Thanks for mentioning me @A_Pariah
Firstly, coming from a traditional perspective and in traditional practice, the Sun is not necessarily afflicted in Capricorn, or in Scorpio or Sagitarrius. He is afflicted in Libra and Aquarius.
Otherwise you might say that Capricorn and Aquarius have a link to death as they are the signs ruled by Saturn, who traditionally rules over death and decay.
Also, the Signs are NOT the Constellations in traditional western astrology. The Signs are unmoving, this is one display of them being spiritually eternal and greatly exalted (With them being higher than all other celestial factors). However, all the Stars are wonderfully exalted and great.
Now, you could simply invoke the spirit of Capricorn. That is, Capricorn, that is her name, called by other names in other languages.
The spirits of the celestial bodies and Signs etc. Are highly benevolent in my view, similar to angels, or the Gods.
Alternatively, you could invoke the angel of Capricorn, Hanael. They are the Angel of Capricorn according to Agrippa (Three Books of Occult Philosophy, Book III, Chapter 24). However, my sense is that this angel is not the same as the Archangel Hanael/Anael.
Light incense appropriate to Capricorn and invoke the spirit. I don’t recall a traditional list of incenses appropriate to the signs, but you could use an incense appropriate to Saturn, such as Pine incense. That is one approach.
Since the spirits of the heavens are benevolent, light candles or make a fire.
However, the most important factor in traditional astrological magick is the election. That is, an auspicious time chosen through traditional electional astrology (having the stars “lined up”). This is quite complicated, and is learnt through study.
The astrological electional rules on this would be more complex and I won’t list them here, I feel it is best if this knowledge is gained through study if you are to recieve it.
You can call upon them at any time, regardless of the state of the heavens, but this would not be as powerful, and I reckon it would make the magick more unpredictable.
However, a basic rule could be to have the Sun in Capricorn. That is a good start.