Sun Farthest from Earth

Sun is far away and still its hot summer in the northern hemisphere. This is the question many have, relating to the distance to the Sun and seasons on earth. The seasons on earth is due to the tilt of the earth at 23.5 degrees. Due to this tilt northern and southern hemispheres are exposed to the Sun during certain months of the year. While Northern hemisphere is exposed to more sun during March to September, the Southern hemisphere will be going through winter and situation reverses after September. From September to March Southern hemisphere is exposed to more Sun and it will be Summer in southern hemisphere while northern hemisphere will be experiencing winter. This is how seasons change on earth.

Earth Tilt and Seasons Credit:CC

Earth makes one full revolution of the Sun in approx 365.256 days. In this orbit around the Sun there are two points where the Sun and earth are closest, called Perihelion, and the other point is the farthest distance between Sun and earth and this point is called Aphelion. The two points Perihelion and Aphelion exists because the orbit of earth around the Sun is not a circular one, it orbits in an elliptical orbit but the difference is very small at an eccentricity of 0.0167. This small elliptical orbit makes the earth”s perihelion distance close to 147 million kilometres and aphelion distance close to 152 million kilometres.

Earth elliptical orbit Perihelion and Aphelion  Credit: ABAA

Earth reaches perihelion on January 5^th and aphelion on July 4^th. During Perihelion the Sun is in the constellation of Sagittarius and earth will be moving around the Sun at a velocity of 1,08,900km/h and has an angular diameter of 32m32s of arc. During Aphelion on July 4^th Sun will be in the constellation of Gemini and earth will be moving around the Sun at a velocity of 1,07,208km/h and will have angular diameter of 31m28s of arc.

Sun Angular size at Aphelion and Perihelion  Credit: ABAA

Happy Observing and Clear Skies.

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Partial Solar Eclipse Volunteering of ABAA members at Planetarium on June 21,2020

The Partial Solar Eclipse on June 21st was a sober affair at Planetarium. This was due to social distancing in the middle of Corona virus situation. Planetarium had arranged live streaming of the eclipse from different types of telescopes. Few ABAA members were invited to volunteer for the event and handle the telescopes. Members following rules of social distancing managed the event very well, taking pictures of the eclipse, guiding the telescopes, helping the press to get good images of eclipse and also giving information on eclipse. Members had mixed feeling about the eclipse, on one side they were happy to see the eclipse without cloud cover at the same time they were feeling sad that they could not share the experience with public. Here are few picture of members at Planetarium during the event.

Projecting the Sun on to a wall or on a white cardboard paper is one of safe methods for observing Sun during eclipse and also while observing Sunspots. Here a projection box is attached to the Planetarium's Telescope, the box has a semi transparent paper in the middle of box where the image of the Sun forms and it can be viewed safely. ABAA member Naveen is headlining the telescope.

One of the live streaming of the Partial Solar eclipse was done from the 6 inch refractor telescope which has a massive focal length of 90 inches. It is coude focus telescope. The image is very stable and does not move as telescope tracks the Sun or any celestial object. This is the main advantage of coude focus.

ABAA helps members to make their own telescope and assemble the telescopes. This is something ABAA is regularly doing from four decades. Members had got their own telescope for the event, here you can see a member using the telescope, the front end of the tube is covered with solar filter making safe to observe the Sun. 

ABAA member is guiding the telescope at Planetarium. This is a favorite type of telescope mount used by amateur astronomers for observing the celestial objects. ABAA is making this kind of mount and using it from couple of decades now. It is easy to make and easy to use, even in deep sky observations.

Binoculars are one more favorite optics of amateur astronomers and in fact ABAA recommends binoculars for starting out in astronomy. Because of its large field of view it makes a good choice. Here the binoculars lens are covered with Solar filters for safe viewing. There are hundred of celestial objects that can be viewed through binocular at night, even small ones like 10X50.  

Another interesting setup at the event was heliostat, a system of mirrors arranged in a particular way which makes the image of the Sun fall on the wall and keeps the image study. The mirrors tracks the Sun but image of the Sun is kept in one place.    

ABAA members do lot of Astrophotography too, and members do discuss lot of techniques involved in Astrophotography at ABAA regularly. Here members are capturing eclipse event through long focal length lens with filters. The filter casing was home made by members, telescope making and astrophotography involves lot of DIY which makes the hobby more exciting...

It was a good session at Planetarium, clouds did not ruin the event and members could enjoy the event for the most part.

