Mammatus over Tucson

During the time I've lived in Tucson, there are two annual weather transitions that I have come to look forward to (and often begin to lose patience waiting for). One is during October when the temperature falls back from the 100's of summer to the more gentle 70's and 80's of autumn. The second is the start of the monsoon season, typically during the first week of July. This is marked by the change in atmospheric airflow that pulls moisture up from the south to bring us thunderstorms. Prior to this, we can go up to 3 months without rain. This year, we went from May 2nd (when .02" was the official measurement) to July 17th (.10") with no rain.

Then, we had our first major storm of the year on the 19th. A severe storm to the east produced the striking mammatus which are pictured. These are rarely seen and are formed from the sinking air and ice crystals on the edge of large thunderstorms that push down on a surrounding cloud deck to produce the puffy, pouch-like features that become visible when they descend into clear air. While looking foreboding, they usually appear after a thunderstorm has passed. The ones here are from a storm that died out before reaching us.

A new storm, however, developed right over Tucson at about 11pm, and was perhaps propagated by that original storm to the east. The result was .61" recorded at the airport and .25" recorded in my backyard rain gauge. The sight of the cloud formations during the day was replaced by the spectacle of lightning well into the night.

Planetary conjunction

The Venus-Mars-Saturn conjunction on August 5th, 2010 (click for a larger view).

A similar conjunction of the Moon, Jupiter, and Venus on December 1, 2008

In the western sky over the next 3 weeks there will be a slow-motion planetary dance, resulting in a conjunction of 3 of our solar system's bright planets. A conjunction simply means a close approach of two or more celestial objects as seen in our night sky. Currently, Venus and Mars are in Leo (Venus makes its own conjunction with the bright star Regulus on July 9th, when the two will be 1 degree, or two full moon widths, apart), with Saturn hanging out in Virgo.

Right now (I'm writing this July 8th), if you look toward the west as soon as the sky gets dark enough, you'll see the very bright white planet Venus. It'll be the brightest object up there. To the upper left will be a fainter, but still conspicuous, spot of light which is Mars. If you hold your fist in front of you at arms length, the two planets will be separated by a distance equal to about two widths of your fist. You'll be able to distinguish Mars by it's reddish or orangey color. Continuing to the upper left (and about 1 more fist distant), is a gold or amber colored object. This one is Saturn.

As the days go by, Mars will slide under Saturn first, reaching its conjunction with the ringed planet on July 30th. The two will be 1.4 degrees apart. Venus catches up a few days after that, when, on August 5, the three will form a triangle, with Mars and Venus both about 3.5 degrees from Saturn. The image at top shows what it will look like. It'll be similar to the Moon-Jupiter-Venus conjunction in December, 2008 (second photo). Click on the images for a closer look.

Subsequent observations will show you even more over the next few days. On August 12th and 13th, the crescent moon will join the group, and Venus and Mars will reach their conjunction on August 16 and be 2 degrees apart as Saturn sinks closer to the horizon. You can gauge this distance by remembering that the full moon is about 0.5 degrees in diameter.

Let's hope that the skies are cloud free a few times between now and the middle of August to allow us to see this spectacle!

Introduction

My name is Chris, and these blogs will have in common topics related to "crossing the horizon." That means I'll be talking primarily about what's above the horizon (weather phenomena, aircraft, astronomy), and what's beyond the horizon (travel destinations). I don't know how often I'll be posting yet, but I hope it'll be worthwhile and that you'll enjoy reading. I've started off with two photos: M27, or the Dumbbell Nebula in the constellation of Vulpecula, and a shot out the window while flying over London just prior to landing.