Forgotten constellations

We go back to a time when herds of pelorovis still roamed the earth, and humans could gaze at a night sky filled with thousands of stars, something we can only witness today in areas that are free from luminous pollution. Randomly scattered and without any particular meaning, some of them have been associated by man with familiar shapes.

Constellations are groups of stars that make up simple shapes, which look like animals, people, objects etc. This involuntary “recognition” of familiar patterns in clouds, on the Moon or freshly-toasted bread is called “pareidolia.”

The first mention of constellations concerned Orion and Taurus, which are supposed to have originated in the Neolithic age.

Most of the constellations’ names and given meanings accompanied the practice of agriculture. Since ancient times man has noticed and used the changes in the sky as a calendar, in order to know when to sow and when to reap the harvest. Much like today, constellations were used as nighttime guidance, especially at sea.

Nowadays we have a total of 88 constellations on the entire sky (northern and southern hemispheres combined), out of which 48 are on Ptolemy’s list (he wasn’t the one to give them their names), classified around 150 AD, along with another 11 constellations contributed by explorers Pieter Dirkszoon Keyser and Frederick de Houtman in the Southern Hemisphere (1590s), and 17 constellations also in the Southern Hemisphere, identified  by Nicolas Louis de Lacaille, who was also the one to divide the Argo Navis constellation into four others during the 1700s. The German astronomer Gottfried Kirch added 3 constellations in the Northern Hemisphere around 1650, and the Polish astronomer Johannes Hevelius added 11 more around the same time. The writings of Johann Elert Bode mention another 7 constellations named by himself, 14 by others, and another 9 categorized by various others, also in the Northern Hemisphere. If you’ve counted over 100, then you’ve counted correctly.

We haven’t always had 88 constellations, and up till the International Astronomical Union’s decision in 1922, when the aspect of constellations was first discussed, many were always adding an asterism or another. Selecting the constellations that would remain as such wasn’t over until 1930, when the official list was published, containing distinct boundaries of the constellations, according to diagrams for each of them. This is the definite list, and no other elements can be added or removed, just in case you’re contemplating purchasing or making up a new one.

The oldest constellations were preserved, having been “in use” for a long time, and several of the lesser-known were removed, whether they had little historical significance or were composed of stars which are barely-visible with the naked eye.

Here are some of the constellations that disappeared in time, and never made it to the top 88:

 

ANSER (The Goose)

Created by Johannes Hevelius, this constellation received its name along with Vulpecula (The Fox), and together they formed “Vulpecula cum Ansere”. It’s composed of stars with a magnitude of 4-5, located between Cygnus and Aquila.

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The constellation disappeared following its omission from the star maps, being associated with Vulpecula. The the International Astronomical Union decided to preserve the initial name of Vulpecula, and its boundaries include the former “Anser”. Nowadays, the alpha star of Vulpecula is known as Anser.

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ARGO NAVIS (The Argo Ship)

Formed of the four constellations: Carine, Pyxis, Vela and Puppis – all ship parts. It’s on Ptolemy’s list, and the only one that did not “survive”. It represents Jason’s ship on his voyage to retrieve the Golden Fleece, in Greek mythology.

It was split into four at the proposal of Nicolas Louis de Lacaille, following his 1752 expedition in the Southern Hemisphere. It was formed of approximately 160 stars, and spanned over 60 degrees (vertical).  It was omitted because of its dimensions.
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The tip of the mast (Puppis) is visible from Romania, near the horizon, to the left of Sirius, the alpha star of Canis Major.

 

Felis (The Cat)

Constellation that we all would have wished could stay and purr in the sky, it was invented by Joseph Jérôme Lefrançois de Lalande using less bright stars (magnitude 5 and below), between Hydra and Antila.

The constellation did not prove popular on the European continent and it was absent from European star atlases, only adopted by American cartographers. In time, it disappeared from 19th century writings, and at the time when the definite limits were drawn, its stars were split between nearby constellations: Hydra, Pyxis and Antila.

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Among the forgotten constellations are several other creations that may seem amusing given that they were once in the sky, and should the 1922 decision have been in their favour, today we would be searching for deep-sky objects and stars in the following constellations:

GLOBUS AEROSTATICUS (“Balloon”) between Capricornus and Piscis Austrinus, concocted by Joseph Jérôme Lefrançois de Lalande in 1798 to honour the invention of the hot-water balloon by the Montgolfiers.

