ESA Venus Amateur Observing Project: Introduction

Original article series

The Venus Amateur Observing Project (VAOP) is an opportunity to contribute scientifically useful images and data to complement the Venus Express (VEX) spacecraft observations of Venus. The project will focus on utilising the capabilities of advanced amateurs to obtain images of the atmosphere of Venus; specifically filtered monochrome images obtained with CCD based cameras in the 350nm to 1000nm (near ultraviolet, visible and near infrared range).

The Venus Express (VEX) spacecraft will observe the planet Venus using seven instruments for at least two Venusian years (1000 days) beginning in May 2006. The instrument package includes the Venus Imaging Camera (VMC), which will image the planet in the near-UV, visible and near-IR range. Although VMC will provide much higher resolution images of the planet than visible from Earth, continuous monitoring of the planet will not be possible.

There may be periods, therefore, when parts of the planet are visible from Earth that are not visible from the spacecraft (due to the spacecraft position in orbit). Additionally it is important to compare Earth-based observations with simultaneous spacecraft observations. In particular this will allow us to extend our understanding of the dynamics of Venus’s atmosphere based on the VEX data to observations made prior to the VEX mission, as well as after completion of VEX operations.

Objectives

The objectives of VAOP is to obtain high quality images of Venus before, after and during VEX operations. Amateur astronomers, using CCD based cameras with filters for specific band passes in the near ultra-violet, visible and near infrared wavelengths (350nm to 1000nm), are encouraged to participate in the gathering of images. Observation campaigns will include:

• Routine images of Venus during each apparition
• Coordinated observations during specific periods of the VEX mission to provide either simultaneous or complementary ground based images to VEX spacecraft observations

Points of Contact

General Enquiries

Please use the Contact link in the page footer

Enquiries on Taking Observations
Detlef Koschny
Tel: +31 71 565 4828
Email: Detlef.Koschnyesa.int

Venus Amateur Observing Project: Equipment

The following are suggestions for the type of equipment required to make useful observations as part of the programme.

Telescope

A high quality telescope at least 8″ (20 cm) in aperture is required, especially for UV-filter imaging. This can be of any optical design, although good results have been obtained with commercial Schmidt-Cassegrain and long focal length Newtonian telescopes. For telescopes with glass lens or windows (refractors and SCT’s) some attention should be paid to the type of glass used in the lens, since this may result in significant attenuation in the UV part of the spectrum. This is also true for other glass elements in the optical train, such as Barlow lens.

Camera

Images can be acquired using either a high-quality monochrome CCD camera or a monochrome digital video camera (e.g. based on webcam technology). Colour CCD cameras / video is not suitable for this project since this limits the possibility to perform meaningful filtered images, particularly in the near-UV regions. Some examples of camera’s successfully employed for Venus imaging include:

• Atik Instruments ATK-1HS or ATK-2HS
• Lumera LU075M
• Modified Philips Toucam camera with a monochrome CCD chip

Filters

To perform worthwhile imaging of Venus a core set of three filters are required:

• U-Band filter (e.g. Johnson-Cousins photometric U-Band or Schott U-360, 300-400nm passband)
• V-Band filter (e.g. Johnson-Cousins photometric V-Band)
• I-Band filter (e.g. Johnson-Cousins photometric U-Band or an infrared custom-filter.

In the case of non-standard infrared filters the cut-on wavelength and / or pass band should be noted) Filters should ideally be photometric quality, i.e. without significant infrared leakage for the filters in the UV/visible filters. In any case the specifications (manufacturer, product number should be noted with all observations). The following filters are also useful to expand imaging possibilities:

• A photometric B-Band filter
• W47 or violet filter in combination with IR-blocking
• Photometric R-Band filter
• 850LP filters (850nm cut-on)
• 1000LP filter (1000nm cut-on)

Venus Amateur Observing Project: Observing Guidelines

Venus is very bright, which permits very short exposures to be made in the visible & near infrared wavelengths with most telescope / CCD combinations. In the near UV, the combination of reduced CCD sensitivity and attenuation by the Earth’s atmosphere requires longer time exposures. Nevertheless, exposures in the UV are typically less than 100ms for typical f-ratio used for planetary imaging.

