Antares, rival of Mars

By popular demand, and personal weakness with this star, I will take leave momentarily aside the stars and constellations near Polaris (called circumpolars) to speak about a star well away from it, Antares.

As shown in the image, Antares is in the constellation Scorpius, one of the Zodiac constellations so, therefore, his name is well known to all. Unlike other constellations, with Scorpio is easy to imagine why astronomers from several different civilizations were able to find the shape of a scorpion in this group of stars. His enormous tail, formed by a series of fairly bright stars, is easily recognizable from the shores of the Mediterranean Sea. The rest of the body, as well as the claws, is highly questionable and discussed. Although most tend to see the "trident " as the head and two claws of the scorpion, in this representation it has been chosen a different position. As I said at the entry about Ophiuchus, in fact, if we want to find the claws of the scorpion we must go to Libra.

About Libra we will talk later, now I just want to show you where are the claws of the scorpion. As you can see, the main shape of Libra is a "comet". The claws of the scorpion are, in fact, the two brightest stars in the constellation Libra, the one furthest to the right in the constellation Libra and the one further to the top. In this case, what once would have considered the two claws and the head is not more than the lower abdomen and the beginning of the tail.

Scorpius is a constellation, in my opinion, very impressive and it is unfortunate that in the northern hemisphere it just can be observed only in summer and, depending on the latitude where we are, may be partially hidden by the horizon. In Englad the tail is always hidden even when there are no elevation of the horizon, like mountains or a single tree. If you want to enjoy a magnificent view of the full constellation I recommend the beaches of Andalusia as it will always appear to the south and only from some Andalusian beaches you will have a totally clean and immaculate horizon and the whole constellation in the sky.

I know I promised also discuss myths associated with the constellations, but in this case, Scorpio is part of the myth of Orion and, therefore, be included when talking about it.

Let's go, finally, to Antares.

Antares is the brightest star in the constellation Scorpius. His position, marked in this figure, coincides with the beginning of the tail (assuming that the claws of the scorpion are in Libra). It has a magnitude of 1.05 making it even brighter than Polaris. Its color (B-V 1.86), and here's what makes this star so striking, is noticeably red. It's so red and so bright that is commonly confused with the planet Mars.

Moreover, his name, "Antares", is actually a derivation of Anti-Ares, "not-Ares". I note that both Mars to Romans and Ares to the Greeks represent the same divinity. Therefore, the planet we call Mars was called Ares by the Greeks and Antares was remembered as that red star that was not to be confused with Ares.

The last point I want to explain what it means that, in this case, is the last line in the description of the star. The coordinates of the star given as right ascension (RA) and declination (DE). These coordinates work the same way that the coordinates of latitude and longitude.

For the surface of the Earth, the latitude is 0 degrees at the equator and progresses to 90 degrees at the North Pole and -90 degrees at the South Pole. Moreover, the longitude is 0 degrees in the meridian of Greenwich and is progressing in an easterly direction. So, what is the west of the meridian of Greenwich have negative longitude (although it may be represented as a longitude greater than 180 degrees).

In the celestial sphere we saw that we also have a north pole and, therefore, a south pole and equator. Thus, the declination (DE) would be equivalent to the latitude and is represented in the same way, 0 degrees at equator, 90 degrees at the North Pole (near Polaris) and -90 degrees at the South Pole.

Right ascension (RA) is equivalent to the longitude, but in this case, is not represented in degrees but in hours, minutes and seconds and the start point is the vernal equinox, which actually is not a meridian, but a point also belong to the equator, specifically, one of the two points where the ecliptic intersects the celestial sphere equator. Right ascension also grows to the east.

Because of precession, the stars change position over time so, as reference, it is often taken the position of the stars in a given year. That is what is the value J2000, it means "the position of the stars in 2000".

Finally, I let you an enlarged picture of the area you can find Antares, showing the equatorial grid.

Antares, la rival de Marte

Por petición popular, y por debilidad personal con esta estrella, voy a tomarme la licencia de dejar momentaneamente de lado las estrellas y constelaciones cercanas a Polaris (llamadas circumpolares) para hablar de una estrella bastante alejada de ella, Antares.

