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Conjunction Observing

Posted: Mon Dec 07, 2020 8:32 pm
by Bsimon
Jupiter and Saturn Conjunction
Closest on 12/21/20

Jupiter and Saturn are rapidly coming together from our perspective and will be in close conjunction on 12-21-20 in what will be their closest angular separation in about 400 years. That one occurred in 1623 but Jupiter and Saturn were not well separated in the sky from the Sun so the glare from the Sun made that one very hard to see, virtually impossible for most people to see. Another 400 years back was a close Jupiter and Saturn conjunction seen in the year 1226. Another good one takes place in 2080 but looking beyond that you will have to wait until the 25th century for a real good one.

Jupiter has steadily been approaching Saturn from our perspective and closing the angular separation between the two. (Jupiter laps Saturn approximately every 20 years appearing to pass either above or below Saturn.) This is what we call a conjunction – when they appear to be very close. In reality Saturn is approximately 452 million miles further out from us in our solar system so there is no danger of a collision! Jupiter is 474.73 million miles from the Sun and Saturn is 926.98 million miles from the Sun.

What makes this conjunction especially interesting and unusual is just how close the two will appear to be. The angular separation will be only 6 arc minutes on 12-21, that is just 1/10th of a degree or from our perspective will be equivalent to 1/5th of the Moon’s diameter. As I said, no danger of a collision as Saturn is approximately 452 million miles further out in the solar system than is Jupiter.

As I write this on 12-7-20 the angular separation of the two is 1.6 degrees or what appears to be the diameter of the Moon times 3 (or side by side). Each day the two will appear to be 1/10th of a degree closer. So 1.5 degrees on the 8th, 1.4 degrees on the 9th and so on. One week from now on the 14th the pair will be less than 1 degree apart in the sky, slightly under the diameter of two Moons side by side. The distance continues to close by approximately 1/10th of a degree per day. So on the 16th it is down to 6/10th of a degree, also designated as 36 arc minutes. The next night the separation at ½ degree (30 arc minutes) will appear equivalent to the diameter of the Moon. The angle still closes until the 21st when the separation is down to 6 arc minutes which is just 1/10th of a degree or 1/5th of a lunar diameter. Some people will not be able to find Saturn without optical aid as it will be lost in the glare of Jupiter. Use a pair of binoculars and you will see both.

So here are some specifics for where I will observe the conjunction from near home. While the specifics will change slightly for other locations these times and altitude and azimuth positions should be good for observing locations around the New Orleans area.

12/7 (Mon) Sunset @ 5 pm Civil Twilight ends 5:26 pm Astronomical Twilight ends at 6:25 pm Separation
Alt- 26.7 degrees, Azm – 221.4 degrees Alt – 17.3 degrees, Azm – 232.3 degrees 1.6 degrees
(approx. 3 lunar diameters)

12/14 (Mon) Sunset @ 5:02 pm Civil Twilight ends at 5:28 pm Astronomical Twilight ends at 6:27 pm Separation
Alt – 23.4 degrees, Azm – 226.2 degrees Alt – 13.4 degrees, Azm - 236.2 degrees 0.9 degrees
(just less that 2 lunar diameters)

12/21 (Mon) Sunset @ 5:05 pm Civil Twilight ends at 5:31 pm Astronomical Twilight ends at 6:30 pm Separation
Alt – 19.7 degrees, Azm – 230.8 degrees Alt – 9.1 degrees, Azm – 240.0 degrees 0.1 degrees
(6 arc minutes or 1/5th of a Lunar diameter)

Best time to view – between about 5:30 pm and 7 pm

Note – the separation closes by about 0.1 degrees every day which is about 6 arc minutes

Where to View the Conjunction?
Any location with a low horizon to the southwest not blocked in that direction by trees, buildings or bright lights. For me the 11 acre park jus one block south of my home is the perfect solution. I went and checked it out using the compass on my phone as well as a handheld “traditional” compass as well as a protractor mounted on a tripod to give me some idea as to altitude heights. The photos attached to this post will give you an idea of the viewing location that I will have.

Optical Aid

In the past week or so Jupiter and Saturn can finally both “fit” in the same field of view in a low power telescope eyepiece in a very fast (short focal length and ratio) telescope. On the 7th a telescope with a wide field eyepiece giving approximately between 25x and 30x magnification can just fit Jupiter and Saturn in the same field. They will appear small but 30x is just enough magnification to see the rings of Saturn. Some extremely wide field eyepieces such as a 22 mm Nagler will yield 41x magnification in a 910 mm focal length scope and will give a better view.