MACHINA ELECTRICA (“Electric Generator”), invented by Johann Elert Bode in the 1800s and placed between Fornax and the Sculptor. Formed partially from the latter’s stars.

OFFICINA TYPOGRAPHICA (“Typography”) the second bizarre constellation named by Joseph Jérôme Lefrançois de Lalande about the same time as the Globus, but later introduced by Johann Elert Bode in star maps. It used to be between Canis Major and Puppis, and was left aside, together with other suggestions by Bode.

HONORES FREDERICI (“Glory of Frederick”) surrounded by stars belonging to Andromeda and Lacerta. Introduced by Johann Elert Bode to commemorate Frederick the 2nd of Prussia, in 1787. It used 76 dim stars, to form a sword and a crown.

MONS MAENALUS (“Mount Maenalus”) between Virgo and Libra, at the feet of Bootes, who is stepping on it. Some of its stars belong to the Bootes constellations. It disappeared in time, and the IAU kept it within the boundaries of the Bootes constellation.

This article was also published in Vega Magazine, no 151/January 2016

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Image processing in astrophysics

Astronomical imaging – acquisition and reduction/analysis

Over the last 200 years, the main technique for astronomical observations has progressed from naked eye monitoring and drawing records, all the way to digital data acquisition. Even though the other, more traditional techniques, remain valued and recognized as scientific ways to observe the sky, digital acquisition became a simpler, faster and reliably accurate way to observe and report astronomical observations. The benefits that came with this advanced technology simplified our work and made it easier for us to discover or to obtain new data on objects that can either reside in our solar system, or millions of light years away.

Nowadays, even in a modest astronomical observatory setting, they will use a CCD camera detector fitted with an array of filters for multispectral photometry, attached to the telescope. The CCD camera guarantees a linear response, an essential functionality when observing brightness variations. Not long ago, astronomical detectors had less than 100 kilo pixels and were far noisier and less sensitive than today’s cameras, not to mention that the colour imaging with CCD cameras is also quite new.  Moreover, the device allows for a longer exposure time which generates a superior result than the use of photographic plates or visual observations.

Another method for observing bright celestial bodies (the Sun, the Moon and some planets) is using a high time cadence image acquisition that can be a CMOS detector or a CCD detector, a so called “planetary camera”. Unlike astronomical CCD cameras, planetary cameras are designed to take a large number of images in a short period of time. Most have sensors with an integrated Bayer filter for colour imaging purposes. The shutter is electronic so there are no moving parts, and the electronic sensors are designed to produce up to 60 images per second with a resolution of 640 x 480px. Although the Bayer array means that the effective resolution is about twice that of the physical pixels, simultaneously recording three colour channels confers a significant advantage on planetary imaging.

Targets for astronomical imaging

In the following paper I will discuss the subject of planetary imaging, especially for Jupiter and it’s satellites. The main targets in planetary imaging are the brightest planets such as Mercury, Venus, Mars and two of the Jovian planets.

Mercury, the closest planet from the Sun, can be observed after the sunset and just before the sunrise, only for a couple of hours. During this time, the planet can achieve a visual magnitude ranging between -2 and 1. It has a high albedo and it is one of the planets on which the surface can be seen. As an inferior planet it can be seen as a full disc when it’s further from Earth and as a narrow crescent when it’s near. The best time to observe it is when the planet is at the quadrature (90° from the Sun) that means that the disc is half lit.

Venus, another telluric planet, like Mercury, can be observed when it’s near quadrature and presents a half-illuminated disc, up to four to five times bigger than that of Mercury.  Without filters, the planet presents itself as covered with clouds, but by applying filters such as violet, red, blue or UV, we can see beneath the upper atmospheric layer.

The optimal period to observe the planet Mars comes about every two years, when the planet is at the opposition, when Earth is physically between Mars and the Sun. Mars then reaches an angular diameter between 14 and 25 arc-seconds. The most favourable season for observing Mars lasts four to six months. The planet presents a full disc at opposition and shows a small phase at quadrature. Its appearance varies enormously, depending on the filter used. In blue light the disc appears featureless, but lighter clouds can be seen over the poles. In red light, the dark surface features and the polar caps can be easily seen.