Como puede verse en la imagen, Antares pertenece a la constelación de Escorpio, una de las constelaciones del Zodiaco y que, por tanto, su nombre es bien conocido por todos. Al contrario que otras constelaciones, con Escorpio es fácil imaginar por qué los astrónomos de varias civilizaciones diferentes fueron capaces de encontrar en este grupo de estrellas la forma de un escorpión. Su enorme cola, formada por una serie de estrellas bastante brillantes, es fácilmente reconocible desde las orillas del Mediterráneo. El resto del cuerpo, así como las pinzas, es muy discutible y discutido. Aunque la mayoría tiende a ver el "tridente" como la cabeza y las dos pinzas del escorpión en esta representación se ha optado por una posición diferente. Como ya dije en la entrada sobre Ofiuco, en realidad, si queremos encontrar las pinzas del escorpión hemos de irnos a la constelación de Libra.

Sobre Libra ya nos detendremos a hablar más adelante, ahora sólo quiero mostraros dónde se encuentran las pinzas del escorpión. Como podéis ver, la forma principal de Libra es una especie de "cometa". Las pinzas del escorpión son, en realidad, las dos estrellas más brillantes de la constelación de Libra, es decir, la que está más a la derecha en la constelación de Libra y la que está más arriba. En este caso, lo que antes habríamos considerado como las dos pinzas y la cabeza no es más que la parte baja del abdomen y comienzo de la cola.

Escorpio es una constelación, para mi gusto, realmente impresionante y es una pena que, en el hemisferio Norte, sólo pueda ser observada en verano y que, dependiendo de la latitud en la que nos encontremos, puede que quede parcialmente ocultada por el horizonte. En España es muy común que cualquier mínima elevación del horizonte (como una cadena montañosa o unos simples árboles) te tape parte de la cola. Si se quiere disfrutar de una magnífica vista de la constelación completa recomiendo las playas de Andalucía ya que esta aparecerá siempre hacia el Sur y sólo desde algunas playas andaluzas tendremos un horizonte totalmente limpio e inmaculado.

Sé que prometí comentar también los mitos asociados a las constelaciones pero, en este caso, Escorpio forma parte del mito de Orión y, por tanto, será incluido cuando se hable de éste.

Pasemos definitivamente a Antares.

Antares es la estrella más brillante de la constelación de Escorpio. Su posición, marcada en esta figura, coincide con el inicio de la cola (considerando que las pinzas del escorpión están en Libra). Tiene una magnitud de 1.05 por lo que es incluso más brillante que Polaris. Su color (B-V 1.86), y he aquí lo que hace a esta estrella tan llamativa, es marcadamente rojo. Es tan roja y tan brillante que es comunmente confundida con el planeta Marte.

Es más, su nombre, "Antares", en realidad es una derivación de Anti-Ares, "la que no es Ares". He de recordar que tanto Marte para la mitología romana como Ares para la griega representan la misma divinidad. Por tanto, el planeta al que nosotros llamamos Marte era llamado Ares por los griegos y Antares era recordada como aquella estrella roja que no había que confundir con Ares.

Como último punto quisiera explicar a qué se refiere la que, en este caso, es la última línea en la descripción de la estrella. Son las coordenadas de la estrella dadas como ascensión recta (AR) y declinación (DEC). Estas coordenadas funcionan de la misma forma que las coordenadas de latitud y longitud terrestre.

Para la superficie de la Tierra, la latitud es 0º en el ecuador y avanza hasta 90º en el polo Norte y -90º en el polo Sur. Por otra parte, la longitud es de 0º en el meridiano de Greenwich y va avanzando en dirección Este. Así, lo que está al Oeste del meridiano de Greenwich tiene longitud negativa (aunque también puede aparecer como una longitud mayor de 180º).

En la esfera celeste ya vimos que tenemos también un polo Norte y, por tanto, un polo Sur y un ecuador. Así, la declinación (DEC) sería equivalente a la latitud y se representa de la misma forma, 0º en el ecuador, 90º en el polo Norte (cerca de Polaris) y -90º en el polo Sur.

