Today the Earth is furthest from the Sun, a point called apehelion. We will be about 152,096,000km (94,508,000miles) from the Sun. Compare this to the 147,099,000km (91,403,000miles) we were be at perihelion on January 1st, a difference of about 4,996,000km (3,104,000miles) occurring throughout one orbit.
It may seem odd that we are actually at the furthest for the middle of northern summer, you just have to remember that proximity to the Sun is not the cause of the seasons. The seasons are caused by the axial tilt of the Earth, creating short and long days throughout the year, with a resulting change in the angle and intensity of the sunlight.
Living south of the Tropic of Cancer we get to experience an interesting phenomena that folks outside the tropics will not see. There are two days each year when the Sun passes directly overhead. In the islands this event is called Lahaina Noon.
Spring Lahaina Noon for 2013
Location
Date
Time
Hilo
May 18th
12:17pm
Waimea
May 19th
12:20pm
Kahului
May 24th
12:23pm
Honolulu
May 26th
12:30pm
Lihue
May 30th
12:36pm
Lahaina noon occurs twice each year as the Sun appears to move northwards with the spring and again as it moves southwards in the fall. For the islands of the Hawaiian archipelago the first day is between May 16th and May 31st. The second Lahaina Noon will be between July 10th and July 25th.
The date on which this event occurs each year depends on your exact latitude, the further north the later in the spring it will occur. Thus the day for Lahaina noon will vary by eight days from Hilo to Honolulu, and another five to Lihue. As you approach the Tropic of Cancer at 23°26’N Lahaina Noon will occur closer to the summer solstice. The date will also slip a little due to the out of sync nature of our seasons and our calendar. This is the reason we insert a leap year into the calendar every four years.
This year Lahaina Noon will occur on May 18th for residents living in Hilo, or May 26th for Honolulu. It is also important to remember that the Sun is not directly overhead at 12:00 exactly. As the islands lie west of the center of the time zone, true local noon occurs up to half an hour after 12:00.
We were all ready to view to eclipse from Keck HQ in Waimea. The gear was ready to go, our astronomers setup to answer questions, the public invited…
It rained.
Not to be deterred I grabbed my little telescope and headed for the Sun. The satellite showed a reasonable possibility of clear skies in Kawaihae. As I rolled into the parking lot at Pu’u Kohala Heiau National Historic Site I found the hole in the clouds needed for eclipse photography.
I was not the first there, I met another gentleman setup with a 70mm Meade ETX, we chatted as I set up beside him. I found out later that a couple of the gals from CFHT were setup at Spencer Beach just below the heiau. For clear skies this was about the only reliable place on the island other than the summit.
I quickly setup my little TV-76mm and got the images I was looking for at maximum. We only got to 47% here on the big island, but still worth the effort to see.
Jan 15th, 2010 annular solar eclipse, photo by Dan BirchallA reminder that this afternoon we will have the opportunity to see a partial solar eclipse. For viewers further south, in Australia and across the South Pacific, this will be an annular eclipse. For viewers here in the Hawaiian islands this will be a deep partial solar eclipse, with well over 40% of the Sun obscured by the Moon. This is enough to produce a noticeable drop in the Sun’s brightness at mid-day.
Please exercise caution when viewing the Sun! Use appropriate eye protection or indirect observing techniques to project an image of the Sun. The link at the start of this paragraph leads to a great discussion on viewing the Sun safely. As always the single best source on the web (or anywhere) for eclipse and transit information is Fred Espenak’s eclipse website at NASA. Stop by whenever you have a question on upcoming events as well as viewing and photography tips.
During a deep partial such as this one check out the shadows under nearby vegetation. Small gaps in leaves can act like pinhole cameras projecting small crescent images of the Sun.
Jan 15th, 2010 annular solar eclipse photographed from Kampala, Uganda by Dan Birchall, used by permissionMay 9th will see a solar eclipse sweep across the Pacific. For viewers in Australia and the southern Pacific Ocean, this will be an annular eclipse, not a total eclipse. With the Moon near apogee and further from the Earth, its apparent size will not be quite enough to cover the entire disk of the Sun, resulting in a ring of light surrounding the silhouette of the Moon.
For viewers here in the Hawaiian islands this will be a deep partial solar eclipse, with well over 40% of the Sun obscured by the Moon. This is enough to produce a noticeable drop in the Sun’s brightness at mid-day.
Please exercise caution when viewing the Sun! Use appropriate eye protection or indirect observing techniques to project an image of the Sun. The link at the start of this paragraph leads to a great discussion on viewing the Sun safely. As always the single best source on the web (or anywhere) for eclipse and transit information is Fred Espenak’s eclipse website at NASA. Stop by whenever you have a question on upcoming events as well as viewing and photography tips.
Today the Earth is closest to the Sun, a point called perihelion. We will be about 147,099,000km (91,403,000miles) from the Sun. Compare this to the 152,096,000km (94,508,000miles) we will be at aphelion on July 4th, a difference of about 4,996,000km (3,104,000miles) occurs throughout one orbit.
It may seem odd that we are actually at the closest for the middle of northern winter, you just have to remember that proximity to the Sun is not the cause of the seasons. The seasons are caused by the axial tilt of the Earth, creating short and long days throughout the year, with a resulting change in the angle and intensity of the sunlight.