The planet Jupiter has the largest angular diameter and presents a lot of details on its disc: belts of coloured clouds, small and big hurricanes, all in constant movement around the sphere.

The features on Jupiter’s disc always change position and require intensive monitoring. In order to have a lot of recordings concerning the planet’s state, observing campaigns are often proposed, and these require involvement from the astronomical community. For example, this year’s JunoCam campaign managed by NASA and Mission Juno (linked to the Juno spacecraft, launched in 2011 and set to arrive mid-2016) is asking for Jupiter images or maps from both the professional and amateur communities. Another recently-ended campaign was PHEMU 2015 that required photometry of Galilean satellites.

Saturn is the second largest planet and its disc is usually without details: just a few cloud bands and the ring system. Sometimes small white cyclones appear which require observations and positional measurements. Although Saturn’s rings are decidedly a popular attraction with observatory visitors and professionals alike, they are not currently scientifically observed from Earth.

 

Obtaining images

Images straight from the CCD camera carry a significant number of unwanted signals. In order to obtain a clean image, the goal is to correct and calibrate a raw image in such a way that the unprocessed image is showing, and accurately portrays the intensity of light that fell on the CCD chip. The unwanted signals in an unprocessed CCD image include two additive components and one multiplicative component. The additive components are a voltage offset, or bias, from zero volts, and a signal generated by thermal emission of electrons that grows linearly with exposure time. The multiplicative error arises because photosites have differing sensitivities to light.

Calibration involves removing the bias, subtracting the dark current, and dividing the image. The standard strategy for an observer to accomplish a satisfactorily calibrated image includes performing a few tasks before and during the observing session. Firstly, the observer shoots flat-field frames either from the twilight sky or from a low intensity illuminated panel. Secondly, during the observing session, it is necessary from time to time to take dark frames that have the same integration time as the images. At the end, the dark frames and flat-field frames are stacked and used on the raw image in order to calibrate it. This procedure delivers high quality images that are suitable for display, and can be used for precise astrometry and photometry.

 

Dark Frames

The dark frames capture a sample of the dark current to be subtracted so as to oust the dark layer from an image. During the time that a dark frame is taken, the telescope is covered so that no light is allowed to strike the CCD. Depending on the calibration protocol, the exposure time for dark frames chosen can be equal to or greater than the exposure time for the images that are going to be calibrated. The dark frames contain the thermal electrons that accumulate during integration and also the thermal noise. The aim is to have a dark frame that is sufficiently accurate that subtracting it from a raw image will not increase the noise in the final calibrated image.

darkframe

Dark frame, exposure 40 seconds

Flat-Field Frames

The flat-field frames record the response of the entire optical system (the telescope, filters, cover glass, CCD, etc) to a uniform field of light. The resulting flat-field images cannot distinguish whether optical vignetting or quantum efficiency produce a particular pixel value in the frame, but as long as the optical system and CCD does not change, a good flat-field allows the observer to correct both effects as if they were one. Like all images, a flat-field frame contains not only the signal that we want but also bias and thermal electrons. To make a high quality master flat-field, about 10 to 15 raw flat-field frames are required. The usual recommendation is for flat-field frames to be taken before the observation session, either in daylight or twilight. The exposure time is varied, so that the frames are not saturated or under saturated.

flat frame

Flat-field frame 20 seconds

Bias Frames

A bias frame contains the readout noise of the sensor which is produced inside the electronic components that read the pixels. It can be low, but never zero. When taking a zero length exposure, each pixel will have a slightly different value, except for a small amount of noise. Since the bias is consistent from image to image, it can be subtracted. A way to reduce the overall noise of the system is to cool down the CCD, a method that is used on all professional CCD cameras.

 

Standard image calibration

This requires multiple dark, flat and bias frames, and produces a corrected image for bias, dark current and dust from the optical path. In order to obtain a satisfactory signal-noise ratio, it’s necessary to create and use a median of multiple frames from all the categories mentioned above. A stack of reduction images from the same type of category is called a “master”. For a master dark frame, between 5 and 7 raw dark frames are needed. To make a master flat-field frame, there are up to 10 raw flat-field frames involved, and for a master bias frame 5 raw bias frames are required. All the masters are then subtracted from the image that is going to be calibrated.

