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 30^th 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 13^th 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.

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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.

Credit: ESA/Rosetta/MPS for OSIRIS Team MPS/UPD/LAM/IAA/SSO/INTA/UPM/DASP/IDA

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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 15^th 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 26^th 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 24^th.

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 26^th 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.

 

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Earth at Perihelion:

Earth will be at Perihelion on 4^th 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.

 

		Sun			Sun
		Max.Angular Dia			Min.Angular Dia
		Perihelion			Aphelion
Earth		0.54183			0.52398
Mercury		1.7324			1.1414

 

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

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Pole star on Different Planets

We have all seen night after night, season after season that one star in the north seems fixed in the sky. This is because the axis of earth rotation passes in the same line and so the star appears stationary; we call this star, pole star or Polaris. This star is the main star of constellation of Ursa Minor with a magnitude of 2. From Bangalore it will be 13degrees in altitude, remember that altitude of the pole star depends on latitude of the place. Here is a chart of the Polaris.

 

 

 

Now every planet rotates on its axis, so what will be the location of pole star for those planets in the solar system. Let’s begin with Mercury the closest to Sun, the location of pole star will be in constellation of Draco, the circle indicates the area where the Mercury pole star is located.

 

 

Venus:

 

We know that there is no way we can have an open sky to see the stars on Venus but based on the orbit orientation of the planet we can say that the pole star will be in the constellation of Draco. Here is the sky chart of the location for Venus pole star.

 

 

 

 

Mars:

The red planet we love to explore, we have seen the sunrise and sunset taken by the landing probes and also transit of Mars moon across Sun’s disk. If we were to find the pole star of Mars it will be in the constellation of Cygnus close to star Deneb.

 

Jupiter:

The giant planet rotates fast taking only 9h55m to complete one rotation, while all constellations and stars are moving at dizzying speed one star in Draco will remain still, as the polar axis of Jupiter lies in Draco constellation.

 

Saturn:

The ringed planet has its pole close to our own pole star. Here is a chart on location of the pole star seen from Saturn.

 

Uranus:

This unique planet rotating with high axis angle seems rotating on its belly. The pole star for this Planet would lie between Taurus and Orion.

 

 

Neptune:

Last among outer “planets” is the planet Neptune and it would have the pole star in the constellation of Cygnus.

 







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AKASHA Newsletter from ABAA

Akasha by abaaonline

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Timelapse showing no Shadow on Bangalore April 24 2013

This small time lapse taken today to show that when Sun's Declination and Latitude of the place are same the Sun will be directly overhead and there will minimum or no shadow at that place. Please refer to the previous post to know  on what date  your location will have no  shadow at noon

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