an apparatus according to the invention according to a second embodiment.

[Fig. 3a] shows schematically an apparatus according to the invention according to a third embodiment.

[Fig. 3b] shows schematically an observation apparatus according to the invention according to a fourth embodiment.

[Fig. 4] shows schematically, front view, a filtration means according to a preferred embodiment.

[Fig. 5] is a transmission spectrum of the different elements analyzed. [Fig. 6] is a diagram showing steps in the process for transforming light rays into an image.

[Fig. 7] is a transmission spectrum of a Bayer matrix.

Description of the embodiments.

[35] The apparatus 30 object of the invention is mainly used for observing the sun. It is also suitable for observing other stars (or celestial object / body) such as planets, stars, nebulae, galaxies, etc. It is preferably a telescope but the device can also be in the form of a still camera or a video camera.

For the sake of clarity, and by way of illustrative example only, the remainder of the description refers only to a telescope suitable for observing the sun.

[36] In the appended figures, the telescope 30 comprises in particular a hollow body 31, an optical system 32, 320, a filtration means 33 and a sensor 34. The optical system 32 may comprise a mirror 32 or a lens 320. The hollow body 31 is preferably in the form of a hollow tube of circular section, but could be a tube of oval, square, octagonal, or other section. It is specified that the hollow body 31 is not necessarily of tubular shape, but may be of conical shape, or formed of portions of tubes or cones, for example.

[37] In the accompanying figures, the filtration means 33, the optical system 32,

320 and the sensor 34 are centered on the optical axis 37 which is preferably rectilinear and which coincides with the axis of symmetry of the tube 31. Other configurations can however be envisaged, in particular with a non-rectilinear optical axis.

First embodiment (Figure 2a).

[38] In Figure 2a, the tube 31 comprises a first end 310 closed by a filtration means 33 through which the light rays 35 penetrate inside said tube, and a second end 311, opposite to said first end 310 . [39] The tube 31 can be made of metal, plastic, composite material, etc. By way of example, its length is between 200 mm and 400 mm, its diameter is between 50 mm and 500 mm and its thickness is between 1 mm and 10 mm.

[40] In a preferred embodiment, the filtration means 33 is fixed at the level of the first end 310 of the telescope 30, for example by clipping or threading. In another embodiment, a broadband filter, for example of the Mylar® type, is installed upstream of the filtration means, so as to attenuate the quantity and / or the intensity of the light rays 35.

[41] Referring to Figure 5, the filtration means 33 is adapted to simultaneously select at least two and preferably three spectral lines, each centered on a wavelength of light rays 35: a first spectral line 381 centered on a first wavelength; a second spectral line 382 centered on a second wavelength; and a third spectral line 383 centered on a third wavelength. These spectral lines are distant from each other and / or do not overlap. The other wavelengths of the light rays 35 are stopped by the filter means 33. Each spectral line 381, 382, 383 is narrow. Preferably, it corresponds to a peak whose width is less than or equal to 3 nm and preferably less than or equal to 0.1 nm.

[42] According to one embodiment, each spectral line 381, 382, 383 corresponds to the absorption or emission peak of a particular chemical element from the sun (or the observed star). The more a chemical element is present on the surface of the sun, the greater its absorption peak 381, 382, 383.

[43] According to one embodiment, the filtration means 33 is configured to select spectral lines belonging to the Fraunhofer spectrum (or Fraunhofer lines) Preferably, the filtration means 33 is configured so that the first spectral line 381 is centered on the Fraunhofer spectral line K (element Ca ⁺ wavelength 393.368 nm), that the second spectral line 382 is centered on the spectral line Di of Fraunhofer (element Na; wavelength 589.592 nm), and that the third spectral line 383 is centered on the spectral line C of Fraunhofer (element Ha; wavelength 656.281 nm). These spectral lines 381, 382, 383 are perfectly distinct from each other.

[44] The filter means 33 can be configured to select a lower number of spectral lines, for example only two spectral lines, or a higher number of spectral lines, for example four or more. As explained further on in the description, the number of spectral lines selected by the filtration means 33 advantageously corresponds to the number of different colors of the filters making up a Bayer matrix.

