Monday, March 2, 2015

An unusual fascination with pinhole projections and other optical analogies from my time in prism

I created a new astronomy presentation last weekend. I'll be presenting it to my club, the Temecula Valley Astronomers, tonight at 7:00 at the Temecula Library on Pauba Road -- nothing like the last minute, as working on it this weekend suggests, but it's based on observations of pinhole projections, also called the camera obscura, that I've been interested in for many years.

I believe the pinhole projection provides all the information to intuitively understand how telescopes work and how focal ratio affects depth of field:



To complete the analogy, I add prisms, which lead me to contemplating William Herschel's discovery of infrared. To resolve a discrepancy, I examine black body radiation curves, which leads me to understanding the green house effect, and for the first time I think I can explain why nearly every illustration of the greenhouse effect is wrong by over simplification.

I'd write more, but it's, as I said, last minute and I have preparation to do.

My presentation (which severely lacks annotations) can be found at this location:

http://www.brightstarstemeculavalley.org/pages/presentations.html


jg

Sunday, February 22, 2015

Hole punch clouds

Shortly after sunset on Feb. 19 I saw what looked like a hole-punch cloud, also called a fall streak hole. It looked a bit like a giant space amoeba from Star Trek:





OK. Maybe a lot like one.

I understand these are caused by a domino-like effect where super-cooled water vapor needs a nudge to create a cascading condensation that then falls out of the cloud. One possibility for the source of the nudge is a passing airplane.
I've seen these before and I assumed updrafts from our nearby mountains were the cause, but I don't know.
At least one of my pictures confirms the hole punch occurred near the flight path of planes. The bright line in this photo is a plane:

However, my pet theory that the mountains are creating updrafts that trigger the condensation suggests that there would be more hole punches to coincide with the few peaks in the area, as shown in this photo from a couple years earlier:
Hole punch clouds above the mountains on my western horizon


I looked around for others and did find one, though it was less impressive:


Though less impressive, it did look a little like a giant rabbit in the sky (on its back), something I've been seeing a bit of recently and shared with the Orange County Astronomers last week:

Multiple hole punches does not eliminate planes as the source, so the cause in my region is not settled.

As the hole punch drift east, the sky was dark enough to bring out a few stars: 


Other hole punch clouds:




jg

Saturday, February 14, 2015

What's Up February 2015

A better blogger would be more punctual in sharing his projects. I continue to create presentations but rarely find time to share the content on the web. I recently presented a What's Up on the night sky to the Orange County Astronomers, which I'll share here.

Before looking at the stars, one has to look through the atmosphere, so I always share any recent observations of parhelia, that is, sun and atmosphere effects. The best example I've had recently are these iridescent clouds from late December:

As this effect occurs close the sun, please be careful to avoid looking at the sun.

And, if you start to see things, you've looked too long:

Giant multi-colored sky rodent

Turning to the night sky, here are the locations of planets, constellations, and areas I chose to discuss:
Venus (yellow) and Mars (red) linger in the west; Jupiter rises in the east. The winter milky way passing over head in the evening, but is visible only from a dark location.

Rectangles represent areas that I photographed and share below.

Comet Lovejoy is in the northwestern sky moving from Andromeda to Cassiopeia.

The green arrow shows the path of comet Lovejoy.

Along with Lovejoy, there are many other fine objects for the telescope or binoculars. Now is a good time to look from a dark location. Soon, these objects will plunge into the western horizon.


Note that on Feb 20, Lovejoy will pass near M76. The two will be worth a look through the telescope.

Here's a photo of comet Lovejoy from this week:


As a side note, while taking the above photo I captured an enjoyable coincidence:


This photo is a plane passing in front of M31. I was alarmed when I saw the photo on my camera's LCD display, for I was sure the trail was an airplane, but I hadn't identified the source of the sudden brightness. When viewing the photo on a computer, it was obvious that the flash was the Andromeda Galaxy (M31) oriented so that the long axis of its oval shape aligned with the path of the plane. Normally I don't boast of my photos of the flight path out of LAX, but this one is an exception.

In the east we see the Big Dipper, also "Ursa Major, the Big Bear" rising:


Lacking a good starry photo of the rising, leading edge of Ursa Major, I used this one taken from June of 2014 from a darker location.

