05 November 2018

Mercury in the evening Sky

In the evening sky, low in the horizon, if we carefully look we can find the smallest planet in our solar system. After sunset, in a place where there are no obstruction like buildings or trees, in this unobstructed view of the western horizon we can spot planet mercury. Since mercury orbits close to the sun we can only find the planets close to the horizon in evening or morning skies.

During its orbit around the sun there are two favorable points where we can observe the planet. This is the maximum separation of angle between Sun and planet. This point of maximum separation is called Greatest elongation. For planet mercury this greatest elongation angle is between 18 degrees to 28 degrees. This is the reason why most people miss the planet, since it is so close to horizon.

On November 6th the planet will reach greatest elongation giving us a good opportunity to catch a glimpse of this planet with naked eye, binoculars and telescopes. The angle for this elongation is 23 degrees, this means just after sunset the planet will be 23degrees above western horizon.

Spot planet after sunset in western sky.

The planet will be at a magnitude of -0.2, although it is bright the drawback is that it is immersed in twilight making it difficult to spot but as twilight fades its easy to spot.

With a telescope we can see the gibbous phase of mercury with an angular size of 6min of arc. The planet will be in half phase on 11th of November and from there on the illuminated side of mercury will start decreasing. This is a nice time to see and enjoy and also understand the phases and orbit of mercury. Since the planet is coming closer to earth the angular size will keep increasing and it will be 9mins of arc before the planet sinks into the glare of the sun and then reach inferior conjunction on 27th of November.

Clear Skies.

26 July 2018

July Total Lunar Eclipse

There are very few astronomical events for which we need not leave our house, or have telescopes, filters or worry about light pollution. One such event is Lunar eclipse, an astronomical event that can be seen from where we live and without any optical aid or equipment.  

This time on 27th July the eclipse happens when moon is high in the sky so no worries of buildings and trees blocking the view.  

Here are the times of the eclipse. Moon will enter Penumbral shadow at 10:45pm on 27th July this is hard to notice as the change in brightness is very less. Moon will start entering the Umbral shadow at 11:55pm, partial eclipse phase, from here we easily see the change in brightness. Moon will be completely inside Umbral shadow from 1:00am, here we say Moon is in total eclipse phase.

 The totality will end at 2:44am when Moon will start becoming brighter. As moon comes out of totality we can see partial eclipse phase as some portion of Moon will be in dark and other will be in brightness. Moon will come out of Partial phase at 3:45am. The Moon will come out of Penumbral shadow at 4:48am.

We urge you watch this amazing celestial show which is viable from all our India

30 January 2018

Watch Lunar Eclipse at Planetarium, Bangalore

Jawaharlal Nehru Planetarium is organizing Lunar Eclipse viewing at planetarium campus, Bangalore. Interested public can visit planetarium and enjoy the eclipse and get questions answered about eclipse and astronomy.

The event is from 6:15pm to 8:45pm on January 31st. 2018. Association of Bangalore Amateur Astronomers (A.B.A.A) members will also be there to help public understand and enjoy the eclipse.

03 January 2018

Earth and Sun Closest

Sun so close yet so cold...Yes Today Sun and earth will be closest to each other at a distance of 14,70,99,586 km. This point of any object closest to Sun is called Perihelion. The reason for the cold in northern hemisphere is due to the orientation of earth's axis and as you can see in the illustration, the Sun is moved to southern hemisphere where they are experiencing Summer now. 

Since earth's orbit is almost circular, at farthest point from Sun which occurs on July 6th the distance will be 15,20,96,155 km. This farthest point from Sun is called Aphelion. The angular size of the Sun which we measure in degrees at perihelion is 0.542018074degrees. And as we know the orbit is almost circular the difference in angular diameter of Sun from Perihelion to Aphelion is very small. At Aphelion the angular diameter is 0.5243709741degrees. 

 If we compare this to Mercury, the perihelion distance is 46,000,000 and this gives the angular diameter of Sun Seen from Mercury at 1.73434325degrees. The Aphelion distance of Mercury is 69,820,000 and this gives the angular diameter of Sun as seen from Mercury at 1.14247784degrees, almost half a degree difference. You can compare this to earth and Sun.

26 September 2017

Remembering names of Moon Phases

We are seeing moon getting brighter in the evening sky every day from the last new moon on 20th. With each passing day more area of the moon is illuminating and we can see lot of features on the moon. Many people have confusion when it comes to naming the phases of the moon, so here is a something useful to remember the names.

