Venus is the second planet from the Sun. It was named after the Roman Goddess of love and beauty, probably because it was the brightest planet.
Venus orbits the Sun between Mercury and the Earth. Its orbit is nearly circular taking 224.65 Earth days for Venus to complete one orbit around the Sun, which is one Venusian year. Venus rotates on its own axis very slowly taking Interestingly, Venus's day (the time it takes to rotate once on its own axis) is longer than its year (the time it takes to revolve once around the Sun). This, combined with the length of the Earth's year, causes Venus to present the same side to the Earth when they are at closest approach. Venus's surface is, however, hidden by clouds. Venus's clouds, on the other hand, move much more rapidly with a 3-5 day rotational period. Venus has a diameter of 12,103 km (7,520 miles) compared to the Earth's diameter of 12,742 km (7,917 miles). Because of their comparable sizes, nearby locations in the inner solar system, and composition, Venus and the Earth have been called sister worlds.
The atmosphere of Venus, however, is extremely different than Earth's, being composed mostly of carbon dioxide with clouds of sulfur dioxide and sulfuric acid, under extreme temperature and pressure. Temperatures on Venus reach 460° C (860° F), making it hotter than Mercury, which is twice as close to the Sun. Venus also has a surface pressure greater than 90 Earth atmospheres. Like Mercury, Venus's brightness and size can vary greatly depending on where it is in its orbit in relation to the Earth. Its apparent magnitude can vary from -3.8 to -4.9. It's apparent size can vary from 9.7 to 66 arcseconds. Also as with Mercury, the other inferior planet orbiting the Sun inside the Earth's orbit, Venus can exhibit interesting phase illuminations, going from gibbous to crescent. Venus is at its largest size near inferior conjunction when it is a thin crescent. At greatest elongation Venus is nearly 50 percent illuminated, about 23.7 arcseconds in diameter, elongated 47 degrees from the Sun. Venus reaches greatest brilliancy when it is a crescent that is about one-quarter illuminated. This is because of a combination of its distance and phase angle. Imaging Venus Venus is a spectacular photographic subject because there are so many different ways to shoot it, even though it is shrouded in clouds and its surface is invisible. Venus can be shot both with wide-angle lenses in scenic shots, as well as at high-magnification through a telescope. Venus can be stunningly brilliant, as seen in the photo below when it was near the Pleiades, shining at magnitude -4.4, nearly a thousand times brighter than Alcyon, the brightest star in the Pleiades at magnitude 3.0.
Venus in Ultra-Violet Light Although no surface detail can be seen on Venus because of the clouds, some photographers have managed to capture detail and structure in the clouds by shooting with ultra-violet (UV) filters that pass light between about 300 and 400 mm, even putting together animations of the clouds rotating. Although DSLR sensors can record UV light, Camera manufacturers put a filter in front of the sensor that filters out UV and IR light. To shoot Venus in UV, you need a special UV filter as well as a specially modified DSLR that has had the manufacturer's short-wavelength filter removed. A telescope with all mirrors should be used as well as most glass does not pass light in the far UV spectrum. It is important to note that these UV filters are not made for visual work and should only be used photographically. Venus in the Daytime Venus is the third brightest natural object in the sky after the Sun and the Moon. It is so bright that it can be seen in the daytime with the Sun up if you know where to look. Venus can also be photographed in the daytime, but extreme care should be taken to put the Sun behind a building to block it when shooting or observing Venus with the Sun in the sky.
This photo of Venus seen directly above was taken with very modest equipment - a simple doublet short-focal length refractor and a fixed tripod. This was possible because Venus is so bright the single-frame exposure was short enough so that it did not require a tracking mount. Although Venus was about 1 arcminute in size, it was not very large in this image taken at just 420mm of focal length. The image above was a 1:1 crop from the full-frame image. Because Venus was so close to the Sun when this image was taken, I had to be especially careful that the scope did not accidentally point at the Sun because no solar filter was being used. I put the Sun behind the peak of my house positioned so that it could not be seen while I was shooting Venus. Finding Venus in the daytime is the trick. You can get a pretty good idea of where it is in relation to the Sun by looking in a planetarium program, but the Sun should be blocked when you actually look for Venus, so there will be some hunting around for it. Actually seeing Venus in the daytime when it is bright is not that hard, if you know where to look. It can be hard to find with the unaided eye if the sky is milky and not very transparent because in a clear sky your eye doesn't have anything to focus on infinity on. It can usually first be found in binoculars and then centered in the scope.
