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Observation by Mike Harlow: Nova Cas 2021: Image and spectrum

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Mike Harlow


Mike Harlow


2021 Sep 11 - 20:40


2021 Sep 12 - 13:55


Nova Cas 2021

Planetarium overlay



Field centre

RA: 23h24m
Dec: +61°11'
Position angle: -2°41'

Field size

0°46' × 0°46'

  • 12 inch F/3.6 astrograph
  • Starlight Xpress H16 CCD (2048 x 2048 pxl)
  • Astrodon luminance filter (400-700nm)
  • 22cm, 12 degree objective prism

Image 20 x 10 seconds. Spectrum 8 x 20 seconds


Ipswich, UK

Target name

Nova Cas 2021 = V1405 Cas


Nova Cas 2021: Image and spectrum

About this image

An image and spectrum of Nova Cas 2021. I just missed the latest peak of ~ mag. 6.5 which occurred early on 10th September but the nova was still just above mag 7 when the image was taken.  The spectrum was taken immediately afterward by attaching the 22cm, 12 degree objective prism to the top of the telescope tube.

The spectrum is slightly different from my previous attempt on 17th August showing much stronger P-Cygni profiles on the hydrogen Balmer lines and stronger emission lines that could be due to Fe II.  A more detailed spectrum appears on the ARAS web site (bottom of the page).

The field of view of the image is 46 x 37 arc minutes with north up.

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Paul Leyland
Paul Leyland, 2021 Sep 12 - 19:34 UTC

Very nice!

How did you obtain your objective prism? For many years I have wondered whether one could reasonably be built by containing some liquid such as water or CCl_4 between two suitably inclined sheets of transparent material.

Mike Harlow
Mike Harlow, 2021 Sep 12 - 21:05 UTC

Hi Paul,

The prism was part of the BAA instrument collection for many years and I was lucky enough to buy it when the collection was sold off a few years ago...I had it on loan at the time. They are very much old technology now but I like the fact that an imaging scope can be converted to a spectrograph just by putting a wedge of glass on the front!

There must be other prisms out there, probably just sitting in storage at professional observatories.  May be worth getting in touch with some to see what they say? Cambridge, Mill Hill (UCL), Edinburgh??? And Norman Lockyer observatory did objective prism work many years I guess David Strange may know if they have anything suitable?

I was so impressed with the 12 degree prism that I made a 3 degree version for fainter objects (lower dispersion), details in the March 2021 OASI Newsletter (as a .pdf file for download). If you know any ex-mirror makers that would like a new challenge that could be a project but getting the optical glass is the problem!

A liquid filled cavity between two sheets of good quality glass may be an option.  But the seal would have to be 100% safe to avoid filling the telescope with water if it failed!!!

So just a few thoughts there, hope they help.


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