"Gear up for Venus Transit: Download the app!"

Astronomy enthusiasts are gearing for one of biggest celestial events of the year, the Venus Transit. AP

Astronomy enthusiasts are gearing for one of biggest celestial events of the year, the Venus Transit.

The event takes place when the planet Venus comes between the Earth and the Sun, and thus appears as a small black dot on the sun to sky-gazers on Earth. Venus appears as a black spot travelling from one limb of the solar disc to the other.

The celestial event can be seen in India after sunrise on Wednesday. The next transit of Venus will only occur after a century in 2117. The last Venus transit took place back in 8 June 2004.

Those who have a smartphone, either an Android or iPhone device, can download this Transit of Venus app to check out the event. Android users can click here. iPhone users can download the app by clicking here.

Your smartphone needs to have GPS capabilities for the app to function. The app comes with a built-in timer to calculate how long Venus takes to cross the Sun. It will show users, the Ingress time — the moment when Venus is entirely inside the disk of the Sun, moving inward and ending with Egress Time, when the planet will be entirely outside the disk of the Sun, moving outward.

It also has simulation and visibility sections to tell users when the transit will begin based on their GPS coordinates. The app conceived by Steven van Roode and François Mignard is part of the group Astronomers without Borders’ Venus Transit project.

There will be a live webcast of the Venus transit by the group from historic Mount Wilson Observatory, in Los Angeles. The webcast will show vintage telescopes, interviews with scientists, historians, and transit experts.

During the transit, the phone app will also connect to the live webcast. Users can also record the event on their app and later share the video on Facebook, YouTube etc.

Registered users could depress a phone button at the moment of internal contact (when Venus appears within the sun, just touching the sun’s edge), and the app would record the exact time and user’s location, which would be sent to the global database. After the transit, users can access their data on a map, edit their entry, and upload descriptions, text, images, or movies. Other users can comment on entries.

The Venus transit will start at 03:40 am IST. The Greatest transit for Indian skygazers is at 07:01 am. The greatest transit is the time at which the distance between the center of Venus and Sun is minimum.