Monthly Archives: November 2015

Vallis Alpes Comparison – 2013-04-21

I recently came across an image of Vallis Alpes on the moon (Alpine Valley) created by the Lunar Orbiter 4 space craft in 1967. It struck me as amusing that my own image taken in April of 2013 compares favourably with the Obiter’s image.

Moon - Vallis Alpes Comparison 2013-04-21

Moon – Vallis Alpes Comparison 2013-04-21

The Orbiter’s altitude varied from 2,100km to 6,000km so I nominally choose 5,000km as the distance of the Orbiter’s image. The mission cost in 1967 was $163m US. In today’s dollars (2015) that works out to about $1,2 billion.

My equipment is a little less expensive and i was about 371,000 km way when i took the image.

To be fair, there is a lot more detail in the orbiters image. For example, the rille (trench) running down the middle of the valley is between 700 and 1,200m across. This detail can just be seen on my image, while it’s quite clear on the Orbiter’s image and even shows the details of some small craters that impacted after the rill was formed.

My image of Vallis Alpes is a close crop to a much a larger image of the area including the crater Plato and the top mare Imbrium.

Moon Plato and Vallis Alpes 11.74days 2013-04-21 v1

Moon Plato and Vallis Alpes 11.74days 2013-04-21 v1

 

Finding the Andromeda Galaxy – 2015-11-05

M31_Andromeda_Galaxy_2010-11-08_v3_SJM
As night sky objects go, i think the Andromeda Galaxy has the most engaging story. And it’s a relatively modern story considering the ancient folklore associated with the constellations and the heavens in general.

In 1920 there was a raging disagreement among astronomers and scientist in general about the size of  universe. The generally accepted view at the time was that our Milky Way galaxy was somewhere between 7,000ly and 30,000 light years in diameter. And the Milky Way was the entire extent of the universe. The fuzzy dense objects visible in telescopes (that we now know are distant galaxies) were described as nebula – “a cloud of gas and dust in outer space, visible in the night sky either as an indistinct bright patch”. And these nebula were thought to be part of the Milky Way.

To jump forward a bit, the Milky Way is currently estimated to be between 100,000ly and 180,000ly in diameter and about 2,000ly thick. The “observable universe” is thought to be somewhere around 93 billion light years across.

The discussions about the size of the universe culminated in what has become to be known as “the great debate” between Harlow Shapley and Heber Curtis. Shapley argued that the Milky Way was the entire extent of the universe and that nebula such as Andromeda were contained within the Milky Way. Although he maintained that the main part of the Milky Way could not be more that 30,000ly across, he did propose that nebula such as Andromeda and globular clusters could form at the distant edges making the diameter 300,000ly. Therefore also fixing the upper size of the universe at 300,000ly. Curtis argued that the Andromeda nebula was in fact at a great distance and an “island universe” (a term coined by Immanual Kant). He accepted the thinking of the day that the Milky Way was no more than 30,000 ly in diameter but proposed that the Andromeda nebula was 500,000ly away and other such nebula as far as 100mly. (Current estimates put Andromeda at 2.5 million light years.)

Well before the debate reached this pinnacle, Henrietta Leavitt, a deaf astronomer working at the Harvard College Observatory, discovered a relationship between the absolute luminosity of a particular type of variable star and its period. In short, she found a way to measure, with certainty, stellar distances using the period of Cepheid Variables.

A variable star changes brightness over a predictable time frame – the period. In 1908, Leavitt noticed a relationship between Cepheid Variable periods and their absolute luminosity and published the results of her initial observations. Then in 1912 after analyzing more stars, she confirmed her observations. Essentially, she found that the actual or absolute brightness of a Cepheid Variable can be calculated from its period. And knowing the absolute brightness, its apparent brightness can be used as a measure of its distance – the further away it is, the dimmer it will appear.

As a side note, Shapley took over as director of the Harvard observatory in 1921 and promoted Leavitt to head of Stellar Photometry.

