Skywatcher's Guides

Skywatcher's Guide - April and May 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)
Edited by: Kevin Hardegree-Ullman (Flandrau Telescope Operator, http://teachastronomy.com), Rich Watson (Flandrau Astronomy Coordinator)
Images contributed by: Tim Van Devender, Alistair Symon (Flandrau Telescope Operator), Nine Planets, and Students for the Exploration and Development of Space (SEDS)

Navigation

Monthly Overview
Observational Highlights
- Solar System
- Deep Sky
Frequently Asked Questions
Interesting Night Sky Events
Interesting Stars to Observe
Interesting Deep Sky Objects
Table of Images
Bibliography

Monthly Overview

April has been designated "Astronomy Month" by Astronomy Without Borders which helped organize the International Year of Astronomy back in 2009.

At the end of April and beginning of May our Milky Way galaxy wraps around the horizon in the early evening leaving us a clear view of the deep sky. The constellations in these months are sparse as the brightest stars are few neighbors as we look out of the galactic plane. The twins, Castor and Pollux, are nearly alone in the region of Gemini above setting Orion. Auriga, the Charioteer and his goats, form a pentagon shape coming out of setting Taurus. Leo and Ursa Major (the lion and big bear) stalk after the twins. Navajo tradition refers to the stars of the "Big Dipper" as Náhookos Bi'ka' or the Male Revolving One. He was considered the family leader and protector. Southwest of Leo is the constellation Virgo forming a wispy maiden. Spica is the only bright star in Virgo but there is a cluster of deep sky objects and galaxy's in this region of dark sky that make for very interesting observations like the "Hubble Deep Field".

Moving east into the morning and May sky we have the constellations Boötes, the herdsman, with its primary star Arcturus and Hercules, the famous son of Zeus. The giant cluster of stars in Hercules known as Messier 13 makes an excellent show for visitors in the Flandrau dome. The constellation form of Hercules kneeling at the head of the dragon, Draco, dates back through Greek myth (Heracles) and on to 4000 BCE where the kneeling figure represented Gilgamesh. Continuing east in the sky leads us to Vega in the constellation Lyra, the harp, and Cygnus the swan in a lovely swath of the Milky Way's dusty lanes.

Observational Highlights - Solar System

The big show for April and May will be our Moon passing directly between the Earth and the Sun creating a total solar eclipse on May 20th. This year's solar eclipse is even more special because the Moon is at its farthest point from Earth leaving only 88% of the Sun's surface covered. The result is called an annular solar eclipse as the sun will be a full ring around the silhouette of the Moon for observers in the direct path of the eclipse. The path of the eclipse will pass through northern Arizona just before sunset from the city of Page heading towards Albuquerque, NM. Tucson is about 250 miles south of the lunar shadow path so Flandrau visitors will see the Moon pass across the disk of the sun slightly off center as shown in the attached video reaching totality at 6:40 PM just before sunset. Solar eclipses happen in a cycle known as the “saros period” which is 18 years, 11 days and 8 hours long. The last annular eclipse in 1994 was also in North America but due to the 8 hours on the end of the saros period the next will be 1/3 of the world away and not visible from North America. The next total solar eclipse in North America will be on August 21, 2017.

Venus continues to be the third brightest object in the sky as it blazes at -4.5 magnitude in our evening sky. During April Venus will reach maximum brightness and then start to decrease its lit surface area (while getting larger) as it continues to head for a pass directly between Earth and the Sun. On June 6th Venus will “transit” or pass across the disk of the Sun as viewed from Earth.

The constellation Leo is currently being visited by the planet Mars. Mars is past opposition and starting to get smaller as we pull away from each other. However the planet is still large and bright in our 2 year cycle and well placed for early evening observing.

Saturn will be passing through the area of Virgo providing a fascinating object for visitors through Flandrau Observatory's 16-inch Cassegrain telescope. Saturn is at opposition (meaning it passes overhead at midnight and thus is in the sky all night) and so is the at the best time for observing. This usually marks the beginning of the observing “season” at Flandrau as we are open in the early evening and have an obstructed view in the east.

Observational Highlights - Deep Sky

The Milky Way will be along the horizon a the end of April and beginning of May. From a pristine dark site offering a low horizon in 360 degrees one could see the Milky Way wrapped about you. From town this means the view overhead is heading straight out of the galaxy. The constellations at this time of year have relatively few bright (magnitude 1) stars which are close by neighbors to our Sun in the Milky Way. This does mean that we have relatively unobstructed views straight out of the galaxy towards other galaxies in the Virgo cluster and beyond. The famous Hubble Deep Field image was taken in one of the “darkest” parts of the sky in Virgo.

Some of my personal favorites to observe are Messier 51, the Whirlpool Galaxy, which gave us a stunning supernova two years ago. Messier 81 and Messier 82, the Cigar Galaxy, are another pair of galaxies to the north which bright and have distinctive shapes. As the evening progresses and the Milky Way lifts from the eastern horizon we have one of the best globular clusters of stars, Messier 13 in Hercules.

Frequently Asked Questions

Why does Venus have “phases” like the Moon while Mars, Jupiter and Saturn do not?

The simple answer is the geometry of light bouncing off of spheres in different locations. Perhaps the best way perceive this is to imagine a large room with a really bright, bare light bulb in the center. Hold a ball half way between the light and the wall and you will see a bright glare coming from the center of the room. The walls around you are fully lit and directly away from the light is your shadow. The “outer” planets (beyond Earth) would be balls spinning around the room out by the wall, fully illuminated by the light at the center of the room. There is some small amount of shadow on edge of an outer ball but basically the ball is always lit from this vantage point.

