|wavelength (nm)||day- or nightside?||from where?||processes involved?||references
||reflected sunlight, locally absorbed -> high contrast
||Ross 1928; Scott & Reese 1972; Caldwell 1972; Murray & al. 1974; Travis & al. 1979
||400-650 (several lines, esp. between 450 und 560)
||Herzberg II O2 airglow
||Lawrence & al. 1977; Slanger & Black 1978; Bougher & Borucki 1994
||TBD (range of the human eye)
||night; sporadic; controversial
||probably upper atmosphere
||TBD (»Ashen Light«)
||Phillips & Russell 1988; Phillips & Russell 1992; Cruikshank
1992; Fischer 2001b
|| sunlight reflected at 60 to 70 km, locally absorbed
||Belton & al. 1991
||emission from atomic oxygen
||Slanger & al. 2001; Crisp 2001
||850 + 900
||weak thermal emission
||Baines & al. 2000
||sunlight reflected at 60 to 70 km, locally absorbed
||Belton & al. 1991
||Carlson 1991; Lecacheux & al. 1993; Meadows & Crisp 1996; Baines & al. 2000; Pellier 2004; Shiga 2004
||thermal emission, modulated by topography; low-contrast
absorption by higher clouds
||Crisp & al. 1991a; Meadows & Crisp 1996
||thermal emission, modulated by the highest mountains;
medium-contrast (up to factor 2) absorption by higher clouds
||Crisp & al. 1991a; Carlson & al. 1991; Anon. 1991; Meadows & Crisp 1996
||night (airglow also: day)
||upper atmosphere (95 km) plus very deep clouds
||airglow from molecular oxygen, added to thermal emission
from the deep, with low-contrast (factor 0.3) absorption by higher clouds
||Connes & al. 1979; Allen 1987; Crisp & al. 1991a; Anon. 1991;
Allen & al. 1992; Bougher & Borucki 1994; Crisp & al. 1996
||very deep clouds
||thermal emission; low-contrast absorption by higher clouds
||Crisp & al. 1991a
||thermal emission by clouds at roughly 25 bar (17 km) with
high-contrast (up to factor 5) absorption by higher clouds
||Allen & Crawford 1984; Allen 1987; Crisp & al. 1989; Crisp & al. 1991b; Carlson & al.
||2300 (esp. 2210 and 2320)
||thermal emission by clouds at 8 bar (32 km) with high-
contrast (factor 5 to 20) absorption by higher clouds
||Allen & Crawford 1984; Allen 1987; Crisp & al. 1989; Bézard & al. 1990; Bell &
al. 1991; Crisp & al. 1991b; Carlson & al. 1991
Discoveries with large ground-based telescopes and spacecraft, however, have in the last decades revealed a much more interesting planet. There are three basic phenomena of Venus that cause contrast phenomena on either the day or night side which are accessible to ground-based telescopes, and some of these are - or may well be - accessible to amateur instruments as well:
Thus the worldwide amateur community - with 21st-century instrumentation - could well support and extend (at least in the time and perhaps also the spectral but surely not the spatial domain) the work of the VMC and VIRTIS instruments on Venus Express, and a joint observing campaign should be worthwile! In particular it would be helpful if the active periods of these instruments would be publicly known, as a motivation for observing runs - and if the VEX community would share some of its data readily with advanced amateur astronomers who would do so vice versa.
Allen 1987: The Dark Side of Venus, Icarus 69  221-229 - further observations at 1.7 and 2.3 µm require new interpretations.
Allen & al. 1992: Variable oxygen airglow on Venus as a probe of atmospheric dynamics, Nature 359 [1992 Oct. 8] 516-9 (with a summary on p. 481) - emission over the nightside at 1.27 µm.
Anon. 1991: The dark side of Venus at three wavelengths, AAO Newsletter # 59 [1991 Oct.] 1 - images at 2.3 and 1.18 µm and in the light of the O2 airglow.