In 1919, the 100″ Hooker telescope – the largest telescope at the time – was installed on Mt Washington. At about the same time, Edwin Hubble started working at the observatory. Between 1922 and 1923, Hubble used the Hooker telescope to photograph the Andromeda “nebula” and was able to identify Cepheid variables. Aware of Leavitt’s observations, he was then able to calculate the distance to Andromeda. His initial estimate put it at 930,000ly – not quite the actual 2.5mly – but sufficient to declare that the Andromeda Nebula was indeed a separate galaxy. Shapley was still unconvinced as were many of the astronomers of the day. But by 1925 it was clear that the results were inescapable and the universe got a whole lot bigger.

Hubble went on to measure the distances to a number of other “nebula”; confirming that they too were separate galaxies. Then in 1929 Hubble published another ground breaking result – the universe was expanding! He discovered that the further a galaxy was away, the faster it was receding from us. (He used redshift to calculate relative velocity.) And if the universe was expanding, they it must have been smaller in the past. In 1931 Georges Lemaître, a Belgian cosmologist and Catholic priest proposed that the universe must have started out as a single point – later to be coined the Big Bang. As early as 1922, Alexander Friedmann had produced a solution to Einstein’s General Relativity field equations that showed space must be expanding.

So as late as 1920, the universe and the size of the Milky Way were thought to be in the range of 7,000 to 30,000 ly across. Then with a series of observations from 1908 (Leavitt) to 1924 (Hubble) the size of universe expanded to millions and billions of lights years.

The background is interesting, but what makes it even more engaging is that the Andromeda Galaxy can actually be seen unaided! At a distance of 2.5 millions light-years, it’s the furthest object that can be seen without a telescope or binoculars and only requires a moderately dark sky to see it.

By November it’s high in the sky facing south in the evening and appears as a faint, but distinct oval smudge. The darker the skies, the more obvious it is.

November_2013_AllSky_Chart

The chart below provides some tips on how to find it. Pegasus is due south in the November evening sky and is the large square (or diamond) shape as wide as your hand is stretched from thumb to baby finger. The Andromeda constellation is the “v” shaped arrangement of stars to the east and they share the star Alpheratz. Step 1: Start with Alpheratz in the upper left corner of Pegasus. Count three stars down to the left to Mirach (with Alpheratz being star No 1). Step 2: Then count three stars up (Mirach as No 1). The second set of 3 stars are faint so may not be obvious at first. Step 3: M31 will be 4° to the right of the 3rd star (about 2 finger widths) and elongated as shown.

finder_m31_star_hopping

Vega and the Constellation Lyra – 2015-10-30

The bright star Vega at magnitude 0.03 is the 5th brightest star in the sky and the third brightest star visible from the 45th parallel (Ottawa). Sirius at magnitude -1.46 is the brightest star in the sky and Arcturus magnitude -0.05 is the second brightest in the north. Although the yellow-orange star Arcturus is only marginally brighter than Vega, Vega has the advantage of being near the zenith on summer nights and the slight blue tint makes it seem even brighter.

Vega Closeup - 2015-10-30

Vega Closeup – 2015-10-30

Vega is in the constellation Lyra – the lyre or harp. Lyra is one of 48 constellations listed by Ptolemy in the second century and is on the International Astronomical Union’s (IAU) official list of 88 constellations. The long exposure image below shows the 4 bright stars of the harp as well as Epsilon Lyra (ε1, ε2 – the Double Double) left of Vega and Kappa Lyra (κ) to the right.

Vega in the Constellation Lyra - 2015-10-30

Vega in the Constellation Lyra – 2015-10-30

The chart overlay below  shows the location of the bright stars as well as the location of the M57 Ring Nebula. Vega is 25ly from earth while the other stars are at various distances. So the lyre shape is just a chance alignment when viewed from earth.

  • Vega: mag 0.03, dist 25ly
  • Epsilon 1: mag 4.65, dist 162 ly
  • Epsilon 2: mag 4.56, dist 161ly
  • Kappa: mag 4.31, dist 238ly
  • Zeta: mag 4.31, dist 154ly
  • Delta: mag 4.21, 906ly
  • Sheliak: mag 3.50, 882ly
  • Sulafat: mag 3.25, 640ly
Lyra Constellation Stick Figure

Lyra Constellation Stick Figure

The next image is modified to reduce the fainter stars and is more representative of what the sky might look like from a dark site. With this image, the bright stars of the constellation Lyra are more obvious.

