Tuesday, October 9, 2018

Upcoming astronomical events



October

  • October 9: New Moon. This phase occurs at 03:47 UTC.
  • October 21-22: Rain of Orionian stars. The Orionids produce up to 20 meteors per hour at their peak. It is produced by the dust grains left by Halley's comet, which is known and observed since antiquity. It can be observed from October 2 to November 7. This year reaches its peak on the night of October 21-22. The nearly full moon will block some of the weaker meteors this year, but the Orionids tend to be quite bright so it could still be a good show. Meteors will radiate from the Orion constellation, but they can appear anywhere in the sky.
  • 23 de octubre: Urano en oposición. El planeta azul verdoso estará en su punto más cercano a la Tierra y su cara estará completamente iluminada por el Sol. Será más brillante que en cualquier otra época del año y visible durante toda la noche. Este es el mejor momento para ver a Urano. Debido a su distancia, Urano solo aparecerá como un pequeño punto azul verdoso en todos los telescopios, excepto en los más potentes.
  • 24 de octubre: Luna llena. Esta fase ocurre a las 16:46 UTC. Esta luna llena era conocida por las primeras tribus nativas americanas como la Luna de Full Hunters o “luna del cazador”, porque su luz se aprovecha tradicionalmente para la caza.


November

  • November 5 and 6: Rain of Taurids. The Taurids are a small meteor shower of long duration that produce only 5-10 meteors per hour. It is born from two separate flows. The first is produced by the dust grains left by Asteroid 2004 TG10. The second sequence is produced by debris left by Comet 2P Encke. The Tauride rain takes place from September 7 to December 10. This year reaches its peak on the night of November 5. The thin crescent moon will leave the skies dark for good observation, especially just after midnight. The meteors will radiate from the constellation of Taurus, but they can appear in any part of the sky.
  • November 6: The planet Mercury reaches the highest eastern elongation of 23.3 degrees from the Sun. This is the best time to see Mercury, since it will be at its highest point on the horizon in the night sky.
  • November 7: New Moon. This phase occurs at 16:02 UTC.
  • November 17 and 18: Leonid meteor shower. The Leonids are a shower of average stars, producing up to 15 meteors per hour at their peak. This rain is unique since it has a cyclonic peak every 33 years, in which hundreds of meteors per hour can be seen. The last of these peaks occurred in 2001. The Leonids are produced by the dust grains left by Comet Tempel-Tuttle, which was discovered in 1865. The rain can be observed from November 6 to 30 and the best day will be from 17 to November 18th. The sky will be quite dark for what could be a good show at dawn. The meteors will radiate from the constellation of Leo, but they can appear in any part of the sky.
  • November 23: Full moon. This phase occurs at 05:40 UTC. This full moon was known by the first Native American tribes as Full Beaver Moon or "beaver moon", as it is the time of year to place beaver traps before the swamps and rivers freeze.



December

  • December 7: New Moon. This phase occurs at 07:20 UTC. This is the best time of the month to observe weak objects such as galaxies and star clusters because there is no moonlight to interfere.
  • December 13 and 14: Rain of Geminid meteorites. The Geminids are the queens of meteor showers. It is considered by many to be the best shower of stars, producing up to 120 multicolored meteors per hour at its peak. It is produced by remains left by an asteroid known as 3200 Phaethon, which was discovered in 1982. This rain occurs annually from December 7 to 17. Its moment of apogee this year will be on the night of December 13 to 14. The Moon will not be a problem. Meteors will radiate from the constellation of Gemini, but they can appear anywhere in the sky.
  • December 15: The planet Mercury reaches the highest western elongation of 21.3 degrees from the Sun. This is the best time to see Mercury, since it will be at its highest point on the horizon in the morning sky.
  • December 21: December solstice. The December solstice occurs at 22:23 UTC. The South Pole of the Earth will be inclined towards the Sun, which will have reached its southernmost position in the sky and will be directly above the Tropic of Capricorn at 23.44 degrees south latitude. This is the first day of winter (winter solstice) in the northern hemisphere and the first day of summer (summer solstice) in the southern hemisphere.
  • December 22: Full moon. This phase occurs at 17:49 UTC. This full moon was known by the first Native American tribes as the Cold Full Moon because this is the time of year when the cold winter air settles and the nights become long and dark.
  • December 21 and 22: Rain of Ursid stars. The Ursidas are a small meteor shower that produces between 5 and 10 meteors per hour. It is produced by dust grains left by Comet Tuttle, which was discovered for the first time in 1790. The rain takes place from December 17 to 25, with its peak this year on the night of December 21-22. This year, the glow of the full moon will hide all the brightest meteors. The meteors will radiate from the constellation Ursa Minor, but they can appear anywhere in the sky.



