Mike Lewis
Staff Member
So firstly, if you are any sort of a serious astroimager and you do not yet have a copy of the wonderful Charles Bracken book 'The Astrophotography Sky Atlas' I submit that it is some of the best money you can spend on your hobby going forward. Here is a link to it on the USA Amazon site: https://a.co/d/byzRclG A truly productive expenditure of ~$33 USD in my opinion. The book lists a plethora of targets, both in an index form and in sky atlas presentation. I use it all the time to find imaging targets. One of the best pieces of info it lists is the 'Ideal Date' for each object. This is the date when the object spends the longest period of time visible in the night sky. That allows you to immediately have a good feel as to whether a particular object might be a good target choice for a particular night.
In my case as I have started to be able to image much more frequently I have begun to branch out to some lesser known targets, some of which do not appear in the fine book I have referenced above. I decided to reach out to Mr. Bracken to see if he would share the calculation required to come up with the 'Ideal Date' for a given object and he was kind enough to promptly email me back with just such a calculation. So I share it here in case anyone want to use it. I have it in my Excel Target List spreadsheet now so I can quickly fill in the Ideal Date column on any targets I wish to go for that might be outside the scope of the atlas. My Excel formula is:
=TEXT((DATE(2025,9,23)+((J16)+K16/60)/24*365),"MM.DD"), where cell J16 hold the Right Ascension of the proposed target object in hours, andcell K16 holds the Right Ascension of the proposed target object in minutes (could be fractional).
This then returns a representation that looks like a decimal value of the form Month.Day, which I copy into the Ideal Date column of my target spreadsheet as a number. This allows an ascending sort of the target table to show the best availability for the targets in order through the year. I also have an additional tab of the same table that I sort by object designator, very useful to show which targets I am looking for currently, as well as listing targets I have already successfully imaged.
Anyway, in case anyone wants this calculation here it is. And even more than that, go take a look at this wonderful sky atlas - I don't think you will regret buying one
ML
In my case as I have started to be able to image much more frequently I have begun to branch out to some lesser known targets, some of which do not appear in the fine book I have referenced above. I decided to reach out to Mr. Bracken to see if he would share the calculation required to come up with the 'Ideal Date' for a given object and he was kind enough to promptly email me back with just such a calculation. So I share it here in case anyone want to use it. I have it in my Excel Target List spreadsheet now so I can quickly fill in the Ideal Date column on any targets I wish to go for that might be outside the scope of the atlas. My Excel formula is:
=TEXT((DATE(2025,9,23)+((J16)+K16/60)/24*365),"MM.DD"), where cell J16 hold the Right Ascension of the proposed target object in hours, andcell K16 holds the Right Ascension of the proposed target object in minutes (could be fractional).
This then returns a representation that looks like a decimal value of the form Month.Day, which I copy into the Ideal Date column of my target spreadsheet as a number. This allows an ascending sort of the target table to show the best availability for the targets in order through the year. I also have an additional tab of the same table that I sort by object designator, very useful to show which targets I am looking for currently, as well as listing targets I have already successfully imaged.
Anyway, in case anyone wants this calculation here it is. And even more than that, go take a look at this wonderful sky atlas - I don't think you will regret buying one
ML