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M42

Raw image of Messier 42 – The Great Orion Nebula

M422

Calibrated image with dark and flat-field frames of Messier 42

 

Planetary camera image calibration

Images taken with a planetary camera are not calibrated in the same way as the CCD images, because a significantly large number of images per second are recorded. A poor atmospheric seeing can be avoided by selecting the best frames from a series of images. On a large number of images it’s simply not practical to subtract master dark frames and master flats, so that the only method to get a final good result is to stack and mediate the series of the top quality images taken. Furthermore, in order to raise and distinguish small details in the resulting image obtained by staking, a few digital adjustments can be made, such as: noise removal by averaging filter, noise removal by median filter, sharpening (edge enhancement), and deblurring.

 

My observing setup

In order to exemplify these procedures and methods, I will present a series of images, as well as the way they were subsequently processed. These images were taken with a C9.25 Celestron telescope, with a primary mirror of 235 mm in diameter and focal length of f/10.

To achieve a greater focal length of the telescope I used a Barlow lens, which is a diverging lens placed in front of the camera (more specifically, the eyepiece) in order to increase the magnification of the image. It is almost always necessary to enlarge planetary images from their size at the focus to scale appropriately for digital imaging. For a better sampling of image detail, the bright central region of the diffraction disk should be twice as large as the pixels that sample the image.

The digital camera used was a DBK 21AU618.AS.  This camera has a minimal noise even in case of long exposures (i.e. 60 minutes, the longest possible shutter speed on this equipment).

The telescope was mounted on a German equatorial mount, fitted with a drive system.

 

My observing session

During the PHEMU 2015 campaign of observations of the mutual phenomena of the Galilean satellites of Jupiter, throughout which the Galilean satellites occulted and eclipsed each other, I captured the moment when satellite Io passed over (transited) Jupiter. The observing session started at 21:42 TLR and ended after almost two hours at 23:22 TLR, on March 21st, 2015. A number of 86 videos were acquired, each with a duration of approximately 1 minute and totalising 108 GB of data. I then selected the best frames from each series of images and turned them into a median image that I processed afterwards.

The second part of processing was achieved using the different filters in the MATLAB program that I mentioned before. Further explanations will be presented later in the paper. The final results revealed smaller details on Jupiter and its satellite, on a sharp and accurate image.

The first filter used was sharpening, to enhance structures or other details in the image. The distortion of an image may be a result of several factors such as the deflection of light rays, defective equipment, and electronic noise or other signals. Sharpness is actually the contrast between different colors. A rapid transition from black to white will create a sharp aspect. In contrast, a more gradual transition from black via gray to white will seem blurry. Sharpening images increases the contrast along the edges where different colors meet.

The MATLAB function used for sharpening

The MATLAB function used for sharpening

 

Raw median images

Raw median images

 

Images processed in MATLAB with sharpening filter

Images processed in MATLAB with sharpening filter


Noise removal by averaging filter and noise removal by median filter

These filters are being used to clean the image from dots (usually hot and dark pixels from the sensor readout). This type of filter can also be used to further increase the signal to noise ratio (SNR).

The averaging filter, called a ‘low-pass filter’, averages out rapid changes in intensity, by calculating the average of a pixel and all of its immediate neighbours and then replacing the original value with the result. The process repeats itself for the rest of the image, every pixel being replaced by the average of the surrounding pixels in a square around it. For example we can choose a 3×3 kernel, where the closest three pixels are being averaged.

 

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 Original pixel values from the image

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 3×3 average kernel

 

Sometimes a 5×5 or a 7×7 kernel is used, depending on the quantity of the noise on the image. A variation of this kind of kernel filter is called a ‘Gaussian Blur’, which allows the user to define a particular shape of the blur kernel. An averaging filter usually blurs the edges of the image, especially on large kernels.

The unwanted noise can be removed with a median filter which, instead of averaging the neighbouring pixels, takes the median value as standard (by sorting all the pixels in an increasing order and calculating the middle value). A median value rejects any values that are substantially different from the others, removing sudden and unrepeating noise such as hot pixels and cosmic rays.

 

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Original pixel values from the image

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  3×3 median kernel

Image sharpening and noise removal in MATLAB

All the filters described above can be applied in MATLAB, with the following commands:

Sharpening an image

Imsharpen – returns an enhanced version of the grayscale or truecolor (RGB) input image, where the image features, such as edges, have been sharpened using the unsharp masking method.