Friday, September 21, 2018

They detect a strange disturbance in the Milky Way




The Gaia space probe, the European mission that aims to develop a detailed catalog with the position, distance and speed of more than a billion stars in our galaxy, has just found a surprising "disturbance" in the Milky Way. And it is that the galaxy in which we live is, still, suffering the effects of a past "encounter". In fact, millions of stars do not follow the "sweet and flat" orbit around the galactic center, as would be expected, but move in a similar way to water waves in a pond after throwing a stone. The surprising find is published this week in Nature.

According to the researchers, the encounter with another galaxy took place sometime in the last between 300 and 900 million years. And that encounter was discovered, precisely, thanks to the pattern of movement of the stars in the disk of the Milky Way.

"We made a graph of the z-coordinate (the height of the stars above or below the disk of the galaxy) versus the velocity Vz (velocity with which the stars move in the vertical direction on the disk) and, surprisingly, what appeared was a perfect spiral, similar to the shell of a snail, "the study's lead author, Teresa Antoja, a researcher at the Institute of Cosmos Sciences at the University of Barcelona (ICCUB), told the Sinc agency.


"So perfect it seemed to us the way we saw in the graphics of the computer - adds the researcher - that we thought that we could have been wrong in something, or that there would be some problem in the data. But after multiple checks and knowing that the Gaia data has gone through an exhaustive quality control, we came to the conclusion that this spiral was something real ".

The helical shape detected by the researchers means that the stars are not moving, as would be expected in an equilibrium galaxy, in simple circles around the center of the Milky Way, but rather follow more complex patterns.

These patterns were revealed because Gaia not only accurately measures the positions of more than a billion stars, but also their speeds in the plane of the sky. And for this subset of a few million stars, Gaia provided an estimate of the full three-dimensional velocities, which allowed a study of stellar motion using the combination of position and velocity.




«I was shocked»

When Teresa Antoja first observed the patterns on her computer screen, she could not believe what she was seeing. One form in particular strongly attracted his attention. It was a spiral pattern, similar to a snail, that emerged in the graph that traced the altitude of the stars above or below the plane of the Galaxy. Never before had seen anything like it.

"At the beginning - explains Antoja - the characteristics were very strange for us, I was shocked and I thought there could be a problem with the data". But the Gaia data had been subjected to multiple validation tests before launch. In addition, together with her collaborators, Teresa Antoja carried out multiple tests to look for errors that could explain the observed forms. When not detecting any error, the conclusion was that everything they were seeing was really happening.

The reason why the phenomenon had not been previously detected is simple: never before had the scientists had in their hands an instrument with the power and capacity of Gaia. "It's as if suddenly you put on the right glasses and you could see all the things you could not see before," says the researcher.

Once confirmed that the structures that reflected the data were real, it was time to find out what had caused them and why they were there. "It's like throwing a stone in a pond, and see how the water moves in waves and waves," says Antoja.

However, unlike water molecules, which end up settling down and recovering their original shape, the stars are able to retain a "memory" of what disturbed them. And that memory is precisely in their movements. With the passage of time, and although the waves are no longer easy to see in the distribution of the stars, it is still possible to locate them when studying their velocities.




Cannibal galaxy

The next question was to find out what it was that had hit the Milky Way for the stars to behave that way. From other research, we know that our galaxy is a "cannibal", which has been growing by "devouring" other smaller galaxies throughout its history. But that does not seem to be the case on this occasion.

Amina Helmi, from the Dutch University of Groningen and co-author of the study, had already done other work on a small galaxy, Sagittarius, which barely contains some tens of millions of stars and which is currently being cannibalized by the Milky Way. And it turns out that his most recent approach to our galaxy was not a direct hit, but it happened very close to it, almost touching it. Something more than enough for its gravity to disturb some millions of stars in the Milky Way, just as a stone thrown into a pond would disturb the water.

In addition, it is the case that this last close encounter of Sagittarius with the Milky Way occurred sometime between 200 and 1,000 million years ago, a time that coincides almost perfectly with the one that Teresa Antoja calculated for the origin of the spiral shape of the movement of the stars observed by Gaia.

Now, researchers want to study this galactic encounter in much more detail. "The discovery was easy," Amina Helmi says, "the interpretations are more difficult, and a full understanding of their meaning and implications could take several years."

The Milky Way, of course, has a very rich story to tell. And we are just beginning to read it.