Skywatcher's Guide - June and July 2012

Visit our public 16" telescope at Flandrau Science Center on Wednesday through Saturday nights (free of charge) where you can meet our astronomers personally. Ask questions, enjoy the night sky, and experience both the telescope and online resources from 7 until 10pm.

Written by: Tim Van Devender (Flandrau Telescope Operator)
Images contributed by: Tim Van Devender, Alistair Symon (Flandrau Telescope Operator), Nine Planets, and Students for the Exploration and Development of Space (SEDS)

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Monthly Overview

Summer has settled on to the Old Pueblo and cooler night time activities abound. Reid Park and the Tucson Pops Orchestra host Music Under the Stars , the Arizona-Sonora Desert Museum offers Summer Saturday Nights, Mt. Lemmon SkyCenter continues hosting their SkyNights evening observing programs and Flandrau observatory continues to be a evening highlight for Tucson families all summer.

http://www.tucsonpops.org/index.php?option=com_content&task=view&id=125&...

http://www.desertmuseum.org/visit/events_saturday.php

http://skycenter.arizona.edu/programs/public/skynights

During the early evening the summer contellations are a bit sparse on bright stars with Regulus (in Leo) to the west and Spica (in Virgo) and Arcturus (in Boötes) overhead. This year we have Mars and Saturn filling in our first magnitude stars. Mars will be moving east away from Regulus toward Saturn and Spica in the constellation Virgo. If you get a chance to head out camping in a southern Arizona's dark desert skies I strongly suggest taking 45 minutes without looking at any lights to let your eyes fully dark adapt. Once your eyes are fully dark adapted look straight up (around 9PM) and you will be looking at the constellation Virgo in a direction straight up with the Milky Way wrapped around you on the horizon. There is a massive cluster of faint “stars” that are actually galaxies known as the Virgo Cluster. This is a major structure of galaxies which we see from the edge. The Hubble Space Telescope “Deep Field” image is in this direction.

Later in the short summer nights we have the “Keystone” of Hercules followed by Vega, then Deneb in the constellation Cygnus (the Swan)and the Great Square of Pegasus with Cassiopeia rising in the East. Cygnus is right in the middle of the Milky Way and has some wonderful highlights like the lovely double star Albireo visible from Flandrau's Observatory as well as dust clouds and “dark nebula” visible under clear, dark skies. Cygnus is a favorite of mine because the thre birght stars in the cross above Deneb this time of year form a shape (asterism) that reminds me of the Starship Enterprise. Starting in July we will see the center of the Milky Way rising to its highest point in the south near the constellation Saggitarrius (look for the “teapot”). In a dark sky the Milky Way rises overhead from the teapot like steam. In the early morning we will have Auriga and Taurus rising before our early morning dawn. If you happen to be up that early Venus, Jupiter and Mercury will be dancing brightly in the early morning sky.

Observational Highlights - Solar System

Early June 2012 will provide some unique opportunities for North American sky watchers. June 4th we have a partial lunar eclipse. Observing the moon pass through the Earth's shadow opposite the sun is always a wonderfully unique way to observe our nearest celestial neighbor. This itself would be a highlight for the Sky Watcher's Guide but the following day we happen to have one of the astronomical events of the century, Venus passing between Earth and the Sun. From our perspective we will see the silhouette of Venus pass across the disk of the Sun, called a “transit”. The Venus transit cycle is currently happening in pairs, the last transit being in 2004. If Earth and Venus orbited the Sun on the same plane we would pass in this straight line every year. Since Venus' orbit is inclined 3.4 degrees from Earth's orbit we only pass through a straight line once or twice every 120 years or so. The next time humanity will get to witness this event (from Earth) will be in 2117 and 2125. On June 5th Flandrau Science Center will be hosting an event to watch the Earth sized planet Venus cross in front of the Sun starting around 3 PM Tucson time. The entire transit will take 7.5 hours so the transit will still be underway at sunset (7:28PM).

Viewing the Sun is perfectly safe using proper solar filters. Do not try to stare or make yourself look directly at the Sun without eye protection or you can damage your eyes. That is the reason we have a nature reflex to look away and blink at bright lights.

Lucky visitors watching the start of the Venus transit through one of the properly filtered telescopes on the U of A Mall may get to witness the “black drop” effect. Venus has a thick, hazy atmosphere of carbon dioxide which is mostly, but not completely, an opaque. That couple with the fact the Venus and the Sun are both large spheres produce an effect that seems to stretch Venus into a tear-drop shape as it just finishes moving fully over the disk of the Sun. The astronomer Halley (of comet notoriety) coordinated a global effort to use accurate timings of a Venus transit to calculate the distance of the Sun to the Earth. These efforts were foiled by this black drop effect as timings varied by several minutes.

June 27th we have the Boötids meteor shower during the new moon. This meteor shower is not well known but it does occassionally have outbursts. There are no major predictions this year but the shower has had surprising shows before. These meteors are a bit larger and slower than average so they should be easy to tell apart from our "normal" background meteors. A good way to watch summer meteor showers is to lay down or recline and allow your vision to relax and take in as much peripheral sky as possible. This is a good way to enjoy the summer constellations and Milky Way as well.

Observational Highlights - Deep Sky

All the excitement of solar events sort of distracts us from talking about the night sky during the early summer. Other than two unique solar events and some die hard solar observers though most casual star gazers will be watching as the the beautifully dense core of our galaxy, the Milky Way, rising in the south. Early June the Milky Way is still lower and the Virgo Cluster is overhead. To the north we have some larger and relatively brighter galaxies from our local group. A summer star party at Catalina State Park or Saguaro National Park will likely be showing these off. We often show these off from Flandrau using our Hyperstar camera as well.