Imsharpen (A)

We can also sharpen the image, specifying the radius and the amount parameters.

imsharpen(A,’Radius’,2,’Amount’,1);

Radius – is the standard deviation of the Gaussian lowpass filter.

Standard deviation of the Gaussian lowpass filter is specified as a numeric value. This value controls the size of the region around the edge pixels that is affected by sharpening. A large value sharpens wider regions around the edges, whereas a small value sharpens narrower regions around edges.

Amount – is the strength of the sharpening effect.

The strength of the sharpening effect is specified as a numeric value. A higher value leads to a larger increase in the contrast of the sharpened pixels. Typical values for this parameter are within the range [0, 2], although values greater than 2 are allowed. Very large values for this parameter may create undesirable effects in the output image.

 

Median filter – 2-D median filtering

medfilt2 – performs median filtering of the matrix A in two dimensions. Each output pixel contains the median value in a 3-by-3 neighborhood around the corresponding pixel in the input image.

medfilt2(A, [m,n])

Performs median filtering, where each output pixel contains the median value in the m-by-n neighborhood around the corresponding pixel in the input image. By default, the neighborhood size is 3×3.

 

Averaging filter

MATLAB has several two-dimensional and multidimensional filtering functions:

The function named filter2 performs two-dimensional correlation, conv2 performs two-dimensional convolution, and convn performs multidimensional convolution. Each of these filtering functions always converts the input to double, and the output is always double. These other filtering functions always assume the input is zero padded, and they do not support other padding options.

In contrast, the imfilter function does not convert input images to double. The imfilter function also offers a flexible set of boundary padding options.

B = imfilter(A,h) filters the multidimensional array A with the multidimensional filter h. The array A can be logical or a nonsparse numeric array of any class and dimension. The result B has the same size and class as A. imfilter computes each element of the output, B, using double-precision floating point. If A is an integer or logical array, imfilter truncates output elements that exceed the range of the given type, and rounds fractional values.

 

Conclusions

Processing astronomical images for scientific results can be difficult, and is very time-consuming. As stressed in this paper, there are a few important and essential steps to transforming a raw image into one that you can get data from. These steps are not far different from the ones needed in the case of processing images of asteroids, supernovas, novas, comets, etc.

MATLAB assists throughout the entire image analysis process, starting with dark image and flat-field frames reduction, and continuing with applying necessary filters in order to emphasise details or image manipulation so as to accentuate key-pixels.  At the same time, MATLAB can perform image adjustments not only to process it scientifically, but to improve its visual aspect and quality. It features a series of available and easy-to-use functions, such as brightness scaling, histrogram shaping, unsharp masking, walvelet spatial filtering, deconvolution, gradient correction, noise removal and others.

Processing images using different filters can benefit but also interfere with or even destroy certain image areas. This is easier to manage using MATLAB, because the scaling and filter-adjustments are performed by the observer, so as to manipulate the image and enhance it without the loss of important data or valuable pixels.

In the case exemplified, from a raw image that seemed flat and without any details, I was able to determine the true colour of the planet, details such as the coloured bands and cyclones of different dimensions became visible, and even a few details on Io, the satellite observed.

Final results after applying filters

Final results after applying filters


Bibliography

1. Richard Berry and James Burnell, “The Handbook of Astronomical Image Processing”, 2nd edition, Willmann-Bell.Inc 2011.

2. Uvais Qidwai and C.H. Chen Digital, “Image Processing-An Algorithmic Approach with MATLAB”, 2009 by Taylor & Francis Group.

3. Gonzalez and Woods, “Digital image processing”, 2nd edition, Prentice Hall, 2002.

4. Vicent Peris, tutorial on “Master calibration frames: acquisition and processing”, PixInsight.

5. https://pixinsight.com/tutorials/master-frames/index.html

6. http://www.mathworks.com/

Constelații dispărute

Ne întoarcem în perioada când „pelorovis-ii” încă se plimbau pe întinderile pământului iar oamenii priveau cerul nocturn cu mii de stele, ceva ce astăzi găsim doar în zonele fără poluare luminoasă. Răspândite aleatoriu și fără vreo semnificație, omul a asmilat anumite zone de pe cer cu forme cunoscute lui.