La ascensión recta (AR) es equivalente a la longitud pero, en este caso, no se representa en grados sino en horas, minutos y segundos y su punto 0 es el equinoccio de primavera, que en realidad no es un meridiano sino un punto que también pertenece al ecuador, concretamente, uno de los dos puntos donde la eclíptica corta al ecuador de la bóveda celeste. La ascensión recta avanza también en dirección Este.

Debido a la precesión, las estrellas cambian de posición a lo largo del tiempo con lo que, como referencia, se suele tomar la posición de las estrellas en un año concreto. Eso es lo que representa el valor J2000, la posición de las estrellas en el año 2000.

Para finalizar, os dejo una ampliación de la zona donde se encuentra Antares con la cuadrícula ecuatorial representada.

Polaris, the compass

One of the first details you notice when you take a long time looking to the sky is to see how, throughout the night, the stars are moving, as the Sun does during the day and throughout the year. I explained in the previous entry that the stars we see in summer are not the same as those we see in winter, the sky changes as Earth rotates around the Sun. The same happens over a day as the Earth rotates on its axis.

Well, imagine that you are in the center of a cubic room (both walls and floor and ceiling are the same size). This would imply that you would have to climb on a chair to be truly in the center but forget about the floor. Imagine that every wall and ceiling, has a different color, as shown in the image below, in which the roof is going to look white.

If you find yourself staring at the wall initially red and turn to your left you will pass to see the red wall to see the blue one, then orange, then green and finally you'll return to see the red one. However, if you do the same movement but always looking at the ceiling you'll see the same thing, an immaculate white ceiling.

The same applies to the starry sky, the "celestial sphere" of which we spoke. However, the rotational movement we do in the room is the Earth that it does in this case and our "axis" does not directly coincide with its, just standing right at the North Pole (or South Pole) would match the two axis but I think it won't be hard for anyone to imagine, therefore, the section of the celestial sphere that is above the North Pole can be seen all the year, to greater or lesser extent, from the northern hemisphere, while part that is above the South Pole can be seen all the year, to a greater or lesser extent, from the southern hemisphere.

I know that playing with spheres is a bit complicated for our mind, so I will put several examples of different situations using pictures that I post below.

In this image the black circle represents the Earth while the blue one represents the celestial sphere. Suppose that we are in the position marked as 1. The dashed line represents the line that we would see as the horizon and, therefore, above it would see the sky. A section of the sky are visible all year round, it is the ceiling of the room we talked about. Another section is only visible at certain times of the year because the Sun during the day and the Earth, the ground, overnight block us from seeing some of the stars of this section of the celestial sphere. However, there is also a section of the sky that, much as the Earth revolves around the sun, we'll never see, are those stars which are as far south in the celestial sphere that the ground prevents us from seeing them throughout the year.

Clearly, as we see in the picture below, when we change our latitude the dimensions of the sections named before change. However, while we remain in the northern hemisphere, there is always a section that can be seen throughout the year and one that can not be seen at any time.

Also, as we cross to the southern hemisphere these sections "always visible" and "always hidden" are exchanged, as can be seen in the picture below.

I would like to apologize to all the inhabitants of the South which passes through this blog because, from now on, I'll concentrate my lessons mainly in the northern hemisphere, since it is the one I know better.

Returning to the geocentric model (Earth at the center of the Universe). We have said earlier that the celestial sphere rotates around the Earth (remember that this is totally false, it is only a model) making all the stars turn at a time. However, what is right in the axis of this sphere does not move even if the sphere turns. Thus, if we had a point in the sky that marks the North Pole of the celestial sphere and what we look for a whole night we would realize that while all the stars appear to revolve around him, that point still.

Well, this "point" is a star called Polaris (or simply North Star). Is not really fair at the North Pole of the sphere but is so, so close you can be considered as it is. Then go with an image representing the North Pole of the celestial sphere and you can see highlighted Polaris and the constellation to which it belongs, Ursa Minor.