Vega in the constellation Lyra - Less Stars -2015-10-30

Vega in the constellation Lyra – Less Stars -2015-10-30

While we think of constellations as the stick figure above or the elaborate drawings of mythical figures, the IAU defines a constellation as a non-overlapping region. So Lyra extends a little past the obvious 7 bright stars and defines a region in the sky between Cygnus to the east and Hercules to the west.

Lyra Constellation Boundaries

Lyra Constellation Boundaries

Lyra is home to a few interesting night sky objects:

Within the “stick figure” there are:

  • Epsilon – the double double
  • Messier 57 – The Ring Nebula
  • Zeta, Delta and Sulafat are doubles

Within the boundaries there are also:

  • M56 – an 8.3 magnitude globular cluster with an apparent size of 5arc-minutes
  • NGC 6791 – an 9th magnitude open cluster spanning 19′

The pair of stars Epsilon Lyra 1 and 2 (ε1, ε2)  are gravitationally bound to each other – meaning they are in the same region and rotate around each other (although in thousands of years). Each of ε1, ε2 is also a pair of stars that can be seen as doubles though a medium to large telescope. ε1, ε2 have a separation of 3.5′ which can be seen in binoculars. The doubles of ε1, ε2 each have separations of 1.3″ and 2.3″ making them challenging doubles to split in a 4″ scope. However, the two pairs are oriented 90° with respect to each other making it easy to compare the star shapes and aiding in detecting the separation. The periods of each pair are in the range of 600 to 1200 years. The finder chart below helps when trying to “split” the doubles.Finder_Chart_Epsilon-Lyra

The image below of the double-double doesn’t quite manage to show a gap between the close pairs. This is what might be typically seen in a smaller scope or a night of poor seeing. Still, by noticing that each pair is actually oval shape, the direction at least of the doubles gives a clue that they are doubles.

DoubleDouble_Epsilon_Lyra_2008-06-10_v1_SJM

Messier 57 (NGC6720) – the Ring Nebula is a large bright planetary nebula. Its visual magnitude is 9.5 and 3 arc-min across. On good nights and a large telescope, the remnants of the central star that exploded is visible. The ring is the expanding cloud of hot gas thrown off when the star shed its outer shell. The image below easily captures this detail as well as the colour which is not discernible through the eyepiece.

M57 - Ring_Nebula - 2011-07-30 - v2

M57 – Ring_Nebula – 2011-07-30 – v2

Vega rises during the late evening in April. It will be low in the north-east at about 9:30pm edt mid-April and makes its way across the sky during the night. By midnight it’s still in the north-east and only 25° above the horizon. It doesn’t transit (crosses due south) until 6am though!

Of course, if one is willing go out at much later times, Vega is also visible in the winter but after midnight. I tend think in terms of what objects are visible during normal evening hours.

Lyra Finder Chart - Sky facing East on 2015-04-15 at 21:30hrs EDT

Lyra Finder Chart – Sky facing East on 2015-04-15 at 21:30hrs EDT

Each month Vega rises two hours earlier. Which means it transits two hours earlier each month. By late summer at 9:30pm edt, Vega is due south and high in the sky near the zenith. The chart below shows Vega and Lyra high in the sky due south nestled between Pegasus and Hercules.

Lyra Finder Chart - Sky facing South on 2015-09-01 at 21-30hrs EDT

Lyra Finder Chart – Sky facing South on 2015-09-01 at 21-30hrs EDT

By December, Vega is low in the west in the evening and soon will disappear altogether from the evening sky.

Lyra Finder Chart - Sky facing East on 2015-04-15 at 21:30hrs EDT

Lyra Finder Chart – Sky facing East on 2015-04-15 at 21:30hrs EDTj

But … as said earlier, if one wanted to go out at other times, Vega can still be seen during winter. Starting in December, Vega is also visible in the early morning sky! The chart below shows Vega rising at 6:30 am (when it’s still dark in Ottawa) the day after it set in the west on the evening before.

Lyra Finder Chart - Sky facing East on 2015-12-16 at 06-30hrs EST

Lyra Finder Chart – Sky facing East on 2015-12-16 at 06-30hrs EST

Each month Vega will rise 2hrs earlier. So in January it rises at 4:30am and in February it rises at 2:30. By April it will be rising at 9:30 again.

So Vega is actual visible all year long, but to see it might mean going outside to look for it while sleeping is a better alternative.