Constelațiile sunt grupări de stele ce alcătuiesc figuri simple ce ne par animale, oameni, obiecte, etc. Această „recunoaștere” involuntară de forme familiare nouă în nori, pe Lună sau în pâinea proaspăt prăjită, se numește pareidolie.

Prima aluzie consemnată a unor constelații a dus referire la Orion și Taurus, ce se presupune că au fost inventate în perioada Neolitică.

Majoritatea numelor de constelații și semificațiilor date au ajutat la practicarea agriculturii. Încă din antichitate omul a observat și a folosit schimbarea cerului pe post de calendar pentru a ști când să planteze, recolte și să secere. Ca și în zilele noastre, constelațiile au mai servit la orientarea pe timpul nopții, în special pe mare.

În prezent avem un total de 88 constelații pe întreg cerul (emisfera nordică și sudică) din care 48 provin de pe lista lui Ptolemeu (nu el le-a inventat) adunate în jurul anului 150 e.n., cu alte 11 constelații au contribuit exploratorii Pieter Dirkszoon Keyser și Frederick de Houtman pentru emisfera sudică (anii 1590), alte 17 au fost inventate tot pentru cerul din emisfera sudică de Nicolas Louis de Lacaille, el a fost și cel care a împărțit constelația Corabia Argo în alte patru iar toate constelațiile propuse de el sunt obiecte din acea perioadă (anii 1700). A urmat astronomul Gottfried Kirch ce a adăugat 3 constelații în emisfera nordică în jurul anilor 1650 iar în aceași perioadă astronomul polonez Johannes Hevelius a mai adăugat 11 constelații, scrierile lui Johann Elert Bode aduc vorba despre 7 constelații inventate de el și amintesc de alte 14 inventate de alții și încă 9 constelații inventate de diverși autori tot pentru emisfera nordică. Dacă v-ați dat seama că sunt peste 100 înseamnă că ați numărat corect.

Nu din totdeauna am avut 88 de constelații și până la decizia Uniunii Astronomice Internaționale din 1922 când s-a discutat pentru prima oară aspectul constelațiilor, mulți mai adăugau câte un asterism. Selectarea constelațiilor ce urmau să rămână pe întreaga sferă cerească s-a sfârșit în 1930 când a fost publicată oficial lista și granițele bine determinate ținând cont de „desenul” reprezentativ pentru fiecare constelație în parte. Din această listă nu se poate modifica, adăuga sau scoate constelații în caz că v-ați gândit să cumpărați sau să inventați o nouă grupare.

Cele mai vechi constelații au fost păstrate fiind de multă vreme folosite, scotându-se din constelațiile mai puțin cunoscute (uitate în timp), fără semnificație istorică sau formate din stele la limita vizibilității.

Iată câteva dintre constelațiile ce cu timpul au dispărut și nu au ajuns în top 88:

ANSER (Gâsca)

Creată de Johannes Hevelius, această constelație a fost formată o dată cu Vulpecula (Vulpea), gruparea numindu-se „Vulpecula cum Ansere”. Localizarea constelației este între Cygnus și Aquila din stele de magnitudinea 4 și 5.

ggsdgs

Constelația a dispărut datorită omiterii ei în atlasele stelare, ea fiind asociată cu Vulpecula. Decizia UAI a fost păstrarea numelui inițial de „Vulpecula” iar trasarea graniței include fosta „Anser”. Astăzi, alfa din Vulpecula mai este cunoscută și sub numele de Anser.

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ARGO NAVIS (Corabia Argo)

Formată din cunoscutele constelații: Carine, Pyxis, Vela și Puppis- părți din corabie. Constelația se găsește în lista lui Ptolemeu și este singura care nu a „supraviețuit”timpului. Corabia reprezintă nava folosită de eroi din mitologia greacă.

Împărțirea constelației a fost făcută la propunerea lui Nicolas Louis de Lacaille după expediția sa din emisfera sudica în anul 1752. Era formată din aproximativ 160 stele și ocupa peste 60 º (vertical). Din cauza mărimii, nu a fost reintrodusă.

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Vârful corabiei (constelația Puppis) se vede și din țara noastră, foarte jos față de orizont, în stânga lui Sirius, alfa din constelația Canis Major.

