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the Transit: Viewing with Observatories
By observing the transit of Venus, you can re-discover a number of physical quantities about Venus and its orbit in much the same manner as astronomers did in the 16th and 17th centuries. Each observatory listed below will make 12 observations of Venus against the sun from sunrise to third and fourth contact. From these images, you should be able to detect the Venusian atmosphere, derive a distance to Venus as well as the Astronomical Unit (AU), calculate an orbital period for Venus, and derive a diameter for the planet. In some cases, such as detecting the Venusian atmosphere, all you have to do is look at an image from a single observatory. In other cases, you will need to compare multiple images taken from different observatories spaced widely in distance and perform calculations based on these observations.
About the Image Viewer
Clicking on an observatory name will take you to its image viewer. Each viewer can display up to 12 images of the transit. By clicking on one of the small images to the right, a larger image will be displayed in the left hand window. You can zoom in and out and move around the image by dragging the shaded image window. In addition, you can save the image to your hard disk where you can do further analysis and printing.
The Virtual Telescopes in Education (VTIE) web site will guide your students through the process of writing a proposal for viewing the Venus Transit.
1. Detect Venus' Atmosphere: By observing Venus near 1st and 4th contact, one can observe the presence of Venus' atmosphere as a bright ring around the planet. This ring is caused by scattering of sunlight through the upper portions of Venus' atmosphere and was first detected in 1761 by the Russian Astronomer, Mikhail Lomonosov. Measurable Quantities: Brightness
2. Derive the Distance from Earth to Venus: Using the phenomenon of parallax, one can calculate the distance from the Earth to Venus by measuring the apparent displacement of Venus as seen against the disk of the sun from two observatories spaced widely (hundreds or thousands of miles) apart.
The Transit of Venus may be a rare event, but it has proved important to early calculations of the distance from Earth to the Sun. Knowing the distance from the Sun to Earth allowed astronomers to calculate distances to all of the other planets. Before the critical measurements of the Transit of Venus in the late 1800s, distances in the solar system were expressed in Astronomical Units (AU). But nobody knew what an AU equaled in terms of miles or kilometers. The AU was simply the distance from Earth to the Sun; all distances from the other planets to the Sun were calculated using Kepler s Laws in comparison with the Earth-Sun distance. So astronomers needed to calculate the AU in kilometers!
To do this calculation for yourself, visit Calculate the Astronomical Unit (AU) to Kilometer.
You can also calculate the AU by using 'Halley's Method' taking into account the Earth's rotation, orbital eccentricity, and longitude.
3. Calculate the Diameter of Venus: By observing the size of Venus against the backdrop of the sun, you can get an angular measurement of the planet's diameter by ratioing its diameter to that of the sun whose angular size is known (~ 0.5 degrees). Then, knowing the distance to Venus from 2. and the actual diameter of the sun, you can calculate its actual size.