Rahu kaala deepam:

Rahu kala deepam is litted in Durga temples during Rahu kalam (check panchangam for rahu kalam timings). Lemons are used as lampholders (Use yellow one's) in this pooja.

Devotees offer this seva on Tuesday and Friday for getting the blessings of Durga maa. Durga kavacham, Devi kavacham, Mahishasura mardini stotra, nava durga stuthi or any shlokas on Durga and Shiva are chanted while observing this pooja.

Rahu Kala pooja using lemons is to be done in temples only. (Check with a learned priest on how to observe this powerful pooja). Temples outside India are closed during rahu kala time. Those who would like to do the pooja at home can light regular deepams using til oil (Without using lemons), chant stotrams like lalitha sahasranama or durga chalisa followed by short shlokas on Shiva. Offer a fruit and conclude prayers with aarthi and kshama prarthana.

Those having trouble getting married, marital problems caused due to Rahu / kuja graha or those having career and financial problems generally observe this pooja.

Ketu kaala deepam:

Ketu kala deepam is generally litted in Ganesha mandir during Dhurmuhurtham time. Coconut oil should be used for litting lamps. Devotees offer this seva on Wednesday's and Sunday's.

Lord Ganesha removes obstacles caused due to ketu graha. So, worshipping HIM during durmuhurtha time removes unforseen dangers and obstacles. For better results, place these lamps on garika/fresh grass blades.

Ganesha is often called as Modaka priyudu, meaning one who love the offerings of MODAK (refer the recipe for modak under Ganesha Chaturthi Vratam from archives). It's a tradition to offer a count of 21 modaks or atleast jaggery and beaten rice/poha during the prayers.

Runamochana ganesha stotra - to remove financial problems and poverty

Santana ganapathy stotra - to be blessed with progeny

sankashtanasaka ganesha stotra - to remove obstacles and troubles

Daridryanivarana ganesha stotram - to remove poverty and sorrows

Here is a short shloka to be chanted on Sankashti Vrata day and also on Vinayaka Chaviti.

"Shree Namo Herambha mama sankashtam nivaaraya nivaaraya" for 21 times.

It is believed that by offering 21 modaks to Lord Ganesha, one can get rid of saptama doshas.

Also offering Aarghyam to Ganesha with jaggery mixed water alongwith some flowers, sandalwood powder (chandan/gandhamu) on special days like Sankasti vratha pleases him the most.

Aarghya Mantras for Ganesha (to be given 3 times):

first time mantra

Gowri sutha namasthesthu sarva siddhi pradayaka

sarva sankatanaashaartham gruhaanaarghyam namosthuthe

.. Shree Sankasta hara ganapataye namaha pradhamaaarghyam samarpayami

Second time mantra

Vighna naasaaya devesha vighna raaja namaamyaham

tathprasaadena sarvaani kaaryaani cha karomyaham

...Shree Sankasta hara ganapataye namaha dwitheeyaarghyam samarpayami

Third time mantra

Phaalachandra namasthubhyam bhakthaanaam bhadhradaayaka

gandha pushpai phalairyukhtam gruhaanaarghyam mayaarpitham

...Shree Sankasta hara ganapathaye namaha trutheeyaarghyam samarpayami