FELIS (Pisica)

Constelație ce poate toți ne-am fi dorit să rămână pe cer și să miaune, a fost inventată de Joseph Jérôme Lefrançois de Lalande din stelele mai puțin strălucitoare (magnitudinea 5 și sub) dintre Hydra și Antila.

felis

Constelația nu a fost populară pe continentul European și aceasta a dus la omiterea ei în atlasele stelare europene, ea fiind adoptată doar de cartografii americani. Cu timpul, a dispărut din scrierile secolului IX, iar când s-au trasat granițele definitive, stelele ce au aparținut constelației Felis au fost împărțite constelațiilor din apropiere: Hydra, Pyxis și Antila.

Printre constelațiile dispărute se mai numără câteva creații ce pot părea amuzante dacă ne gândim că acestea au fost pe cer la un moment dat, iar dacă decizia din 1922 ar fi fost luată în favoarea lor, astăzi ne-am fi uitat după obiecte deep-sky sau aștri în următoarele constelații:

GLOBUS AEROSTATICUS (Balonul) ce se afla între Capricornus și Piscis Austrinus și a fost concepută de Joseph Jérôme Lefrançois de Lalande în 1798 în onoarea invenției balonului cu aer de către frații Montgolfier.

MACHINA ELECTRICA (Generatorul electric), constelație inventată de Johann Elert Bode la 1800 și plasată între Fornax și Sculptor, formată și din stelele constelației Sculptor.

OFFICINA TYPOGRAPHICA (Tipografia) a doua constelație bizară inventată de Joseph Jérôme Lefrançois de Lalande în aceași perioadă ca și Globus dar introdusă de Johann Elert Bode în atlasele stelare. Constelația se afla între Canis Major și Puppis și nu a fost adoptată ca multe altele din sugestile pe care le-a avut Bode.

HONORES FREDERICI (Gloria lui Frederick) este formată din stelele dintre Andromeda și Lacerta. A fost introdusă de Johann Elert Bode în comemorarea lui Frederick al-II-lea de Prusia în anul 1787. Pentru crearea constelației s-au folosit 76 de stele slabe ca strălucire, ce au format o sabie și o coroană.

MONS MAENALUS (Muntele Mainalo) se găsea între stelele constelațior Virgo și Libra, la picioarele lui Bootes ce stătea pe munte. Această constelație a fost formată din stele ce aparțineau și constelației Bootes. A dispărut cu timpul iar UAI a luat decizia de păstra zona fostei constelații și granița trasată constelației Bootes include și stelele ce conțineau constelației Mons Maenalus.

– articol apărut și în revista Vega numărul 151 ianuarie 2016 –

Vega 149

Descarcă numărul 149 revistei Vega din luna iunie de aici: http://astro-urseanu.ro/biblioteca/vega/Vega149.pdf
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Luna asta aflăm despre apropierea dintre planetele Jupiter și Venus în rubrica „Întâmplări astronomice de vară”, activitatea solară, cum se determină anul nou pe alte planete și cum Ruxandra Toma și-a descoperit pasiunea pentru astronomie.

Curpins:
1. Întâmplări astronomice de vară – Adrian Bruno Șonka
2. Observarea astronomică a Soarelui – Alex Burda
3. Anul Nou pe planete – Elisabeta Petrescu
4. Pasionat de astronomie – Ruxandra Toma
5. Galerie de imagini cu Luna
6. Calendarul astronomic și harta cerului

 

Dacă vreți să contribuiți cu articole sau fotografii, contactați-ne la revista.vega@outlook.com sau pe noua pagină de facebook a revistei: https://www.facebook.com/revista.vega.bucuresti

Lovejoy aproape de Polaris

Cometa C/2014 Q2, una din cele mai frumoase comete din ultimul timp, cu o coadă impresionantă ce a fost observată de mulți astronomi amatori, se apropie de steaua Polaris (alfa din Ursa Minor). Ne bucurăm pentru că asta înseamnă că obiectul nostru este foarte bine poziționat, destul de sus pe cer la 43° și nu avem nevoie de orizont, doar de partea nordică liberă și cer senin.

În seara de 28 mai cometa este la doar 1° de Polaris. Ceea ce înseamnă ca printr-un binoclu le vom vedea pe amanândouă în același câmp. Cometa în continuare are o magnitudine favorabilă de 6.8 deci nu ne putem face probleme că nu o putem vedea.

Pentru cei care nu au văzut o cometă niciodată este un prilej bun de a o observa pentru că este ușor de găsit, iar pentru astrofotografi va fi un moment unic pentru a fotografia o cometă lângă Polaris.

