Wednesday, May 30, 2012

Tuesday's Weather - NASA Coverage

The forecast for Fresno, CA says that there will be 34% overcast next Tuesday so it looks like it will be wait and see for a while.
The NASA TV Daily Schedule indicates that there will be some coverage of the Venus Transit but it is tagged TBD (to be determined). There is a 60% chance of rain in Mauna Kea with an indicated 0% cloud cover for next Tuesday. The time zone in Hawaii is HAST which is UTC - 10 hrs.

Venus Transit Subsolar Point

The picture of the Venus Transit shown in the map in the Wikipedia article is somewhat misleading due to the map projection. One can use MICA to determine the subsolar point for midtransit.
Ploting the midtransit subsolar point on a Google map showing the hemisphere where the Sun is visible gives the following result.
This gives a better picture of where the Venus Transit will be visible from. Note that the transit will also be visible from a good portion of the land bordering the Artic Ocean weather permitting. Throughout the transit the declination of the subsolar point is essentially constant and it moves along the same latitude as the Earth rotates.

Tuesday, May 29, 2012

Transit of Venus in One Week

As mentioned before the Transit of Venus will occur one week from today on Jun 5th or 6th depending on which side of the International Date Line you are on. It will be best observed in time zone UT + 10 hours which runs through Eastern Australia. One should be able to see the silhouette of Venus on the Sun's surface quite easily using eyepiece projection as one would do to observe sunspots. The entire transit will be observable in Australia and Eastern Asia after sunrise on the 6th. MICA details for Austrailia are shown in the image below. Note that the times are given in UT1 and can be converted to local time and correct for daylight savings time.
The entire transit will also be visible from Hawaii.
On the west coast of North America sunset will prevent the end of the transit from being seen.
If one does not have a telescope one should be able to see the transit on images of the Sun taken at Big Bear which are regularly updated. The transit may also be streamed live online from Hawaii.

Monday, May 21, 2012

Synchronizing Clocks & Network Time Protocol

Time displayed on the NIST time widget is seen to agree with the file's Modified time given in MS Office Picture Manager in the image below that was used to sychronize the camera's clock with the official time. So the best procedure may be to synchronize these two times.
The times used can vary by a second or two. Network Time Protocol is used to synchronize clocks over the internet. W32Time is used by some Windows computers to set the System Time for the computer. NISTIME 32 appears to use this method. The time zones are based on Universal Time (UT) which is adjusted periodically to maintain a correspondence with the Earth's rotation. The error is known as ΔT. We are due for a correction to UT1 in about a month from now on Jun 30. The times given by MICA for the eclipse use UT1. This may be a partial explanation for the problems encountered.
Above is a comparison of some of the times obtained by different methods showing a range of values. The times shown will depend on the time the image is captured.

Maximum Eclipse May 20, 2012

The following is an image captured near the time of maximum eclipse in Fresno, California at 6:34:00 pm.

The image is orientated with up corresponding to the local zenith. As one follows the Sun along the local azimuth the vertical changes.

The image above is one of the better images in terms of detail. The breeze tended to cause the telescope to rock back and forth which made capturing an image difficult. It was taken at 5:39:06 pm.

Supplemental (May 21): Google does not appear to be uploading EXIF image info any more. MS Office Picture Manager indicates two times for an image, a "Modified" time in "Picture properties" and a "Date Taken" in "Camera properties". The "Modified" time was 1 second earlier and is probably the one that agrees with the time shown on the NIST widget.

Sunday, May 20, 2012

Eclipse Images

Thumbnails of today's eclipse as see from Fresno, California. The images are spaced approximately 10 minutes apart starting at 5:20 pm.
The eclipse events were very close to what was predictions by MICA.


Here are some webcams for Northern California and Nevada.

Today's Weather

Today's weather for the eclipse is looking fairly good about the state. The best weather along the path of maximum eclipse at 6pm will be near Reno, NV. The expected cloud cover is about 11% so there is still some risk that has to be dealt with. One might want to use the WunderMap to choose a suitable viewing site.
I've been doing a few checks like weather conditions. If you are going to take pictures it might be a good idea to check the time setting for the camera. Just take a photo of the time widget to the right and compare it with the time given on the camera info for the image. One might also want to have extra batteries and an extra memory card for the camera. A check list might be good for future use.
The best view of the eclipse is not that from a particular location but that of a group at different locations. The timing and details of the events of the eclipse could be used to determine relative latitude and longitude. Observing an eclipse properly requires teamwork. The best strategy is not to put all your eggs in one basket.
Supplemental (May 20): I set the camera clock so that the indicated minute was correct a :00 sec and when I took a picture there was a 2 second offset for the camera image data. Setting the camera for :01 sec resulted a compromise with the image info showing 1 second after the official time.