Winter solstice occurs today at 01:12HST. Today the Sun will occupy the most southerly position in the sky of the year. The term solstice comes from the latin terms Sol (the Sun) and sistere (to stand still). On this day the Sun seems to stand still as it stops moving southwards each day and begins move to the north. This is the first day of winter as marked by many cultures in the northern hemisphere.
Transit is over, an exhausting and exhilarating day! I am headed to bed, but still totally jazzed with the experience. Keeping the webcast going for seven hours was a huge effort. Given the comments from our viewers it was worth it. I will have to more fully write up the experience for a later post.
The best visual for the day was the few minutes just before second contact… A beautiful, razor thin arc of light coming through the Venusian atmosphere, connecting the two horns of the occluded Sun. It was delicate and sublime, one of the most memorable sights I have ever seen through a telescope. With the excellent seeing of Mauna Kea, and the wonderful optics of my TV-76 telescope, the sight was clear and steady. I have yet to find a photograph that captures what I saw through the eyepiece.
I will post a quickly processed version of one of the frames from the second camera…
Aiming a telescope at the Sun is deceptively difficult. You can not use a optical finder for risk of eye damage. Unit power finders, like a Telrad, are of little use as you can not see the projected image. Telrads can also be damaged by sunlight. In a pinch you can simply use the shadow of the telescope, positioning for a minimum shadow. This at least gets you close.
A Sun Finder mounted to a TeleVue 76mm 'scopeThe best solution is to build a finder designed just for the Sun… A Sun Finder.
There are many plans for Sun Finders posted to the web. Most use a shadow or projected point of light. The version I built is no exception, using a pinhole to project a point of light on a translucent screen. The trick is to make such a device simple and accurate.
With simple metal working capability a Sun Finder like this one can be made from sheet metal, or machined from solid aluminum. I chose the latter as I had the capability. This design uses a pinhole that projects a similarly sized dot of light at the rear of the finder. The front face or the finder, through which the pinhole is drilled, creates a shadowed area for in which the projected dot can be seen.
A Sun Finder in use with the projected dot visibleA longer distance from the pinhole to the screen will increase the sensitivity in aiming. In practice I have found that at least three inches is sufficient for most telescopes while keeping the device compact. Experimentation with the design can be entertaining and educational. No need to stick strictly with this design, just borrow the basic ideas, a lot of variations will work.
This design is based on an aluminum extrusion, a 3″ x 1.5″ channel. This save a good deal of machine work in creating the finder. As much of the machining is done along the length, a number of finders can be made at the same time. I made six finders from a seven inch scrap of extrusion out of the shop scrap pile.
Plans for the Sun FinderThe screen is made from a small piece of 1/8″ thick acrylic. Common 0.1″ thick material will work as well. One side is frosted with sandpaper to create a translucent screen. Use of a clear screen allows the solar dot to be seen from front or behind while aiming the telescope. The screen is simply secured with a glue, preferably RTV. The frosted side should be mounted towards the pinhole.
To keep the device simple there is no adjustment in aiming. If the finder is mounted reasonably well, the dot of light will be on the screen. The first time out it is necessary to first get the Sun in the field of view. You can then mark the position of the projected dot with a permanent pen (Sharpie or similar). After that aiming is simply a matter of positioning the dot on the mark. If the mark is made on the smooth side of the acrylic screen it can be easily erased and re-marked if necessary.
Done, a simple and reliable Sun Finder to work with just about any small telescope.
It was a full dress rehearsal. Both telescopes, two cameras, the entire streaming rig set up on the lanai. No less than three computers with cables all over the driveway! Surprisingly enough, everything went pretty well!
The Sun on June 2, 2012If you had been watching the Keck Transit of Venus stream, you would have been looking at a live image of the Sun for several hours. The seeing from my driveway was pretty poor, but there is a nice collection of smaller sunspots across the disk.
Everyone wandering by the house noted the telescopes. I gave peeks to our mail-lady and a couple young women who stopped by, intending to read me a bible verse or two (that was fun;)
Two technical issues were key today… Using thirty feet of active USB extension cables to run the streaming camera remotely, no problem. Co-aligning the two telescopes to aim at the same point, no action needed, aligned from the start. I had thought I might need to shim the mount for the piggyback ‘scope. I was also able to play with the streaming camera further. The Baader film filter gives a blue-white image. Adjustment of the camera white balance will restore a little yellow cast. I do not have much problem with the white, but a hint of yellow will allow people to instantly realize they are seeing the Sun. The same reason I adjust my processed photos for a golden orange hue.
We are all swapping gear around to get the set-up ready. Chris was nice enough to loan me a Canon T-ring and some Baader film. I built a battery pack and some sun-finders for several telescopes. Last night I picked up a whole solar rig from Cliff for delivery to Olivier. Olivier lent a 40mm eyepiece to Keck for the public telescope that will be setup at HQ. The list goes on…
I was not the only one doing a dress rehearsal. So far today I have been on the phone to other folks setting up and using a sunny Saturday to check gear. Some of the guys over on Maui even posted a video of their test run. I should have thought to do the same thing! Will have to time lapse the summit setup.