First, we start with couple of days after the new moon, the phase we are seeing is crescent phase a thin sunlit part of the moon and since the sunlit part is getting bigger with passing days we call it waxing crescent. This is from old English meaning something that grows, here the brighter side is growing.

Waxing crescent moon. Sunlit part towards west.

Next is First quarter, this phase happens when the Sun, earth and the moon align in such a way that Sun and moon are at right angles as seen from earth. We can seen this in the evening sky, on the evening of the first quarter at sunset, we can measure the angle between Sun at the horizon and the moon and the angle will be 90 degrees or close to 90 degrees depending on actual time of alignment.

First Quarter moon. Sunlit part towards west.

Between First quarter and Full Moon, when more then half of the moon is lit up by sunlight we call it gibbous phase and since the brightness is increasing its waxing gibbous phase.

Waxing gibbous moon. Sunlit part towards west. 

After the first quarter comes the Full moon phase, which we are all familiar with, in astronomy we call moon is in opposition. The moon and the sun are on the opposite sides of the earth, if they are exactly aligned then we have a lunar eclipse.

Full moon

From new moon phase the moon was in the sky before the sunset and would set late as the days passed until Full moon when it rises at sunset. After this the moon rises late after sunset and the brightness starts decreasing.

Waning gibbous moon. Sunlit part towards east.

Since its decreasing and more then half is lit, but not fully lit, we call it waning gibbous phase. After that moon reaches last quarter again attaining right angle with the sun. This means the moon will by high in the sky at sunrise. The next phase in waning crescent where we see thin lit surface of the moon and finally reaching new moon phase.

From new moon to full moon, we see the lit part is towards west and from full moon to new moon, we see the lit part towards east, the lit part will be towards the sun.

Now I think there is no problem in telling the phases below,

Last Quarter moon. Sunlit part towards east.
Waning crescent moon.Sunlit part towards east.


01 March 2017

Venus Watch at ABAA

After I announced about Venus being in its brightest phase many people showed interest in looking at Venus through telescope following Sunday. On Sunday we were happy to see public and members coming in large numbers to watch Venus in crescent phase. After sunset we put the telescope out and focused on to Venus, members of ABAA were present there in showing and explaining all about Venus. Using the 6 inch telescope of ABAA people saw amazing sight of the crescent phase, and immediate reaction of most people was “is it Moon?”, that lead to discussions and members helped them in getting idea of orbits and phases of inner planets.

ABAA is open on all Sundays from 5:30pm and always ready to show the celestial wonders to people and members showing interest. People can come and see moon and planets, learn about them and also learn about telescopes and how to use them. Observing through a telescope has steep learning curve, its best to learn about them before buying or going out for observing and ABAA can really help in that section. ABAA can help in choosing the best telescope for you or help you in building your own telescope, you can come to ABAA on any Sunday evening and discuss your needs.

Here are photos of Sunday sessions of Venus watch



15 February 2017

Watch Brightest Venus on Friday

After Sunset in the western twilight sky we see a bright star outshining all the starts in the evening sky, this is the planet Venus. The visual apparent magnitude of the planet Venus is now -4.6 and the apparent magnitude of brightest star in the night sky, Sirius, in the constellation of Cains Major is -1.46 this makes Venus 18 times brighter than Sirius. 
Brocken Inaglory, Venus-pacific-levelled, CC BY-SA 3.0
On February 17th Venus will reach its brightest crescent phase and this is called Greatest Illuminated Extent, the amount of illuminated crescent and the angular diameter of the planet Venus. Venus will have an angular diameter of 39 arc seconds and fraction of illumination is .273 of the angular diameter. After this day the illuminated side will start decreasing and we will see the crescent getting thinner. By second week of March the illuminated fraction will be only .085 of the diameter of the planet and magnitude would have come down to -4.4 still brightest in the evening sky. 

View Through the Telescope on 17th of Feb

View Through the Telescope on 10th March

The planet Venus will slowly fade into glare of the Sun and will reach inferior conjunction on March 25th. In April we will see Venus in early morning sky before sunrise and again the Greatest Illuminated Extent will happen on April 30th. Time to take out the telescopes and observe Venus in coming days, if you don't have one you are always welcome at ABAA on Sundays evening and see the Venus through our telescope. Venus sets at 9pm now and in middle of March the planet will set at 7:30pm.