WITS¶
Where Is The Sun?¶
This turns out to be part of this mystery in our story.
Of course, we know where the Sun is, but where is it in relation to the rest of our galaxy?
Where is the centre of our own galaxy, the Milky Way?
The conventional wisdom is that Sagittarius A* is an impressive sized black hole, around 4 million times the mass of our sun.
Impressive though this is, it is nowhere near large enough to drive a good sized spiral galaxy.
A mass of tens if not hundreds of billions times the mass of the sun is required.
Let’s see if astropy can help.
Astropy¶
It seems astropy can help a great deal.
It is not long before we encounter coordinate reference frames.
A coordinate or frame in the Geocentric Celestial Reference System (GCRS).
Running help(coordinates.GCRS) lead me to this link:
https://arxiv.org/abs/astro-ph/0602086
It is a wonderful paper discussing the subtleties of celestial frames of reference.
Earth based astronomy is very interested in how the earth rotates and moves, but is also vey interested in the whole solar system as that has an impact on how the earth moves.
The GCRS reference introduces different ways to measure time: the earth’s rotation versus the vibration of an atomic clock.
If we ignore time, briefly, GCRS introduces a geocentric coordinate system for space. There is a related reference system called ICRS, which is centred
The positions of a catalogue of distant fixed stars is used to define a fixed frame in space, centered on earth at a point in time.
Our observations are now of such precision that a tiny wobble, or nutation, of the earth as it spins on its axis, needs to be taken into account to make observations. It is possible to predict this nutation out some considerable time into the future (???).
Where is the centre of our galaxy?¶
According to The Geometry of the Universe
Sgr A* is just about half-way in towards the centre from the Sun. It is roughly on line to the centre, but visibly NOT directly on line.
It appears to have recently moved into a star producing region (page 119) which accounts for the paradox of youth whereby many of its stars appear to be young, so it could be inside an active arm.
With a little work on the The Gaia Mission module it should be possible to zoom into the gaia data and get an idea of the view around Sgr A*, or indeed any other location across the galaxy.
- class gotu.wits.SolarSystem(args=None)[source]¶
Visualise the solar system
astropy has all the data
This magic.Ball just needs to get the data and plot it in various frames of reference.
For now, it trecks through time plotting planets and the moon.
It is now at least at the point where it can be used to find planets in the night sky.
- gotu.wits.get_body(name, at=None)[source]¶
astropy helper function to get a body.
astropy needs one of its time.Time() objects as a time.
Here we hope at is something it understands and if None, then we just use our current time according to datetime.