Friday, May 18, 2012

Getting Ready For The Eclipse

The eclipse is just two days away and today I made some modifications for eyepiece projection with my little telescope. I made a new 81/2 x 11 inch screen, resurfaced it with the 20 pound paper and added a shade made from Walgreens Outer Space Poster Board.
The sunspots can be seen more clearly and the extra shade does appear to help. One has to constantly reposition the telescope since with large magnification the motion of the Sun is also magnified. The image below is unmodified and is how the camera saw the Sun. Manual focus was fairly easy.
I still need to get in a little more practice capturing images in the time prior to the eclipse.

Thursday, May 17, 2012

The Sun Viewed Through Crossed Polarizers

The Sun is so bright that one needs reduce it illuminance by a filter of some sort. A simple one can be formed by crossed polarizers for which the optical density is a maximum. The polarizers used below are from a Polarizer Pak that I got a few years ago from They don't seem to be available any more.
One can look at the Sun through them be it is still a little too bright. To capture an image of the Sun one needs to use the minimum manual exposure setting available (f/8 at 1/2000 sec. with ISO 64). The image below is reduced in brightness and contrast enhanced. The quality is reduced by the small aperture but one can just make out the sunspot clusters.
Getting the manual focus right can be quite challenging.

Wednesday, May 16, 2012

Sundial Bridge, Redding, CA


Sundial Bridge, Redding, California
Sundial Bridge in Redding, CA is an example of a site that one might choose to view Sunday's eclipse from. It is within the region in which the maximum eclipse will occur and has a good view of the western horizon. The details given by MICA for the eclipse at this location are shown below.
There is also an interactive map at the NASA Eclipse site. One can zoom in on the map to any location and then click on it to get details for the eclipse. The Redding forecast for Sunday is "Partly Cloudy" with about 40% overcast and so one will probably be somewhat at the mercy of the weather. One should also note that the clouds tend to be thicker towards the horizon.

Eclipse Weather

Weather will have an effect on one's ability to view Sunday's eclipse. Here are some links that might be helpful in choosing a viewing site.
NOAA Satellite flash loops   (flash info)
Wunderground map and forecasts
Along the path of maximum eclipse
Eureka, CA    Redding, CA    Reno, NV
Along the California coast
San Francisco, CA    Monterrey, CA
California Central Valleys
Sacramento, CA    Modesto, CA    Fresno, CA
For the cities in California and Nevada one can check the forecasts for Sunday at the time of the eclipse (5:20 pm to sunset). Some clouds are expected along the path of maximum eclipse and along the Pacific coast. Conditions improve to the south in the San Joaquin Valley.

Wednesday, May 9, 2012

Transit of Venus June 5/6, 2012

There will be a Transit of Venus this year on June 5/6, 2012. It is a relatively rare event occurring about twice in one hundred years. The last one was in 2004. Here are a few related links.
The 2012 Transit of Venus - Goddard Space Flight Center
Transit of Venus 2012 - Royal Astronomical Society of Canada
Transit of Venus March - John Philip Sousa

Tuesday, May 8, 2012

Don't Let Them Fool You!

What's wrong with this memo on this month's calendar?
It appears to be on the wrong date. Solar eclipses do not occur on the last quarter of the Moon but at the new moon. Then again it's probably better to be too early than too late. The memo appears in the Astronomy 2012 Calendar.

The Moon and Venus, Friday May 4, 2012

I was out again Friday evening taking some pictures of the Moon and Venus. It's not quite the Supermoon but these turned out the best. These images have just been cropped.
One can see that Venus has a crescent shape.
To get the camera information for one of the images click on it to get the enlarged image and then save that image. The information will be downloaded along with the image and can be view in an image editor. Cropping doesn't delete the information. I had trouble doing that with the original 14 megapixel images so I tried uploading the cropped images.

Thursday, May 3, 2012