Baines & al. 2000, Detection of Sub-Micron Radiation from the Surface of Venus by Cassini/VMS, Icarus 148  307-11 - thermal emission at 850 and 900 nm from the surface.
Bézard & al. 1990: The deep atmosphere of Venus revealed by high-resolution nightside spectra, Nature 345 [1990 June 7] 508-11 - the first hi-res spectra confirm a thermal origin of the emission from great depth.
Bell & al. 1991: Spectroscopic Observations of Bright and Dark Emission Features on the Night Side of Venus, Science 252 [1991 May 31] 1293-6 - observations during the 1990 campaign.
Belton & al. 1991: Images from Galileo of the Venus Cloud Deck, Science 253 [1991 Sep. 27] 1531-6 - contrast-rich image sequences at 418 (violet) and 986 (NIR) nm.
Borucki & al. 1981: Optical Search for Lightning on Venus, Geophys. Res. Lett. 8 [1981 March] 233-6 - an upper limit set by PVO's star sensor.
Bougher & Borucki 1994: Venus O2 visible and IR nightglow, JGR 99  3759-76 - thermosphere dynamics & chemistry derived from the Herzberg and 1.27 µm lines.
Boyer & Guerin 1969: Etude de la rotation rétrograde, en 4 jours, de la couche extérieure nuageuse de Vénus, Icarus 11 [1969 Nov.] 338-355 - French; wind speed determined from UV images.
Caldwell 1972: Retrograde Rotation of the Upper Atmosphere of Venus, Icarus 17  608-16 - Planetary Patrol UV pictures at 360 nm from 1970 analyzed.
Carlson & al. 1991, Galileo Infrared Imaging Spectroscopy Measurements at Venus, Science 253 [1991 Sep. 27] 1541-8 - provides a telling NIMS spectrum and quantitative contrast data for the various NIR windows.
Connes & al. 1979: O2 Emission in the Day and Night Airglow of Venus, Astrophys. J. 233 [1979 Oct. 1] L29-32 - at 1.27 µm it's 1000 times stronger than the visible one.
Crisp & al. 1989: The Nature of the Near-Infrared Features on the Venus Night Side, Science 246 [1989 Oct 27] 506-9 - the bright features at 1.7 and 2.3 µm are explained by thermal emission from the depth of Venus' atmosphere.
Crisp & al. 1991a: The Dark Side of Venus: Near-Infrared Images and Spectra from the Anglo-Australian Observatory, Science 253 [1991 Sep. 13] 1263-6 - discovery of four new thermal emission windows between 1.10 and 1.31 µm during the 1990 campaign.
Crisp 2001: The Nightside of Venus, Science 291 [2001 Jan. 19] 444-5 - puts Slanger & al. 2001 into context.
Crisp & al. 1991b: Ground-Based Near-Infrared Imaging Observations of Venus During the Galileo Encounter, Science 253 [1991 Sep. 27] 1538-41 - the morphology of the NIR nightside features was tracked over time.
Crisp & al. 1996: Ground-based near-infrared observations of the Venus nightside: 1.27-µm O2 airglow from the upper atmosphere, JGR 101  4577-94 - it's patchy, with more than 5 MR in some areas.
Cruikshank 1992: The Ashen Light of Venus, in Edberg (Ed.), Research Amateur Astronomy, ASP Conf. Series 33  43-60 - indepth review of the (lack of) knowledge about the nature of the Ashen Light.
Fischer 1992: Neue Fenster zur Venus? Lehren aus Galileo, Violau Today 1/1992 [June 7] 1 - German; reviews the Galileo and concurrent groundbased results from 1990.
Fischer 2001a: Gibt es das »Aschgraue Licht« wirklich? Skyweek 17 # 3 [2001 Jan. 25] 2-3 - German; reviews the key literature on the Ashen Light phenomenon.
Fischer 2001b: Venus & das Ashen Light: Was Experten sagen, Skyweek 17 # 5 [2001 Feb. 20] 6-7 - German; collected assessments of the nature of the Ashen Light from Slanger, Russell, Crisp and Cruikshank.
