Sunday, December 27, 2020

A Great "Get-together"

 

One of the rare events in the sky is a conjunction of the two largest planets in our solar system.

I logged into Slooh.com on December 21 to watch their live presentation as this conjunction was in progress. There was also a link to the International Astronomical Center in Abu Dhabi, U.A.E.  The image below originated there; it was shown during the presentation, Saturn at the upper left, Jupiter lower right. 

One day later, the Simon Fraser University's Trottier Observatory did the same thing through its telescope on line, with assistance by the RASC. I also watched that well done presentation via YouTube.

Jupiter/Saturn conjunction (International Astronomical Center)

This conjunction was the result of a particular positioning of Jupiter, Saturn, and Earth in their respective orbits. At the time pictured, the visual separation in the sky of Jupiter and Saturn was about six arc minutes, which is about one fifth of the apparent diameter of our Moon as we see it from Earth. That essentially "united" the two planets into one brighter "star" when looking with our unaided eyes. In reality, Saturn is about 700 million kilometres "behind" Jupiter from Earth's point of view. For perspective, Jupiter is approximately five times Earth's distance from the Sun, Saturn almost twice as far.

The large planets in our solar system orbit the Sun in approximately the same plane; Earth's orbital plane is taken as the reference. As a result, the sun 's annual apparent motion across the sky from Earth appears to be the same from year to year with very small changes over time. This path is called the Ecliptic. The larger planets have orbital planes which are close to the ecliptic, but deviate from it to varying degrees. From our Earth-bound point of view, therefore, for them to appear very close together, such as the Jupiter-Saturn conjunction, happens only now and then. Jupiter can even cover (occult) Saturn, but that is a very rare occurrence. It would require that the centres of Earth, Jupiter, and Saturn be exactly on one specific line. The latest Jupiter-Saturn conjunction came very close to that possibility.

The two planets move quite slowly. Jupiter takes about 3 hours for a distance equal to its own diameter, Saturn is even slower. Both move in the same direction. That means the they will be visible in a pair of binoculars at the same time for a number of days. Standard binoculars have fields of view in the order of 5 to 7 degrees. On January 1, 2021, Saturn and Jupiter are about 2 degrees apart, easily within the same  binocular field of view. Unfortunately they are positioned so close to the sun at this time that they will set closer to sunset every day, so following both planets is going to get more difficult. For this purpose, use your binoculars only after the sun sets. Never look at the sun directly through binoculars, or even with your unprotected eyes only; permanent eye damage may be the result!

Covid-19 is forcing us to keep separate for the time being, it was a good thing to see at least one "heavenly" get-together.
 


Monday, November 30, 2020

An old Workhorse


Since the invention of the telescope and its use for astronomical purposes, the exploration of the universe has progressed at first slowly, and then much faster. That also included advancement in the performance of telescopes themselves. The two main types of telescopes, refractors and reflectors have been around for about 350 years.

Among both types of telescopes, I own one that is my particular favourite. It's a 75mm refractor, purchased used in 1964; its true age I don't know. Here is a picture:


This 75mm, f16 refractor came with a solid wooden equatorial mount tripod (hand-driven tracking). 
The telescope is now mounted on an used EQ5 tripod, purchased about three years ago. 
Right-ascension-tracking and declination motors are powered by a D-battery power pack (not shown).

The telescope has the brand name "Polaris", and someone told me that it is the European version of the "Unitron" brand which was very popular here in North America in the middle of the last century. It has an achromatic objective - chromatic aberration is almost unnoticeable because of the large f-ratio. The telescope produces beautiful views of the major planets, the moon, and open star clusters, but is just on the borderline of dissolving globular clusters into individual stars (i.e. M 13). It's also pretty good at showing the brighter nebulae (Orion nebula, Dumbbell, etc.) and double stars (Mizar, Alcor, the "double double" Epsilon Lyra when pushed to 130 times magnification power, and much more). It's my preferred telescope for Public Astronomy Nights.

In previous centuries, instruments of this size and performance (3", 4", and somewhat larger telescopes) were used to do serious scientific work. For instance, Johann Heinrich von Mädler and Wilhelm Beer produced a highly accurate atlas of the Moon (in four volumes fro 1834 to 1836). It was used by astronomers for over a century.  Mädler  and Beer also produced the first reliable Mars maps and were instrumental (pun intended) in assigning Sinus Meridiani as the Prime Meridian on Mars. Photography was not yet available, so all maps were hand-drawn. Here's an example:  

A part of the "Mappa Selenographica" by Mädler and Beer.