[45] A preferred embodiment of the filtration means 33 is illustrated in Figure 4. This filtration means 33 comprises a common support 330, for example made of steel, carbon, or a plastic material. The support 330 is preferably circular in shape but can also be square, octagonal, oval, etc. In general, the shape and the dimensions of the support 330 are adapted to the shape and to the internal diameter of the hollow body 31 in which it is positioned.

[46] In Figure 4, three separate filters, respectively 331, 332 and 333 are installed on the support 330, in the plane thereof. These filters are thus arranged to be simultaneously crossed by the light rays 35. Each of these filters is configured to allow only one spectral line 381, 382, 383 to pass, and can be considered as a band-pass filter. The filtration means 33 formed by the combination of the various filters 331, 332 and 333, can then be likened to a multi-band-pass filter, of simple, robust and inexpensive design. It will be understood that if the filtration means 33 is suitable for simultaneously selecting n spectral lines (n being an integer greater than or equal to 2), then n distinct filters will be installed on the support 330. Thus, and as illustrated in FIG. 6, only the filtered light rays 350 corresponding to the selected wavelengths will continue their course towards the sensor 34.

[47] Three arrangements are provided in the thickness of the support 330. Each of these arrangements receives: a first filter 331 adapted to select the first wavelength associated with the first spectral line 381; a second filter 332 adapted to select the second wavelength associated with the second spectral line 382; and a third filter 333 adapted to select the third wavelength associated with the third spectral line 383. The filters 331, 332, 333 are preferably circular, but could be of another shape, for example square, rectangular, oval, polygonal, etc.

[48] According to one embodiment, the filters 331, 332, 333 partially cover only the surface of the support 33. The part 334 of the support 33 which is not covered by the filters 331, 332, 333 can be opaque so as to do not allow any light rays 35 to pass. According to an alternative embodiment, the uncovered part 334 can be made of a transparent or translucent material allowing light rays 35 to pass. The material used can advantageously be Mylar® or another similar material, to reduce the brightness of the light rays passing through it.

[49] According to another embodiment, the filters 331, 332, 333 cover the entire surface of the support 33. The filters 331, 332, 333 may in this case have, for example, the shape of a portion of a pie chart.

[50] According to one embodiment, the support 330 comprises several first filters adapted to each select the first wavelength associated with the first spectral line 381, and / or several second filters adapted to each select the second wavelength. associated with the second spectral line 382; and / or several third filters adapted to each select the third wavelength associated with the third spectral line 383. These different filters can for example be arranged to cover the entire surface of the support 33, or only part of it.

[51] According to another embodiment, the support 330 comprises, in addition to the aforementioned first, second and third filter (s), other filters adapted to each select a different wavelength. It is for example possible to provide one or more filters suitable for selecting infrared and / or one or more filters suitable for selecting ultra-violet.

[52] According to one embodiment, polarizing filters (not shown in the figure) are added behind the filters 331, 332, 333 of the filtration means 33.

These polarizing filters can select one of two polarizations of light. Light is a wave described by signals that oscillate in space and time. These signals are the electric and magnetic fields, hence the name electromagnetic wave. These two fields each have a direction and are perpendicular to each other. Depending on one or the other of the selected polarizations, it is possible to modify the contrast and / or the saturation of the colors. Polarization makes it possible to better observe the granularity of the surface of the star in one polarization or another.

[53] Each filter 331, 332, 333 is advantageously associated with a different polarization from the other said filters. For example, when the solar filtration means 33 has only two filters, one of them is associated with a first polarization and the other is associated with a second polarization. Yet another example, when the filtration means 33 comprises the three filters 331, 332, 333, the first is associated with a first polarization, the second is associated with a second polarization and the third is not associated with a polarization.

One could also envision that the third solar filter be associated with one or the other of the polarizations so that there are two filters associated with one polarization and one filter associated with another polarization.

