2002
March 4/5 : Saturn's Titan satellite identified from methane absorption
bands - the only satellite with a substantial atmosphere that modifies
reflected sunlight. Rainbow diffraction grating used in non-objective mode
immediately before the CCD. Compare to 1994 results below via large
objective prism. Vesta [similar mag 8.2 to Titan in nearby field]
reflects the G-type solar spectrum virtually unmodified. Its motion
obvious in 30 minutes via dual star images in co-added 30s exposures.
The comparison spectra below shows Titan, with deep methane absorption bands, is identical to Mars in the blue [LH] region whilst Vesta is overall much bluer and a fair match for b Ari ie as if illuminated by a hot A-type star in the blue region. All satellites and planets are illuminated by the sun - a G5 type star.
1999
Sept 3/4: Uranus and Neptune targeted for their spectra and appear
[as they did 1998 Oct -see below] essentially identical showing wide methane
lines. With their current southern Dec and low altitude, there is sharp
cut-off in blue due to Earth's atmospheric absorption.
Pluto at mag ~13.5 is at about the limit of the 30cm SCT with Rainbow
grating - and included here for novelty value only.
1998
Dec 21: Mercury is a challenging object at the best of times - and
no less so its spectrum ! This spectrogram, snapped at dawn, finished off
a session on the redshifted quasar 3C273 in Virgo. As Mercury has no atmosphere
the spectrum is just reflected sunlight but essentially records the strong
lines superimposed by the Earth's atmosphere - mainly watervapour and oxygen.
The blue end of the spectrum is partially absorbed due to Mercury's low
altitude at the time. The IR region of the spectrum (immediately right
of the strongest line - A) is far less effected by such absorption and
is well recorded to include the Z band etc. Mercury's
curved spectrum explained
Spectrum of Venus (reflected sunlight) and Aldebaran compared - both show the strong absorption lines A, a and B in the far red from oxygen and water-vapour in the Earth's atmosphere. Spectrum of Venus snapped in bright evening twilight with the Meade SCT stopped down with an off-axis mask to about f/50. Rainbow grating ~50mm from the MX9 CCD for somewhat higher spectral resolution via this grating. The spectrograms have been colorized and do not represent true colours.
1994 Dec 5: an early [and now reworked above] spectrogram of Saturn and Titan showing methane lines with Mars for comparison via a full aperture OG before a dedicated 26cm f/4 reflector - the camera at first focus within the telescope tube. Some of the finer lines are artefacts of image processing. Interestingly the scale and resolution of Venus image [above] via the Rainbow grating at the Meade SCT focal plane [note the A, a and B lines] is reasonably comparable to the massive OG prism before its dedicated 'scope!
1998 Nov 5: more recent 'methane' spectrograms of Saturn via the Rainbow
grating at the focal plane of Meade SCT.
A
composite colour image of the spectra of Uranus and Neptune which shine
by reflected sunlight were captured with the home-made Mk1a spectroscope
[featured on 'spectroscopy' page - top image centre+right]. Both planets
located automatically in the sky via the Meade LX200 telescope's 'goto'
facility and were immediately identified on download by their unusual (non-starlike)
spectra. The methane absorption bands in Neptune's atmosphere are reputedly
stronger than those of Uranus but only marginally so as shown here.