15 November 2016

Aldebaran occultation by Moon tonight

Most of you would have enjoyed the supermoon yesterday evening and most of you have taken wonderful photos. Today evening we have one more exciting astronomical event and that is occultation of star Aldebaran by Moon. Tonight moon will occult giant Aldebaran. since both objects are bright enough it will be easy to observe even with naked eye, a pair of binoculars and of course with telescopes. I would suggest you get all the setup ready before the given time and wait for the event rather than waiting until last minute. The chart below will be helpful to show the entry point and exit point of the star during occultation. 

Astronomers have used occultation to know about the size, shape and distance of the objects. Aldebaran is the brightest star in the constellation of Taurus, it is at a distance of 65 light years from Sun. By measuring the time taken for that star from disappearing and reappearing and getting reports from different parts of the world we get a pretty good idea of the shape of the object. Today evening moon will occult Aldebaran from the south near the crater Tycho. Use the chart below to follow the star from disappearance to its re emergence. Try and measure the time taken between the star disappearance and re emergence using stop watch. All the best and hoping for clear skies. 

Time of disappearance 15:26:46 UT
Time of re emergence 15:57:45 UT

 Moon in the constellation of Taurus and close to star Aldebaran.

Moon about to Occult the star.

Aldebaran re emerging after Occultation.

14 November 2016

A Hype called Super Moon:

I am sure you have come across this Super Moon through print media, TV Channels, blogs, Face Book, Twitter or through friends. Today's Full moon will be the closest in 70 year and if you miss it now, you will have to wait until 2034 for next Super Moon. Moon in its orbit around earth come close to earth and this is called Perigee and moves farthest from earth called Apogee every month. Perigee can happen at any phase of the moon, it may be in Crescent, Half or gibbous phase. When Perigee and Full moon phase coincides, the name given is Super Moon.

What to Expect?

Looking at this picture of Moon can you tell if the Moon is bigger or smaller? 

You will agree just by looking at the picture its not possible, you will need reference, something to compare with or measure the size. This is the same thing that will happen when you go out tomorrow and look at the Moon. Lets for a moment see the numbers involved. This month perigee distance is close to 3,56,509 km and when we compare this with last perigee month's perigee in the month of October, distance which was close to 3,57,861 km the difference is just 1352 km. This when we convert it to angle subtended by moon in the sky and the difference from two perigee is 0.127 arc minutes. This as you can imagine is not possible to notice just by looking. You may need to photograph this full Moon and take photographs of upcoming full moons with the same settings and compare the difference.

This is also the implies to the brightness of the moon today. If we have not really observed the moon form some time it will not be evident to casual observer the difference in brightness in this light polluted conditions.

I would suggest that people should observe the moon not during full moon, but to observe in crescent to half moon and take guidance from local astronomy group. If you come to ABAA on any Sunday evening, you can learn about night sky and also when there is moon in the sky you can use our telescope and learn to observe moon and other celestial objects.

20 October 2016

Highest Resolution Image of Eta Carinae

VLT Interferometer captures raging winds in famous massive stellar system

An international team of astronomers have used the Very Large Telescope Interferometer to image the Eta Carinae star system in the greatest detail ever achieved. They found new and unexpected structures within the binary system, including in the area between the two stars where extremely high velocity stellar winds are colliding. These new insights into this enigmatic star system could lead to a better understanding of the evolution of very massive stars.

Led by Gerd Weigelt from the Max Planck Institute for Radio Astronomy (MPIfR) in Bonn, a team of astronomers have used the Very Large Telescope Interferometer (VLTI) at ESO’s Paranal Observatory to take a unique image of the Eta Carinaestar system in the Carina Nebula.
This colossal binary system consists of two massive stars orbiting each other and is very active, producing stellar winds which travel at velocities of up to ten million kilometres per hour. The zone between the two stars where the winds from each collide is very turbulent, but until now it could not be studied.
The power of the Eta Carinae binary pair creates dramatic phenomena. A “Great Eruption” in the system was observed by astronomers in the 1830s. We now know that this was caused by the larger star of the pair expelling huge amounts of gas and dust in a short amount of time, which led to the distinctive lobes, known as the Homunculus Nebula, that we see in the system today. The combined effect of the two stellar winds as they smash into each other at extreme speeds is to create temperatures of millions of degrees and intense deluges of X-ray radiation.
The central area where the winds collide is so comparatively tiny — a thousand times smaller than the Homunculus Nebula — that telescopes in space and on the ground so far have not been able to image them in detail. The team has now utilised the powerful resolving ability of the VLTI instrument AMBER to peer into this violent realm for the first time. A clever combination — an interferometer — of three of the four Auxiliary Telescopes at the VLT lead to a tenfold increase in resolving power in comparison to a single VLT Unit Telescope. This delivered the sharpest ever image of the system and yielded unexpected results about its internal structures.
The new VLTI image clearly depict the structure which exists between the two Eta Carinae-stars. An unexpected fan-shaped structure was observed where the raging wind from the smaller, hotter star crashes into the denser wind from the larger of the pair.
Our dreams came true, because we can now get extremely sharp images in the infrared. The VLTI provides us with a unique opportunity to improve our physical understanding of Eta Carinae and many other key objects”, says Gerd Weigelt.
In addition to the imaging, the spectral observations of the collision zone made it possible to measure the velocities of the intense stellar winds. Using these velocities, the team of astronomers were able to produce more accurate computer models of the internal structure of this fascinating stellar system, which will help increase our understanding of how these kind of extremely high mass stars lose mass as they evolve.
Team member Dieter Schertl (MPIfR) looks forward: “The new VLTI instruments GRAVITY and MATISSE will allow us to get interferometric images with even higher precision and over a wider wavelength range. This wide wavelength range is needed to derive the physical properties of many astronomical objects.

News Credit:ESO