Rahu is basically ruler of Ardra nakshatra in Gemini, and represents the farthest point from the Mula nakshatra, of house Sagittarius in which the Galactic centre, or Brahmsthan resides when seen from earth. This means Ardra is also farthest point from the Milky way's Galactic centre and hence the constellation where Rahu, the darkness, can exalt.
Now, Ardra which mean tears(of face) is ruled by Rudra, while Mula which means the root or tail is ruled by Niriti, the goddess of desolution and destruction. Rudra and Niriti are the original names of Shiva-Shakti used in Vedic astrology and Vastu Shastra and represents the head and feet which also signify Rahu, the head(ego) and Ketu, the tail(moksha). Hence, Rahu exalts in Ardra, Gemini and Ketu in Mula, Sagittarius. Animal sign for both the constellations is a pair of dogs, which represents the outcast planet Ketu and ride of Bhairava/Bhairavi.
The same 27 constellations and 9 planets rule any piece of land on earth via Vastu Shastra in the form of Vastu Purusha, and the Ishan kona(North-East corner) ruled by Shiva/Jupiter or head(place for temple) while the Nairutya kone(South-West corner) ruled by Nirrti/Rahu and between them is the centre of Brahmsthan.
Since, Nirrti is the original name of Goddess Durga, who controls Rahu(the darkness) or South-West(Nairutya) corner in an earthly house or horoscope(as Rahu debilities in Sagittarius or Mula nakshatra), hence to pacify Rahu, astrologers talk about worshipping Durga.
Note: The world is facing current COVID-19 pandemic because Rahu was in Gemini, from March 2019 till September 2020(18 months) and in Arda, the constellation of tears and destruction in the beginning of 2020 as Rahu moves in retrograde or reverse direction. Earlier, Rahu was in Gemini transit, 18 years back, i.e. in around 2000-2001 and brought calamities and several changes after World Trade attack on 9-11-2001 and Gujarat Earthquakes in 2000. Rahu also represents ego, research and changes, hence scientists are involved in finding vaccines for COVID-19 virus in 2020.