How Far Can We See? (part two)

Now for the exciting conclusion--and the second answer--to Matt's question of last week, which you may recall was:

"Is there a specific star that represents the farthest a person can see with the naked eye?"

Although the Andromeda Galaxy is the farthest object the average person can see with the naked eye, there is a star that is reportedly the most distant that can be seen naked-eye. It's a variable star in the constellation Cassiopeia the Queen, and it has the unromantic name of V762 Cas.

A variable star is a star that periodically brightens and dims. In the case of V762 Cas, it's most likely doing that because it's in a red supergiant phase, and it's begun to swell and shrink. A red supergiant is approaching the end of its life. It has burned up all its hydrogen fuel, and has begun burning other elements in a specific sequence. This causes rather dramatic changes in the star's size, temperature, and "behavior."

Image from Palomar Observatory Sky Survey

V762 Cas lies about 15,000 light years away. As we learned last week, one light year is nearly six trillion miles. Now multiply that by 15,000, take two aspirin, and go lie down.

V762 Cas must be a big honkin' supergiant, if it's that far away and we can still see it, yes? Unfortunately, I have not yet been able to spot V762. It is right on the outer limits of naked-eye accessibility, so I need to try again at a really dark site. Acquiring this sort of faint target, along with a faint target like the Andromeda Galaxy, benefit greatly from an effort to properly dark adapt (see last week's post).

To give it a try yourself, face north and locate the Lazy W asterism of Cassiopeia, which looks like a W or an M, depending on its orientation when you look. Download a free sky map for the month at http://www.skymaps.com/, if you don't know how to locate Cassiopeia.

Now draw an imaginary line between the star at the roof peak of the House asterism of Cepheus--it looks like a child's drawing of a house--and the leftmost star of the Lazy W, if it were oriented as a right-side-up W. V762 lies on that line. The star map below will help you pinpoint its location.

Looking north toward Cassiopeia and Cepheus

If you have success spotting it, please post your results in the Comments. Also, if you can spot it with binoculars or a telescope, let us know that also; I'm curious to know if anyone sees any color in the magnified image. Sometimes color is significantly enhanced with a little magnification.

Good luck to us all!

Tripping the Light Fantastic - Part 2

Let’s continue our trip along the Winter Milky Way, this time exploring the northern end.

1) About an hour after your local sunset time, face north. If you don’t know the cardinal directions at your location and you don’t have a compass, make note of where the sun sets on the horizon. That spot is approximately west. Stand with your left shoulder to the west, and you’ll be facing approximately north.

Star maps created with Your Sky

2) Moving up from the northern horizon, the first asterism (star pattern) you’ll spot is the House in the constellation Cepheus the King. It's a simple five-sided shape, not unlike a child’s drawing of a house. Its peaked roof is currently pointing straight up (toward the south).

3) Follow the westward curve of the Milky Way (toward the left) to find the Lazy W asterism of the constellation Cassiopeia the Queen. The W is standing on end, with the top of the W— the open end— facing right, or east.

4) Next in line on our glowing path is the asterism known as the Segment, in the constellation of Perseus the Hero. This is a curved line of six stars, oriented with its bulge protruding westward (to the left).

5) Continue a little farther along the Milky Way to finish up at the Pentagon asterism of the constellation Auriga the Charioteer. The very bright star that marks one of the Pentagon corners is the yellow-white Capella, sixth brightest star in Earth’s night sky.

6) With your head now tipped all the way back, can you spot where you left off last week when you swept up the Winter Milky Way from the southern horizon? The Milky Way is again bracketed by Taurus and Gemini, but this time Taurus the Bull is on the left (west) and Gemini the Twins are on the right (east).

Enjoy the spectacle of the Winter Milky Way through the warming spring, as it each night inches its way incrementally westward (or appears to, as the Earth continues eastward on its journey around the Sun). And don’t be sad when our friend WMW drops below the western horizon in June, because rising in the east to replace it will be another "light fantastic" we can trip together: the Summer Milky Way.

Cassie's Cluster

Note: There will be no September 17 post so that I may prepare for the STAR-HOPPERS weekend workshop in astronomy for grandparents & grandkids. Enjoy the September 10 post or browse my older posts. I'll be back with a new post on September 24.

Messier 52 in the constellation Cassiopeia the Queen is one of my favorite open clusters. I like its rich star field and its somewhat fan-shaped appearance. I also consider it a big plus that it’s easy to find.

An open cluster is a loose collection of stars that formed around the same time in the same nebula (cloud of gas and dust). You might think of an open cluster as a sort of family group.

Messier 52, or M52 as it is commonly known, is one of the 110 celestial objects in the catalog of famed 18th century French astronomer and comet-hunter Charles Messier (pronounced MESS ee yay). This catalog is used extensively by amateur astronomers as an observing list, since it contains some of the “best and brightest” deep-sky objects in the night sky. Messier discovered M52 in 1774, while “chasing” a nearby comet.

M52 is easy to find because you can use the distinctive Lazy W asterism (star pattern) of Cassiopeia to locate it. Grab your binoculars, and let’s take a look at Cassie’s cluster.

1) About an hour after your local sunset time, face north. If you don’t know the cardinal directions at your location and you don’t have a compass, make note of where the sun sets on the horizon. That spot is approximately west. Stand with your left shoulder to the west, and you’ll be facing approximately north.

Looking north to Cassiopeia's Lazy W
Star maps created with Your Sky

2) Look for a W-shaped group of stars east of the meridian. This is the central asterism of Cassiopeia, the Lazy W. Cassiopeia is a circumpolar constellation, one that circles the North Celestial Pole, the imaginary fixed point in the sky directly above the North Pole. Luckily for us, there is a star extremely close to that point in the sky, which serves as a navigational marker. This is Polaris, the North Star.

Cassiopeia and the other circumpolar constellations appear to make a complete counterclockwise circuit around the North Star, over the course of one day. But they’re not really spinning around the North Star. This apparent motion, or the way they appear to move in our sky, is caused by the rotation of the Earth, as it spins on its axis like a top, 24/7.






3) From Shedar (SHEDD-er), the lower right star of the W, draw an imaginary line through Caph (KAFF), the upper right star of the W. Then extend that line the same distance again past Caph, plus a skosh. Train your binoculars on that spot, and you should see a fuzzy patch. With a small telescope, you’ll be able to resolve the stars in the cluster, that is, they’ll separate into distinct points of light.

M52 lies around 5,000 light years from Earth. One light year is the distance light travels in one Earth year, nearly six trillion miles. The cluster is estimated to contain 200 members.

The open cluster M52
Credit: AURA/NOAO/NSF

Two hundred family members in one place at the same time makes for quite a reunion. Pass the potato salad, please.







Astronomy Essential: The universe began with the Big Bang.

The Big Bang is a widely accepted scientific theory of the origin of the universe. It postulates that about 13.7 billion years ago, the visible universe was extremely dense and extremely small— about the size of a dime. This singularity suddenly expanded to create the large-scale universe, which continues to expand today.

Many astronomers accept that a Big Bang event is the best current explanation for some key observable features of the universe, such as: its continuing expansion from a smaller, denser state; the microwave radiation “glow” that is present throughout the universe; a consistent abundance of simple elements such as hydrogen and helium throughout the universe, even in the oldest objects; and a limit on the age of stars in the cosmos.