Category: Astronomy

Exploring the cosmos

Mercury and Venus

The two inner planets will rendezvous in the sunset over the next few days. Venus appeared in the sky a few days ago having just emerged from superior conjunction. Mercury will emerge quickly from the solar glare to pass Venus only 10° from the Sun. This conjunction will be quite low and a bit in the bright glow of sunset, perhaps somewhat challenging to spot.

This evening the two will be about 2° apart, and will quickly converge. On July 16th the two will be only 32′ apart, about the diameter of a full Moon. After that the two will quickly separate. Interestingly on the 17th the pair will pass through the M44 star cluster, though perhaps it will still be a bit bright to appreciate this dimmer cluster.

Late in the month this trio of bright planets will continue their dance in a set of conjunctions that lasts into September. The highlight will be on August 27 when Jupiter and Venus will pass within 12′ of each other while Mercury is only 5° away.

Moon and Mercury
The Moon appears as a thin crescent beside the planet Mercury, photo taken from the summit of Mauna Kea on 12Oct2007

Apehelion

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 at perihelion on January 2rd, 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.

2016 Solstices and Equinoxes
  UT HST
Perihelion Jan 2 22:49UT Jan 2 12:49HST
Vernal Equinox Mar 20 04:30UT Mar 19 18:30HST
Summer Solstice Jun 20 22:34UT Jun 20 12:34HST
Apehelion Jul 4 16:24UT Jul 4 06:24HST
Autumnal Equinox Sep 22 14:21UT Sep 22 04:21HST
Winter Solstice Dec 21 10:44UT Dec 21 00:44HST
 
Source: USNO data Services

 

Summer Solstice

Summer solstice occurs today at 12:34HST. Today the Sun will occupy the most northerly 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 northwards each day and begins move to the south. This is the first day of summer as marked by many cultures in the northern hemisphere. Alternately this is the first day of winter for those living south of the equator.

2016 Solstices and Equinoxes
  UT HST
Perihelion Jan 2 22:49UT Jan 2 12:49HST
Vernal Equinox Mar 20 04:30UT Mar 19 18:30HST
Summer Solstice Jun 20 22:34UT Jun 20 12:34HST
Apehelion Jul 4 16:24UT Jul 4 06:24HST
Autumnal Equinox Sep 22 14:21UT Sep 22 04:21HST
Winter Solstice Dec 21 10:44UT Dec 21 00:44HST
 
Source: USNO data Services

 

Warp3

I have previously covered the importance of warping, tuning the Keck primary mirror segments for optimum optical performance. Warping has been my responsibility for some years now. Reading out the settings of the thirty strain gauges on the back of each segment is performed by a test fixture, a computer and a sensitive data acquisition system. Over the last year I have designed, built, and programmed a new test fixture.

Keck mirror segment warping fixtures
The old and new warping fixtures being tested side-by-side on a spare segment
The old warping fixture was showing its age. Built in 2000 it has been in use for 16 years. It is the computer that I was most worried about, it has begun to crash randomly, usually at the worst possible time. Replacing the computer has some issues as well, the A/D system uses a parallel interface, something not found on any modern computer. The operating system is Windows XP, while unsupported, at least you can still install and use this old operating system. The software is in an ancient version of LabView. I have no love for LabView, too many bad experiences with it, it crashes too often and the licensing issues are horrible.

As this is the third generation warping test fixture the name of the software is obvious… Warp3

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