A celestial classic that I love to revisit every year. This time was also an opportunity to test a friend's CEM25-EC with my astrophotography rig, with the help of the ASIAir Pro to manage the session und command the mount.
We didn't have any issue during the night and we could gather about 3 hours of light frames plus calibration frames.
Well, this is Messier 31 in the constellation Andromeda. Do I need to write something more about our closest galaxy? ;-) Maybe yes, when astronomical knowledges back in the 19th century was still questioning celestial wonders and observations made at this time with given astronomical instruments.
Let me transcript you what French astronomer Camille Flammarion wrote in his book "
Les étoiles et les curiosités du ciel" in 1882 about the "
Andromeda nebula". You'll find also screenshots of that book in rev. B, C and D to focus on the illustrations mentioned in the text below.
(Start page 75)
However, let's not go any further without stopping at the Andromeda nebula, the first one to be discovered in the sky, and the only one that can be seen easily with the naked eye (because the Pleiades, the Cancer cluster, and a few groups of nearby stars that have a nebulous appearance, are not real nebulae). On a clear night, direct your eyes towards the star v of Andromeda, the third star in the belt of this chained beauty, and near this star, as seen in Fig. 41, you will see a pale nebula. We are surprised to see it absent from the first star catalogs, and it is quite probable that the ancients saw it as well as the moderns, but that they did not consider it worthy of their attention and neglected it as an insignificant glow. The oldest mention we find is that of the Persian astronomer Sûfi, who, in the tenth century of our era, reports it as a "small celestial cloud" generally observed and known by Arab astronomers. However, it was not until 1612 that it was reported in Europe by the astronomer Simon Marius de Franconie, who, in his work on the satellites of Jupiter recently discovered by himself and Galileo, reports that he saw it for the first time with a telescope, on December 15 of that year: "Its intensity, he says, increases as we approach the center. It looks like a candle seen through a transparent horn, and I find it similar to the comet of 1586. Whether it is new or not, I will not decide. Tycho-Brahé, who carefully described the position of the neighboring star (v), did not mention it."If we examine this nebula with a small telescope, we find it as represented in our fig. 49, and we see above it a small companion of the same order of creation, which was described for thefirst time by the French astronomer Le Gentil, in 1749. (...)This Andromeda nebula has been the object of a great number of observations. One of the first astronomers who studied it, Halley, saw in it that a light arriving from an extraordinarily large space in the ether, through which a luminous medium is diffused, which shines by its own light." I translate literally, leaving the vagueness of the expression and if I am not mistaken the author's thought, for there is nothing quite clear in this sentence: the spot is nothing else but the light coming from an extraordinary great space in the ether, through which an Iucid medium is diffused that shines with its own proper lustre."Curious remark, we are hardly more advanced than two centuries ago on the explanation of this immense nebula. While, among those that have been discovered since, some have resolved themselves into star clusters in the field of the telescope, and others have proved by their chemical constitution to be of a gaseous nature, this one has remained silent and mysterious. Its spectrum is continuous, without transverse lines, and consequently the substances which compose it remain unknown; a curious remark: the red end is missing. This does not prove, however, that it is not gaseous: gases can, at low temperatures, give a continuous spectrum. The most powerful magnifications have revealed fifteen hundred stars, but it is not certain that these stars belong to it: they may be in front of it. Let us add that its shape varies strangely according to the magnifications used. A telescope of 75 mm, magnifying 80 times, shows the image reproduced in fig. 49. A telescope of 108 mm, magnifying 200 times shows the image reproduced in fig. 50. But this primitive regularity disappears completely if one uses a powerful instrument, as Bond and Trouvelot did, in Cambridge the equatorial of 38 centimeters represents this distant creation such as one sees it fig. 51, drawing made by my learned friend Trouvelot in 1874. A central focus appears, as well as two other secondary focuses, one round, the other oval, and, what is perhaps even more surprising, two black cracks seem to cut the nebula in the direction of its length: if these are voids through the gas, it is incomprehensible; if they are two trails of obscure matter placed there in front, it is even more extraordinary. As for the stars, they seem to project forward and are less condensed in the center. Who could stop his mind for a minute in front of this figure without being absolutely amazed, fascinated, confounded?And what grandeur! It is without doubt one of the largest in the sky. To the naked eye, it measures a quarter of a degree. A 108-millimeter telescope shows it to be 1 1/2 degrees long and 24 feet wide. Bond was able to follow its track to 4 degrees in length and 2 1/2 degrees in width.And what a size! It is without doubt one of the largest in the sky. To the naked eye, it measures a quarter of a degree. A 108-millimeter telescope shows it to be 1 1/2 degrees long and 24' wide. Bond managed to track it to 4 degrees in length and 2 1/2 degrees in width. Assuming it to be no farther away than the nearest stars, it would still be incomparably larger than our entire solar system, although it measures more than two billion leagues in diameter. Indeed, at the distance of the nearest star, the half-diameter of the Earth's orbit (37 million leagues)¹ is reduced to 0.928". So here, an object measuring 928'' or 15'28'' would already be a thousand times wider than the distance from the Earth to the Sun and would measure 37 billion leagues ². But the Andromeda nebula occupies in the sky a space extending up to 4 degrees, i.e. 15 times larger than the previous figure, which leads to 555 billion leagues ³ ! If this is a planetary system in the process of formation, it would therefore be two to three hundred times larger than ours in diameter. Undoubtedly, it is unimaginable. But, to refuse such a conception, we would have to admit that this nebula was closer to us than the neighboring stars, which is not probable. It must be, on the contrary, much more distant, and consequently much more immense.(End page 79)
¹ one french metric league = 4 km
² 148 billion km
³ 2'220 billion km = 0,234 l.y.Translated with www.DeepL.com/Translator (free version)
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