BASIC COSMOLOGY
When we look at the stars, we’re looking outside the solar system, since all the points of light we see are outside it, we only have one star, the Sun, and our solar system is ridiculously small compared to the rest of the universe.
The universe could be like an infinite ocean with countless islands, the galaxies, our galaxy, the Milky Way, would be an island with a beach where every grain of sand is a star, and our solar system would be one of those grains of sand.
From our solar system, we can see only a very small number of stars, since they must be relatively close or emit a great deal of light. That is why we have associated the stars we’ve observed with shapes and patterns found in myths and legends.
OUR GALAXY
Where are we: Our planet is located in a small solar system on the periphery of an immense galaxy called the Milky Way.
Contellations year: The Earth makes a translational movement around the sun, which means that during one half of the year the sun covers one half of the constellations in the sky and in the other half of the year it covers those on the opposite side.
Imperceptible movement: In turn, the solar system is not static, rather, it orbits around the center of the Milky Way, however, the Milky Way is so immense that this movement is imperceptible over the course of a human lifetime, and we will not see new parts of the galaxy that we have not seen before.
See out galaxy: It is impossible to see our own galaxy as a spiral, since that is its complete shape, and to appreciate it that way we would have to leave it. Since we are inside it, it surrounds us, and we can only see parts of it. Because it is a flat structure, we see it as a band full of stars and diffuse light that stretches across the sky from one place to another.
The Milky Way is made up of dust, gas, and stars, which are more concentrated the closer they are to the galactic plane, since gravity causes everything to be concentrated in the galactic disk.
In the arms, there would be many nebulae with stars forming, while others would be dying off, releasing dust, metals… And in the core, where everything is highly concentrated, we know that everything is orbiting a supermassive black hole. That’s why, when we look at the galactic plane, we can’t make out any individual stars; what we see is a band of diffuse light, since we’re looking toward the most concentrated part of the galaxy—the mixture of light from billions of stars at different distances.
HOW TO SEE THE MILKY WAY
When: The Milky Way is visible during the whole year, the galactic center is visible from March through October. At first, it’s only visible just before the sunset, but it becomes visible a little earlier each day until, from May through July, it’s visible all night long. Although this applies to both hemispheres, in the Southern Hemisphere it will appear higher in the sky and therefore be visible earlier.
Summer: When we look at it in the summer, we’ll be looking toward the center of the galaxy, so through its arms we’ll even be able to recognice the nucleus, which appears as a wider, brighter section of the band
Winter: When we look up in winter, we’ll be looking outward, observing the Perseus Arm, an outer arm that is fainter than our own, which is why the band will appear narrower and fainter.
Where: To find the band, look for its most prominent area, the galactic center. It’s close to the constellation Sagittarius. Look for eight stars that, when connected, form a teapot; the point where steam would rise from the teapot points directly to the galactic center, the brightest area of the entire band. To be sure, check that it is located toward the south.
How: The Milky Way isn’t white; our eyes only process a fraction of a second of light, but a camera can capture many seconds of light, allowing us to see more colors in the Milky Way.
Most of the Milky Way’s brightness comes from millions and millions of stars mixed together, many of which are similar to the Sun and emit a slightly golden glow. In the sky, there are red, orange, yellow, white, and bluish stars. … but less than 1% are actually blue; what we see is the average of all of them, a warm hue between cream and ochre.
What we know: If you pointed a powerful telescope at any point in the band, you would see that there are millions more stars behind it that we cannot make out with the naked eye. For now, even though we have star maps containing more than 2 billion stars, we only know 1% of them.
Nebulae: The pink patches are nebulae of ionized hydrogen; they are called H2 regions and are star-forming regions. Suns are being born in these areas right now.
Clouds: The gaps in the band are not holes in the galaxy; they are clouds of dust and gas that block the light from the stars.
Andromeda
Deep space objects: Not everything we see in the night sky belongs to our galaxy, for example, the Andromeda Galaxy, which can be seen with the naked eye or binoculars, is outside the Milky Way.
New knowledge: We know very little about this galaxy, and a little more is discovered every day. It is known to be a barred spiral galaxy; it has a central bar from which four main arms extend, and secondary arms or spurs branch off from these.