(from planetologia.elte.hu)

Mädler and Beer were also able to determine the rotation period of Mars to within 1.1 seconds. It is highly admirable that astronomers made such demanding observations with telescopes of really moderate size. Even today, refractors built many years ago are still in use for scientific research. 

Photography through my 75mm (3") telescope is also possible. With today's digital cameras and technology it's much easier to take some good pictures. Below is an image of the southern part of the Moon, taken with a handheld Samsung smartphone.  



Handheld smartphone photography through a telescope held against the telescope's eyepiece is difficult, because aligning the optical axes of the smartphone with that of the telescope is a matter of luck. Smartphone holders which attach to a telescope and position the camera lens of a smartphone precisely in line with the telescope eyepiece are available. In the Vancouver area and the Lower Mainland, one place to find new and used telescopes and accessories is Markarian Fine Optics on Kingsway in Vancouver (https://markarianfineoptics.ca).

You can see that even old and relatively small telescopes are really useful for getting involved with Astronomy. One additional requirement is a sturdy tripod on which to mount the telescope. It should be included in any telescope purchasing budget. Nothing spoils the performance of telescopes more than a wobbly tripod.

Old workhorses indeed.










Saturday, October 3, 2020

An old Standby

 
In these days of Covid-19, getting together with others to have a look at the night sky is an exercise of don'ts: don't get too close to each other, don't touch or look through the telescope, don't come without a mask, etc. On-line meetings are substituting for the in-person ones. My wife and I are practicing voluntary self-isolation (we are old enough to make this necessary). That means that I'm confined to observing the sky from our home. 
 
We live in a highly light-polluted and horizon-limited area. The smoke from the wildfires in the U.S. has added to the lack of visibility of the stars. There were just a couple of acceptable evenings which led me to look for one of my favorite objects in the sky: The Whirlpool Galaxy not far from the end of the Big Dipper's handle. In a dark sky, M51 can be seen in larger binoculars as a small, diffuse patch of light.

I used my 15x50 Canon stabilized binoculars to try and see it. I did not detect it at all. The gray sky here made it an impossibility.  In earlier years M51 was easy to see from our house; high-rises, new and under construction, now limit our horizon and add much light pollution.

I decided to get my "M51 fix" by posting an image I took a couple of years ago by connecting my computer to Slooh.com to use one of their remotely accessible telescopes and take a picture; below is the result:
 

 Messier 51 
Image taken through the wide-field, 17 inch remote-control Slooh.com telescope located at the Institute of Astrophysics of the Canary Islands. 


 Some history (from Wikipedia):

"What later became known as the Whirlpool Galaxy was discovered on October 13, 1773, by Charles Messier while hunting for objects that could confuse comet hunters, and was designated in Messier's catalogue as M51. Its companion galaxy, NGC 5195, was discovered in 1781 by Pierre Méchain, although it was not known whether it was interacting or merely another galaxy passing at a distance. In 1845, William Parsons, 3rd Earl of Rosse, employing a 72-inch (1.8 m) reflecting telescope at Birr Castle, Ireland, found that the Whirlpool possessed a spiral structure, the first "nebula" to be known to have one. These "spiral nebulae" were not recognized as galaxies until Edwin Hubble was able to observe Cepheid variables in some of these spiral nebulae, which provided evidence that they were so far away that they must be entirely separate galaxies even though they are seen close together. The advent of radio astronomy and subsequent radio images of M51 unequivocally demonstrated that the Whirlpool and its companion galaxy are indeed interacting."

There are still some uncertainties regarding M 51. For instance, the distance of it is variously quoted as 31 million light years (NASA), Wikipedia says about 23 million, universetoday.com states 19 to 27 million light years. A location chart is shown above. A dark sky will allow for M 51 to be seen in 10x50 binoculars as a faint patch of light. An 8" (200mm) telescope will begin to show its spiral structure.

Messier 51 is circumpolar, so it is accessible for most of the year. At this time of year, the Big Dipper skirts the northern horizon through the night. M51 is therefore moves along above the northern horizon as well. Give it a try under a dark sky anyway. Its position will improve as we progress through winter and into next year.