[54] In Figure 2a, the optical system is formed by a mirror 32 disposed inside the tube 31, and centered on the optical axis 37. The mirror 32 is disposed near the second end 311 of the tube 31 It is preferably concave. Its shape and dimensions are adapted to those of the tube 31. The filtered light rays 350 are reflected by the mirror 32 so that they converge in a focal plane 39 where the sensor 34 is positioned. In this first embodiment. , the filtering means 33 is arranged upstream of the mirror 34, so that the light rays 35 are filtered before their convergence in the focal plane and therefore before the formation of the image in said focal plane.

[55] The sensor 34 is centered on the optical axis 37, in the focal plane 39 so as to acquire the spectral lines 381, 382, 383 of the filtered light rays 350. The sensor 34 is a photosensitive component making it possible to generate data (or electrical signals) from the acquisition of spectral lines 381, 382, 383.

[56] According to a preferred embodiment illustrated in FIG. 6, the sensor 34 is a matrix color sensor comprising a mosaic 341 of color filters. [57] This type of sensor is known to those skilled in the art. Color filters are usually disposed on the photosensitive surface 340 of the sensor. This surface is generally composed of a plurality of photosensitive pixels. A filter is placed in front of each photosensitive pixel so that it receives only the color that is not absorbed by the filter. A mosaic of colored filters known to those skilled in the art is the so-called Bayer mosaic, arranged in a pattern of tiles (one tile = one filter) arranged in a checkerboard pattern, comprising 50% green filters, 25% red filters, and 25% blue filters. This drawing is specially adapted to the perception characteristics of the human eye. It presents a periodic alternation of colored filters of two colors on each line, green and blue on one line, red and green on the next line; and the same periodic alternation on the columns.

[58] The color qualifying the colored filters of the matrix, namely “red filters”, “green filters” or “blue filters” means that the colored filter in question is designed to pass only a range of length of waves corresponding to this color. This is illustrated in FIG. 7 showing the transmission curves of the red (R), green (V) and blue (B) filters of the sensor 34. It can be seen in this figure that the spectral lines 381, 382, 383 selected by the means filtration 33 are centered on the wavelengths corresponding to the colors of the filters of the matrix 341. In general, the number of colors making up the mosaic of filters 341, corresponds to the number of spectral lines 381, 382, 383 selected by the solar filtration means 33. Also, if the filtration means 33 selects only two spectral lines, the colored filters of the mosaic can only be of two colors.

[59] According to one embodiment, the matrix may also comprise pixels not covered with filters and / or pixels covered with filters which only allow infrared and / or ultraviolet to pass. This embodiment is suitable in particular when the filtration means 33 is suitable for selecting other spectral lines, in particular centered in the infrared and / or the ultraviolet.

[60] The main advantage of the matrix color sensor 34 is that it is relatively inexpensive and has small dimensions. So we can easily install it in the hollow tube 31 without losing space. In addition, this type of sensor makes it possible to avoid post-processing of the image since the color of its pixels is automatically given by said sensor.

[61] With a color matrix color sensor with color filters, each photosensitive pixel provides an electrical signal coming from the filtered rays 350, in the color that the associated color filter lets through. Each electrical signal remains associated with the photosensitive pixel 21 which generated it, and therefore with a well-defined position on the matrix, which makes it possible to constitute an image of the star observed through image processing. This image processing is preferably configured in an automatic mode commonly called “automatic white balance” or AWB (standing for “Automatic White Balance”). Typically, an AWB algorithm averages and correlates the pixel values on each channel (red, green, and blue) of the captured image.

[62] Referring to FIG. 6, the image processing is preferably carried out by electronic unit 36 connected to the sensor 34. The connection between the sensor 34 and the unit 36 can be carried out in a wired or wireless manner, by example by means of a proximity communication protocol, such as, by way of non-limiting example, the Bluotooth®, Wifi®, Zigbee® protocol.

[63] The unit 36 is adapted to process the first data resulting from the acquisition of the first spectral line 381 (eg: acquired by the photosensitive pixels associated with the blue filters of the matrix 341), the second data resulting from the. acquisition of the second spectral line 382 (ex: acquired by the photosensitive pixels associated with the green filters of the matrix 341) and the third data resulting from the acquisition of the third spectral line 383 (ex: acquired by the photosensitive pixels associated with the filters red of matrix 341). Unit 36 combines the results of these treatments to generate a single image combining the results of the first processed data, the second processed data and the third processed data.

