Comparison of a WFPC2 thermal vacuum globular cluster-mask image to WFPC1: Right panel: Real image taken with the Wide Field/Planetary Camera-2 of a "globular duster" pinhole mask in the April 1993 WFPC2 Thermal Vacuum test at JPL (Pasadena, CA). The image is a 80 sec exposure through the F555W ("V") filter about 40x34" on a side, and approximates closely what HST+WFPC2 should see in a few-orbit exposure after refurbishment on a distant globular cluster (like Omega Centauri, but up to 70x further away). This HST image has a resolution of ~0.10 (FWHM), or about 10x sharper than can be ordinarily achieved from the ground. Note the apparent lack of spherical aberration wings in the expected refurbished HST image, and that individual stars can now be distinguished for the first time down to the very cluster center. The faint cosmic-ray streak in the middle of the left edge shows that this is a real (WFPC2) CCD-image. Left panel: Simulation of the same globular cluster as in the right panel (shown at the same intensity scale), but as it would have appeared to WFPC-1 before HST's refurbishment. Note that most of the stars in the cluster center cannot be separated because of the spherical aberration wings in the pre-refurbishment HST images, and that all the faintest stars in the cluster outskirts have disappeared, because of spherical aberration and the higher read-noise in WFPC1. Note how similar this image is when compared to a real WFPC1 observation of the Galactic globular cluster M15 (see Lauer et al. 1991, Astrophysical Journal 369, Letter 45, Plate L11 and L12). Both show a central diffuse halo of starlight from HST's spherical aberration wings and a lack of faint stars.

Name: M 15, Messier 15, NGC 7078
Type: Local Universe : Star : Grouping : Cluster : Globular
Category: Star Clusters
Release date: 17 June 1993, 06:00
Credit: Dr. J. Jeff Hester of Arizona State University, and the Wide Field Planetary Camera-2 Instrument Definition Team (P.1.: Dr. John Trauger at JPL), and was sponsored by NASA/ESA/GSFC.

Spiral disk and globular star clusters at the core of a colliding galaxy: [Left] Ground-based Telescopic Photograph NGC 7252 has been considered the prototypical example of a merger between two disk-shaped galaxies. The galaxy has a pair of long tails that are unambiguous evidence of the effects of gravitational tidal forces from a galaxy merger. The galaxy is nicknamed the "Atoms-for-Peace" galaxy because its stars form a bizarre loop-like structure that resembles a schematic diagram of electrons orbiting an atomic nucleus. (In December 1953, U.S. President Dwight 0. Eisenhower made his "Atoms for Peace" speech to foster peaceful applications of nuclear energy.) The galaxy is located 300 million light-years away in the constellation Aquarius. [Right] Hubble Space Telescope Planetary Camera Image of Galaxy CoreA NASA/ESA Hubble Space Telescope image of the core of the peculiar galaxy NGC 7252 reveals a striking "mini-spiral" disk of gas and stars, and about 40 exceptionally bright and young globular star clusters.

Name: IRAS F22199-0422, NGC 7257
Type: Local Universe : Galaxy : Type : Interacting
Category: Galaxies
Distance: 220 million light years
Release date: 25 May 1993, 06:00
Credit: Dr. Francois Schweizer, taken with 4-meter telescope at the Cerro Tololo Inter-American Observatory.

NGC 7257: spiral disk and globular star clusters at the core of a colliding galaxy: A NASA Hubble Space Telescope (HST) image of the core of the peculiar galaxy NGC 7252  reveals a striking "mini-spiral" disk of gas and stars, and about 40 exceptionally bright and  young globular star clusters. The strong spiral structure is 10,000 light-years across (7 arc seconds); the  entire picture is 46,000 light-years across. Hubble's resolution is so good the astronomers can  measure the diameters of the clusters (0.04 arc seconds, the apparent size of a dime at a  distance of 60 miles). They turn out to be about 60 light-years in diameter, the same size as  globular clusters that orbit our Milky Way galaxy. This visible light image was taken with the Wide Field and Planetary Camera (WFPC) in PC  mode, on October 10, 1992.

Name: NGC 7257
Type: Early Universe : Galaxy : Type : Spiral
Category: Galaxies
Constellation: Aquarius
Distance: 220 million light years
Release date: 25 May 1993, 06:00
Credit: B. Whitmore (STScI), and NASA

HST image of hot blue stars at the core of M15: A NASA/ESA Hubble Space Telescope (HST) image of the center of globular cluster M15 reveals a new population of about 15 very hot stars isolated at the core. The most likely explanation for their existence is that they are the 'naked cores' of stars that have been stripped of their outer envelope of gas. This could only have happened if stars were so crowded together in the cluster's core they can gravitationally pull material form each other.

Name: M 15, Messier 15, NGC 7078
Type: Milky Way : Star : Grouping : Cluster : Globular
Category: Star Clusters
Constellation: Pegasus
Distance: 35000 light years
Release date: 9 June 1993, 06:00
Credit: G. De Marchi (STScI and Univ. of Florence, Italy) and F. Paresce (STScI)/NASA, ESA.

A stellar close encounter at the core of globular cluster M15  (artist's impression): The sky is ablaze with several hundred thousand stars in the imaginary view from the surface of a hypothetical planet at the center if the globular star cluster called M15 (located 30,000 light-years away in the constellation Pegasus). The average distance between stars is a fraction of a light-year. A new population of extremely hot and blue stars - recently discovered by NASA/ESA Hubble Space Telescope - stand out like diamonds on black velvet. At the center of the image, a bypassing star gravitationally pulls the outer envelop of gas from a red giant star. This process will expose the giant's core - the nuclear fusion "engine" that powers the star.

Name: Messier 15, NGC 7078
Type: Milky Way : Star : Grouping : Cluster : Globular
Category: Star Clusters
Distance: 35000 light years
Release date: 9 June 1993, 06:00
Credit: G. Dana Berry, STSCI

DSS sample images: Astronomers at the Space Telescope Science Institute (STScI) in Baltimore, Maryland report that their ambitious program to make a digitized sky survey (DSS)available to astronomers around the world.

Name: Digitized Sky Survey, DSS
Type: Unspecified
Category: Miscellaneous
Release date: 7 June 1993, 06:00
Credit: STScI