Looking south towards Sagittarius looks straight in that arm of the galaxy toward the center of the Milky Way's great bulge. The arms of our galaxy are made of great clouds of dust and gas heated by stars in different types of groupings. Looking into the heart of the Milky Way has all of these beautiful objects to observe. Cygnus and Cassiopeia continue the trail as the galaxy wraps around us into the northern summer sky. The 16” telescope at the Flandrau Observatory allows our visitors to see some of the brighter objects with their own eyes. One of the fun things to show visitors is how a simple sweep of the Milky Way with a pair of binoculars can reveal an amazing amount of stars even in the city lights.

Frequently Asked Questions

What is the difference between an eclipse, a transit and an occultation?

Astronomers have lots of terms for three objects lining up in a direct line depending upon what and where you are observing the event from. Essentially a transit is the same as an eclipse and an occultation. One celestrial object passes directly between two others forming a straight line. The difference would be the perspective of someone observing the event and where the sunlight is coming from. Usually one of these object is the Sun and another is the Earth (since we are always on the Earth). An eclipse is us looking at our shadow passing over the Moon or the Moon's shadow passing over us. The annular solar eclipse on May 20th could technically be called a transit as well as the silhouette of the Moon passed in front the disk of the Sun. A full solar eclipse is when the Moon is closer and completely covers the visible Sun. A full eclipse is the same as an occultation in which an object's light blinks out temporarily due to something passing between us. The term occultation is usually applied to very distant objects that are so far or reflecting light so faint you would not normally consider it as casting a “shadow”. An asteroid passing in front of a star or the moon passing in front of Jupiter for instance.

Interesting Night Sky Events

06/01/12	Venus 0.26 degrees SSW of Mercury. The closest planetary conjunction of the year.
06/04/12	Full Moon and partial lunar eclipse. Partial eclipse begins at 3 AM and reaches maximum (37% across the diameter) at 4:03 AM. Parial eclipse ends at 5:06 AM, ten minutes before sunrise.
06/05/12	Venus tranits the Sun. Transit begins 3:06 PM continuing through sunset at 7:28 PM. Venus will be about 65% of the way across the disk at sunset in Tucson.
06/11/12	Moon at last quarter.
06/19/12	New Moon. Dark skies of the new moon make dim, deep sky objects easier to see as the background sky glow is lowest creating more contrast.
06/20/12	Summer solstice. This is the first time (due to precession) the solstice happens on June 20th.
06/24/12	Mercury at its highest. Mercury is the highest in the early evening sky at 18 degrees above the horizon.
06/27/12	Boötids meteor shower. Favorable time to observe close to full moon.
06/29/12	Pluto at opposition. I'll be honest... I'm not sure this one matters as Pluto is so far out there. :) No disrespect intended to the senior Kuiper Object.
07/01/12	Mercury at greatest elongation east. Mercury will be 25.7 degrees east of the Sun. Ironically this is not when Mercury is "highest" in the sky due to the inclination of the ecliptic. Mercury was highest in the evening sky on June 24th.
07/03/12	Mercury 1.6 degrees SSW of the Beehive Cluster (Messier 44). Moon 1 degree SSE of Pluto. The Moon's brightness and Pluto's dimness make this a challenging pair to observe together.
07/09/12	Venus at peak brightness. Venus has pulled back into the sunlight for us at magnitude -4.5.
07/11/12	Moon at last quarter.
07/13/12	Friday the 13th. The third and final Friday the 13th for 2012.
07/19/12	New Moon. Dark skies of the new moon make dim, deep sky objects easier to see as the background sky glow is lowest creating more contrast.
07/24/12	Moon 4 degrees S of Mars. This conjunction could turn up some interesting photo opportunities.
07/26/12	Moon at first quarter. Good time to observe the moon which is half lit from the west in the early evening sky.

Table of Images (Click on an image to expand)

Monthly Night Sky Charts - Image Credits (Tim Van Devender using Stellarium)
June 4 - Partial lunar eclipse (38%)
June 5 - Venus tranist of the Sun
June 24 - Mercury at greatest elongation from the Sun
July 3 - Mercury near Beehive Cluster
July 9 - Venus brightest
July 24 - Moon 4 degrees SW of Mars
Sketches and Images - Image Credit (Tim Van Devender)
Mars
Saturn
Jupiter
The Moon
Jupiter and Io Moon Shadow
Messier 45 (Pleiades)
NGC 884 and NGC 869 - Perseus Double Cluster
NGC 2024 - The Horsehead and Flame Nebulae
NGC 2237 - The Rosette Nebula
NGC 2264
Images from Alistair Symon
Messier 27 (Dumbbell Nebula)
Mssier 31 (Andromeda Galaxy)
Messier 33 (Triangulum Galaxy)
Messier 45 (Pleiades)
Messier 57 (Ring Nebula)
Images from Nine Planets
Jupiter
The Moon
Images from SEDS
Messier 13 (Hercules Globular Cluster)
Messier 15
Messier 27 (Dumbbell Nebula)
Messier 31 (Andromeda Galaxy)
Messier 33 (Triangulum Galaxy)
Messier 44 (Beehive Cluster)
Messier 45 (Pleiades)
Messier 57 (Ring Nebula)
NGC 7009 (The Saturn Nebula)
NGC 7293 (The Helix Nebula)