23 September 2014

Happy Equinox Everyone

Today, September 23rd at 7:51am, Sun reached Zero declination, if we observe Sun’s position at Equator on this day, we will see Sun will be exactly overhead at noon. In coming days if we keep observing the Sun’s position we will notice that Sun is moving towards south with each passing day. Sun will reach southernmost point on December 21st. 
Sun reaching the Zero declination point is called Equinox. This happens twice in a year; first one will be on March 20/21 and second will be on September 23rd.
From March, the Sun will be in northern hemisphere of the sky reaching northern most point on June 21st at 23.50 and returning to Zero declination in September. From September Sun will be in Southern hemisphere of the sky reaching extreme south point of -23.50 on December 21st , from December Sun will start moving towards north and reach Zero declination on March 21st .
March Equinox is called Vernal Equinox and September Equinox is called Autumnal Equinox.

02 August 2014

Daytime Occultation of Moon and Saturn August 4th

Daytime occultation, second of this year will be of Moon Occulting Saturn. Earlier this year in February we saw Moon occulting Venus in the daytime, both Venus and Moon were easily visible because of their brightness.  

On August 4th, we will see Moon occulting Saturn in the daytime, but we will need telescope to see Saturn as the surrounding sky will be very bright.
Stellarium generated image.
The occultation will begin 2pm IST as seen from Bangalore, its always a good practice to start observing as early as possible. Saturn will disappear from dark side of the moon and emerge from the sunlit side at 2:40pm.
Do not try to locate Saturn with the telescope if you are new to finding planets during daytime. As bright Sun will be very close, accidental viewing of Sun through the telescope will be disastrous to the eye.
Here are the times and positions of the Planet for those who have setting circles
August 4th Occultation.
Right Ascension
14:00 Start
14:40 End

Its a matter of luck to have clear skies in this monsoon season, but its always better to be prepared and hope for the best. 
Clear Skies 

14 July 2014

Mars and Spica so close yet so far

Mars and Spica will be just one degree apart today evening. We can see the red planet mars and Spica shining bright in the southwest sky after sunset. The pair is easy to spot due to their colour difference, mars will be red and south west of mars will be blue-white star Spica. Although they appear just one degree apart from each other, the closeness ends there.
The distance from earth to these two celestial bodies are truly immense.  Mars after coming close earth on April 14th, it is slowly moving away from us and now mars is close to one AU.  Spica is at a distance of 15810494 AU form us, one AU is the distance between earth and Sun, which is 150 million kilometres. As we can see, the difference is immense. If the skies are clear, in the evening, we will enjoy the view and now we know they are so close yet so far.

07 July 2014

City Constellations

It happens every time, we attend an astronomy talk or see an astronomy documentary and after finishing that when we come out, we always involuntarily look up at the night sky. We expect to see star-studded sky as seen in that talk or documentary, diamonds in the sky. 
Credit: ESO
However, as it turns out due to high light pollution, this is what we end up getting in the city skies. Light pollution is increasingly taking stars away from us. There is no immediate solution for the light pollution issue although efforts are on around the world.
Until then we have make use of what few stars we have under city conditions. I always advice new comers interested in night sky, to go and get familiarize with the constellation whenever they get time. Although sky may look disappointing at beginning with hand full of stars in the night sky, we can in fact make that work in our favour.
It will be easy to start and recognise the basic pattern of the constellation when there are few stars. Once we have the basic shape with the help of bright stars, when we have dark skies, it will be easy to pick up rest of the constellation.
We will take couple of examples here of constellations, bright ones that can be seen easily under city conditions.  These days at 8pm we can see the bright constellation Ursa Major in the north, even with light pollution its easily spot seven stars in the constellation. Now this forms the outline of the Ursa Major, if we are familiar with the bright stars, under dark skies we can pick up full constellation, which will help in finding deep sky objects.
We can see only few stars in Ursa Major, but I am sure you can spot all the seven bright stars.
Once we are familiar with bright stars, we are ready for dark skies; here is how it will look under light pollution free conditions.
Along with bright stars, we have many stars that complete the constellation.
Like Ursa Major, there are similar constellations that we can spot even with light pollution, and spending some time getting to know the bright stars and the constellation outline will really help when we have dark sky conditions, sometimes it is difficult for newcomers to recognize the patterns with thousands of stars around.
 Cygnus also has bright stars that make the constellation easy to pick up in light polluted areas. Deneb is the brightest star in the constellation and the stars that make the outline are close to or brighter than third magnitude. The constellation lies in the mily way band and its good idea to use light pollution to our advantage and get familiar with the basic shape of the constellation, under dark skies it is a highly star-studded region. Seeing the constellation under darks skies shows what light pollution is doing to our night sky.
Under Dark Conditions:
One more wonderful constellation is Scorpius in the south. Along with Scorpius, the constellation of Sagittarius lie in the most star rich region of the night sky, as these two constellations lie in the region of centre of our galaxy, the milky way. These two are easily visible from the city skies, shows in a very frustrating way on how light pollution is affecting astronomy enthusiast. This is a region with numerous star clusters and nebulae and a favourite region for astrophotographers.
Under Dark conditions we can see the milky way...
These are just couple of examples to show how we can use light pollution to our advantage and to show how it is affecting our night sky.
With a basic star map, keep practicing in identifying the constellations with the help of bright stars, which will really help under dark skies.

01 July 2014

Occultation Demonstration setup at ABAA

At ABAA, we try to make concepts of astronomy simple so that everyone can visualise and understand. This setup I made at ABAA using materials that we can find easily and we can build this at very low cost and fast. The setup is to show occultation concept, consists of a motor, a light source that acts as a star and a dick attached to motor to show an object coming in front of the star, Occulting the star.