By December 14th when the separation is down to 0.9 degrees, magnification can be increased yielding more detail and still getting both planets in the same view. Play with the numbers using the specifications for your telescope (it’s focal length) divided by the eyepiece data (it’s focal length) and it’s field size to see what might work for you.

For instance – on the 14th the separation is 0.9 degrees. In my TMB 130 refractor, it has a focal length of 910 mm. A 17 mm 92 degree field ES eyepiece will yield 53.5 x with this scope. To get true field of view divide the apparent field of this eyepiece (92 degrees) by magnification (53.5) and that gives you a true field of 1.7 degrees. So this combination will easily fit both planets in the same field of view at 53.5x magnification. Going to a higher magnification eyepiece, the ES 12 mm with 92 degree field, the math tells me I am at 75.8x with a 1.2 degree field. So it can still be done but the planets are maybe a bit tight in this field.

Higher magnification can be achieved with most telescopes at magnifications over 200 x in and one or two days on either side of 12-21-20. The planets appear close. The view below approximates the view thru a 1800 mm focal length scope with a 7 mm eyepiece with an 82 degree apparent field of view. This is a high magnification of 257x but as the angular separation of the planets is so close at 0.1 degrees (6 arc minutes) they both fit and good detail can be seen.

Barry Simon

Re: Conjunction Observing

Posted: Tue Dec 08, 2020 12:26 pm
by Lmccormick
Last night from my driveway (12/7). Canon 50D (cropped sensor) & 100mm "L" lens (for full frame camera). I think this is equivalent to a 160mm focal length.


Re: Conjunction Observing

Posted: Tue Dec 08, 2020 2:39 pm
by Bhousey
Yesterday evening I was able to see both in the same field in my 66mm refractor (380mm FL) and a 9mm Nagler eyepiece. They were near opposite sides of the field, but I could very clearly see the rings of Saturn and banding on Jupiter, as well as its moons. This is really exciting!

Re: Conjunction Observing

Posted: Tue Dec 08, 2020 6:34 pm
by Bhousey
Ok, I just got in from today's look at the planets getting closer. My thinking today was that if my view yesterday with the 66mm refractor with 9mm Nagler was fantastic, my 8" planetary Newtonian with a 40mm Pentax would be mind-blowing. Wrong. I've heard about this but never encountered it before. I built my scope with a tiny 18% obstruction and a very low profile Feathertouch focuser to keep the eyepiece close to it... gives breathtaking views at planetary high powers (only drawback is eyepiece swings all over the place on an equatorial, but that's another story).

Difference is, at this early point in the conjunction, I needed a wide field, meaning low power. The 40mm Pentax gave me 25x. Problem is, the shadow of the inch-and-a-half secondary, normally tenths of a millimeter on the exit pupil, turns out to be over a whopping millimeter or two at this low power! So looking at either of the planets in the field had the shadow covering my fovea, where all the eye's resolving power is. Averted vision worked better... first time ever on planets!

So upshot is, until the planets get closer together and I can use high power, sticking with unobstructed scopes seems like a better idea. Score one for refractors, this round.


Re: Conjunction Observing

Posted: Wed Dec 09, 2020 1:35 pm
by Lmccormick
This was shot using a Vixen ED80/f7.5 and a Cannon Rebel T2i (cropped sensor) at 1600 ISO and 1/30sec. I had to turn the camera vertical to get them both in the frame. Saturn comes out better with a shorter exposure but that makes the moons of Jupiter invisible.

Re: Conjunction Observing

Posted: Thu Dec 10, 2020 10:57 am
by Bsimon
I did observe Jupiter and Saturn last night from Tourmaline Park (center of East Lakeshore). I walked from home carrying a camera tripod, heavy eyepiece case and a case with my AstroTech 102 EDF (f = Feathertouch). I set up just at about sunset/5 pm and then waited with Jupiter popping into view just at about the end of Civil Twilight/5:30 pm.

The first eyepiece used was a 26mm Nagler which in the 709 mm focal length scope has a magnification of 27x and a field of view of 3 degrees. Way more than enough to capture both Jupiter and Saturn but really to low to do much in respect to seeing the rings of Saturn. I then switched to a 22 Nagler which kicked the magnification to 32x. The rings were visible and the field was now 2.5 degrees. I did not go to higher magnification as the field would have been too tight.

Philip Wollenberg (PAS president-elect) walked over with his wife and young son. He had his 13 mm Ethos eyepiece for his use in my scope. It produced a magnification of 54.5x and a field of 1.8 degrees which was just enough to squeeze in both planets.

