[June 21] – June Solstice

The Solstice is an astronomical event that happens twice, once in summer and once in winter, each year when the Sun reaches its highest position in the sky as seen from the North or South Pole. During Solstices the tilt of the axis of the Earth (with respect to the Sun) is the maximum at 23° 26′. The International Space Station(ISS) generally reaches a period of full illumination favoring the northern hemisphere around this time.

Summer Solstice

During June it is Summer Solstice in the Northern hemisphere and Winter Solstice in the Southern hemisphere. In other words during June Solstice it is summer time in the UK, the USA, Canada, Russia, India and China and it is the longest day of the year while it is winter time in Australia, Argentina, Chile, New Zealand and South Africa and it is the shortest day of the year.

Summer Solstice Time in India:

Summer Solstice Time = 21st June 04:04 Hrs
Sunrise = 05:42:54
Sunset = 18:53:05
Day Duration = 13 Hours 10 Mins 10 Secs 

Note:  Grishma Ritu (Indian Summer) ends with Summer Solstice and Varsha Ritu (Indian Monsoon) starts with Summer Solstice.

Also readWitness the solstice spectacle at these ancient structures

[May 21] – Full Moon & Seasonal Blue Moon!

What is a blue moon?

The term blue moon does not refer to any change in the Moon’s color, but is traditionally given to the third full moon of four full moons to fall within one of the Earth’s seasons (defined astronomically to start and end on the Earth’s solstices and equinoxes). Normally, only three full moons occur in each of the Earth’s four seasons each year. However, there are on average 3.11 full moons within each season. This is because full moons occur on average once every 29.5 days. As a result, blue moons occur on average once every 2.7 years. So, the third full Moon falling between the March 21 (Spring Equinox) and June 21 (Summer Solstice) which occurs this year on May 21st would be called “seasonal blue moon”. This type of Blue Moon is found only in February, May, August, and November, one month before the next equinox or solstice.

In more modern usage, the term blue moon is often used alternatively to refer to any full moon which is the second to fall within a single calendar month. This type of Blue Moon can occur in any month but February, which is always shorter than the time between successive full Moons. This usage is originally seems to have stemmed from a misprint in Sky & Telescope magazine in March 1946. This mistake caused widespread misunderstanding until it was finally corrected in 1999. However, coincidentally this blue moons also occur once every 2.7 years by that definition, since according to both definitions, a blue moon occurs whenever 13 full moons fall within a single year-long period. Full moons were traditionally given names such as the harvest moon and the hunter’s moon, when ran in sequences of three names through each of the seasons. Since there were only three of these names for each season, a fourth full moon was left without a name. So, the name Blue Moon.

Can’t we see real blue moon..?

One way to make a blue moon: use a blue filter. The date of a full moon, all by itself, doesn’t affect the moon’s color.

Moon captured using blue filter

But, there was a time, not long ago, when people saw blue moons almost every night. Full moons, half moons, crescent moons–they were all blue, except some nights when they were green. The time was 1883, the year an Indonesian volcano named Krakatoa exploded. Scientists liken the blast to a 100-megaton nuclear bomb. Fully 600 km away, people heard the noise as loud as a cannon shot. Plumes of ash rose to the very top of Earth’s atmosphere. And the moon turned blue. Krakatoa’s ash is the reason. Some of the ash-clouds were filled with particles about 1 micron (one millionth of a meter) wide–the right size to strongly scatter red light, while allowing other colors to pass. White moonbeams shining through the clouds emerged blue, and sometimes green. Other less potent volcanos have turned the moon blue, too.

People saw blue moons in 1983, for instance, after the eruption of the El Chichon volcano in Mexico. And there are reports of blue moons caused by Mt. St. Helens in 1980 and Mount Pinatubo in 1991. The key to a blue moon is having in the air lots of particles slightly wider than the wavelength of red light (0.7 micron)–and no other sizes present. This is rare, but volcanoes sometimes spit out such clouds, as do forest fires: Yes…smoke from forest fires can cause blue moons, too. If any of those fires produce ash or oily-smoke containing lots of 1-micron particles, the Blue Moon there could be blue. More likely, it’ll be red. Ash and dust clouds thrown into the atmosphere by fires and storms usually contain a mixture of particles with a wide range of sizes. Most are smaller than 1 micron, and they tend to scatter blue light. This kind of cloud makes the Moon turn red; indeed, red Blue Moons are far more common than blue Blue Moons.


[May 9] – Transit of Mercury

Our solar system’s innermost planet, Mercury passes directly in front of the sun on May 9, 2016.

What causes a transit of Mercury? 

– Only planets that orbit the sun inside of Earth’s orbit – Mercury and Venus – ever transit the sun, as seen from Earth. If Mercury orbited the sun on the same plane that Earth does, there would be three to four transits of Mercury each calendar year. However, Mercury’s orbital plane in inclined at 7 degrees to the ecliptic (Earth’s orbital plane). That means when Mercury swings in between the Earth and sun at inferior conjunction (see illustration below) every four or so months, Each time Mercury circles the sun in its short and swift orbit of 88 Earth-days, Mercury travels north of the ecliptic for about half its orbit, and south of the ecliptic during the other half of its orbit. Twice in its orbit, Mercury crosses the Earth’s orbital plane at points called nodes. When Mercury is traveling from north to south, it’s called a descending node; and when Mercury is traveling south to north, it’s called an ascending node. Whenever Mercury crosses a node in close vicinity to reaching inferior conjunction, a transit of Mercury is inevitable.