Since Venus is never that far from the Sun, putting the Sun behind the peak of a house to block it is very important for safety reasons, but viewing and shooting over a roof can cause serious seeing problems. Heat from the Sun is absorbed by roof tops and re-radiated, causing very poor seeing. I was lucky on this day because I was shooting with a short focal length which was not impacted as much by the seeing. For higher-resolution work in the daytime, it is better to wait to shoot Venus when it has a larger angular separation from the Sun, so you can put the Sun behind something and still be able to shoot Venus when it isn't over a roof top. Focusing on Venus in the daytime has the same problems and solutions as focusing on the Sun during the daytime. You must use some type of cover over your head and the LCD screen that you are going to use to focus. If you are going to shoot only a single frame at a time, it is still a good idea to shoot a lot of frames in the hope of lucking out and getting one with good seeing. Extreme Crescents and The Ring of Venus When Venus is at inferior conjunction, between the Earth and the Sun, it is closest to the Earth and at its largest apparent size. Within a few days of inferior conjunction, it is possible to photograph the extreme crescent of Venus. The crescent, instead of stretching 180 degrees, as one would expect from the lighting geometry, actually extends more than that. The closer to the Sun it is, the more the crescent extends. If it is close enough, and if the seeing is good enough, the crescent can extend all the way 360 degrees around forming a ring around Venus.
This effect is caused by sunlight scattering in the highest cloud deck in the atmosphere of Venus. This is a different phenomenon than the Aureole of Venus seen at the top of the page, which is caused more by refraction of light through the atmosphere of Venus. The Aureole is only visible during a transit of Venus and it is bright enough so that it can be photographed with a safe solar filter in place, and indeed it must be shot with a safe solar filter because the Sun is in the frame.
The Ring of Venus, and extreme crescents can only be photographed when Venus is very near the Sun, but must be done without a safe solar filter. This makes it extremely dangerous, so you need to be exceptionally careful and knowledgeable about how to do it. I photographed this extreme crescent with a sunshade on the end of a long pole taped to the telescope to block the direct light from the Sun falling onto the objective of the scope. This was necessary both for safety reasons, and because the glare from the nearby Sun would have washed out the image of Venus, even if the Sun was not in the frame. Additionally, at no time did I ever attempt to visually observe Venus through the scope while making this image. I used a computerized Go To mount and focused and centered it with a computer monitor. After acquiring the Sun with a safe solar filter in place, I focused and drift aligned the scope on a Sunspot. Then I synced the scope on the Sun so the Go To computer knew where the scope was pointing in the sky, and issued a Go To command via the computer running the scope. Then I adjusted the sunshade at the end of the pole so it blocked the Sun from the scope and taped the pole with duct tape to the scope so it could not accidentally move. I could barely see Venus because of the low contrast between it and the bright sky background. I knew a red filter would darken the sky background and that the seeing would be better in red light, so I put an Astronomik 6nm narrowband hydrogen-alpha filter in the camera. This filter is normally used for deep-sky emission nebulae, and is NOT safe for solar work however! But I was not trying to shoot the Sun, I was shooting Venus, so it was ok. Using the hydrogen-alpha filter darkened the sky background, but visually it was still very hard to see Venus because the image was in color and the red was overwhelming. I also knew that putting a filter in the light path between the scope and the camera sensor would change the focus. So I needed to re-focus, but the image was not bright or contrasty enough to focus on Venus. I decided to put the Baader solar filter back on the scope with the hydrogen-alpha filter still in place, and go back to the Sun and focus on a Sunspot since this image was much brighter. Again, I must emphasize, the only reason I could do this with this deep-sky hydrogen alpha filter was because I was also using the safe solar filter.
After focusing on a sunspot, I issued a Go To command and went back to Venus. I removed the solar filter, and started shooting 640x480 movie crop mode with the Canon T2i (550D) DSLR. Note that the focus did not change from the Baader solar filter because that filter is used in front of the objective. A filter used in front of a camera lens usually does not change the focus. However, filters used behind the camera lens in between the lens and the sensor will change the focus by the thickness of the filter multiplied by the refractive index of the glass used in the filter. The best frames from the video were selected with AutoStakkert!2 and stacked. The red channel was extracted since it was the only one that had any data in it from the hydrogen-alpha filter. This red filter filtered out all of the blue light of the sky background, and combined with the difference in exposure between Venus and the Sky, it caused the sky to go black in the resulting image, even though it was shot in the daytime. Transits of Venus A transit takes place when Venus moves directly between the Earth and the Sun. Because of the orbital geometry between the Earth, Venus, and the Sun, these transits occur in pairs eight years apart every 105.5 or 121.5 years. The last two took place in 2004 and 2012. The next one does not occur until 2117.
Early instrumental astronomers were especially excited by transits of Venus because it gave them a method of directly measuring the distance from the Earth to the Sun by geometric calculation. The entire scale of the solar system could then be calculated, something that was not known 250 years ago when astronomers went to great lengths to observe the transits of 1761 and 1769. With measurements from those transits, astronomers were able to calculate the distance between the Earth and Sun as 153 million kilometers (95 million miles), a value within one percent of the current modern-day value. Today a transit of Venus gives astronomers a chance to refine techniques they use to discover extrasolar planets that transit in front of other stars.
Tips for Photographing Venus
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