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Targeting stars that can see the earth transiting the sun

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Joined: 2010-04-22
Posts: 4

(note I posted this on the universe today forums as well)

Logic being that any intelligent life would probably have their own exoplanet search program and hence focus their seti efforts on planets they might find within the habitable zone.

These stars must be plus and minus some angle from the ecliptic.

My calculation is that the angle is given by
Tan(theta) = (Rs-Re)/SunToEarthDistance.
i.e. +-15.83 arc min

200ly = a parallax of 16.308

This is the SIMBAD Criteria query that returns them
plx > 16.308 & region(box ecl,0.0 +0.0,179d 31m)


You might change the simbad output options to include the parallax and ecliptic co-ordinates.
The two closest stars are Van Maanen's star, a white dwarf at 14 lys and HD 4628 (LHS 121) at 24ly.

LHS 121 is pretty interesting (http://en.wikipedia.org/wiki/HD_4628). Only 24ly away, the star is about 80% the size of ours and about 5.4 billion years old (i.e. enough time) AND its thought to have a Jupiter mass planet at 4.29 AU out (far enough to allow the development of inner rocky planets and to act as an asteroid shield).

Joined: 2010-04-22
Posts: 4
There are 54 stars.The query

There are 54 stars.

The query below gets all of them bar HR 7327
plx > 16.308 & (
region(box ecl,0.0 +0.0,45d 31.67m) |
region(box ecl,45.0 +0.0,45d 31.67m) |
region(box ecl,90.0 +0.0,45d 31.67m) |
region(box ecl,135.0 +0.0,45d 31.67m) |
region(box ecl,180.0 +0.0,45d 31.67m) |
region(box ecl,225.0 +0.0,45d 31.67m) |
region(box ecl,270.0 +0.0,45d 31.67m) |
region(box ecl,315.0 +0.0,45d 31.67m) |
region(box ecl,360.0 +0.0,45d 31.67m))

I also worked out that stars take approximately from 400 years to 168000 years to cross the transit area.
The average being ~18000 years.

If I was an avocate for active seti, I'd be transmitting to these stars while they can see our transit.

[Edit added below]
>Tan(theta) = (Rs-Re)/SunToEarthDistance.
this should be
Sin(theta) = (Rs-Re)/SunToEarthDistance.

Joined: 2010-04-22
Posts: 4
After reading

After reading http://kepler.nasa.gov/Science/about/characteristicsOfTransits/ and a bit of maths
(http://www.bautforum.com/showthread.php/126869-Stars-within-200-light-ye....) and some feedback from SIMBAD the correct query is

plx > 16.308 & region(ZONE ecl,0.0 +0.0,360.0d 27.98m)

It returns 47 stars of which 16 are G type.