Comparing spectra when spectroscope pointed at garden and at sky above garden (DIY Spectrometer)

I decided to compare the spectra when I pointed the spectroscope at the grass in the garden as opposed to pointing it at the sky. The sky gives a solar spectrum (cloudy today).

Please note that after posting the following, I later discovered that there were some significant errors in the calibration values obtained here, although this does not affect the main lessons of the post re spectra from pointing at garden vs. sky – see https://roslistonastronomy.uk/solar-spectrum-taken-at-lro-26-8-2018-using-diy-spectrometer

Andy

The following spectra were taken using the optical cable from the DIY Spectrometer connected to its modified Cheshire attachment but WITHOUT either beam splitter or telescope being used.

They both show the solar spectrum but the intensity on the y-axis is nearly 20x as high when pointed at the (cloudy) sky than at the grass – I did not expect this degree of difference as although I say it was pointed at the grass it was only vaguely in that direction and I would have expected large amount of light to have got in any way. The modified Cheshire does only allow reasonably collimated rays of light to get in to the optical fibre which would amplify this effect. The higher intensity solar spectrum when pointed at the sky is also a lot cleaner with less noise.

With optical cable pointed at the grass in the garden:

With optical cable pointed at cloudy sky above garden:

The following spectra were taken using the optical cable from the DIY Spectrometer connected to its modified Cheshire attachment which was then attached to Sky Watcher Equinox Pro 80mm via beam splitter (so this is with telescope).

With the telescope and beam splitter, I needed to use longer exposure times. Note that with cable alone above I only used 50 ms. The exposure time when using the telescope and beam splitter and with the combination pointed at the garden required a lengthy 60,000 ms to obtain the spectrum below. I got away with a lower 500 ms when pointing the telescope at the sky.

Although requiring a longer exposure time with telescope than with optical cable alone, when pointing both at the sky excellent clean solar spectra are obtained.

The telescope pointed at the garden does have the features of the solar spectrum in it but they are largely swamped by noise.

Note that these spectra are all taken during DAYTIME.

With telescope pointed at garden:

With telescope pointed at sky above garden:

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