Members have taken lot of good pictures of the eclipse, next blog post will feature the efforts of ABAA members in capturing the Partial Solar Eclipse.

Be safe and Clear Skies.

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Partial Solar Eclipse from Bangalore 21 June 2020

After the partial solar eclipse on December 26, 2019 which was visible from Bangalore, now after six months we have one more partial solar eclipse visible from Bangalore. 

On June 21^st Sunday we are going to witness the partial solar eclipse in the morning sky. The eclipse will start at 10:12:56 and at this time Sun will be 58 degrees above the eastern horizon. With proper solar filter or using different safe observing methods its a good idea to start observing couple of minutes before the given time. The start of eclipse is when you see moon disc starts coming inside Sun's disc, this is called first contact, when Sun and Moon discs touch each other. As we observe the dark disc of moon will start covering more and more of the Sun's disc and after reaching a certain point the disc of moon starts to move away. This is called Maximum eclipse, the point or time when Moon covers the maximum surface of Sun's disc. This will occur at 11:47:38 and at this time Sun would have moved higher in the sky at close to 77 degrees from eastern horizon. As we continue observing or photographing we will see that the dark disc of moon getting smaller and it will come out of Sun's surface completely at 13:31:44 marking the end of eclipse, the time of moon disc coming of Sun is called last contact. At this time Sun will be in the western part of the sky at close to 70degrees from the western horizon. 

Solar Eclipse Bangalore 21 June 2020

As we all know June 21st is Solstice, on this day Sun's reaches the northern most point from equator at 23.5degrees. From June until December Sun will move in southern direction. Sun on June 21st will be on the border of Taurus and Gemini constellations. The borders of constellations are set by International Astronomical Union (IAU). The shapes and borders differ in different regions and cultures, Astronomers use the shapes and borders set by IAU.

This eclipse is an annular eclipse and parts of north India will witness the ring of fire, that is Sun will appears like a ring with moon obstructing the disc of Sun leaving only edges around the Sun glowing. The reason for this ring is because of different apparent sizes of Sun and moon. These two objects subtends an angle of half of degree in the sky, if one of them is smaller or bigger we get annular eclipse. If moon has an angular diameter smaller then the Sun we have annular eclipse as moon cannot cover the entire disc of Sun. Here are the angular sizes of Sun and Moon on June 21^st Sun will have a of Diameter: 31'28.4" and Moon will have a Diameter: 31'16.0". As we can see Moon is smaller and this is the reason for annular eclipse. The difference in sizes happens due to elliptic orbit of earth around the Sun and elliptic orbit of moon around the earth. 

Eclipses are rare and we have to travel long distances to be in the center path, we have to go to north India around Kurukshetra to see the ring of fire, annular eclipse on June 21st. Last year on December 26^th we had to go to Kerala and Tamil Nadu to witness the annular eclipse. Since we are unable to travel in these lock down situations, we will have to wait until May 21^st 2031 to enjoy the solar eclipse in India. The path of annular in 2031 will be in south India.

If some one decides not to leave Bangalore for eclipse but wants central path of eclipse to come to Bangalore, they will have to wait for the year 2085. Yes, on June 22^nd 2085 people in Bangalore can see the ring of fire, the annular eclipse. Mark your calendars, it just 65 years away.

For now we have to be content with partial eclipse on Sunday and hope for clear skies. Happy observing every one, observe safely with proper filters or pin hole camera projection on the wall. NEVER LOOK AT SUN DIRECTLY.

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Zero Shadow Day in Bangalore

Tomorrow 24^th of April as every year Bangalore will witness Zero Shadow Day. Sun as we all know appears to move in north and south directions which we call uttarayana and dhakshinayana. At present Sun is in northern motion and will reach the northern most point of 23.5 degrees on June 21^st . 

During this motion, tomorrow Sun will be exactly overhead at local noon in Bangalore. To find out when Sun will be exactly overhead on your location just check the declination of Sun, if Declination of Sun and latitude of your location is same then on that day Sun will be exactly overhead at local noon. 

To observe the Zero Shadow Day you need a vertical reference like a pole which is straight and perpendicular to the ground, this can be pencil, a small nail, a water bottle etc,. Since we are all in lock down, we can spend few minutes observing this phenomenon. Setup your experiment well before 12 noon and start observing from 12 noon to 12:30 and you will see the shadow move from one side of the reference to other side and with no shadow at 12:17pm. 

Hope skies will be clear and you all will enjoy this activity with full family.

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