Hashimoto & al. 2005: Venus' Nightside Near-Infrared Thermal Radiation: Windows for Sensing Venus' Surface, American Geophysical Union Fall Meeting 2005, abstract #P23E-04 - volcanos could be detected.
Kamp & al. 1988: Structure of Venus' atmosphere from modelling of night-side infrared spectra, Nature 336 [1988 Nov. 24] 360-2 - discovery by Allen & Crawford 1984 explained by thermal emission.
Lawrence & al. 1977: Excitation of the Venus Night Airglow, Science 195 [1977 Feb. 11] 573-4 - airglow between 300 and 800 nm.
Lecacheux & al. 1993: Detection of the surface of Venus at 1.0 µm from ground-based observations, Planet. Space Sci. 41 # 7  543-9 - images with the Pic du Midi 1.05-m show a correlation of low flux features with Magellan topographic maps.
Meadows & Crisp 1996: Ground-based near-infrared observations of the Venus nightside: The thermal structure and water abundance near the surface, Journal of Geophysical Research 101 E2  4595-4622.
Murray & al. 1974: Venus: Atmospheric Motion and Structure from Mariner 10 Pictures, Science 183 [1974 March 29] 1307-15 - TV images at 355 nm full of cloud detail.
Pellier 2004: Thermal Emission on the Venusian Nightside, www.astrosurf.org/pellier/venusthermal - website with his own observations from May 2004; more details on the ALPO Japan site of 2004 May 19, 18, 17, 16 and 12.
Phillips & Russell 1988, The Ashen Light of Venus, Sky & Telescope 75 [1988 March] 250-2 - introduces the 1988 campaign.
Phillips & Russell 1992: The Venus Ashen Light: Results of the 1988 Observing Campaign, Adv. Space Res. 12 # 9  51-6 - no correlations of sightings with anything useful were found ...
Ross 1928: Photographs of Venus, Astroph. J. 68  57-92 - long paper with UV pictures showing cloud structure.
Russell & Phillips 1990, The Ashen Light, Adv. Space Res. 10 # 5  137-41 - the Ashen Light campaign of 1988 and the leading explanations before it.
Scott & Reese 1972: Venus: Atmosphere Rotation, Icarus 17  589-601 - image sequences at 370 nm.
Shiga 2004: Amateur Images Venus' Surface, skyandtelescope.com/news/article_1266_1.asp (2004 June 2) - describes Pellier's breakthrough in imaging the night side in the 1 µm window on May 12, 2004
Slanger & Black 1978: The O2 Bands in the Nightglow Spectrum of Venus, Geophys. Res. Lett. 5  947-8 - nightglow from 400 to 700 nm, as discovered by Venera 9 and 10.
Slanger & al. 2001: Discovery of the Atomic Oxygen Green Line in the Venus Night Airglow, Science 291 [2001 Jan. 19] 463-5 - green line emission at 558 nm.
Travis & al. 1979: Orbiter Cloud Photopolarimeter Investigation, Science 203 [1979 Feb. 23] 781-5 - PVO observations at 365 nm.
Venus Watch by Hans G Lindberg
Lots of amateur pictures of Venus (ALPO Japan collection)
Amateur pictures of Venus since 2001 (ALPO collection)
Galileo's images of Venus from the 1990 flyby (alt. collection)
Mariner 10 images of Venus (and more)
VIRTIS on Venus Express (DLR page on the instrument)
Die Augen des Venus Express (German; Interview with U. Keller on the VMC)
Venus Express' instruments (short descriptions and links to homepages)
Venus Science Planning (PDF)
Europa erkundet den Nachbarplaneten der Erde (German; DLR Press Release on Venus Express, describing among others VMC and VIRTIS)
Venus in K band with the NOT
BAA Venus section's, J. Sussenbach's (!), M. Weigand's J. Warell's and D. Niechoy's Venus and homepages