SuperMoon of 2014

Have you ever wondered about or even tried to look at the size of the Full moons in different times throughout the year? You may ask why? Moon goes around the earth in an elliptical orbit so it is not at the same distance from us all the time (as its not a circle), as a result it appears to grow and shrink (not too much) as seen in the skies (though it does not grow or shrink physically!!).

And its more apparent on the day of the full moon when we see the whole disk illuminated. Now just imagine seeing a bigger full moon - it means that moon is at perigee (point nearest to earth) or near perigee at that time. As its a bigger moon then there has to be a name to it as we humans are very much inclined towards giving names to each and every thing!! They call it SuperMoon!! And this word was coined recently in late 70’s(if we talk about time scales in astronomy).

And its interesting to know that SuperMoon is a word which was not coined by astronomers but by an astrologer , Richard Nolle, who is credited with coining the term supermoon. He arbitrarily defines this as

. . . a new or full moon which occurs with the moon at or near (within 90% of) its closest approach to Earth. But for us its the Perigee full/new moon happening at the exact time of perigee so there is no ambiguity about the definition. Now our new definition becomes - . . . a new or full moon which occurs with the moon at its closest approach (perigee) to Earth. The technical name is the perigee-syzygy of the Earth-Moon-Sun system. We astronomers do not use the term “Super Moon” but to take it among the masses its a catchy word! As we have Supermoon, there has to be Micromoon which happens at Full moon at the time of Apogee. And if you happen to click both the moons with same setup, you would find a drastic change in diameter which is around 14% and thats quite large!!

Now lets see how many Full Moons fit into this definition. We have not taken New Moon in this category as it can't be seen at all!!! But a supermoon at new moon at the time of the eclipse play a different game, that i leave to you people to ponder. 

In present century we have the following SuperMoons which fit in the definition of Full Moon and Perigee moon happening exactly at same time (Perigee happening at F +/- 0 h):

2011 356577 km    3/19/2011    

2012 356953 km     5/6/2012   

2013 356989 km     6/13/2013   

2014 356896 km      8/10/2014   

2034 356447 km     11/27/2034   

2054 356511 km     1/24/2054   

2073 356720 km    5/23/2073   

2094 356867 km      8/26/2094   

2095 356685 km      10/13/2095   

 

There are quite a lot of more so called supermoons if we relax our stringent rules to allow for few hours +/- difference between Full Moon and Perigee Moon

We come back to our discussion about supermoon again. You can see that there is one supermoon coming on 10th August 2014. So what big deal about it? Well On that day the Full Moon will be approximately 14% bigger than the Full Moon on Apogee and will be 30% more brighter than it. If you plan to click the image on that day then make sure that you click with same setup another image on March 5th next year when we have the Full Moon happening near to Apogee and then you can actually calculate the difference we have talked about. Above Image is an example which we did in 2011. And interseting when you see the above image and the once you will take, you will see the phenomenon which we call as liberation of the Moon, well that's another story to tell!!!! But Do enjoy the illuminated Moonlight dinner on that night with your near and dear ones!!

Sun as seen at two vantage points in the earth's orbit

We all have learnt that earth while going around the sun in an elliptical orbit comes closer and goes farther away from the sun and in an year during its orbit, we have two days perihelion (earth being closest to Sun) and Aphelion (Earth being farthest away from the sun).

So that in layman's term means we should see Sun slightly bigger on the day of Perihelion day and slightly smaller on the Aphelion day (as compared to average distance what we call as the 1 Astronomical Unit). To put that to visual understanding, I clicked one image of the sun near Aphelion day on 6th July (though 4th July was Aphelion day but clouds did not permit me to click the sun, anyways in 2 days earth hasn't moved much as far as astronomical distances are concerned) and my next target is to click it on Perihelion day on around 3-4 January and then compare the size of the sun's image. While searching through my archives, I found that I clicked few pics of sun during December last year with same set of equipment. That was on 1 December, 2013. So I tried comparing these two images just to get a visual idea as how much the difference is there. You can have a look at the combined image and see how big and small sun looks while being at perihelion and aphelion. It is quite a visual treat to see the difference, and also a nice tool to teach our educators and students as how and why we have longer total solar eclipses in July and not in January!! Well that's another point to ponder about!!

For those who are technically aligned, here are the numbers to play with during the days i took the image

Canon 500D, 250 mm FL

On 6th July, 2014:

earth distance from Sun: 1.017 au or  152.1 million kms

Apparent Size of Sun:  31 arc min  26 sec

On 1 December, 2013
Earth distance from sun: 0.9859 au or 147.5 million kms
Apparent Size of sun:  32 arc min  25 sec

So we have almost 1 arc min difference in apparent dia of Sun

Have a look at the image and enjoy!!

Written by CB Devgun, President, SPACE Foundation

Earth farthest from sun

Earth farthest from sun

4^th July, 2014 – Aphelion day

We all know that earth goes round and round around the sun. Well it almost does that but there a small twist to the statement. It ALMOST goes in a circle. Thanks to Kepler, who gave us insight into how these wanderers go around the sun, all planets in our solar system travel around the Sun in elliptical orbits. It's Kepler's 1st Law. Some planets go around sun in more elliptical orbit than others. Most planets follow orbits that are more elliptical than Earth's orbit. So in a sense earth’s orbit is closest to being a circle in the whole solar family. Even then the slight deviation from a circle gives us two positions of earth when it’s farthest and closest to sun.

The orbits of Mercury (red), Earth (blue) and Mars (black). The solid lines indicate each planet's elliptical path around the Sun. The dotted lines show circular paths with the same mean separation from the center. Earth is almost exactly the same distance from the Sun at aphelion and perihelion, but the orbits of Mars and Mercury depart significantly from a circle.

On July 4th, 2014 at 15 hrs UT or at 20:30 IST, the Earth is at its farthest point from the Sun (aphelion), the distance at that time is 152,097,040 km, which is about 5 million km further away than its closest point in early January. It does appear strange that in July we have earth farthest away from sun. Isn’t it? And to top it all total energy received from sun by the globe on aphelion is around 7% less than what we receive when it is closest to the sun (perihelion).

Now you may ask if sun is farthest then why is the temperature not going down?  There are many reasons to it. Blame it on the tilt of earth’s axis. Actually, our seasons are determined by the tilt of the Earth and not by how close the Earth is to the Sun. Well that’s another story to tell.

Sunlight raises the temperature of continents more than it does oceans. (Land has a lower heat capacity than water) In July (aphelion) the land-crowded northern half of our planet is tilted toward the Sun. Aphelion sunlight is around 7% less than sunlight at perihelion, but it nevertheless does a good job warming the continents. In fact, say climate scientists, northern summer in July when the Sun is more distant than usual is a bit warmer than its southern counterpart in January.

So enjoy the warm or rather scorching sun (or cloudy day!) on 4^th July as a celebration to the Aphelion day.