Local transit times

By Steven van Roode and François Mignard

Your local circumstances are computed below. You can change the location by either dragging the marker on the map or searching for an address. From the menu on the top right you can specify the year of the transit (1639 to 2125). Clicking the icon at the top right corner of the map, you can switch the area of visibility on and off. Click on the icon on the lower right for more detailed information, including times of sunrise and sunset.

Notes on the data

Planetary transits start when the planet’s disk is externally tangent with the sun (ingress, exterior). From then, the planet may be discerened as a little black dent in the solar limb, gradually growing bigger until the entire planet is seen on the solar disk (ingress, interior). During the next five to six hours, the planet will traverse the sun’s disk until the planet’s disk will touch the opposite solar limb (egress, interior). The transit ends when the planet’s disk is externally tangent with the sun (egress, exterior).

You can switch to a graphical representation of the data, or to a more detailed data sheet. To switch, click the icon in the bottom right corner.

Graphical representation

For all four contacts the local time is given in 24-hour format. The analogue clocks also indicate whether the sun is above or below the horizon: if a clock’s colour is dark, this means that the sun is below the horizon and, subsequently, the particular will not be visible from the specified location.

The diagrams below to the clocks show the movement of Venus across the solar disk relative to the zenith, the point directly overhead. This is how you will see Venus advancing on the solar disk when observing with the naked eye or a telescope on an altazimuth mounting. Because of the diurnal motion of the celestial sphere, the sun’s disc rotates with respect to the direction of the zenith in the course of a day. The initially straight chord, representing Venus’ trajectory with respect to the north point, is now transformed into a curved path. You can see this curved path up close here.

The slider can be used to select any instant between the start and end of the transit, and to show the position of Venus on the solar disk at that instant.

Detailed data sheet

For all four contacts and the instant of least distance between Venus and the sun the local time in 24-hour format, the altitude h and the azimuth A of the sun are given. The altitude is measured in degrees above the horizon. If the sun’s altitude is negative, this means that the sun is below the horizon and, subsequently, the particular contact will not be visible from the specified location. The azimuth is the compass direction in degrees, measured westward from the south.

Also the position angle P of Venus and angular distance d between the centres of Venus and the sun are displayed. The position angle of Venus with respect to the centre of the solar disk is measured in degrees from the north towards the east. The distance between the centres is expressed in seconds of arc.

Finally, the approximate times of setting and rising of the sun on June 5 and June 6 are given in local time.