Of course, when flipping a western photo to make it look like an eastern one, keep in mind the trees or any other incongruities:

A little cropping and diagramming shows the location of some worthwhile deep-sky targets for this time of year:


Each year I forget to spend quality time observing M81, M82, M108 and M97, which all require a telescope to see. The reason is that these are rising in February, when it's cold, and by late spring when I am out at a dark location, these objects are already setting in the western sky glow or lost in the trees at Palomar Observatory Campground. This year, my goal is to catch them rising, and take some photos to help me remember their qualities and locations. If I fail, there's always next year: unlike a beautiful open space on Earth, you don't have to see it before someone changes it. E.g., no one is going to enter Ursa Major with earth movers and develop it. So, it's safe to fall in love with a part of the sky, knowing it's never going to go away for good. (I once mentioned this to my former County Supervisor, who joked if there was a way to make money developing the constellations, developers would try anyway.)

The darkest part of the sky, regardless of your location, is overhead. Now, the view overhead reveals Auriga, the Charioteer:


Auriga offers some star clusters that can be found in binoculars.

However, these clusters, such as M35, are best viewed in a telescope:

No winter sky presentation is complete without calling out the location of the best nebula in the night sky, visible high in the south in binoculars as well as the telescope:


Find Orion in the south, then find its belt of three aligned stars. From there, look below the belt to the region named as Orion's sword. This region is a star cluster and nebula. Some people will see this with the naked eye, but all will see it well with binoculars. 

Back to the planets, there is a delightful conjunction of Venus, Mars, and the crescent moon on Feb 20. Also, Jupiter is falling into an alignment in which the orbits of its moons can be seen edge on, making the moons pass in front of each other and making for eclipses:

Imagine Jupiter moving through it's orbit carrying it's moons with it. Our view of it's tilt will change from year to year, This year, the view appears edge on.

I recorded a similar series of eclipses 12 years ago and had the wits to document my observations. The following illustration shows my pictures of the moon Io being occulted by the shadow of the moon Ganymede.

Happy star gazing, and local viewers may want to plan to attend the Wildomar star party at Marna O'Brien Park on April 25, 2015.

jg


Sunday, February 1, 2015

Small differences

With my small scope, I can capture the span and colors of the Orion nebula with a 45-second exposure on my digital camera: 

However, tracking is rarely good with my small setup, so the photo above has noticeable elongation of the stars. 

This second photo is made from three shorter duration photos, which reduced the elongation of the stars. The small improvement in image quality is a result of computer processing. 


My methods for combining photos are still crude. I omitted a blank image to use for compensating for my camera's noise, and I could have combined more short photos.

Here's one of the 15-second shorter photos I used:


Apparently, all the information to get the 2nd photo is in three of these shorter ones, but less error from tracking.

jg

Sunday, January 25, 2015

Entering the processing fray

The greatest advancement in astronomy is probably the computer, for amateurs and professionals alike. Stacking images is now routine procedure for images published by amateurs. I'm coming to this software angle rather late in the game. Here are my first attempts using Comet Lovejoy as my target and the free software Registax:

Single 3-minute image, no processing

Stack of 4 images

What a fabulous sinkhole for my time that has just opened up!

jg

Friday, January 9, 2015

Cold Fuzzies

The past two nights I was able to photograph Comet Lovejoy, despite the onsite of clouds and rain. The sky was more clear on Wedns. night, shown by the better color and contrast in the first photo.
However, I was surprised to see the last night, when photographing through clouds, the comet had a more noticeable tail. 


Also more noticeable is the slight drift or elongation of stars, caused by not having my camera mount accurately polar aligned. I couldn't see Polaris, so I had to guess at the alignment, and so the stars and comet show a little drift. I wonder if the drift motion, being at a right angle to the direction of the tail, helped enhance the tail.

jg


Thursday, January 8, 2015

What's that bright star in the south?

This time year people notice a bright star rising in the south in the early evening. While low, the star's light is scattered, creating a sparkling effect that's noticeable because of it's brightness. That star is the brightest star in our night sky, Sirius. (Pronounce in English as "serious"). Sirius is also the heart of Canis Major, the great dog:


Sirius is a binary star system: two stars orbiting a common center of gravity. Sirius A is the brighter star, and Sirius B is the dim but observable companion. Sirius B can be seen in a telescope, but it requires good optics and good viewing conditions. However, the orbit of Sirius B is taking it to it's farthest point in relation to Sirius A, making it easier to see apart from the glare of Sirius B:


When Sirius is at its highest point in the sky, viewers in the lower part of the United States, Southern California for me, can also see the second brightest star in the night sky, Canopus. It appears in the bush of the picture above, but the following picture shows Canopus a little brighter after moving out of the bush:


Look just to the right of the bush, the lower right, and you'll see Canopus just above the horizon.

jg