Mercury crosses its descending node at inferior conjunction on May 9, 2016, to present a rather rare transit of Mercury, only happening 13 to 14 times per century.

Dates for transits of Mercury in the 21st century!

Descending node transits can only happen during the first half of May, and ascending node transits in the first half of November. At other times of the year, Mercury at inferior conjunction would either pass north or south of the sun’s disk.

May 7, 2003
Nov 8, 2006
May 9, 2016
Nov 11, 2019
Nov 13, 2032
Nov 7, 2039
May 7, 2049
Nov 9, 2052
May 10, 2062
Nov 11, 2065
Nov 14, 2078
Nov 7, 2085
May 8, 2095
Nov 10, 2098

Who will see the May 9 transit of Mercury?

As shown on the worldwide chart below, the transit will be visible (at least in part) from most of the globe, with the exception of Indonesia, far-eastern Asia, Australia and New Zealand. Mercury takes some 7.5 hours to cross the sun’s disk, and this transit of Mercury is entirely visible (given clear skies) from the eastern half of North America, most of South America, Greenland, Iceland, far-western Africa, western and northern Europe, plus the Arctic.


From Hyderabad, India


Equipment needed to watch a Mercury transit:

Mercury’s diameter is only 1/158th of that of the sun, as seen from Earth. That’s why we recommend using a binoculars or telescope with a magnification of 20 and above for witnessing the event. Plus your binoculars/telescope must be equipped with a safe solar filter to watch this transit, or else you risk permanent eye damage. Click here to learn how to view the sun safely

Find the public show events happening near you in India:

Watch the transit of Mercury online:

[May 5, 6] – The Eta Aquarids meteor shower

Halley’s Comet is the source of the Eta Aquarid meteor shower. Every year, our planet Earth crosses the orbital path of Halley’s Comet in late April and May, so leftover comet dust smashes into Earth’s upper atmosphere at nearly 240,000 kilometers per hour and light up the nighttime as Eta Aquarid meteors.

By good fortune, in 2016, the moon turns new at the Eta Aquarids meteor shower peak during May 5th & 6th. This origin point of meteor shower on the sky’s dome is called the radiant of the meteor shower. For Eta Aquarids it is near the faint star Eta in the constellation Aquarius the Water Bearer. Hence, the meteor shower is named in honor of this star.

Halley Orbit

The radiant comes over the eastern horizon at about 4 a.m. local time. For that reason, the hour or two before sunrise tends to offer the most Eta Aquarid meteors, no matter where you are on Earth. However, this shower favors the Southern Hemisphere, and is often the Southern hemisphere’s best meteor shower of the year. At northerly latitudes  – the meteor numbers are typically lower. But watch on May 7 as well! some meteors may fly in the dark hour before dawn for a few days before and after the predicted optimal date. Give yourself at least an hour of viewing time for watching any meteor shower. Meteors tend to come suddenly. Also, it can take as long as 20 minutes for your eyes to adapt to the dark. You need no special equipment to watch a meteor shower, but a little luck always helps. Meteor watching is a lot like fishing. Sometimes you catch a good number of them and sometimes you don’t.

Screenshot (02-May-2016 11-16-03 PM)
Google Sky Map screenshot of radiant point

[May 6] – Shortest lunar month of 2016 begins

Lunar month is just the duration between successive new moons called synodic month. Although the lunar month has a mean period of 29.53 days (29 days 12 hours and 44 minutes), the actual length varies throughout the year.

Lengths of the lunar months in 2016

Successive new moons Length of lunar month
January 10 to February 8 29 days 13 hours 08 min
February 8 to March 9 29 days 11 hours 16 min
March 9 to April 7 29 days 09 hours 29 min
April 7 to May 6 29 days 08 hours 06 minutes
May 6 to June 5 29 days 07 hours 30 min
June 5 to July 4 29 days 08 hours 01 min
July 4 to August 2 29 days 9 hours 44 min
August 2 to September 1 29 days 12 hours 19 min
September 1 to October 1 29 days 15 hours 08 min
October 1 to October 30 29 days 17 hours 27 minutes
October 30 to November 29 29 days 18 hours 40 min
November 29 to December 29 29 days 18 hours 35 min

Why the difference in the lengths of lunar months? 

The longest lunar months happen when successive new moons occur near lunar apogee – and in addition, the Earth is near perihelion (Earth’s closest point to the sun in its orbit). Because Earth is always closest to the sun in early January, the very longest lunar months take place in between December and January new moons.

On the other hand, extremely short lunar months happen when successive new moons fall near lunar perigee – and in addition, the Earth is near aphelion (Earth’s farthest point from the sun in its orbit). Because Earth is always at aphelion in early July, the very shortest lunar months take place in between June and July new moons. As you noticed, the shortest lunar month this year happens in between the new moons of May 6 and June 5. This lunar month is only 29 days 7 hours and 30 minutes long, or 5 hours and 14 minutes shorter than the mean lunar month of 29 days 12 hours and 44 minutes.

Simulated view of the cycle of the moon's phases from new moon to new moon. This cycle is known as the lunar month. From the years 1760 to 2200, the longest lunar month was 29 days 19 hours and 58 minutes and the shortest 29 days 6 hours and 34 minutes.


Citations: earthsky.orgshadowandsubstance.com

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