[64] In Figure 6, the various data is transmitted to unit 36 by a connection or communication channel 351.

[65] The processing unit 36 can also be configured to separate each part of the image acquired by the sensor 34 so that the image of the star displayed on the screen 40 shows the distribution of the chemical element corresponding to the first spectral line 381 and / or the distribution of the chemical element corresponding to the second spectral line 382 and / or the distribution of the element corresponding to the third spectral line 383. A dedicated key installed on the telescope 30 may for example be provided to allow the user to select the type of image to be displayed on the screen 40: an image showing the arrangement of a single chemical element , or an image combining the arrangement of two or more chemical elements. In other words, the user can combine the images or select a particular one.

[66] More generally, if the filtration means 33 selects n spectral lines (n being an integer> 2), the sensor 34 transmits to the unit 36 n distinct data resulting from the acquisition of said lines. And unit 36 processes these n data and combines the results of these n processed data. The user can view one image or n images depending on what he wants to observe.

[67] Deep sky objects, and in particular nebulae or galaxies, are very faint. Therefore, bad conditions can interfere with its observation. Especially if the user is located in or near a city, the light pollution of the city alters the observation because of a sharp decrease in contrast. But the elements of the deep sky emit certain particular spectral lines which are characteristic of them. The use of filtration means 33 makes it possible to select n spectral lines of light rays 35 emitted by deep sky objects. The processing unit 36 can then be adapted to increase the contrast corresponding to each of said lines.

[68] According to one embodiment, the electronic unit 36 comprises a computer 360 in the form of a processor, microprocessor, CPU (for Central Processing Unit), a memory card and generally comprises the computer resources allowing to ensure the processing of the electrical signals received from the sensor 34 for the formation of a digital image of the sun. These components are preferably mounted on an electronic card 361. The card 361 makes it possible to group together in a single place, and on a single support, all the electronic components of the processing unit 36. This design makes it possible to minimize the number of integrated electronic cards. in the telescope 30, and reduce the number of wiring. In addition, the manufacture of the processing unit 36, its installation in the telescope 30 and, where appropriate, its maintenance are greatly facilitated.

[69] The screen 40 can be attached to the card 361 so that the processing unit 36 and said screen form an easily manipulated one-piece assembly. In this case, a flat screen is advantageously used, for example a full color liquid crystal screen LCD (for Liquid Crystal Display) or OLED (for Organic Light-Emitting Diode).

[70] According to another embodiment, the screen 40 is separate from the processing unit 36 and from the electronic card 361. It is physically distant from the tube 31. In this embodiment, the screen 40 may be that of a user's mobile terminal, for example the screen of a smartphone (smart phone) or of a touchscreen tablet. The connection between the processing unit 36 and the screen 40 can be made via a wired link (for example by means of a USB cable) or via a wireless link, for example according to a proximity communication protocol, such as as a non-limiting example, the Bluetooth®, Wifi®, ZigBee® protocol. This embodiment makes it possible to reduce the compactness of the telescope 30, since the size of the screen 40 is not taken into account.

Second embodiment (FIG. 2b).

[71] Compared to the embodiment of Figure 2a, the optical system of Figure 2b includes a lens 320 disposed inside the tube 31 and centered on the optical axis 37.

[72] The filtered light rays 350 are refracted by the lens 320 towards the sensor 34. The shape and the dimensions of said lens are adapted to those of the tube 31. The operation of the telescope 30 is identical to that described with reference to the first mode of achievement.

[73] This embodiment allows those skilled in the art to consider another mounting alternative for the telescope 30 depending on the optical system available to him.

Third embodiment (Fig. 3a). [74] In the embodiment of FIG. 3a, the filtration means 33 is disposed between the mirror 32 and the sensor 34. The dimensions of the filtration means 33 can then be smaller compared to the previous embodiments, reducing by makes the compactness of the telescope 30 as well as the manufacturing costs.

