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ngc457 

 

The Owl Cluster is sometimes known as the E.T cluster as is shows a similar resemblance to both an owl and the movie character from ET- The Extra-Terrestrial. It is an easy object to find in both binoculars and small telescopes lying underneath the bottom of Cassiopeia's famous W shape. It comprises of about 100 stars and is estimated to be about 21 million years old which is quite young in stellar ages. The brightest star phi Cassiopeia is thought to be separate from the rest of the cluster as it shows different properties than the rest of the cluster and has a distance of about 4000 light years where the rest of the cluster is about 9000 light years away.

 

As Cassiopeia is circumpolar, you can enjoy this object at any time of the year.

 

Click here to view this in ObsPlanner

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There are a number of techniques to estimate the brightness of a variable star and each method has its own merits. In this post I will quickly outline the main ones used by amateur astronomers today, but first it is important to get hold of star charts that are better suited for variable star observing.

Star Charts

 

The best online resource for charts is the AAVSO which has an online tool that will dynamically generate a star chart to your orientations and fields of view. It can be found athttps://www.aavso.org/apps/vsp/

 

image

Fractional method

 

This is perhaps the easiest method to get started with as it doesn't require the knowledge of star magnitudes before observing.
Firstly once the field surrounding the variable star has been located, use a star chart with a smaller field of view such as what the BAA variable star section and AAVSO uses. Then once comparison stars are found, choose two with one being brighter and the other being dimmer than the variable star. Then estimate a fraction that the variable stars brightness is compared to the two comparison stars. For example the variable V is almost, but not quite as bright as star A, say three quarters the brightness. Then record it as:-

A3V1B

You can do this using as many comparison/variable pairs as you want. Then after your observing run, find out the brightness of the comparison stars and use this simple formulae taking star A as magnitude 4.6 and star B as 5.0.

Star A
4.6 + (3 * 0.1) = 4.6 + 0.3 = 4.9

Star B
5.0 - (1 * 0.1) = 5.0 - 0.1 = 4.9

One of the merits of this method is a number of estimates for different variable stars can be done in a relatively short time and it is the calculation that gives the results after you have got back inside to a warm drink.


Hershel-Argelander method


This method is more complex than the fractional one, but does yield better results. It is a step method and uses the principle of the smallest magnitude difference that can be perceived by the eye. So you firstly find a star of knows magnitude that is the same brightness as the variable noting it down as as A0V. By doing this with a number of stars some brighter than the variable and some dimmer than it, they can be recorded as:-

A0V
B1V
V2C

Where the brightest star comes first and follows these rules:-


- If both stars look the same brightness then A0V

- If star A is a little brighter, this is called 1 step and denotes as A1V
- If star A is without ant doubt brighter than the variable the it is 2 step and denoted as A2V
- If star A is clearly brighter than the variable it is 3 step and denotes as A3V
- Finally if it is still brighter it is 4 step and denotes as A4V

 

By reversing this method so the variable is 1 step dimmer than star A, it is denoted as V1A and all the other rules are applied and reversed so the brightest star is always first.

The Pogson Method


This is a refinement of the Hershel-Argelander method in that each step is precisely 0.1 magnitude difference. It requires the observer to compare a previously memorized star with the variable. So if a comparison star is 3 steps fainter than the variable it is denoted as A - 3 (for a difference of 0.3 magnitudes). Like wise if a comparison star is 1 step brighter than the variable it is denoted as B + 1. So once several measurements have been made an estimate can be calculated like this:-

A = 4.6
A - 0.3 = 4.9

Also
B = 5.0
B - 0.1 = 4.9


AAVSO method


The American Association of Variable Star Observers uses a variation of Pogsons method, but instead of memorizing the magnitudes of the comparison stars, an estimate of how much brighter or dimmer a variable is when compared to another star. So for example the variable brightness lies somewhere between comparison star A and B. Now if the difference between the two comparison stars is 0.4 an estimate can be made as to how much the variable is closer to star A or star B. For example the variable may be half way between the two stars so:-

A = 4.6
B = 5.0
Difference / 2 = 0.2
V = 4.8


The Manual for Visual Observing of Variable Stars can be downloaded from:-http://www.aavso.org/visual-observing-manual

References:-

 

Astronomy: a Handbook
edited by G.D. Roth

Observing Variable Stars: A Guide for the Beginner
By David H. Levy

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Setting up the Equatorial Mount

If you want to look at the Sun with a telescope, there are a couple of hoops you need to jump through first.

