Observing with Street Lights

Observing with Street Lights
Dark sky sites not always necessary to see the Milky Way (This image was taken ouside of a B&B in Julian, CA)

Tuesday, July 10, 2018

Hooray, first observing session at Mt. Wilson Observatory 60 inch telescope; Is an image from 60 inch brighter than 6 inch scope?

Greetings from Palmia Observatory


Well, our opportunity to observe through the Mount Wilson Observatory (MWO) 60 inch telescope finally came to be.  We had been disappointed many times in past and had to reschedule our session due to weather several times and even forest fires when the dome could not be opened due to flying ash.
After many attempts to reschedule a diverse group of OCA members, I elected to break off and form a separate group of observers, who were not constrained by the need to schedule weekend only viewing sessions, and we were able to put together another group of twelve observers and our first available date was Sunday, July 8.  So we were able to drive up to MWO, about 45 minutes drive from Pasadena up in the mountains above Los Angeles.  Traffic conditions were very good with light city traffic on Sunday and most of our gang didn't have to go to work on Monday morning, so it all worked out just fine.


While we were there waiting, we were entertained by a song and dance routine from Science Nerd and Theatre Impresario, Scott's new Tesla, which raised and lowered its doors and mirrors and lights and sound and went through quite a light, sound and motion show.  Sadly, the other Science Nerd and Theatre Impresario, Sandy, could not make it because of healing up from a recent surgery.  Next time, Sandy, and thanks for that show, Scott!

This meeting at MWO was the first time that many of us had actually been together in person, often just being someone at the end of an email chain, but we all got a long fine.  Thanks for that everyone and I know we all had a great time, even though some of us, gave up at midnight or before!

Also a young University of Arizona astrophysics graduate student, who was taking a class at Caltech, showed up and just on a chance had driven up the mountain to see if she would be lucky enough to see any of the telescopes.  Well, we each had chipped in $85 for every pair of eyeballs, but how can you say no to some interested observer.  Besides, I know for me, as an aspiring astrophysics wannabe, I really enjoy and have appreciated the discounted conference fee that the professional American Astronomical Society (AAS) gives to amateur astronomers.  I often take advantage of that savings and then chose to donate back a portion of my savings to a fund that provides travel expenses so that that real graduate astronomy students can attend these conferences.  So, it was great to give back and let her join our group.  Besides, she answered many of our astronomical questions and she even showed me how to setup my iPhone so that the display was illuminated in red light rather than bright light.  Thanks for all that, Samantha!


July 8 group of OC Astronomers at Mount Wilson or Mt. Wilson 60 inch telescope (Source: Palmia Observatory)
July 8 group of OC Astronomers at Mount Wilson 60 inch telescope (Source: Palmia Observatory)



Part of the success of the evening half night observing session is the observatory staff, who first of all escorted us through the observatory gates, so we could park next to the 60 inch telescope dome, and then explains the history and helps us select available targets for the evening.  Below, our session director, Evan, tells us of the history of the 60 inch dome, which was constructed in 1908 by observatory founder George Hale, and Evan helps us inside and lets us go up the stairs to the observing floor.


Resident Astronomer Peggy listens to MWO Session Director Evan tell about the 60 inch (Source: Palmia Observatory)
Resident Astronomer Peggy listens to MWO Session Director Evan tell about the 60 inch (Source: Palmia Observatory)



Once we were inside the dome, and met telescope operator, John, we had a chance to experience what it must of been like for the early astronomers using this instrument.  Both MWO staff members were so helpful in suggesting targets and helping align and set up our cameras.  They also provided lots of hot chocolate and coffee. Thanks for all of that and everything, Evan and John!

While we were waiting for the sun to go down, we had a chance to climb the ladder and view the bright star Arcturus through the eyepiece.  Viewing some target objects required us to actually lean out and off the top rung of the ladder with maybe one foot resting on the telescope so this first practice session, with the lights on, was very useful.


Getting practice on the observing ladder with Arcturus in the scope at sundown

Observing sessions on the 60 inch MWO telescope are mostly conducted with viewing through the two available eyepieces, but some time is available to take photos through the eyepieces.  Most of our little session group wanted to take photos through the eyepiece and also take some images with our own attached DSLR cameras.  While we were still waiting for darkness, I took one image of Arcturus, without the use of the special MWO adapter, and you can see Arcturus and some of the dome lights reflected in the eyepiece.

iPhone image of Arcturus and reflected dome lights at 60 inch eyepiece without adapter (Source: Palmia Observatory)
iPhone image of Arcturus and reflected dome lights at 60 inch eyepiece without adapter (Source: Palmia Observatory)


When the sky got a lot darker, we moved on to Jupiter.  After we all had a chance to view Jupiter through the eyepiece, the MWO staff (Evan and Telescope Operator, John) installed the little adapter that held the phone cameras in place over the eyepiece.  The adapter would have prevented any reflections from the dome lights, which by this time were turned off.  Take a look at this iPhone image of Jupiter.  Wow, you can even see a little moon in the image too!

iPhone Image of Jupiter taken through the MWO 60 inch telescope eyepiece (Source: Palmia Observatory)
iPhone Image of Jupiter taken through the MWO 60 inch telescope eyepiece (Source: Palmia Observatory)

Next up we had a chance to observe some globular clusters through the eyepiece and some nebulas, but we had to wait a bit for objects to show up in locations where the city lights from Los Angeles did not wash out any detail.  We had everyone participating with either eyepiece viewing, iPhone image capturing, or DSLR imaging.  Attaching a DSLR to the 60 inch scope was just as easy as it is with smaller amateur scopes, which just use a 2 inch T-ring adapter that matches the camera and takes the place of where a 2 inch eyepiece would normally go.

