Venus features at 300 to 3000 nm wavelength

A systematic survey of known spectral »windows« in which Venus is more

than a clean white disk with phase and absolute darkness beyond the terminator and which are in the NUV to NIR range and thus accessible - in principle - from the ground, as a motivation for observation attempts by amateurs during the mission of Venus Express

wavelength (nm) day- or nightside? from where? processes involved? references
350-370 day cloud deck 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) night upper atmosphere 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
418 day upper clouds sunlight reflected at 60 to 70 km, locally absorbed Belton & al. 1991
558 night upper atmosphere emission from atomic oxygen Slanger & al. 2001; Crisp 2001
850 + 900 night surface weak thermal emission Baines & al. 2000
986 day upper clouds sunlight reflected at 60 to 70 km, locally absorbed Belton & al. 1991
1010 night surface thermal emission Carlson 1991; Lecacheux & al. 1993; Meadows & Crisp 1996; Baines & al. 2000; Pellier 2004; Shiga 2004
1100 night surface thermal emission, modulated by topography; low-contrast absorption by higher clouds Crisp & al. 1991a; Meadows & Crisp 1996
1180 night surface 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
1269 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
1310 night very deep clouds thermal emission; low-contrast absorption by higher clouds Crisp & al. 1991a
1740 night deep clouds 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. 1991
2300 (esp. 2210 and 2320) night deep clouds 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

Summary (draft! to be extended)

Looked at through a telescope in visible light the planet Venus is a dazzling but totally bland white disk with the phase and some limb darkening the only effects detected reliably. Whether dark features on the disk seen by some visual observers are real at all is a matter of debate; CCD imaging - which has hugely advanced amateur studies of e.g. Mars and Jupiter in the past decades - does not verify these sightings conclusively yet.

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:

Amateur astronomers with CCDs could try - and have sometimes already succeeded - to detect and track the cloud streaks on the dayside with suitable filters and high-pass spatial filtering. And they could go for the shortest-wavelength window in which thermal emission escapes - as has been done soon after its discovery with a 1-m telescope (Lecacheux & al. 1993) and recently even with a much small amateur instrument and a regular CCD camera (Pellier 2004).

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.

References

Allen & Crawford 1984: Cloud structure on the dark side of Venus, Nature 307 [1984 Jan. 19] 222-4 - discovery paper of the NIR emission windows.

Allen 1987: The Dark Side of Venus, Icarus 69 [1987] 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 [2000] 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 [1994] 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 [1972] 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 [1996] 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 [1992] 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 [1993] 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 [1996] 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 [1992] 51-6 - no correlations of sightings with anything useful were found ...

Ross 1928: Photographs of Venus, Astroph. J. 68 [1928] 57-92 - long paper with UV pictures showing cloud structure.

Russell & Phillips 1990, The Ashen Light, Adv. Space Res. 10 # 5 [1990] 137-41 - the Ashen Light campaign of 1988 and the leading explanations before it.

Scott & Reese 1972: Venus: Atmosphere Rotation, Icarus 17 [1972] 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 [1978] 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.

Other relevant websites

VAOP, ESA's Venus Amateur Observing Project (related BAA announcement)!

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

Preparation of document started 2005 Nov. 21, extended Nov. 24 and 30 and 2006 April 18 by Daniel Fischer