Moon Occulting Venus 

Occultation is an astronomical event when one astronomical object comes between observer and a distant object. For example, moon in its journey in the night sky comes in between background stars and us, this we call moon is occulting stars.

I made the video with external lights on and off, to show the setup working. With lights on, we can see the disk coming in front of the light source and Occulting the Star and with lights turned off we can simulate night sky and we can measure star light disappearing and re appearing. Using different sizes of disc, we can show that occultation helps in determining the size and shape of an object using the time of appearance and disappearance to the star.  

30 June 2014

Moon at Apogee

We end the month of June with Moon being farthest to earth today, 30/06/2014 at a distance of 4,05,932km. The 3-day-old crescent moon will be an amazing site in the evening twilight. After sunset crescent moon will be high in the western sky at an altitude of 30degrees and will set at 9pm.

Graphic: Stellarium 

Moon orbits the earth with an eccentricity of 0.0549, not a circle, and that makes moon to have farthest and closest points from earth.  Apogee is when Moon is farthest from earth and Perigee is when moon is closest to earth.

Moon on 30th June will be at Apogee at a distance of 4,05,930km from earth with an angular diameter of 0.49degrees.  As moon continues in its orbit, it will reach closest point to earth, Perigee, on July 13th at a distance of 3,58,260km and this will make the angular diameter of moon 0.55degrees.

As we can see, the difference is too small to be observed without any reference, best way to measure this difference is to take photographs of moon at Apogee and Perigee and compare the prints. Today if the skies are clear in the evening sky, go out and enjoy the crescent moon.

15 May 2014

Comet develops a coma seen by Rosetta

This series of images taken by Rosetta shows the development of Coma around the nucleus of comets. As the comet moves closer to Sun, the nucleus gets heated and this causes the ice particles to evaporate and sublimate around the nucleus as a gas cloud. More closer it gets to sun, more evaporation happens and the coma expands.

A sequence of images showing comet 67P/Churyumov–Gerasimenko moving against a background star field in the constellation Ophiuchus between 27 March and 4 May 2014, as the distance between the spacecraft and comet closed from around 5 million to 2 million kilometres. The comet (and Rosetta) were between 640 million km and 610 million km from the Sun during the sequence. The comet is seen to develop a dust coma as the sequence progresses, with clear activity already visible in late-April. Exposure times are 720 seconds for each image, taken with the OSIRIS Narrow Angle Camera.


24 February 2014

Daytime Venus Occultation

Daytime skies are little boring to people with only one star to observe. Occasionally we get treats like solar eclipse and transits, amazing celestial daytime events that make the long wait worthwhile.  On 15th February 2013, a meteor entered earth atmosphere and as it burnt up, it lit up the skies of Chelyabinsk, Russia. Apart from these rare events, the actions in the skies hide behind the glare of the sun during the day.
Lunar occultation of stars and planets are events normally associated with night sky. Moon occults stars and planets during daytime too but we cannot see these events because, the bright Sun outshines everything in the sky. However, every rule has an exception; we see Moon during daytime without any difficulty, and with practice, we can also spot Venus with naked eye and it is an easy target for telescope in the daytime.
This February 26th there is an event involving Moon and Venus during daytime(Readers of AKASHA will already know this from JAN-FEB issue). Moon will occult Venus on this day. Occultation of planets by Moon is rare event, for example from Bangalore the next Occultation of Venus by Moon will be in 2023 March 24th.
We have to take Extreme precaution when planning to observe the event, equipment  always has be pointed away from the Sun. Even very small duration exposure to Sun’s rays through telescope or binocular can damage the eyes permanently.
The brightness of both Moon and Venus makes it good challenge for daytime occultation observation with Moon at crescent phase and Venus close to half phase at -4.5 magnitude, will be a great sight through the eyepiece.
Venus will disappear from the lit part of the crescent Moon and reappear from the dark part of Moon. Venus will be close to 15 minutes of arc from the brighter edge of the moon at 10:30am IST, both should fit in to the same field of view in a 6-inch telescope.
Here are the times and altitude of Moon for February 26th Occultation:
Venus will disappear at 11:05am IST and at this time the altitude of Moon will be 53 degrees.  Venus will reappear from the darker side of the Moon at 12:29pm IST. The altitude of Moon at the reappearance of Venus will be 38 degrees.
Hope for clear skies.

03 January 2014

Earth at Perihelion:

Earth will be at Perihelion on 4th of January; this is the closest distance from earth to Sun. At perihelion the distance between earth and sun is close to 147.09 million km. Since Earth’s orbit eccentricity is very low at 0.016 which is very close to circle the distance between perihelion and aphelion (furthest point from Sun) does not differ much. The Aphelion distance of earth and Sun is 152.10 million km, making the difference just 5.01 million kilometres. This is not much to cause any problem to us, but due to proximity to sun earth receives 7% more sunlight.
The angular size of the Sun seen from earth does not differ much during perihelion and aphelion due to low eccentricity for earth’s orbit. The sun subtends an angle of 0.54183 degrees during perihelion, and at aphelion (furthest distance from sun) the angle subtended is 0.52398 degrees the difference is very small at 0.01785 degrees.
When compared with Mercury which has highest eccentricity of 0.2056 the difference in angular size is apparent during perihelion and aphelion.


Max.Angular Dia
Min.Angular Dia


Say Hi to Sun when you go out on January 4th!