URANUS RETROGRADE MOTION 2023

Uranus is in retrograde motion now, starting from 30th Aug 2023. All planets move from west to east with reference to stars, this is the direct motion. Months before reaching the opposition, we notice the daily angular motion of the outer planet, in this case, Uranus keeps reducing and at a point it appears stationary. The planet’s motion will be eastward until the stationary point.

After this we see the planet moving westward with respect to stars and the angular motion also increase but in westward direction. This movement, westward, we call it retrograde motion.

Months after Opposition, the opposition of Uranus will take place on 13^th November 2023, again we observe the angular motion reducing and becoming stationary at one point, this will be Jan 28th 2024, and the planet will start moving eastward again with slowly increasing in angular motion as days passes.

Uranus will move 4 degrees west in the retrograde motion before turning east again.

Using binocular or telescope you can track the movement and measure the changes. Even with necked eye it is possible but interval of each observation should be far enough (in days) to notice the changes.

If you pick delta and rho Arietis, you can notice the movement of Uranus from delta to rho…

 

Happy Observing 

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Mercury in the evening Sky

In the evening sky, low in the horizon, if we carefully look we can find the smallest planet in our solar system. After sunset, in a place where there are no obstruction like buildings or trees, in this unobstructed view of the western horizon we can spot planet mercury. Since mercury orbits close to the sun we can only find the planets close to the horizon in evening or morning skies.

During its orbit around the sun there are two favorable points where we can observe the planet. This is the maximum separation of angle between Sun and planet. This point of maximum separation is called Greatest elongation. For planet mercury this greatest elongation angle is between 18 degrees to 28 degrees. This is the reason why most people miss the planet, since it is so close to horizon.

On November 6^th the planet will reach greatest elongation giving us a good opportunity to catch a glimpse of this planet with naked eye, binoculars and telescopes. The angle for this elongation is 23 degrees, this means just after sunset the planet will be 23degrees above western horizon.

Spot planet after sunset in western sky.

The planet will be at a magnitude of -0.2, although it is bright the drawback is that it is immersed in twilight making it difficult to spot but as twilight fades its easy to spot.

With a telescope we can see the gibbous phase of mercury with an angular size of 6min of arc. The planet will be in half phase on 11^th of November and from there on the illuminated side of mercury will start decreasing. This is a nice time to see and enjoy and also understand the phases and orbit of mercury. Since the planet is coming closer to earth the angular size will keep increasing and it will be 9mins of arc before the planet sinks into the glare of the sun and then reach inferior conjunction on 27^th of November.

Clear Skies.

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Venus Watch at ABAA

After I announced about Venus being in its brightest phase many people showed interest in looking at Venus through telescope following Sunday. On Sunday we were happy to see public and members coming in large numbers to watch Venus in crescent phase. After sunset we put the telescope out and focused on to Venus, members of ABAA were present there in showing and explaining all about Venus. Using the 6 inch telescope of ABAA people saw amazing sight of the crescent phase, and immediate reaction of most people was “is it Moon?”, that lead to discussions and members helped them in getting idea of orbits and phases of inner planets.

ABAA is open on all Sundays from 5:30pm and always ready to show the celestial wonders to people and members showing interest. People can come and see moon and planets, learn about them and also learn about telescopes and how to use them. Observing through a telescope has steep learning curve, its best to learn about them before buying or going out for observing and ABAA can really help in that section. ABAA can help in choosing the best telescope for you or help you in building your own telescope, you can come to ABAA on any Sunday evening and discuss your needs.

Here are photos of Sunday sessions of Venus watch

    

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Watch Brightest Venus on Friday

After Sunset in the western twilight sky we see a bright star outshining all the starts in the evening sky, this is the planet Venus. The visual apparent magnitude of the planet Venus is now -4.6 and the apparent magnitude of brightest star in the night sky, Sirius, in the constellation of Cains Major is -1.46 this makes Venus 18 times brighter than Sirius. 

Brocken Inaglory, Venus-pacific-levelled, CC BY-SA 3.0

On February 17th Venus will reach its brightest crescent phase and this is called Greatest Illuminated Extent, the amount of illuminated crescent and the angular diameter of the planet Venus. Venus will have an angular diameter of 39 arc seconds and fraction of illumination is .273 of the angular diameter. After this day the illuminated side will start decreasing and we will see the crescent getting thinner. By second week of March the illuminated fraction will be only .085 of the diameter of the planet and magnitude would have come down to -4.4 still brightest in the evening sky. 

View Through the Telescope on 17th of Feb

View Through the Telescope on 10th March

The planet Venus will slowly fade into glare of the Sun and will reach inferior conjunction on March 25^th. In April we will see Venus in early morning sky before sunrise and again the Greatest Illuminated Extent will happen on April 30^th. Time to take out the telescopes and observe Venus in coming days, if you don't have one you are always welcome at ABAA on Sundays evening and see the Venus through our telescope. Venus sets at 9pm now and in middle of March the planet will set at 7:30pm.