To the left of the image may be a number of details about the star. Since this notation we will still find useful in future entries I will stop and explain it a little. For now, we just stop at the first two lines. In the first of these may be the traditional name that the star has, if any, which in this case is Polaris, between brackets, his real name, and after the dash, the number in the Hipparcos Catalog (I will not stop to explain this now, but not all stars are in this Catalog)

The stars, even those with no traditional name, are named according to their apparent magnitude and the constellation to which they belong. The apparent magnitude is the brightness of a star that seems to have seen with the naked eye. All celestial bodies have apparent magnitude associated with them, including the Sun and the Moon. How to define the magnitude is a bit complicated to explain here but we just left with the idea that the smaller the size, the greater the apparent brightness of the star. For example, the Sun has a magnitude of -26, Sirius (the brightest star in the night sky) has a magnitude of -2 and, as you can see, Polaris has a magnitude of about 2.

The value in parentheses after the letters B-V refers to the color. According to their values, the star would be the following colors:

 <0.15 = Blue

 -0.15 / -0.05 = White Teal

 -0.05 / +0.2 = White

 +0.2 / +0.5 = White Beige

 +0.5 / +0.9 = Yellow

 +0.9 / +1.5 = Orange

 > +1.5 = Red

Thus, Polaris is a star of yellow color.

Well, the stars of a constellation, including those not part of his original drawing, but they just are in the region of the celestial sphere that is defined by the constellation, are ordered from lowest to highest magnitude (from highest to lower brightness). However, instead of calling to Polaris, the brightest star in the constellation Ursa Minor, 1-UMi (Ursa Minor), it is done using the Greek alphabet and becomes α-UMi.

Therefore, and unlike many people think, Polaris is NOT the brightest star in the sky, so Sirius is much brighter than it. However, as we have seen, is a star that can be viewed throughout the year and, moreover, is fixed in the evening sky for being in the North pole of the celestial sphere. Of course, that as the Earth's axis coincides with the axis of the alleged celestial sphere, that this star is in the North Pole means that the north pole of the Earth itself points to the star, making it incredibly useful in guiding and especially in navigation, because the star always mark the terrestrial North Pole.

Also, contrary to what many people believe, Polaris does NOT belong to Ursa Major, but her younger sister, making it, at first, a star hard to find, since Ursa Minor is not so easily visible and recognizable as Ursa Major. How to find it I'll leave to the next entry, because I do not want entries get too long.

I'll just let me add one more detail about the usefulness of knowing place Polaris, represented by the following image. If we messure (for example, with a protractor and a plumb) the angle the form theline unites us with the pole star and the line unites us to the horizon will give us, directly, the latitude at which we find ourselves. If we were at the North Pole would have to Polaris just above our heads, at 90 degrees to the horizon, while being in Equator Polaris is just over the horizon, forming an angle of 0 ° with it.

As I said, Polaris is the most most useful star and, therefore, one of the the most popular of the northern hemisphere and in many cases, the path to follow to find it serves as a basis for finding the other constellations which has close to it and that we will see in subsequent entries. The impressive figure of Draco (the Dragon) and the fascinating history of Cepheus and Cassiopeia, kings of Ethiopia, will soon be revealed.

Ophiuchus, the thirteenth zodiac constellation

This was a blog published this morning in my company's blog so it was first written in English.

It seems that, some days ago, the news was spreading the chaos among horoscope readers and followers saying that an american "investigator" had "discovered" a "new" zodiac constellation making the rest moving from the dates everybody thought they must be. Actually, this horoscope stuff is part of Astrology, a kind of religion that, at present, nothing has in common with the actual science, Astronomy, but the starting "astro". So, I would like to explain everyone interested what were the astronomic bases of Astrology and how this "new discovery" affect our horoscopes.

