predict planetary alignment?

Question

Two parts:
1) From the perspective of someone in sri lanka, when will the moon, sun, and jupiter appear in or near the the constellation cancer, especially near the lower left star and middle two stars. I realize the sun would prevent anyone from viewing it.

2) When will all three conjoin/superimpose in this area.

Bonus: show me how I can replicate your work if it isn't too hard for a novice.

Answer 1

The synodic period of Jupiter is 399 days, which means that, as seen from Earth, Jupiter passes behind the Sun once every 399 days. So in N * 399 days Jupiter will be near the Sun. A year is 365.25 days, which means the Sun takes that long to go from one constellation all the way around the sky and back to the same constellation again. Now find the date when Jupiter last passed behind the sun (in conjunction with the Sun as they say), and then check how far the Sun was from Cancer on that date. Let's say it was X days from Cancer on that date. So in another X days the Sun will again be in Cancer, and in X+365.25 days it will be there again, and in X + 2 * 365.25 days it will be there yet again. So all you need to do is find a number, N, such that X + N * 365.25 is an even multiple of 399. You probably won't find an exact match even in millions of years, but within a few days is good enough. The Moon will pass Cancer once a month, and both the Sun and Jupiter will spend a whole month in Cancer, so you only need to find the date of the new Moon nearest the date you calculate for the Sun and Jupiter to get a date when all three are in the same area.

Or you can just use the source to display what the sky looks like on different dates until you find a match. I used it to find that the Sun is in the middle of Cancer on or about August 1 of every year, so just use the source to check the sky on August 1 of every year until you see Jupiter there too, then check a few days before and after that to get the moon in the same area. I did that and after only a few tries I found the Sun, Jupiter and the Moon all in Cancer on July 26, 2014.

Answer 2

The configuration will be tightest on 26 July 2014. The three won't superimpose. The moon will be northeast of the sun, and Jupiter will be between them in declination but be west-most in right ascension.

I wrote my own program. I got the formula for the moon's sky position from a book by Jean Meeus. For the positions of the Sun and Earth, it was straight reduction of the Keplerian orbital elements.

Answer 3

What Campbelp2 said! that is a very good answer....give him the 10 pts.