  • How do you align the telescope if you cannot see any stars?
  • How do you track it to stop having to slew manually as it moves?

Well in this post I will show you a good technique to get you going; these instructions apply to equatorial mounts and in this post I am using my trusted SkyWatcher MakCas 127 on top of a EQ5 Equatorial mount with GoTo capabilities.

Firstly though - NEVER look at the Sun without any kind of specialist Solar filter or you will definitely damage your eyes.

Now you need to find North, and the best way obviously is with a compass. Some telescope mounts have it marked 'N' on one of the tripod legs. Get this leg pointing as close to North as possible.

 

sun-1

 

Then with your scope declination set at your locations altitude, in theory you will be roughly polar aligned and if the stars were out you should see the Pole Star in your finder scope.

 

sun-2a

 

Make sure you have your solar filter fitted and it is secure before slewing anywhere near the Sun.

sun-2b

 

Incidentally, also take off your finder scope now as you don't want that to be pointing anywhere near the Sun either.

 

Finding the Sun

 

Release the RA and Dec locking nuts and swing the scope around to point towards the sun. Looking at the shadow the scope makes on the ground try and make the smallest possible and then lock the nuts again.

 

sun-3

 

Take out the diagonal from the eyepiece end and look straight up the tube. You should see bright patches inside the tube which will be coming from the Sun. The Sun will be opposite this light, so using the slow motion control slew the scope so that the white patch is now as close to the centre as possible. Put the diagonal back in with an eyepiece and you should be pretty spot on. Just centre it a bit more if needed. It might be easier to just release the locking nuts and swing the scope without using the drive to position perfectly.

 

sun-4

 

Set up the hand controller with your latitude and longitude, date and time as you would if you were setting up at night but cancel out of the alignment process.

 

Tracking the Sun

Most GoTo scopes have tracking speeds for different items, on the hand controller select Solar tracking as opposed to Sidereal tracking and the Sun should stay in the centre of the eyepiece.

 

sun-5

 


Although Sidereal and Solar tracking rates seem similar, a solar day is different to a sidereal day because we are also moving around the Sun as well as spinning 360 degrees on our axis. After setting up this way I checked the position of the after 10 minutes and again after 20 minutes and the Sun was still in the centre of the eyepiece.

 

Clear skies.

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Our Top 3 Astronomical Space Telescopes

 

The quest to find out more about “space and beyond” has been around since the beginning of time, right up to today. It is our continued advancements in science and technology that have proven to us that both the expected and the unexpected exist in space!

It is through these advancements in space technology, that I am able to present to you our Top 3 Space Telescopes that today continue to help us to understand the universe much more now than ever before.

 

Hubble Space Telescope

On the 24th April 1990 at the Kennedy Space Center, Florida – the Hubble space telescope was launched into space just above the Earth’s atmosphere, and it continues to orbit Earth today, some 24 years later and approximately 600km above the ground! The Hubble was a one of a kind at the time, because it was the first optical space telescope to orbit Earth!

Hubble Space Telescope thanks to Greg Goebel

Hubble Space Telescope thanks to Greg Goebel

Named after the great American astronomer Edwin Hubble (November 20, 1889 – September 28, 1953), the Hubble was built in the USA by the United States Space Agency NASA, to be able to take detailed photographic images of space that would be impossible from Earth due to distortion, bad lighting and even pollution, among other things.

 

Spitzer Space Telescope

Not long after the Spitzer space telescope, was launched into space on the 25th August 2003 from Cape Canaveral, as part of NASAs Great Observatories Program and is in orbit 26 million miles away from Earth. Originally planned to be part of a 2.5 year mission, and now 11 years on and with no liquid helium supply, the Spitzer telescope has a camera that remains in operation with its data being collected by NASA.

640px-Spitzer_space_telescope

Spitzer Space Telescope thanks to NASA/JPL-Caltech

Originally named the Space Infrared Telescope Facility (SIRTF), it went on to be renamed after Lyman Spitzer (June 26, 1914 – March 31, 1997) an accomplished 20th century astronomer and physicist.

 

The James Webb Space Telescope

As NASA continues its space race they have announced the planned launch of the James Webb space telescope that will be launched in October 2018, from Guiana’s Space Center, Guiana.

Built to succeed both of its predecessors – the Hubble and the Spitzer space telescope. This telescope will enable us to study the universe including its stars and planets in much more detail, as it is able to capture resolution and sensitivity, ranging from long visible wavelengths up to the mid-infrared range!