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Looking and Observing

When crowd gather around binoculars and see the Moon for the first time through binoculars, their reaction is that, the moon looks the same even without the aid of binoculars. Ask them to spend some time at the binoculars and slowly they will start enjoying the view, as they start to Observe the details on the moon surface. This is true even with low power telescopes.

This is the difference between looking and observing which I am sure most people would have experienced in their initial stages.

Even when it comes to other celestial wonders, the situation is the same spend very little time at eyepiece and there is little to be seen but spend more time at eyepiece and details we can see are amazing.

Let me give an example of difference between looking and observing. Take a look at the image and at first sight it appears the same, little closer look will show couple of differences but as on spending time and studying the details will show lots of differences in the images.

When at eyepiece spend as much time as possible studying the object, for example if it is the moon study the shape of the craters, the shadow patterns at different phases of moon and so on. If it is a galaxy, study the dust lane, the arms and structure.  Cluster offers their own challenges like resolving and types of stars in the cluster. We cannot pick up such fine details if we are in a hurry, more time at eyepiece more details we will pick up.  Change the magnification, use different filters, study the object in different telescopes, you will be amazed on how on objects appears in different magnification, filters and apertures.

I always advice people not to fill the pages with number of objects they saw in a single night, but to fill the pages with the details on what they observed. There is no rush, take time in observing and keep challenging yourselves on how much more details you can see and minimum aperture needed to see the details. 

Why just Look when you can Observe!

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Venus and Jupiter Conjunction on July 1st

In the western evening sky we have 2 bright objects, one closer to horizon is Planet Venus and next is Planet Jupiter. As we are observing from past couple of weeks, we have noticed something curious, Venus and Jupiter are getting closer to each other.

These two planets appear getting close to each other, this is as seen from earth, the fact is Venus, the brightest planet in the sky and Jupiter the largest planet in the solar system are 0.5AU and 6AU respectively from earth (1 Astronomical Unit =14,95,97,871 km).  

We will continue to track these planets in coming days and we will notice that the separation will get even smaller. The separation of these planets as seen from earth is measured in angles.

In the middle of June the separation between Venus and Jupiter will be 14 degrees and on 20th the separation will be reduced to 6 degrees.

Minimum separation between Venus and Jupiter will happen on July 1st with a separation of 24 minutes, close enough to fit both planets in field of view of telescope. Venus and Jupiter will set at 9:30pm on 1st July.

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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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Sun's Angualr size as seen from different planetary distances

When we look at the sun, we always wonder how big it would appear looking at it from different planets. I have made this Image to show the relative size of Sun as seen from different planetary distances (scroll down after the table). The angular size of Sun with respect to distance is easy to calculate. Divide diameter of Sun by its distance form earth and then multiply the result by 57.3 to get the angular size of sun. Using this we can get angular size of Sun from different planets...

Angular size = diameter/distance * 57.3

Diameter of Sun = 1391000km

Distance from Earth = 150000000km

Angular size = 1391000/150000000

= 0.0092 * 57.3

Angular size of Sun as seen from earth = 0.531degrees.

We can calculate and compare the relative angular size of Sun seen from different planetary distances.

Sun Diameter = 1391000 kilometers
Planets	Distance from Sun  (when planet is closest to sun)	Angular diameter(in degrees)
Mercury	46000000	1.73
Venus	107000000	0.74
Earth	150000000 (mean distance)	0.53
Mars	206000000	0.38
Jupiter	740000000	0.10
Saturn	1352000000	0.05
Uranus	2741000000	0.029
Neptune	4444000000	0.017

Here is the a graphic of sun's appearance at different distances...

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ABAA News: Discussion on Kepler and Titius-Bode Law

On Sunday 23rd September, members were discussing about Kepler laws at ABAA, when calculating periods of planets, to remember the distance in AU, members spoke about Bode's law...Here is a small Jpg I made explaining Titius-Bode Law...until Uranus, numbers match beyond that the error increases...Now you will never forget the distances of Planets from the Sun :-)

Here is the Image and couple of photos of the session

Titius-Bode Law for remembering Planets distances in AU

Ravindra Aradhya explaining  Titius-Bode Law

ABAA Members at the session

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ABAA NEWS: Demonstration of Planets motion in curved space.

First Sunday of September members had fun with demonstrating and discussing the motion of planets in a curved space created by massive objects like Sun. The discussions and experiments went on to different size and different density planets and also binary objects revolving around center of gravity.

These were just few updates on Sunday activities at ABAA, you can get involved by visiting ABAA on Sundays evening and take part in all the activities.

Here are few photos of the session, members called it...Come Roll the Planets...

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