I have already explained yesterday that, at present, almost everyone accept that actually is Earth who is orbiting around the Sun and, while is turning around its own axis, make us, seeing everything from Earth surface, feel like the Sun, the Moon and the stars are turning around us. However, the ancient Greeks didn't know that. They, as many other ancient civilizations, believed that actually the earth was fixed and surrounded by a sphere, the celestial sphere, in which surface the stars was painted as shiny dots. These "dots" are in fixed positions on the celestial sphere surface so, when the celestial sphere is moving, all the stars keep the same position one respect each other. That effect leaded our ancestors to think that the stars were really grouped in so called constellations and, joining dots like a child game it was, they saw in these constellations things, animals or characters from the nature or their believes and folk. Each culture, each civilization, found in the sky different forms, different characters, different constellations, but all of them believed that they were groups of stars that were really close. Some of them, like the zodiac constellations, are very known today, at least their names.

Between the celestial sphere and Earth they thought the planets (from ancient Greek "planetai", meaning wandering star) was, stars which position was not fixed in the celestial sphere. To the Greeks, even the Sun and the Moon, since they were moving from the other stars, were planets. They also thought that, if the constellations were characters from their mythology, the planets (stars with enough power to move by themself) must be Gods. The name of the Sun and the Moon has evolved depends of the language but didn't happened the same with the rest of planets. In that way, they found 7 planets: Sun, Moon, Mercury, Venus, Mars, Jupiter and Saturn and they gave these names to the days of a week, as so we do today. To show this I must to mix English with Spanish (a Latin root language that I know very well) so sorry if you get a little lost.

Monday (in English) is the Moon Day.

Tuesday (Martes in Spanish) is the Mars Day.

Wednesday (Miercoles in Spanish) is the Mercury Day.

Thursday (Jueves in Spanish) is the Jupiter Day.

Friday (Viernes in Spanish) is the Venus Day.

Saturday (we come back again to English) is the Saturn Day.

Sunday (English again) is, as we can directly read, the Sun Day.

Actually, I don't know where your planet names came from, I suppose I must investigate a little about it for next time.

But we know that Earth and the rest of planets (we'll forget the Moon from this point) are orbiting the Sun in nearly circular orbits. If we still were thinking the celestial sphere exists but, in this case, with the centre in the Sun, we still were seeing the stars as fixed points in the night sky. Because we are moving around the Sun, the celestial sphere must be static so we can see different stars and constellations in summer than in winter. May be this is a mess for many so I'll try to explain it slowly.

"When are you going to talk about Horoscope?" Be patient, we are close.

Think in a cross like the image below. In the centre of the cross we have the Sun and at the end of each line we have the seasons: winter, spring, summer and autumn. If you are in summer and you try to see through the Sun to the celestial sphere at the other side (don't do it, you'll be blind!) you can't see any star because the bright of the Sun are hiding then at daylight, but they are there indeed. At night, you are looking to the outside of the cross, seeing the summer stars and constellations. When you are in winter and try to look to the summer constellations the Sun is in your way, blocking your line of sight.

Season Cross

So, coming back to the geocentric model (the Earth in the centre) it actually looks like the Sun is moving not only around Earth but also from the background of stars, following a path along the year called ecliptic. Because the orbits of all the planets are all of them, more or less, in the same plane as our one, from our point of view, they follow a path in the celestial sphere in the same area that the Sun does. This area, a band that fills about 8 degrees above and below the ecliptic (distances on the surface of a sphere is usually measured by degrees) is called the zodiac band. The word "zodiac" comes from ancient Greek, again, and means "wheel of animals". That was because most of the zodiac constellations are animals, like the crab, the lion, the bull or the goat.

In theory, and it was originally, Astrology used the positions of the Sun and the planets in reference to the background of stars, the zodiac constellations, to predict the future. So, if you are Aquarius that is because, in the moment of your birth, "the Sun was in Aquarius", which means that, from our point of view, if we looked to the Sun and it didn't blind us, the constellation that we'd see behind it would be Aquarius.

But, actually, the astrologists forgot to look at the sky a long time ago. They started to use tables and charts to know where the planets must be instead looking where they really are. The rules they are using have been out of date for more than 2000 years, and so they still are today. Moreover, it's very probable that the modern astrologists are using a different system than their babylonic colleagues, who first developed the astrology, mixing and integrating on their system the changes that other people were discovering in the sky but still without looking at it, just changing their charts.