The James Webb telescope will orbit 1.5 million kilometres away from Earth, and it will features the largest telescope mirror ever to be sent into space with a 21 ft diameter.

James Webb Space Telescope thanks to NASA/MSFC/David Higginbotham/Emmett Given

James Webb Space Telescope thanks to NASA/MSFC/David Higginbotham/Emmett Given

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Computer Control Your Telescope

If you have a GoTo telescope such as those from Skywatcher, they come with a built in database of thousands of objects. This may be fine if you know what objects are visible in the part of sky you have access to, but if you have your own observing program with some less obvious objects, then controlling the telescope from a computer could be a good option. This could also be handy if you are an imager and want to capture a few objects, but don’t want to be sat outside getting cold. By connecting and controlling your telescope from the comfort of your armchair you could achieve this. In this post I will briefly run through what is needed both from the setting up the scope and configuring the computer. This run through is done using a Skywatcher 127mm GoTo telescope pictured below.

Connect Up The Cables.

 

1

 

Here are the adapters and cables you will need.

 

2

3

 

These can bepurchased from USB Nowand are normally less than £10.

 

4

 

This cable normally comes with your scope when purchased new.

Connect them all together (you may not need the serial to USB adapter and extension if your computer has a serial port, but they are becoming rare on more modern computers).

Connect up the hand controller to the scope base and also connect up the telescope to serial cable like this:-

 

5

 

The telescope mount as usual like this:-

 

6

 

Set Up The Hand Controller

Go through the setting of date and time and align the scope as you would normally, but leave it as that. For Stellarium to work, you must not be in PC Direct mode on the hand controller as it will not be able to communicate.

Configure The Software

For this demonstration I am using Stellarium , which is free and can be downloaded from here.

You need to have the location and time settings in Stellarium set as the same as that in your telescope hand controller.

Firstly you need to enable the plugin for computer controlled telescopes.

Choose the Configure button on the left hand side.

 

7

 

Select the Plug-Ins tab and choose the telescope Control. Make sure the Load at Startup check box is ticked.

 

8

 

Then Save the settings

 

9

 

Now to configure the port that the software will listen on, so for this you need to go to the Control Panel in Windows.

 

10

 

Choose Device Manager under Devices and Printers

 

11

 

Find the Com port number, in the case above it is COM3. I am using a serial to USB adapter, so it will appear under USB Serial Port, but your control panel may show different.

You have to specify this port in Stellarium, so go to the bottom menu and choose telescope control

 

12

 

Configure the telescopes

 

13

 

14

 

Click on the Add button to add a new telescope

 

15

 

Make sure ‘Stellarium, directly through a serial port’ is selected and enter an name for the scope connection. Further down the screen you can enter the serial port number we found earlier.

 

16

 

Click the OK button

 

17

 

You can now Start the connection.

Control your Telescope with the Computer

Make sure the status is Connected, if not then start it.

 

18

 

Choose an object you want to slew the telescope to.

 

19

 

20

 

Select Current object, the RA and Dec will change to that of the selected object. Press the big Slew button and the scope should start to move.

 

21

 

As the scope gets nearer to the chosen object, you will see a circular icon with your scope name move closer to the chosen object.

 

22

 

Finally the telescope icon will be directly over the chosen object and you should be able to view the object through the scope.

Clear skies.

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4954621859_24689348fc_z-800x500_c

 

What is a Supernova?

Before the invention of telescopes, astronomers had noted the appearance of stars in the sky where none had been before. These were called new stars and it was not until telescopes were turned to the skies and all sky surveys were conducted, that it was discovered there were already stars there, just not as bright. As the word Stella nova originates from the Latin term for a new star, a supernova was thought to be in the same class as these events, so were called supernovae as they were much brighter. It was only around the 1930’s that more research showed that nova and supernova are caused by different physics.

Characteristics of the Two Types of Supernova

Comparative_supernova_type_light_curves

Type I

These types have a maximum brightness typically in the order of 10 billion solar luminosities, then gradually decrease. Stars that form this type are from Population II stars and are observed in elliptical galaxies.

  • Type Ia – Spectrum show Silicon but no Hydrogen
  • Type Ib – Spectrum show no Silicon, no Hydrogen but show Helium
  • Type Ic – Spectrum show no Silicon, no Hydrogen and no Helium

Type II

With a less sharp peak than a type I supernova, type II decrease in brightness faster initially until a plateau is reached, then the brightness slowly decreases again. Because they are not observed in elliptical galaxies, it is though these types are from population I stars in the spiral arms of galaxies. Studies have shown that just prior to a core collapse event, the star undergoes a vibrating period much like a loud speaker.