[75] The light rays 35 are filtered here after they start to converge towards the focal plane, that is, during the formation of the image in said focal plane. In other words, the image is in the process of being formed when the light rays 35 reach the filtration means 33.

[76] By using a filtration means 33 of the type described with reference to FIG. 4, certain rays 350 can pass only through the first filter 331, or only the second filter 332 or only the third filter 333. There is therefore a risk that the final image generated by the processing unit 36 does not show the arrangement of the chemical elements over the entire surface of the star observed, but over only a part of it (the part of the image in short formation whose rays pass through the first filter 331, the second filter 332 or the third filter 333).

[77] To remedy this, the filtration means 33 is advantageously placed at a distance of at least 1 cm from the sensor 34. Indeed, the applicant has been able to observe that this particular arrangement makes it possible to attenuate the effects of spatial selection. described in the previous paragraph.

Fourth embodiment (Figure 3b).

[78] Compared to the embodiment of Figure 3a, the optical system of Figure 3b includes a lens 320 disposed inside the tube 31 and centered on the optical axis 37.

[79] The light rays 35 are refracted by the lens 320 before being filtered by the filtration means 33 and converging towards the sensor 34. The shape and dimensions of said lens are adapted to those of the tube 31. Operation of the telescope 30 is identical to that described with reference to the third embodiment. [80] This embodiment allows those skilled in the art to consider another mounting alternative for the telescope 30 depending on the optical system at his disposal.

[81] One or more features disclosed only in one embodiment may be combined with one or more other features disclosed only in another embodiment. The arrangement of the various elements and / or means and / or steps of the invention, in the embodiments described above, should not be understood as requiring such an arrangement in all implementations. Other variants can be envisaged and in particular:

- The optical system 32, 320 of the telescope 30 does not necessarily consist only of a lens 320 or of a single primary mirror 32 but may also include a secondary mirror in addition to the primary mirror.

- The filtration means 33 does not necessarily consist of three filters 331, 332, 333 but can also be in the form of a single multi-bandpass filter.

A matrix color sensor 34 formed of colored filters other than red, green and blue filters (for example magenta, cyans and yellow filters) can be envisaged. The choice of colors depends in particular on the spectral lines selected by the filtration means 33.

- Other types of sensors 34 can be considered. For example a CCD, CMOS or Foveon type sensor, colored or black and white.

Claims

[Claim 1] A method for generating an image of a star, comprising the steps of:

- filtering the light rays (35) coming from the star so as to select at least one spectral line centered on a wavelength of said light rays,

- make the light rays (35) converge in a focal plane (39),

- generate data from an acquisition of the spectral line,

- process said data to generate an image of the star on a screen

(40), characterized in that the step of filtering the light rays (35) consists in: simultaneously selecting at least a first spectral line (381) centered on a first wavelength of the light rays (35) and a second spectral line (382) centered on a second wavelength of said light rays (35) and stop the other wavelengths of said light rays, said first line and said second line being distant and / or not overlapping.

[Claim 2] A method according to claim 1 comprising the steps of:

- generate the first data from the acquisition of the first spectral line (381) and the second data from the acquisition of the second spectral line (382),

processing the first data and the second data and combining the results of said processing in order to generate a single image combining the results of the first processed data and the second processed data.

[Claim 3] Method according to one of claims 1 or 2, consisting in selecting, simultaneously with the first spectral line (381), and the second spectral line (382), a third spectral line (383) centered on a third wavelength of light rays (35), said first line, said second line and said third line being distant and / or not overlapping.

[Claim 4] A method according to claims 2 and 3, comprising the steps of: - generate third data from the acquisition of the third spectral line (383),

processing the first data, the second data and the third data and combining the results of said processing in order to display a single image combining the results of the first processed data, the second processed data and the third processed data.