For example, astronomers and astrologists set the beginning of the year on the same moment, the vernal equinox (the moment that the day and the night last the same and give the beginning of the spring in the north hemisphere), at about the 21st of March. But astrologists say that, in this day, the Sun is entering in Aries, and that's why you are Aries if you've born between about 21st of March and 21st of April. Nevertheless, currently the Sun is very inside Pisces constellation on that day making all the zodiac constellations to move about a month backward, what means that you must be the previous constellation you though you were. For example, if you were born on 25th of April, astrologists say that you are Taurus but astronomers say you must be Aries.

"Where do this difference come from?" The third movement of the Earth, the precession, produces this difference. It's not the moment to explain how it works but one the effects of this movement is that the position of the Sun at the moment of the vernal equinox is moving respect the background of stars. Every year, the Sun is in a slightly different position moving in the opposite direction at the order of the zodiac constellations, from Aries to Pisces and, in a future, from Pisces to Aquarius. But the astrologists are fixing the position of the Sun every year in the same place, the border between Pisces and Aries, since more than 2000 years ago. They, of course, are totally wrong.

“OK, that's why the zodiac constellations has been moved but, what's about the thirteenth constellation, Ophiuchus?” This is astronomically a zodiac constellation, and it was actually known by the Greeks, but it is not for astrology. The ecliptic (remember, the path the Sun draw on the celestial sphere) crosses Ophiuchus between Scorpio and Sagittarius. Also, for astronomy, the zodiac constellations have different sizes and the Sun is not spending the same time on each one. Nevertheless, astrology divides the path of the Sun in 12 regions of exactly the same size. Each region has the name of a sign (they are not constellations, they are signs) that, originally, corresponded with the constellation the Sun was expending more time in that period of time, leaving Ophiuchus out of the wheel.

Ophiuchus

As I said before, they forgot to look at the sky a long time ago and didn’t notice that, at present, the signs don’t correspond with their original constellations at all. They [the astrologist] insist in the astrology don’t follow the same pattern that the astronomy but, at the same time, they are trying to make people believe they predict the future looking at the sky. You are free to believe in what you want but, in my opinion, they must lose the starting “astro” a long time ago.

"But then, this american investigator, has he discovered something new?" No, he just said what was known for centuries. The issue was the press has made from this a very productive "new" story.

A couple of additional small differences between astronomy and astrology are:

• Exists another astronomic zodiac constellation, Cetus, the Whale, in which the Sun spends about one day.
• The names of two of the stars of Libra are “northern claw of the scorpion” and “southern claw of the scorpion” in arabic. This fact leads to think that Libra was probably added by the Romans or even introduced by modern astrology 2000 years ago as a way to made more equitable the zodiac distribution. If we take Libra as part of Scorpio and count Ophiuchus as a zodiac constellation, Scorpio would last about a month and a half and Ophiuchus only two weeks.

Introduction

Well, I will use the first entries to explain a little what this is. The idea is to upload regularly interesting little things related to astronomy, particularly what is called the visible sky, so the one can be directly observed by human eyes without any additional element. This is, therefore, the sky Greeks, Egyptians, Babylonians and Aztecs were watching at and the only one that they knew. The knowledge acquired and transmitted by various civilizations is what led us to set the map of 88 constellations that define the night sky.

The constellations, as many of you already know, are nothing more than arbitrary groupings of stars that, from the point of view of the earth's surface, appear to be spatially close to each other but, in fact, may be extremely remote. Today, despite being very well demonstrated the falsity of the geocentric model, to locate stars in the sky is still considering it as a sphere surrounding the Earth and its surface is painted with the stars. Between this surface and the earth the planets (Greek name came to mean "moving stars") are moving. This planets originally included the Sun, Moon, Mars, Mercury, Jupiter, Venus and Saturn, the only planets known by the ancient Greeks.

Grouping these stars in constellations come to separate the night sky in different regions to help astronomers locate stars in the sky. The result can be seen in the picture below which shows that any point in the sky belongs to a constellation even though at this point there is no star.

Step by step, we will analyze the different constellations and regions of the sky. I hope you'll enjoy with me during this journey.