The effective focal length of the instrument should be adjusted so that the image scale per pixel is approximately twice the resolution limit of the instrument (for example: if the resolution of the telescope is 0.5″, then the image scale for pixel should be approximately 0.25″). The image scale can be calculated according to the following equation:

Alternatively, the actual image scale can be measured from the image (e.g. by dividing the number of pixels the planet takes up on the screen by the angular diameter of the planet). Typically to achieve the necessary image scale (generally between f/20 to f/40) a 2x to 3x telenegative Barlow lens is required.

The image exposure should be adjusted to ensure a good dynamic range, without saturating the image. The optimal settings for each filter combination will need to be determined experimentally and will vary depending on conditions (for example transparency). For example with a 235mm SCT at f/35 an ATK-1HS camera at 10fps required 1/25s exposure for U-band, and 1/250s for V-band images.

Imaging should ideally be performed under good seeing conditions, although routine monitoring even during poor seeing conditions is often sufficient to record major atmospheric features. Venus is bright enough be observed and imaged in daytime when the planet is generally at higher elevations than during nighttime. Care should be taken that the telescope does not accidentally point at the sun during daytime observing. However, daytime seeing conditions can often be poor, especially if the telescope tube is exposed to direct sunlight. Often around sunrise and sunset seeing conditions can often be good.

Prior to making routine observations the imaging setup for Venus observations should be optimised by experimenting with camera settings, filter combinations and focal ratio.

The observer should be familiar with planetary imaging their instrument and camera. Sky & Telescope magazine (http://www.skytelescope.com) has published several articles on planetary imaging that may be of interest to Venus imagers:

• Davis, M., and Staup, D. (2003) Shooting the Planets with Webcams Sky and Telescope 105, 117-122
• Grafton, E. (2003) Get Ultrasharp Planetary Images with your CCD Camera Sky and Telescope 106, 125-12
• di Cicco, D. (2003) The New Face of Planetary Astronomy Sky and Telescope 106, 30-32
• Dantowitz, R. (1998) Sharper Images through Video Sky and Telescope 96, 48-54
• Shiga, D. (2004) Amateur images Venus’s surface http://skyandtelescope.com/news/article_1266_1.asp

Venus Amateur Observing Project: Taking Observations

Observing Logs

Key details of images must be recorded for the data to be useable. Therefore an observing log should be kept which records the following data:

• Name of observer
• Observing location (latitude, longitude, height)
• Weather conditions during observation including cloud cover, seeing conditions, transparency, wind & temperature
• Telescope type, size, f-ratio
• Camera type
• Effective focal length of instrument while imaging, image scale per pixel, camera settings (gain, shutter speed, number of frames) for each filter
• Filter types
• Processing methodology (nature of image processing, including corrections & post processing)
• Image orientation (direction of celestial south & proceeding / following side of image)

Dark & Flat Fielding

Although many observers do not routinely perform dark & flat field correction to planetary images, the validity of images is improved using this method especially when faint atmosphere features are detected. Dark fields should be taken using the same exposure settings as for actual images, but with the optics covered to prevent light reaching the camera. For the exposures likely to be used for most Venus imaging dark current is unlikely to be a significant concept except for UV imaging where higher gain settings and longer exposures are necessary.

Flat fields should be taken at approximately 2/3 the linear range of the detector chip. Flat fields can be taken either of the daytime sky, a white screen held over the telescope aperture or the inside of a telescope dome.

Image Processing

Image processing can be performed with a variety of freeware and commercial software applications. For digital video data the freeware Registax (http://registax.astronomy.net/) is a highly recommended tool for processing, since this permits automated selection, stacking & post processing of images. Additionally, dark & flat field images can be automatically subtracted from the video stream.

Image processing should include selection of sharp individual frames from video, followed by alignment & stacking of individual images to reduce noise. Generally post processing using wavelets or unsharp masking is required to reveal fine detail. However, care should be taken during processing to prevent introduction of processing artifacts.