[Claim 5] Optical apparatus (30) for observing a star, characterized in that said apparatus is adapted for carrying out the method according to claim 1, said apparatus comprising:

- a hollow body (31) inside which penetrate, in use, light rays (35) from the star,

- filtration means (33), positioned in the hollow body (31), adapted to select at least one spectral line centered on a wavelength of light rays (35),

- an optical system (32, 320) positioned in the hollow body (31), to make the light rays (35) converge in a focal plane (39),

- a sensor (34) positioned in the focal plane (39), to generate data from the acquisition of the spectral line,

- an electronic image processing unit (36) connected to the sensor (34), which unit is suitable for processing the data from the sensor (34) and generating an image of the star on a screen (40), and in which the filtration means (33) is adapted to simultaneously select at least a first spectral line (381) centered on a first wavelength of light rays (35) and a second spectral line (382) centered on a second length of wave of said light rays and stop the other wavelengths of said light rays, said first line and said second line being distant and / or not overlapping.

[Claim 6] An apparatus (30) according to claim 5, wherein:

- the sensor (34) is suitable for transmitting, to the electronic unit (36): o first data from the acquisition of the first spectral line (381) and, o second data from the acquisition of the second spectral line (382), - the electronic unit (36) is suitable for processing the first data and the second data and combining the results of said processing in order to generate a single image combining the results of the first processed data and the second processed data.

[Claim 7] Apparatus (30) according to one of claims 5 and 6, wherein the filter means (33) is adapted to select simultaneously the first spectral line (381) and the second spectral line (382) , a third spectral line (383) centered on a third wavelength of light rays (35), said first line, said second line and said third line being distant and / or not overlapping.

[Claim 8] Apparatus (30) according to claims 6 and 7, wherein:

- the sensor (34) is also suitable for transmitting, to the electronic unit (36), third data from the acquisition of the third spectral line (383) and,

- the electronic unit (36) is adapted to process the first data, the second data and the third data and combine the results of said processing in order to display a single image combining the results of the first processed data, of the second processed data and of the third data processed.

[Claim 9] Apparatus (30) according to one of claims 5 to 8, wherein the filter means (33) is configured so that the first spectral line (381), the second spectral line (382) and the third line spectral (383) are spectral lines belonging to the Fraunhofer spectrum.

[Claim 10] Apparatus (30) according to one of claims 5 to 9, wherein the filter means (33) is configured so that the first spectral line (381) corresponds to the Fraunhofer K spectral line.

[Claim 11] Apparatus (30) according to one of claims 5 to 10, wherein the filter means (33) is configured so that the second spectral line (382) corresponds to the spectral line Di of Fraunhofer.

[Claim 12] Apparatus (30) according to one of claims 5 to 11 taken in combination with claim 7, wherein the filter means (33) is configured so that the third spectral line (383) corresponds to the spectral line. C from Fraunhofer. [Claim 13] Apparatus (30) according to one of claims 5 to 12, wherein the filter means (33) comprises a common support (330) on which are installed an integer number n of filters (331, 332, 333 ) distinct from each other, n corresponding to the number of spectral lines to be selected.

[Claim 14] Apparatus (30) according to one of claims 5 to 13, wherein the optical system (32, 320) comprises at least one mirror (32) adapted to converge the light rays (35) towards the sensor ( 34), the filtration means (33) being disposed between said mirror and said sensor.

[Claim 15] Apparatus (30) according to one of claims 5 to 13 wherein the optical system (32, 320) comprises at least one lens (320) adapted to converge the light rays (35) towards the sensor (34). ), the filtration means (33) being disposed between said lens and said sensor.

[Claim 16] Apparatus (30) according to one of claims 5 to 15, wherein:

- the sensor (34) is a matrix color sensor formed of a mosaic (341) of color filters (341),

- The spectral lines (381, 382, 383) selected by the filtration means (33) have wavelengths included in the spectrum of the color filters of the sensor (34).

[Claim 17] Apparatus (30) according to one of claims 5 to 16, wherein the filter means (33) is positioned before the optical system (32, 320).

[Claim 18] Apparatus (30) according to one of claims 5 to 16, wherein the filter means (33) is positioned between the optical system (32, 320) and the sensor (34).

[Claim 19] Apparatus (30) according to claim 18, wherein the filter means (33) is disposed at a distance of at least 1 cm from the sensor (34). !