What are the day, colour and gem of each of the Navagraha?
Each of the seven grahas from Surya to Lord Shani rules a day of the week, with a gem of its own: Surya on Sunday (ruby), Chandra on Monday (pearl), Mangala on Tuesday (red coral), Budha on Wednesday (emerald), Guru on Thursday (yellow sapphire), Shukra on Friday (diamond) and Shani on Saturday (blue sapphire). Rahu and Ketu, the shadow planets, have no day of their own; their gems are hessonite and cat’s eye.
The nine grahas
Day · colour · gem
Surya (The Sun)
Sunday · Red or copper · Ruby
Grain: Wheat
Chandra (The Moon)
Monday · White · Pearl
Grain: Rice
Mangala (Mars)
Tuesday · Red · Red coral
Grain: Chickpea, or toor dal
Budha (Mercury)
Wednesday · Green · Emerald
Grain: Green gram (moong)
Guru (Jupiter)
Thursday · Yellow · Yellow sapphire
Grain: Bengal gram (chana)
Shukra (Venus)
Friday · White · Diamond
Grain: White beans
Shani (Saturn)
Saturday · Black or dark blue · Blue sapphire
Grain: Black sesame
Rahu (The north node of the Moon)
No day of his own · Smoky or dark blue · Hessonite
Grain: Black gram (urad)
Ketu (The south node of the Moon)
No day of his own · Smoky grey, or many colours · Cat’s eye
Grain: Horse gram (kulthi)
Questions
Which day belongs to which graha?
Sunday is Surya’s, Monday Chandra’s, Tuesday Mangala’s, Wednesday Budha’s, Thursday Guru’s, Friday Shukra’s and Saturday Shani’s. Rahu and Ketu have no weekday of their own in most lists.
What are the colour, grain and gem of each graha?
In the lists most often printed: Surya red, wheat and ruby; Chandra white, rice and pearl; Mangala red, chickpea and red coral; Budha green, green gram and emerald; Guru yellow, Bengal gram and yellow sapphire; Shukra white, white beans and diamond; Lord Shani black, black sesame and blue sapphire; Rahu smoky blue, black gram and hessonite; Ketu smoky grey, horse gram and cat’s eye. The lists differ in places.
Why are Rahu and Ketu called shadow planets?
They are not lights in the sky but the two points where the paths of the Sun and the Moon cross, where eclipses fall. In the story they are one asura, Svarbhanu, cut in two by Lord Vishnu’s discus after he drank the nectar.