APOD: Two Clusters and a Comet (2020 Jan 30)

[APOD Robot]

Two Clusters and a Comet

Explanation: This lovely starfield spans some four full moons (about 2 degrees) across the heroic northern constellation of Perseus. In telescopic exposures made during the nights of January 24, 26, and 28 it holds the famous pair of open or galactic star clusters h and Chi Persei with comet PanSTARRS (C/2017 T2) captured each night as it swept left to right across the field of view. Also cataloged as NGC 869 (right) and NGC 884, both star clusters are about 7,000 light-years away and contain stars much younger and hotter than the Sun. Separated by only a few hundred light-years, the clusters are both 13 million years young based on the ages of their [url=http:/messier.seds.org/open.html]individual stars[/url], evidence that they were likely a product of the same star-forming region. Discovered in 2017 while still beyond the orbit of Saturn, Comet PanSTARRs is a new visitor to the inner solar system and just over 13 light-minutes from planet Earth. Always a rewarding sight in binoculars, the Double Cluster is even visible to the unaided eye from dark locations. C/2017 T2 could remain a telescopic comet though. One of the brightest comets anticipated in 2020 it makes its closest approach to the Sun in early May.

<< Previous APOD

This Day in APOD

Next APOD >>

[Ann]

Nice picture!

Double Cluster and comet.png (285.36 KiB) Viewed 2561 times

Double Cluster in Perseus (at 7,000 light-years) and comet
(at a number of light-hours). Photo: Rolando Ligustri.

Click to view full size image

Alpha Persei Cluster at ~500 light-years.
Photo: MarioSS.

As a diehard lover of blue things, I would of courser have liked the Double Cluster to look a little bluer, especially since there are many intrinsically blue stars there. But I can't complain. The Double Cluster is 7,000 light-years away from us, and the stars are quite reddened. The brightest stars in cluster NGC 869 (right) belong to spectral classes B2Ia and B3Ia. Their intrinsic color index should be something like -0.15, but they are so reddened that their color index (as seen from our location) is about +0.50 instead.

I posted the beautiful picture of the Alpha Persei Cluster because I wanted to give you an idea of how reddened the stars of the Double Cluster really are. While the Double Cluster is some 7,000 light-years distant, the Alpha Persei Cluster appears to be located between 500 and 600 light-years away. The Alpha Persei Cluster is barely reddened at all, and its brightest star, Mirphak, has a spectral type of F5Ib and a color index of +0.48. In other words, the hot B-type supergiants of NGC 869 of the Double Cluster appear to be exactly the same color as mid-F-type lesser supergiant Mirphak. All because of the reddening caused by 7,000 light-years of an extremely tenuous "soup" of dust particles between ourselves and the Double Cluster.

Click to view full size image

Illustration: Michael Hague.

There appears to be virtually no dust between ourselves and the Alpha Persei Cluster, so I guess that the old woman tossed up in a blanket has already been up there, far higher than seventeen times as high as the Moon, and swept the nearest 500 light-years in the direction of Alpha Perseus free of cobwebs of the sky!

I admire MarioSS' image, and I think he captured the colors of the stars of the Alpha Persei Cluster perfectly. Note the whiteness of Alpha Persei (center) and the blue-tinted Delta Persei near bottom of the image.

The comet seen in the APOD displays a properly green coma and what looks like a short yellowish dust tail.

Ann

[orin stepanek]

I've only seen 1 comet with unaided eye; that being Hale Bopp! I was working nights; we got up on the roof to see it! Was really neat!

[neufer]

I've only seen 1 comet with unaided eye; that being Hale Bopp!
I was working nights; we got up on the roof to see it! Was really neat!

Alan Hale and Thomas Bopp discovered Comet Hale–Bopp separately on July 23, 1995 before it became visible to the naked eye. It is difficult to predict the maximum brightness of new comets with any degree of certainty, but Hale–Bopp met or exceeded most predictions when it passed perihelion on April 1, 1997. It was visible to the naked eye for a record 18 months, twice as long as the Great Comet of 1811, the previous record holder. Accordingly, Hale–Bopp was dubbed the Great Comet of 1997.

Its lengthy period of visibility and extensive coverage in the media meant that Hale–Bopp was probably the most-observed comet in history, making a far greater impact on the general public than the return of Halley's Comet in 1986, and certainly seen by a greater number of people than witnessed any of Halley's previous appearances. For instance, 69% of Americans had seen Hale–Bopp by April 9, 1997.

Hale–Bopp was a record-breaking comet—the farthest comet from the Sun discovered by amateurs and with the largest well-measured cometary nucleus [40–80 km] known after 95P/Chiron [117 km]. It was also brighter than magnitude 0 for eight weeks, longer than any other recorded comet.

Carolyn Shoemaker and her husband Gene, both famous for co-discovering comet Shoemaker–Levy 9, were involved in a car crash after photographing the comet in Australia. Gene died in the crash and on July 31, 1999, some of his ashes were carried to the Moon by the Lunar Prospector space probe. The brass foil wrapping of Shoemaker's memorial capsule is inscribed with images of Comet Hale–Bopp ("the last comet that the Shoemakers observed together"), the Barringer Meteor Crater, and a quotation from Shakespeare's Romeo and Juliet reading:

• And, when he shall die
  Take him and cut him out in little stars
  And he will make the face of heaven so fine
  That all the world will be in love with night
  And pay no worship to the garish sun.

[Ann]

Click to view full size image

Comet Hyakutake. Photo: Frank Zullo.

I never even tried to see super-blue comet Hyakutake.

I can't get over it!!!

Ann

[Chris Peterson]

I never even tried to see super-blue comet Hyakutake.

Seeing it well required good dark skies. But to the eye, it didn't look very blue. Just not bright enough to stimulate color vision. It looked rather like the Milky Way, but with more distinct edges. What made it impressive was its size, spanning half the sky.

[orin stepanek]

Mercury had a Comet!!

280px-1964_Mercury_Comet_Caliente_Coupe_(9321170381).jpg (20.08 KiB) Viewed 2377 times

Picture from wikipedia