Astronomy

Orion M42
I am an astronomy keen and used to be a member of the Club JANUS  in Gennevilliers and of the  SAF (Société astronomique de France)

The observation of the sky in the Parisian area is seriously challenged by the light pollution. More, weather in our zone is most of the time disappointing.

 

 

  Topics  

 

  The Moon and the planets

 

 

The planets, the Moon and the Sun are the allowed targets in a hardly light-polluted sky. For that, I put my SC8 Celestron (203 mm aperture, f/d 10) in my third floor loggia, facing the south-west. I use an Olympus OM1 camera and a Barlow or ocular projection to get a resultant focal length from 4000 to 7000 mm .

Jupiter Jupiter SC8 200 mm - ocular projection.
Enhancement of the equatorial zone.

Saturne Saturne
SC8 200 mm - ocular projection

Vénus Vénus
SC8 200 mm Barlow 2x
       
  The Sun   SoleilThe Sun in Octorer, 1991SC8 with a TOO grade 2 filter.
Activity was at its maximum.

taches Sun spots
Barlow x2. Low resolution; the seeing on the Sun is disastrous from a balcony.
       
  Photography of meteors

 

 

This is a summer entertainment. The Perseids offer the easiest opportunity, with a regular flow spread on two or three days from the 11th to the 13th of August and a ZHR about 50/80 (ZHR = zenith hourly rate).
I used up to 4 cameras with 50 and 58 mm f 1,2, 24 mm f 1,4 and 35 mm f 1,4 lenses.
(by the way I lost my collection of the few photographs that I took at the mid 90' and can't display any - no matter, none was great)

With a lens of 50 mm f 1,2 fitted on a 35 mm camera loaded with a film of 400 ASA, the mean score is about one hit on thirty photographs of 5 minutes each. The score grows up to one hit on ten pictures with a lens of 24 mm f 1,4. However on the film the image of an ordinary weak meteor measures only 3 to 5 mm with a 24 mm lens, pretty small to enlarge it.


Suggestions for the photography of meteors :

If the Moon is there, keep sleeping in your bed or do anything else but not meteor photographs.

- forget absolutely the zoom lenses (this idea sounds funny).
- use a lot of cameras, with a mix of 50 mm and 24/28/35 mm lenses. Mechanical cameras are by far better to avoid waste of cells. Have releases with clamps.
- it is hard to manage more than 4 cameras. Plan place, order, time of exposure, number of films and so on. Have a check list. Have hot drink, appropriate clothes, a red light and a straight light to find what you would have let fall.
- load cameras with B&W 400 ASA that you will develop hard. Write numbers on film canisters.
- travel to a dark place (absolutely impossible in suburbs)
- stand firmly the cameras on tripods or any firm mount (a pier, a wall etc..). Load the legs with weights. If you have an astro mount, you may use it to have stars like points but this is not mandatory at all.

Open your lenses at their maximum aperture. Expose about five minutes at f 1,8 and other lenses according to their aperture. Nota : the maximum time for an exposure depends on the darkness of the sky. It could be possible to reach 20 minutes in a wild desert and no Moon.

Sample of an heavy set : (positions for the Perseids)
- two cameras facing north, on left and right of Polaris, with an 35 mm f 1,4 lens and/or 24-28 mm 1,4
- two cameras facing south with 50-58 mm f1,2, 45 ° up on horizon, left and right of meridian for the first part of the night, coming west for the second part of the night.
- one camera with a wide angle facing the radiant (a joker if nice close bees occur)
- one more joker : a camera with a fish-eye pointing to the zenith (to record a possible bolid of negative magnitude).

During the night, you have to adjust the position of the cameras to keep them towards the zone of probability : 45 ° up and 90 ° from the radiant point. Thanks to the Perseids, the holly gift for meteor photographers, pointing to Polaris remains valid all the night long.

Photographs may be achieved only during the astronomical night and   The positive flow spread on an hour and a half coming after dusk and before twillight. Therefore, at 48° north, and close to the meridian zero, the schedule is around 9 h 30-11h00 TU and 1h30-3h00 TU.

A lot of other streams of meteors exist all the year long. Some have higher ZHR than Perseids, but no one is altogether strong, spread and constant like them.
  - the Quadrantids 4/5 January ZHR 100 but only a few hours
  - the Geminids 12 December ZHR 80
   - and a special mention to the Leonids, about the 17th of November, which may produce meteor showers every 33 years. It may or may not happen and is about one hour long, so it may be seen only by the happy few.

Catching such a shower is a dream, not impossible but the glory of an astronomer's life.

The opportunity was serious in November of 1998 as the Moon was very weak (two days before the new Moon), and as the Earth crossed the main streams of the Leonids.

The 1998 flow was deceptive everywhere but in the Canaria Islands. It was also deceptive in Thailand, China and Japan, where the predictions were the most positive. I was in the northern Paris area and weather was foggy. Wandering from place to place to find holes of clear sky, we saw very few weak meteors, but were lucky enough to see a magnificent fireball crossing the third quarters of the sky right upon us.

In 1999 the Moon was at 56 %.

 

       
  Comets

 

 

Hyakutake and Hale-Bopp

After 20 years without great comets (the last beeing the comet West in 1976) 1996 and  1997 have been golden years.

Hyakutake near the North pole Hyakutake

Hyakutake, in it's own, is a somewhat faint comet, but it travelled so close to the Earth that it sight was breathtaking. It could be seen with the naked eye even in an urban light-polluted sky. In a widefield telescope its moving  was noticeable nearly directly.

       
     

Hale-Bopp is a big comet, wich remained 2 years as a target for telescope observers and grossly 4 months at the naked eye.

Hale-Bopp in the dusk, april 1997 Hale-Bopp

Hale-Bopp300 mm 2,8 - the tail is recorded only on 2 or 3 degrees
Kodak Elite II 400 ASA -  50 seconds.

Hale-Bopp noyauthe core with an SC8 - 200 mm
Kodak TMax 400 ASA

The core showed circular shells. That picture is far from the view in the ocular

       
       
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Copyright of the author : © Dominique Césari - mail
Last update :  03 - 07 - 2001