Mai jos aveți calculată poziția cometei în următoarele zile.

pozitia cometei lovejoy

Vega mai 2015

A apărut numărul pe luna mai al revistei Vega și se poate descărca aici.
coperta vega 148

Cuprins:

1. Întâmplări astronomice de primăvară – Adrian Bruno Șonka
2. Observarea astronomică a Soarelui – Alex Budra
3. Time Lapse partea a II-a – Zoltan Deak
4. România observat din România – Adrian Bruno Șonka
5. Pasionat de astronomie – Cristi Diaconescu
6. Galerie de imagini cu planeta Jupiter
7. Calendarul astronomic și harta cerului

România observat din România

„România observat din România” este o campanie pentru observarea asteroidului cu numele țării noastre. În această campanie s-au format echipe cărora vă puteți alătura pentru a fi de față la capturarea imaginilor cu acest asteroid. Până acum a fost observat din Cluj, București și Bârlad.

Programul observațiilor la fel și mai multe detalii despre asteroid și despre participarea la observații, le găsiți pe site-ul Institutului Astronomic al Academiei Române.
http://observer.astro.ro/roro/

Eu l-am observat în seara de 27 spre 28 aprilie, la marginea Bucureștiului în localitatea Gruiu, împreuna cu colegii mei de la Observatorul Astronomic, câtiva elevi de liceu, studenți de la UNATC și o familie.

Sunteți așteptați să observați România de pe cer, de la Institutul Astronomic sau de pe câmp împreuna cu echipele de astronomi.

asteroidul Romania

Citește revista Vega

„Vega” este o revistă de astronomie din ţară cu apariţie constantă, de 14 ani (minus o pauză de patru ani), la care am avut și am onoarea să particip ca redactor șef de la relansarea acesteia, din ianuarie 2015. În paginile revistei veţi găsi articole de astronomie, relatări ale activităţilor, proiectelor şi expediţiilor realizate de astronomi amatori sau profesioniști din țară.

Colaborează și tu! Dacă aveți articole, relatări sau imagini astronomice, nu ezitați să ne contactați.

Abonarea la revistă este gratuită! Trimite numele tău, adresa pe care vrei să primești revista și de unde ai aflat de acestă revistă la astroclubul@gmail.com, și noi vă vom trimite revista înainte de publicarea acesteia pe site-ul oficial al Astroclublui București.

Ultimul număr aici: aprilie 2015

vega147_page_01

Eclipsă pe Jupiter

Dacă ne bălăceam pe Jupiter pe 21 martie, am fi văzut încă o eclipsă asemănătoare celei de pe 20 de pe Pământ. În cazul aceasta, oricum nu am fi vazut-o de atmosfera planetei, deci degeaba ne cumpăram filtru.

De pe Pământ am avut șansa de a observa satelitul cum trece peste discul planetei lăsând umbră pe aceasta. Acest fenomen nu se întâmplă așa rar, o dată la 42 ore Io trece peste Jupiter și dacă aveți un instrument astronomic merită observat acest eveniment, și de ce nu, înregistrat.

Filmulețul de mai jos este compus din 86 de filme de 50 secunde fiecare. Sună puțin, dar mi-a ocupat 112GB.

Durata observației este de 1h 40m.

Jupiter si IO

Dacă pierzi o eclipsă de pe Pământ ce durează câteva minute, iar de cele mai multe ori nici nu te afli în locul potrivit, cele de pe alte planete sunt la fel de fascinante și durează mai mult.

Cometa C/2014 Q2 (Lovejoy)- prima imagine din România

Descoperită anul acesta în luna august, cometa a început să fie vizibilă din România de abia pe 15 decembrie, dar la o înălțime deasupra orizontului foarte mică.

În noaptea 21-22 decembrie, a ajuns la 10 grade deasupra orizontului în constelația Columba.
Fotografiată în condiții de cer suburban dar cu poluare luminoasă în zona aceea, cometa s-a arătat chiar și la 10sec expunere.

lovejoy 2014

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Detalii despre cometă, când poate fi observată și cum, pe blog-ul Observatorului Astronomic „Amiral Vasile Urseanu”: https://sonkab.wordpress.com/2014/12/03/ne-paste-o-cometa/