DSLR Photometry Experiments. 4. How many darks?

When performing photometry on DSLR images, should dark frames be stacked and subtracted from the light frames? If so, how many dark frames should be used, and which stacking method should be employed? This experiment attempts to answer the first question by evaluating the signal-to-noise ratio (SNR) of stars on an image from which different numbers of dark frames have been subtracted.

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Working with constellations in DOCdb

Constellations, of course, aren’t “real” objects, but they are a handy way of slicing up the night sky into more manageable chunks.

Having the sky sub-divided in this way immediately suggests an observing project: carefully examine each chunk of sky for anything and everything interesting. This raises the question: when is a particular part of the sky well-placed for observing?

With the recent addition of “constellation place holders” to the DOCdb database, this is now easy to answer, using the DOCdb List Plan option. Here’s the step-by-step guide.

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"Nightfall" - the deep-sky observing newsletter

[1] Editorial

[2] News Notes

[8] Three in: Carina by Dave Blane & Auke Slotegraaf

[19] E3 — A curious globular cluster in Chamaeleon by Douglas Bullis

[28] Heartbeat of a Unicorn — Exploring the fascinating but often overlooked constellation of Monoceros by Carol Botha

[31] Birth of a Deep-Sky Marathon — A report from the 2014 Free State Star Party, with guidelines and recommendations for conducting a deep-sky observing marathon by Hannes & Pieter Pieterse

[50] At My Eyepiece — Veteran deep-sky observer Magda Streicher gives us a look at how she observes. by Magda Streicher

[56] Deep-Sky Projects

[57] Photo Gallery

[59] On The Cover

[appendix] Big 5 of the African Sky

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Earth Hour lights-out seeks to illuminate climate plight

Earth Hour – South Africa

Earth Hour: What is the carbon footprint of an email?

Boyden Observatory in the light pollution glow

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The Boyden Observatory is not next to the light pollution from "next door neighbours" anymore. It is right in the glow. Not long before the Milky Way will be an image on the screen and not a magnificent object in the Boyden night sky.

"next door neighbours" -  Maselspoort resort and all the owners on the banks of the Modder River.

• A close-up view of the Bloemfontein area

Earth Observation Group (EOG)

The NGDC Earth Observation Group (EOG) specializes in nighttime observations of lights and combustion sources worldwide. The group started working with DMSP data in 1994 and has produced a time series of annual cloud-free composites of DMSP nighttime lights. EOG's current focus is on nighttime VIIRS data.

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15P/Finlay is now a binocular object due to a series outbursts.

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Hot bright news (26 January 2015) Chart date 26 January 2015, 20:30
from Bloemfontein, South Africa.
Source: Comet Chasing in January; Chart: Skytools 3

15P/Finlay is now a binocular object! It brightened by several magnitudes on January 16, on top of a similar episode in mid-December, apparently due to a series outbursts.

Coma Diameter: 3.9'
Earth Distance: 1.4 AU
Sun Distance: 1.1 AU
Elongation:  49°
Tail Position Angle:  65°
Tail Forshortening: 30%
Actual Coma Diameter: 240000 km
DC:  1
Total motion: 3.06 "/min
   RA:  2.71 "/min
   Dec: 1.44 "/min

Print a Naked Eye Star Map for the Southern Hemisphere

 

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• Download and print Naked Eye Star Map for the Southern Hemisphere
  
  (Select Southern hemisphere, the time and the type of map)

Examples

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C/2014 Q2 (Lovejoy)

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Comet C/2014 Q2 (Lovejoy) from 11 - 25 January 2015 (21:00) in the South African Night Sky.

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