My wife, Susan, also walked into the park and took a peek. She said it was one of the best astronomical views she had seen in a long time.

It will only get better as they move closer and we can bump the magnification to higher and more impressive levels. Note - we could see banding on Jupiter as well as 3 of the Galilean moons.

Barry Simon

Re: Conjunction Observing

Posted: Thu Dec 10, 2020 11:54 am
by Bhousey
"with Jupiter popping into view just at about the end of Civil Twilight/5:30 pm"

Barry, just wanted to let you know about something I tried the other night that's changed things for me. A few months ago, I loaded "SkySafari Plus" on my iPad, about $7 I think. This has an AR mode (augmented reality) that lets you point an iPad and it shows you the actual trees in front of you, with the current position of Jupiter/Saturn superimposed over it. Not espousing too much tech with a nature hobby, but this really helps. I was able to locate Jupiter like this starting at 5:00, letting me even do it from my yard (the trees actually helped since the iPad showed me right where to set up).

Also as a side note, and I'm sure you're aware of this already, but viewing Jupiter (or Mars) at twilight is often better than after dark. After dark the contrast with background is too intense and it's difficult to see Jupiter cloud tops / Saturn ring detail / etc. 5pm is a fantastic view right now!

Enjoying your reports!

Re: Conjunction Observing

Posted: Wed Dec 16, 2020 5:24 pm
by Bjohnson
As if this is not a big enough event on it's own, there is a transit of Ganymede across Jupiter about 6:05 PM on the 21st.
Hoping to see this as well, and that some of our more experienced photographers can get some good pix to share.

Re: Conjunction Observing

Posted: Wed Dec 16, 2020 9:49 pm
by Bsimon
The past few days has been bad for observing the Jupiter-Saturn Conjunction but Thursday evening looks promising. The separation is down to 1/2 degree (one lunar diameter) so Jupiter and Saturn are close enough to fit into the field of view of many eyepieces that are operating at magnifications of 50 to 100x (depending upon field of view). Plenty enough magnification to see the belts of Jupiter, and the rings of Saturn with detail and all in the same field!

You do need a low horizon. The 11 acre park in the middle of East Lakeshore where I live and just a few blocks away from our new President-Elect's home. No, not Joe Biden, I am talking about Philip Wollenberg, our next PAS President. I will be there at about 5 pm tomorrow. Note - I will have a scope, but because of Covid, I cannot share views thru any of my eyepieces. You can bring your own and we can put it in my scope if you do not bring a scope so you can take a look.

Will post direction instructions on Thursday.

Barry Simon

Re: Conjunction Observing

Posted: Thu Dec 17, 2020 11:18 am
by Bsimon
As I said in the last post on this thread I and a few others will be observing the conjunction tonight, as well as Friday night (if clear) from Tourmaline Park in the center of East Lakeshore. See the 3rd image attached to the first post in this thread for a map.

The road running along the bottom of the image is Robert E. Lee Blvd. (soon to be renamed "Morgus (the Magnificent) Drive" The road running in a vertical direction near the left side of the image is Canal Blvd. If coming up Canal Blvd,, continue north past the light at Robert E. Lee and turn right on Jewel Street which is about 1/4 mile or so north of R.E.Lee. Go two blocks and you are at the northwest edge of the park. Continue along the north side of the park and you should see me and others set up in the park. I will be there no later than 5 pm.

Note - sharing of eyepieces for those that do not bring their own telescope: Most people, including me, will not share views thru eyepieces that we are using as long as Covid is still a very real risk. I will bring several extra eyepieces for use in my telescope. If someone wants to look at the conjunction I will remove the eyepiece I am using and replace it with a "fresh" eyepiece. Once that eyepiece is used by someone it goes into quarantine and I will not look thru it that night nor would I suggest that others look thru it either. I am only bringing appropriate eyepieces that I have that will properly frame Jupiter and Saturn. Magnification should be in the 50x to 80x range depending upon the eyepiece. If anyone wants to bring their own eyepiece that is fine too. I would suggest at least a 24 mm to 40 mm in a 1.25" format with a large apparent field, at least 65 degrees. Anything less and we will not be able to get Jupiter and Saturn in the same field. If bringing a 2" format eyepiece, I would suggest eyepieces with a 65 degree to 100 degree apparent fields.

What others are willing to do with their equipment is up to them. Sorry to sound anal about this but we are going to spend time with the kids and grandkids over the holidays and we do not want to take any unnecessary risks with COVID still rampant.

Barry Simon