It is believed that, A Star never seen before in the sky appears on the day of Makarajyothi day(Jan 14) and it will be seen from Sabarimala before the sighting of the Jyoti. A Jyoti is seen for a little time on the hilltop showing the presence of Swami Ayyappan gracing his devotees.
Actually what happens is,
A star appears in the sky, That is true, Its the Serius star. We can see the same star around the same place in next days also.
And the makara jyothi is man made.
Makara jyothi is a fire is lit by TDB on the makara joyothi day at ponnambala medu. With the help of forest department, KSEB and Kerala police. It will be seen from shabarimala as a star. Ponnambala medu is at a height of 1170m and shabarimala is at a height of 544m above MSL.
The above picture shows where the firing is held and you can see shabarimala sannidhaanam in the back ground.
Read this report by TN Gopakumar
See this video from Sabarimala sannidhaanam
see this video report
Read the full stories here:
http://sinosh.wordpress.com/tag/ponnambalamedu-map/
http://www.thehindu.com/news/states/kerala/article2780957.ece