  • Type II – Spectrum show Hydrogen lines

sn_classification

Supernovae Classification Chart

Core Collapse Supernova

Types Ib, Ic and type II are all core collapse supernova; stars that have reached the end of their productive life and have reached the point where the outward forces are weaker than the gravitational force. This is brought about when the star has finished fusing hydrogen and helium and…

Close Binary Supernova

In a nova, matter is pulled from a companion star onto a white dwarf until the Chandrasekhar limit is reached, then a massive fusion event occurs where Hydrogen converts into Helium increasing the brightness. If the nuclear fusion only occurs on the stars surface and does not destroy it, then it is known as a novae. If the event destroys the white dwarf star, then it is called a type Ia supernovae.

Notable Supernova in History

Crab Nebulae

Exploding in 1054 and observed by Chinese astronomers, this was a core collapse supernova of type Ib, Ic or type II. The evidence for this is a central pulsar of which type Ia supernova do not produce.

6409518821_05120991b0_z

M1 Crab Nebula thanks to flickr.com/photos/madmiked/

SN1987a

This is one of the best studies supernova because not only did astronomers have before and after images of the progenitor, but neutrinos were detected coming from it before visual observations were made. Over the years several telescopes such as Chandra and Hubble have been keeping a watch on SN1987a and have observed the expanding cloud of gas and its interactions with surrounding space.

Observing a Supernovae

Unless you have the equipment and time to conduct sky surveys, there is slim chance that you could discover a supernova. However notable astronomers such as Tom Boles and Mark Armstrong have discovered over 100 each using there home observatories and moderate sized telescopes. This may put you the typical astronomer off, but don’t let this deter you. If a new supernova is discovered, there is a chance you could get a photo or observe it after it has reached its maximum brightness. When new supernova are discovered, The Astronomers Telegram will announce it to any subscriber and web sites such as the British Astronomical Association and the American Association of Variable Star Observers will list them with details as how bright it is and what galaxy it is located. Early in 2014 astronomers using a moderate telescope discovered one of the closest supernova 2014j in the cigar shaped galaxy M82.

12172135884_555636a654_z

Supernova sn2014j, thanks to flickr.com/photos/uclmaps/

 

Clear skies

 

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Who Was Eratosthenes?

Eratosthenes was a mathematician, poet and geographer who lived between 276 and 195 BC in the city of Alexandria in modern day Egypt. His nickname with the people who knew him was Beta, because he was second best in almost every subject that was of importance at the time.

 

eratosthenes_2-800x500_c

 

Calculating the Earths Circumference

Being a geographer he came across may instances of peculiar things from travelers passing through the port at Alexandria. One of the things he noted was on a certain day each year in the town of Syene in southern Egypt, the Sun does not cast a shadow inside a well. However from his location in Alexandria a pole put in the ground did cast a shadow. By calculating the difference between these two angles, and knowing the distance between the two locations he could calculate the circumference around the Earth.

He used what seems today very elemental geometrical techniques to calculate a reasonable value to the Earths circumference, he did it like so:-

eratosthenes_1

 

In this image, the two angles A are equal, if it assumed that the Sun is so far away that the light path is parallel.

Location 1 is Syene and location 2 is Alexandria.

Using the formula:-

Tan(A)=l/h

Where l = length of shadow and h = height of pole.

He calculated this angle to be 7.2 degrees, which happens to be 1/50th of 360 degrees. Now knowing the distance between Syene and Alexandria he could get the circumference like this:-

C=D∗(360∘/7.2∘)

His calculation for D was 5040 stades, where a stade was the length of a stadium approximately 1/10th of a mile or 160 m.

So:-

C=160∗5040∗(360/7.2)=40,320km

By using modern techniques, it is known that the circumference of the Earth is 40,075 km

The Problem With This Method

The Earth is not a perfect sphere, it is slightly oblate; the circumference is greater measured around the equator than that measured going through the poles. Eratosthenes method can better be described as the circumference going through the poles as that is the axis he used to measure the distance between Syene and Alexandria.

The other issue is with the length of a stade; it was known that this is the length of a sports stadia commonly used at that time. However there is not a standard for this length and some stadia are known to differ in size so we don’t really know what length he was using as a stade.

 

Clear skies