We especially liked seeing M57, The Ring Nebula, and this was the first object we elected to try our hand at doing DSLR imaging on the MWO 60 inch telescope.


First attempt at M57 Ring Nebula in this 15 second DSLR image on the MWO 60 inch scope (Source: Palmia Observatory)
First attempt at M57 Ring Nebula in this 15 second DSLR image on the MWO 60 inch scope (Source: Palmia Observatory)

The screenshot below shows the Sky Safari Pro view of M57 with some visible stars.  I had adjusted the field of view to match the roughly 3 x 2 arc minute field of view provided by the 60 inch scope in combination with my DSLR with its given image sensor size of 22.3 x 14.9 mm.  You can also see at least two of the dim stars shown in the actual camera image, even though the field of view is rotated a bit between these two displays.


Sky Safari Pro Screenshot of M57 with approximate 3 x 2 arc minute field of view (Source: Palmia Observatory)
Sky Safari Pro Screenshot of M57 with approximate 3 x 2 arc minute field of view (Source: Palmia Observatory)


Have you ever wondered if objects seen through a large telescope, like the 60 inch, would be brighter than if it were seen through a small amateur scope?  Well, I had read in one of my astrophysics textbooks that the image is not actually any brighter.  How can that be?   We have already seen that in thee DSLR image of M57 that it required long exposure times, in this one case of 15 seconds.

Ok, so here is my take on that issue and question.  Consider two telescopes, one like the 60 inch telescopes with f/16 optics and 960 inch focal length and another, somewhat like a small amateur scope of same f/16 optics, but only with 6 inch reflector.  This small scope would then have 96 inch focal length, which is quite long for amateur scopes, which for both of my earlier telescopes had f/10 optics, but let's use this f/16 as an example, just to make the calculations easier.

So the 60 inch scope would gather much more light than the 6 inch scope.  The amount of light goes up as the square of the ratio of mirror diameters, so the large scope would capture (60/6)^2 = 100 times as much light.  Now we have to ask, how large is the image in these two cases?  The image in a scope scales up with the focal length.  So the image as seen in a 60 inch scope could have an area that would be (960/96)^2 = 100 times larger.  So, yes you gather more light with the larger scope and the image can be larger as well so the image need not be any brighter.


Finally, as many folks were tiring out and Resident Astronomer Peggy and I decided to call it quits just a bit past midnight (ok, ok, so we don't hang out like we used too), we had a chance to see Saturn.  Now in this image and the previous DSLR image, I really couldn't turn the focus knob enough to get much improvement in focus.  I turned the focus knob all over the place and couldn't see much difference.  Telescope Operator, John, mentioned that some DSLR observers will move the scope slightly so that a bright enough star is visible to focus on that and then move back to the target.  I didn't take the extra time to do that and the stars, which ultimately showed up in the long exposure, could not be seen in LiveView mode.  So, I left the evening not quite sure if the fuzzy nature of the images was due to focusing or to atmospheric seeing or what.

I did confirm though that by looking at the angular size of the targets, and using the 60 inch telescope's focal length of 960 inches, and of my DSLR camera's sensor size, and resultant camera field of view, that the measured size of M57 and Saturn agree with published sizes.  I have seen much clearer DSLR images from the 60 inch scope, so maybe next time, if there is a next time, I will spend some more time and get better focus control.

First attempt at Saturn in this 1/125 second DSLR image at MWO 60 inch telescope (Source: Palmia Observatory)
First fuzzy attempt at Saturn in this 1/125 second DSLR image at MWO 60 inch telescope (Source: Palmia Observatory)


So, that is about it for our first night of observing at the 60 inch telescope at MWO.  It was fantastic just being in such a historic location and imagining all of the astronomical history made at such locations.  As the telescope slewed to different targets it was fun seeing the dome move, along with its own almost tortured sounds of grinding and growling, and then also seeing the telescope move and slew to its next target.  The MWO staff was very diligent about moving the stairs out of the way before moving the scope, of course a collision between the scope and the stairs would probably be a career ending event for the telescope operator.

Any way it was a lot of fun and we had plenty of energy to last most of the night, except Resident Astronomer Peggy and I gave up at midnight, and had also wimped out and already reserved a hotel room in Pasadena.  Even though I am not an astronomical eyepiece observer, relying mostly on my DSLR Liveview, it was neat to look through the eyepiece on this historic telescope.  So, if you choose, and want to have your own experience, join an observing group and make your way to the mountain.


Until next time,
Resident Astronomer George



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