Now, have someone hold another ball and walk in a tight circle around the light. This would be Mercury or Venus inside our orbit. Sometimes they will be lit from the side then fully lit as the pass opposite the Sun from Earth, moving back to side lit and finally it becomes dark as we see the silhouette of the ball passing between yourself and the light. Venus has just passed through the side lit phase and is now heading to pass directly between Earth and the Sun on June 6th. In fact Venus is lined up so well on this pass it will actually “transit” or across the disk of the Sun as seen from Earth.

In this analogy the Moon would be a small child running about you in a tight, dizzying circle holding a lollipop. One moment they are in the glare of the Sun and totally lost from sight, the next they are beside you in a half lit blur, then they are fully lit behind you and so on. Occasionally the child's lollipop would pass directly into the shadow of your ball or between the ball and the light bulb. Those would be lunar and solar eclipses respectively.

Let’s give this scale some perspective. If we were to build a scale model of the solar system with Earth being one millimeter in diameter (our entire civilization shrunk down to the size of a salt crystal) the Sun would be 4.3 inches wide and 39 feet away. Neptune would be about a quarter of a mile away and the entire solar system would fit within a square mile. Assuming this model was based in Tucson, AZ, our nearest neighboring star system (possibly two square miles across) would be 2000 miles away at the eastern seaboard in North Carolina!

Interesting Night Sky Events

04/03/12	Venus 0.4 degrees SSE of Alcyone (in M45). This will make an interesting view in low power binoculars and telescopes.
04/06/12	Full Moon.
04/13/12	Moon at last quarter.
04/15/12	Equation of Time = 0. Saturn at opposition. Saturn will rise at dusk, cross the middle of the sky at midnight and set at dawn. This is considered the best time to observe Saturn as it is highest in the sky in the darkest part of the evening.
04/18/12	Mercury at greatest elongation. Mercury will be 27.5 degrees west of the Sun making it the highest/farthest from the Sun in the early morning.
04/21/12	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.
04/22/12	Lyrid meteor shower. The dark of the new moon makes this a favorable year for the Lyrid meteor shower. Watch for trails coming from Vega in the northwest sky between 11PM and 1AM.
04/28/12	Astronomy Day.
04/29/12	Moon at first quarter. Good time to observe the moon which is half lit from the west in the early evening sky.
04/30/12	Moon at maximum libration. The moon “wobbles” as it spins about us allowing Earth observers to see about 59% of the moon's surface. This is called libration and in April we see one of the maximum angles as the moon is fully “tilted” by a few degrees. Venus brightest at magnitude -4.5. Venus will continue getting larger in apparent size but will become less illuminated as it heads between Earth and the Sun.
05/04/12	Venus farthest north. Venus will not be this far north in the celestial sphere again until the year 2239.
05/06/12	Full Moon. Normally this is when astronomers are catching up on sleep… when planets aren’t putting on such a pretty show that is.
05/12/12	Moon at last quarter.
05/20/12	Spring (vernal) Equinox. The Sun crosses into the northern part of the sky. Spring is awesome in Arizona by the way!
05/20/12 @ 6:40 PM	New moon & Annular Solar Eclipse. total solar eclipse in North America until Aug 21, 2017. See the solar system highlights section for details.
05/22/12	Mercury 0.4 degrees NW of Jupiter. This conjunction puts our inner most planet in the same telescopic field of view as our largest planet, Jupiter for early morning observers.
05/28/12	Moon at first quarter. Good time to observe the moon which is half lit from the west in the early evening sky.

Interesting Stars to Observe

Name / Designation	Apparent Magnitude (lower = brighter)	Distance (light-years)	Notes
Sirius	-1.44	8.6
Arcturus	-0.05	36.7
Vega	0.03	25
Capella	0.08	42
Rigel	0.18	770
Procyon	0.4	11
Betelgeuse	0.45	427
Altair	0.76	17
Aldeberan	0.87	65
Spica	0.98	262
Pollux	1.16	38
Deneb	1.25	3230
Regulus	1.36	77	means “Little King”
Castor	1.58	52
Polaris	1.97	431
Algol	2.09	93	variable star
Denebola	2.14	36.2
Enif	2.38	670
Eta Cassiopeiae	3.5 / 7.4	19	480 yr orbit

Interesting Deep Sky Objects

Designation	Name	Apparent Magnitude	Apparent Size	Distance (light-years)	Type
Messier 45	Pleiades	1.6	110'	440	open cluster
Messier 31	Andromeda Galaxy	3.4	3° x 1°	2,900,000	spiral galaxy
Messier 44	Beehive Cluster	3.7	95'	577	open cluster
Messier 42	Orion Nebula	4	85' x 60'	1400-1600	diffuse nebula
Messier 33	Triangulum Galaxy	5.7	67' x 42'	3,000,000	spiral galaxy
NGC 7009	Saturn Nebula	8	36"	2,400	planetary nebula
Messier 81	Bode's Galaxy	8.5	21'	1,200,000	spiral galaxy
Messier 82	Cigar Galaxy	9.5	14'	1,200,000	galaxy

Table of Images (Click on an image to expand)

April and May Night Sky - Image Credits (Tim Van Devender, Starry Night Pro)
April 3 - Venus and M45 Conjunction
April 3 - Night Sky Toward the West
April 6 - Full Moon
April 22 - Lyrid Meteor Shower
May 20 - Annular Solar Eclipse
May 20 - Annular Solar Eclipse
May 22 - Moon Occults Zeta Tauri
Mars
Saturn
Sketches and Images - Image Credit (Tim Van Devender)
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)