PHaST and the Transit of Venus

PHaST Preparations


The transit of Venus is a rare event which has not been seen for nearly 122 years. The last transits were in 1874 and 1882. Only very limited observations of the transit of Venus in H-alpha were made in 1874 (and perhaps in 1882). Peter Abrahams reports that G.L. Tupman observed the first contact of the transit of 1874 as a member of the British expedition to Hawaii using a spectroscope set up to observe prominences. He also reports that Pietro Tacchini of Palermo Observatory observed the 1874 transit from Muddapur, India using a spectroscope with a wide slit before second contact. The spectrohelioscope, Lyot filter, interference filter or Fabry-Perot etalon (all modern methods of observing the Sun in H-alpha light) had not yet been invented in 1882.

I will be using the PHaST telescope to observe the transit of Venus in H-alpha from Dubai in the United Arab Emirates. I hope to make high-cadence observations of the ingress and egress phases of the transit.

The 2004 Transit

The 2004 transit occurs on June 8. The locations where it can be observed are seen here in this drawing.

Visibility of the June 8, 2004 transit of Venus from Richard Proctor's 1882 book Transits of Venus. The light colored region indicates where the whole transit is visible, while the gray regions are where the transit is in progress at sunrise or sunset. The black region is where the transit cannot be seen at all. Notice how only part of the coastline of Antarctica and Greenland is shown; that's because the rest was unknown in 1882.

As you can see, California is in the black region so the transit is not visible from here. On the other hand, Dubai is perfectly placed for the transit. Weather statistics indicate that it is very likely to be clear.

Dubai transit information from the USNO server is shown below. Local time in Dubai is UTC + 4 hours. UT1 is based on the rotation of the Earth, while UTC (Coordinated Universal Time) is atomic time (TAI) corrected to within 0.9 seconds of UT1 by the use of leap seconds. Civil time is based on UTC. The location in Dubai given by the coordinates is most likely that of Fort Dubai, which is now the Dubai Museum.

                        Transit of Venus of 2004 June 08                        
     
                                      Dubai                                     
                 Location:  E 55°16'48.0", N25°15'08.0",     5m                 
                   (Longitude referred to Greenwich meridian)                   
     
                                                Sun's          Position   Angular
                               UT1       Altitude   Azimuth     Angle    Separation
                            h  m   s         °          °          °          '
Transit Begins              5:18:06.9      49.1       83.6      116.8       16.2
Ingress Interior Contact    5:37:07.0      53.4       85.1      119.9       15.3
Least Angular Distance      8:20:16.7      87.6      192.9      -----       10.5
Egress Interior Contact    11:03:22.6      52.3      275.3      213.2       15.3
Transit Ends               11:22:18.4      48.1      276.8      216.3       16.2
     
       Solar Semidiameter:   15' 45.4"
    Semidiameter of Venus:    0' 28.9"

What will the transit look like? A movie of the transit of 1882 as seen in white light can be found here. The observations were made by David Todd at the site of Lick Observatory. The movie was made from his digitized plates by Anthony Misch and Bill Sheehan of Lick Observatory last year. However, what the complete transit will look like in H-alpha no one really knows. We can get some idea from this BBSO movie of the 1999 transit of Mercury, but Venus will appear much larger. Venus also has an atmosphere, so it's unclear what it will look like before first contact when it will be seen against the chromosphere. If there happens to be a prominence in the right place it could be very interesting indeed.

Some images of Dubai.

On to the transit day itself.

For more information about the transit of Venus, see this site.

This Way to the Egress!

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Comments:
John Varsik varsik@bbso.njit.edu
Last modified: January 12, 2005.