Digital Video Imaging

1. Take dark field video
2. Take flat field video with each filter
3. Take images of Venus using filters, recording end time & duration of video acquisition
4. Process video image sequences to yield high quality stacked images that are dark & flat field corrected
5. Perform moderate post processing (wavelet processing of image)
6. Annotate images with details of image, including filters, observing time
7. Submit images to British Astronomical Association Venus Coordinators

Venus Amateur Observing Project: Sample Images

Figure 1: U-Band filtered images of Venus taken using a 235mm Schmitt-Cassegrain SCT telescope and a SAC-8 CCD camera in video mode

An example of routine monitoring of Venus, with images taken at approximately the same time of day between the 8 March & 18 April 2004. Changing cloud structure is apparent on the planet. The resolution of individual images varies from day to day due to differences in the seeing conditions (atmospheric turbulence). Over the course of the 6 week observing period the phase and apparent diameter of the planet changed significantly. All images by Jason Hatton (jason.hattonesa.int)

Figure 2: Filtered images of Venus, 13 October 2004

A set of images showing the changing appearance of Venus at different wavelengths. Both the U-band (ultraviolet) and W47+Infrared blocking (violet) images show cloud structure, which is most apparent in the ultra-violet images. In contrast the planet was largely featureless in the visible and near infrared images. All images obtained by Jason Hatton using a 235mm SCT from Mill Valley, California (jason.hattonesa.int)

Figure 3: Faint markings detected in the infrared, 2 October 2004

Routine monitoring is important to detect unusual features. In this set of images, a faint dusky marking in the northern hemisphere is detectable in the infrared (most prominent in the strongly processed 850LP image). Several other observers detected similar features in the infrared around the same time. All images obtained by Jason Hatton using a 235mm SCT from Mill Valley, California (jason.hattonesa.int)

Venus Amateur Observing Project: Submission of Images

Final processed images should be submitted to the Venus coordinator of British Astronomical Association. The current coordinator for the BAA Venus section is Dr Richard McKim and images can be submitted by email to: Rmckim5374aol.com

Generally the BAA is accepting high quality JPEG images, with either annotation of details of the observation on the image or in an attached file. This should include the following information:

• Name of observer
• Observing location (latitude, longitude, height)
• Weather conditions during observation including cloud cover, seeing conditions, transparency, wind and temperature
• Telescope type, size, f-ratio
• Camera type
• Effective focal length of instrument while imaging, image scale per pixel, camera settings (gain, shutter speed, number of frames) for each filter
• Filter types
• Processing methodology (nature of image processing, including corrections and post processing)
• Image orientation (direction of celestial south & proceeding / following side of image)

To facilitate use of the images by the VEX team it is also preferable to have images in FITS format with all image details recorded in the FITS header.

Venus Amateur Observing Project: Observing Campaigns

Routine Observations

Routine observations of Venus are needed throughout the period that VEX is observing the planet, as well as after completion of the mission. Since Venus has a high surface brightness it is potentially observable anytime it is far enough from the Sun to be safely observed. Here is a list of Venus apparitions from 2006 to 2011.

Special Observing Campaigns

Coordinated observing campaigns in conjunction with spacecraft observations will be organised periodically. Information on observing campaigns will be posted on this site.

Venus Amateur Observing Project: Useful Websites

British Astronomical Association Venus Section http://www.take27.co.uk/BAA_MV/BAA_MVS.html

Association of Lunar and Planetary Observers (ALPO) Venus Section http://www.lpl.arizona.edu/~rhill/alpo/venus.html

The website of Damian Peach (an experienced planetary imager) http://www.damianpeach.com/

The website of Christophe Pellier (the first amateur astronomer to detect the 1?m emission from the night side of Venus). There is an excellent introduction (in French) to planetary imaging on this website http://www.astrosurf.org/pellier/

Registax image processing software website: http://registax.astronomy.net/

A news article describing Chris Pellier’s observation of the 1?m emission from the night side of Venus http://skyandtelescope.com/news/article_1266_1.asp